GEWEX STUDIES OF AMERICAN MONSOON SYSTEMSNorth American Monsoon System (NAMS) South American Monsoon...

NEWS NEWSVol. 15, No. 1 February 2005Global Energy and Water Cycle Experiment

World Climate Research Programme(A Programme of WMO, ICSU and IOC)

5th International Scientific Conference on the Global Energy and Water CycleJune 20–24, 2004, Costa Mesa, California (Program Outline on Page 4)

Vertical (longitude-pressure) cross section throughthe NAMS at 27.5°N showing the locations of thekey elements of NAMS, including both low-level jets.

GEWEX STUDIES OF AMERICAN MONSOON SYSTEMSTWO HEMISPHERES WITH SIMILAR MONSOON

MECHANISMS, DYNAMICS AND FEATURES

North American Monsoon System (NAMS) South American Monsoon System (SAMS)

Multi-tiered approach of the North American Mon-soon Experiment (NAME). Also shown are mean(July–September 1979–1995) 925-hPa vector windand merged satellite estimates and raingaugeobservations of precipitation (shading) in milli-meters. GAPP warm season precipitation researchwill benefit from NAME. See article on page 13.

Shading indicates precipitation and dashed blacklines indicate convergence zones. Small arrows showlow-level (900 hPa) winds, and thick dashed linesrepresent low-level jets. "H" shows a subtropicalsurface high center and "A" indicates the monsoonanticylone. SAMS is being addressed by LBA, LPBand VAMOS studies. See article on page 12.

Schematic of SAMS showing the opposite phases ofthe dominant mode of variability over South Americaduring the warm season.

February 20052

COMMENTARY

PERSPECTIVES ON THE17th GEWEX SSG MEETINGSoroosh Sorooshian, Chairman

GEWEX Scientific Steering Group

Contents PAGE

Commentary: Perspectives on the 17th 2GEWEX SSG Meeting

Recent News of Relevance to GEWEX 3

Preliminary Program Outline for the 5th 4Int'l Scientific Conference on GEWEX

Land-Surface Processes and the Monsoon 5

Aerosol-Hydrologic Cycle Interaction: A New 7Challenge in Monsoon Climate Research

New Geostationary Data Set for Climate 9Science

Measuring Precipitation in High Places— 10Space-Time Variability in the Himalayas

South American Monsoon System 12

Results from the NAME 2004 Field Campaign 13

GEWEX Relevant Publications of Interest 15

GCSS Pacific Cross-Section Intercomparison 16Project

Workshop/Meeting Summaries:– GCSS Science Panel Meeting 16– Workshop on American Monsoon 17 Systems– 9th GISP Meeting and 6th GAME Study Conf. 19

Welcome to the first issue of GEWEX News in2005. This issue focuses on monsoons and is a goodintroduction to the discussions between GEWEX andthe Climate Variability and Predictability (CLIVAR)Project on pan-WCRP monsoon research. Mon-soons were also discussed at the GEWEX ScientificSteering Group (SSG) meeting, which was recentlyheld in Kunming, China. I am happy to report thatwe had a very productive SSG meeting. The progressbeing made by the GEWEX Panels was very evidentin the presentations made at the meeting. The Inter-national Satellite Land Surface Climatology Project(ISLSCP) Initiative II data sets are now complete andgoing through their final evaluation (see the workshopannouncement on page 3). I anticipate that thisproduct will be as successful and beneficial to theclimate and educational communities as the ISLSCPInitiative I data sets. The proposal from the AfricanMonsoon Multidisciplinary Analysis (AMMA) Projectto become a Continental-Scale Experiment (CSE)was accepted, thereby facilitating strengthened col-laboration between AMMA and the other CSEs, aswell as with the model development activities of theGlobal Land-Atmosphere System Study (GLASS)and the GEWEX Cloud System Study (GCSS). Thehydrometeorological transferability studies are pro-gressing nicely and are stimulating a great deal ofinterest within the regional modeling community. Plansfor an integrated approach between modeling landsurface, boundary layer and cloud processes holdpromise for an effective approach to developing coupledland-atmosphere models.

GEWEX has also been supportive of sciencecommunities beyond GEWEX. Through our Euro-pean GEWEX Coordinator, Dr. Peter van Oevelen,GEWEX is starting to develop more visibility andconnections with science groups in Europe. GEWEXhas also addressed issues related to the Intergovern-mental Panel on Climate Change. Workshops toassess satellite-based cloud, precipitation, water va-por and aerosol products are underway and willprovide guidance on the opportunities and limitationsof using these data sets in climate trend analysis. Weare continuing to work with the CLIVAR Project todevelop a strong pan-WCRP monsoon activity thatwill be a central focus in the Coordinated Observa-tion and Prediction of the Earth System (COPES).

GEWEX support to the Earth Observation Summitad-hoc Group on Earth Observations (GEO) andIntegrated Global Water Cycle Observations (IGWCO)data integration efforts continues to come through theCoordinated Enhanced Observing Period (CEOP)Project, which has just successfully completed itsfirst phase and is now developing plans for its sec-ond phase.

However, GEWEX also faces significant challenges.We need to develop stronger integration across theGEWEX Panels on the three GEWEX cross-cuttingthemes, namely precipitation, the diurnal cycle, and theglobal water and energy budget studies. We also needto ensure that the GEWEX projects that support COPESmove forward quickly and in close coordination withother WCRP projects. Also, maintaining and increasingthe funding committed to GEWEX science, observationsand data activities will continue to be a challenge giventhat positive changes in the fiscal climate for Earthscience are not expected in the short term. Clearly wehave a substantive agenda that will require the commu-nities’ commitment as we prepare for future Phase IIinitiatives. We look forward to seeing all of you at the5th International Scientific Conference on the GlobalEnergy and Water Cycle, June 20–24 in Costa Mesa,California (see preliminary program outline on page 4)and having a lively discussion about the important roleof GEWEX in the international climate research agenda.

3February 2005

RECENT NEWS OF RELEVANCE TO GEWEX

WATER CYCLE TRENDS WORKSHOPOn 3–5 November 2004 the Integrated Global

Water Cycle Observations (IGWCO)/GEWEX/UNESCO Workshop on Trends in Global WaterCycle Variables took place at UNESCO in Paris. TheWorkshop attracted 50 scientists, including a numberof French scientists and authors from chapters forthe upcoming Working Group I IntergovernmentalPanel on Climate Change (IPCC) assessment. A pri-mary purpose of the workshop was to identifysignificant advances in understanding trends and tomake recommendations that could be taken underconsideration by the IPCC.

Preliminary conclusions from the workshop in-clude: (1) while there is considerable confidence inthe trends derived from in situ data records fortemperature, the same confidence does not exist forwater cycle variables such as precipitation or clouds;(2) current model reanalysis products do not providean adequate basis for identifying changes in climatevariables due to issues such as data inputs, modelphysics, and resolution; and (3) while global mapsderived from satellite data are reaching the pointwhere they have sufficiently long time series forconfirming trends, many of these products have notbeen optimized for homogeneity of record and forclimate analysis. These satellite products need to bereprocessed on an urgent basis to provide a reliablebasis for future assessment of recent climate trends.

GEO-5 MAKES A DECISION ABOUTTHE GEOSS SECRETARIAT

At the 5th meeting of the ad-hoc Group onEarth Observations (GEO) held in Ottawa in No-vember 2004, it was agreed that the Secretariat forthe new Global Earth Observing System of Sys-tems (GEOSS) would be housed at the WorldMeteorological Organization (WMO) in Geneva. Thisdevelopment can be viewed as recognition of theimportant role that WMO has played in the coor-dination of global observing systems through itssatellite program.

AFRICANS EXPAND USE OF SATELLITEDATA IN WATER RESOURCE

APPLICATIONS THROUGH TIGERIn November 2004 the European Space Agency

(ESA) held a Terrestrial Initiative in Global Envi-ronment Research (TIGER) Workshop in Pretoria,South Africa to explore the potential applicationsof remote sensing data in addressing water prob-lems on the African continent and to review thelarge number of proposals that had been submittedby investigators wishing to use satellite data insolving African water problems. Over 120 people,including 90 from Africa, attended the Workshop.In addition to reviewing specific proposals, linkswith Africa Vision 2025 were developed as a resultof the Workshop. Rick Lawford presented IGWCOand GEWEX activities and several African nationsindicated an interest in learning more about AMMA,the newest GEWEX CSE, and in contributing toits goals. In addition, there is considerable interestin capacity building activities in the water sector.

ISLSCP INITIATIVE II WORKSHOP4–6 May 2005

The International Satellite Land-Surface Climatol-ogy Project (ISLSCP) Initiative II data collection,containing 50 global time series spanning the 10-yearperiod 1986 to 1995 (selected data sets span evenlonger periods), is complete and can be accessed athttp://islscp2.sesda.com. The data were acquired froma number of U.S. and international agencies, univer-sities and institutions, and have been quality checkedand co-registered to equal-angle grids of one-degree,one-half and one-quarter degree resolution. A com-mon land-water mask was applied, gaps filled and thedata reformatted into a common ASCII format. Eachdata set has been uniformly documented. Both dataand documentation have undergone two peer reviewsfocusing on quality and ease of use.

Over the next 6 months the broader communityis invited to provide a thorough evaluation of theentire Initiative II data collection and its user inter-face. A science and evaluation workshop is beingplanned to present and discuss the results on 4–6May 2005 in Greenbelt, Maryland, USA. Based onthe findings of the workshop the data will beaugmented and released as a DVD set. GEWEXcommunity members are encouraged to participatein the evaluation of the Initiative II data collection.For more information, contact Forrest Hall (e-mail:[email protected]).

AMMA – NEW GEWEX CSEThe African Monsoon Multidisciplinary Analy-

sis (AMMA) Project was accepted as the newestGEWEX Continental-Scale Experiment (CSE) atthe 17th meeting of the GEWEX Scientific SteeringGroup in February 2005.

February 20054

Sunday, 19 June 20051700-2000 Early Registration and Icebreaker

Monday, 20 June 20050700-0900 Conference Registration0900-1020 Introduction and Key Note Speakers

P. Lemke, Alfred-Wegener-InstitutK. Olsen, OSTPAndrás Szöllösi-Nagy, IHP[Others To Be Confirmed (TBC)]

1040-1220 Simultaneous Sessions on Themes 1 & 21400-1500 Simultaneous Sessions on Themes 1 & 2

Theme 1 – Clouds and their Effect on theRadiation Budget

P. Try, IGPOJ. Kaye, NASAE. Raschke, GermanyD. Randall, CSU(Additional Oral Presentations TBC)

Theme 2 – Predictions for Water ManagementG. Carter, NOAAK. Takeuchi, Yamanashi UniversityP. Graham, Rossby CentreT. Pagano, USDA(Additional Oral Presentations TBC)

Tuesday, 21 June 20050830-1010 Plenary

P. Morel, FranceS. Solomon, NOAA(Others TBC)


Theme 1 – Clouds and their Effect on theRadiation Budget

G. Stephens, CSU(Additional Oral Presentations TBC)

Theme 2 – Predictions for Water Management(Oral Presentations TBC)

Theme 3 – Roles of Land Fluxes in Waterand Energy Cycles

A. Betts, Atmospheric ResearchC. Peters-Lidard, NASA(Additional Oral Presentations TBC)

1830-2000 Reception & Townhall Meeting for GAPP

Wednesday, 22 June 20050830-1010 Plenary

P. Lemke, Alfred-Wegener-InstitutA. Busalacchi, ESSICJ. Slingo, University of ReadingT. Koike, University of Tokyo(Others TBC)

5th INTERNATIONAL SCIENTIFIC CONFERENCE ON THEGLOBAL ENERGY AND WATER CYCLE

Westin Hotel, Costa Mesa, California, USA

PREMLIMINARY PROGRAM OUTLINE(NOTE: Details of the list of speakers is not final)

Wednesday, 22 June 2005 (Cont.)1040-1250 Simultaneous Sessions on Themes 3 & 4

Theme 3 – Roles of Land Fluxes in Waterand Energy Cycles

(Oral Presentations TBC)Theme 4 – The Role of Modeling in Pre-dictability and Prediction Studies

T. Palmer, ECMWFD. Jacob, DKRZR. Koster, NASA(Additional Oral Presentations TBC)

1400-1800 Special Side Sessions for Committees1900-2130 Banquet

Thursday, 23 June 20050830-1010 Plenary

K. Trenberth, NCARM. Chahine, JPLA. R. Ravishankara, NOAA(Others TBC)


Theme 4 – The Role of Modeling in Pre-dictability and Prediction Studies

(Oral Presentations TBC)Theme 5 – New Strategies for Characterizingand Predicting Energy and Water Budgets

T. Yasunari, HyARCW. Lau, NASA(Additional Oral Presentations TBC)

Theme 6 – Measuring and Predicting Pre-cipitation

R. Adler, NASAB. Rudolf, Deutscher Wetterdienst(Additional Oral Presentations TBC)

1830-2000 Reception & Townhall Meeting for CEOP

Friday, 24 June 20050830-1010 Plenary

R. Birk, NASAS. Sorooshian, UCID. Cayan Scripps Inst. of Oceanography(Others TBC)

1040-1250 Simultaneous Sessions on Themes 5 & 6Theme 5 – New Strategies for Characterizingand Predicting Energy and Water Budgets

(Oral Presentations TBC)Theme 6 – Measuring and Predicting Pre-cipitation

(Oral Presentations TBC)1400-1530 Possible Panel Discussion (TBC)1530-1540 Conference Close

5February 2005

LAND-SURFACE PROCESSESAND THE MONSOON

Yongkang XueUniversity of California, Los Angeles, USA

Monsoon circulations are forced and maintainedby land-sea thermal contrasts and latent heat re-leased into the atmosphere, which influence monsoonstrength, duration, and spatial distribution (Websteret al., 1998). Land-surface processes are crucialin modulating monsoon processes through chang-ing the heat gradient and moisture supply, andhave a major influence on climate over monsoonregions (e.g., Xue et al., 2004; 2005). This articlebriefly reviews some results from vegetation/mon-soon interaction studies, which focus on the influenceof vegetation biophysical processes (VBP) andland cover and land use (LCLU) change on mon-soon variability and anomalies at seasonal todecadal scales.

Monsoons possess the largest annual amplitudeof any subtropical or tropical climate feature, aswell as considerable variability at annual, interannual,and interdecadal time scales (Webster et al., 1998).Studies have shown that VBP contributes to mon-soon annual evolution and decadal anomalies. Therole of the East Asian and South American VBPon monsoon annual evolution was investigated usinga general circulation model (GCM) with two differ-ent land-surface parameterizations—one with explicitvegetation processes and the other without (Xue etal., 2004; 2005). Both have similar monthly meansurface albedo and the same initial soil moisture.It was found that the GCM without explicit vegeta-tion processes (GCM/soil) was able to simulate awet season in both regions, but that no clearmonsoon evolution processes were simulated. Onlythe GCM with explicit vegetation parameterization(GCM/veg) was able to simulate the abrupt north-ward jump of the East Asian monsoon at the earlymonsoon stage (see figure on left side of page 20)and its evolution process. In South America, thedifference between GCM/veg and GCM/soil simu-lations was clear in reference to the seasonalsouthward displacement of the monsoon during theonset, and the monsoon’s northward merging withthe Inter-tropical Convergence Zone during themonsoon's mature stage. GCM/soil failed to simu-late the southward movement and produced a muchstronger rainy season (Xue et al., 2005). Thisdifference in monsoon evolution caused a signifi-cant difference in monthly mean precipitation at thecontinental scale, which would have substantialimplications for water resource management.

The impact of LCLU change on decadal cli-mate anomalies was also explored. The Sahel andChina experienced large precipitation anomalies duringthe 1980s. The Sahel suffered its most severedrought, but the rainfall to the south of the Sahelincreased due to a shift of the maximum monsoonrainfall band to the south. In East Asia, the sum-mer monsoon anomaly appeared in a dry-wet-drypattern (i.e., a dry northern China, a wet YangtzeRiver Basin, and a dry southern China). Since bothregions experienced severe desertification during thepast half-century, desertification experiments usinga GCM were conducted to test its impact (Xue andShukla, 1993). The results indicated that by dra-matic degradation of land surface conditions in thesetwo regions, the models were able to simulate theobserved monsoon decadal rainfall anomaly patternsand the shift of the rainfall band. In another nu-merical experiment using a tropical atmospheric modelcoupled with a simple dynamic vegetation model,50-year simulations with/without interactive vegeta-tion showed that the Sahelian decadal rainfall anomalytrend could be better simulated only when the modelincluded the interactive vegetation processes (Zenget al., 1999).

The changes in precipitation were caused bycirculation changes. The characteristics of mon-soon circulation and the influence of heating andmountains on the large-scale, time-mean monsoonflow are important subjects of monsoon studies(Webster et al., 1998). In the experiments of mon-soon intra-seasonal evolution, it was found that themajor difference between GCM/soil and GCM/vegsimulations was the surface sensible heat flux, whichmodified the heating gradient between ocean andcontinent and, in turn, influenced pressure gradients,wind flow (through geostrophic balance), and mois-ture transport. The VBP-produced heating gradientcontributed to the clockwise or counterclockwiseturning of the low level wind in the East Asian,African, and South American continents at the earlymonsoon stage, which affects the strength and ex-tent of monsoon development (see figure on page 6).

In the desertification experiments, the degrada-tion of the land-surface caused less net radiation atthe surface, leading to a large reduction in evapo-ration. The convective latent heating in thetroposphere was lower and relative subsidence wasproduced, which in turn weakened the northwardmonsoon flows in East Asia and Africa.

The changes in atmospheric circulation alsoaltered some major features in the monsoon sys-tems. For instance, in the African desertification

February 20056

experiment, land degradation reduced the intensityof the easterly wave propagation, but not the totalamount (Xue and Shukla, 1993). In South America,vegetation-induced heating helped simulate a Boliv-ian high (Xue et al., 2005). In the GCM/soil case,the Bolivian high was not simulated.

The effect of surface water and energy budgetson monsoons depends upon temporal and spatialscales, topographic features, and background cli-mate conditions. Interaction characteristics andmechanisms are highly sensitive to different geo-graphic situations. For example, evaporation andmoisture flux convergence played different roles inour East Asia, Sahel and South American monsoonstudies.

The relationship between the changes in theslowly varying boundary conditions at the Earth’ssurface and changes in atmospheric circulation andmonsoons are the focus of many studies. It hasbeen suggested that sea surface temperature (SST)contributed to the climate anomalies in the Saheland East Asia. It seems that SST anomalies andland forcing work in the same direction in thesetwo regions, such that large-scale climate anomalieswere amplified. On the other hand, the causes ofthe anomalies in some regions could not be easilyseparated and sometimes were confused, for ex-ample in South America (Henderson-Sellers andPitman, 2001). More comprehensive investigationsare required to understand the role and mecha-

nisms of land surface process interactions in dif-ferent continents.

Validation and comparisons with observationaldata and reanalysis data are important in under-standing monsoon/land-surface interactions. Recentlyavailable Coordinated Enhanced Observing Period(CEOP) data should provide a good opportunity tofurther explore the monsoon/land relationship.

References

Henderson-Sellers, A., and A. J. Pitman, 2002. Comments on“Suppressing impacts of the Amazonian deforestation by theglobal circulation change,” Bull. Amer. Meteor. Soc., 83, 1657-1661.

Webster, P. J., V. Magana, T. N. Palmer, J. Shukla, R. A.Tomas, M. Yanai and T. Yasunari, 1998. Monsoons: processes,predictability, and the prospects for prediction, J. Geophys.Res, 103, No. C7, 14, 451-14, 510.

Xue, Y., and J. Shukla, 1993. The influence of land surfaceproperties on the Sahel climate. Part I: Desertification,J. Climate, 6, 2232-2245.

Xue, Y., H.-M. H. Juang, W. Li, S. Prince, R. DeFries, Y.Jiao, R. Vasic, 2004. Role of land surface processes in mon-soon development: East Asia and West Africa. J. Geophys.Res., 109, D03105, doi:10.1029/2003JD003556. 24pp.

Xue, Y., F. De Sales, W. Li, C. R. Mechoso, C. Nobre, andH.-M. H. Juang, 2005. Role of land surface processes monsoondevelopment: South America. Submitted to J. Climate.

Zeng, N., J. D. Neelin, W. K.-M. Lau, and C. J. Tucker, 1999.Vegetation-climate interaction and Sahel climate variability.Science, 286, 1537-1540.

1987 wind field (ms–1) 850hPa (a) Reanalysis; (b)GCM/Soil; (c) GCM/Veg forEast Asia (May, 925 hPa);Africa (June, 850 hPa);and South America (Sep-tember, 925 hPa). Toclarify the circulationpatterns, the bold linesshow the locations wherethe zonal wind was zero.

7February 2005

AEROSOL-HYDROLOGIC CYCLEINTERACTION: A NEW CHALLENGEIN MONSOON CLIMATE RESEARCH

William K. M. LauLaboratory for Atmospheres

NASA/Goddard Space Flight Center

It has been estimated that aerosols may reduceby up to 10% the seasonal mean solar radiationreaching the Earth's surface, producing a globalcooling effect that opposes global warming (Cli-mate Change, 2001). This means that the uncertaintiessurrounding global warming may be far greater thancan be detected at the present time. As a keycomponent of the Earth climate system, the watercycle is profoundly affected by the presence ofaerosols in the atmosphere (Ramanathan et al.,2001; Rosenfeld 2000). Through the so-called “di-rect effect,” aerosol scatters and/or absorbs solarradiation, thus cooling the Earth's surface and changingthe horizontal and vertical radiational heating con-trast in the atmosphere. The heating contrast drivesan anomalous atmospheric circulation, resulting inchanges in convection, clouds, and rainfall. Aero-sols also affect the water cycle through so-called“indirect effects,” whereby aerosols increase thenumber of cloud condensation nuclei, inhibit thegrowth of cloud drops to raindrops and prolong thelife of clouds. This leads to more clouds, andincreased reflection of solar radiation, and furthercooling at the Earth's surface.

In monsoon regions, the response of the watercycle to aerosol forcing is especially complex, notonly because of the presence of a diverse mix ofaerosol species with vastly different radiative andhydroscopic properties, but also because the mon-soon is strongly influenced by ocean and landsurface processes, land use, land change, as wellas greenhouse warming. Thus, to determine theimpacts of aerosol forcing and that interaction withthe monsoon water cycle is a very pressing prob-lem. Up to now, besides the general idea that sinceaerosols significantly alter radiative heating patternsthey should have an impact on the monsoon, therehas been very little information regarding the spe-cific signatures and mechanisms of aerosol-monsoonwater cycle interaction. This article offers someinsights on how aerosols may impact the Asianmonsoon based on preliminary results from theNational Aeronautics and Space Administration(NASA) climate model. It also discusses somefuture challenges that lie ahead in aerosol-watercycle dynamics research.

Numerical experiments have been conductedwith the NASA finite-volume GCM (fvGCM) withmicrophysics of clouds in a relaxed Arakawa Schubert(McRAS) cumulus parameterization scheme to teaseout possible signatures of aerosol direct forcing ofthe water cycle variability in monsoon regions (Sudand Walker 1999). In the control, the model isforced by three-dimensional aerosol forcing func-tions for all five major aerosol types (i.e., dust,black carbon, organic carbon, sulfate and sea salt)derived from outputs of the Goddard Chemistry Aero-sol Radiation Transport (GOCART) model (Chin etal., 2002). In the anomaly runs, the initial andboundary conditions are identical, except that all orselected aerosol forcings were withheld. The re-sults described here pertain to the Asian monsoonregions. Comparing the control and anomaly ex-periments for the Asian monsoon, we find thatabsorbing aerosols, consisting of dust transportedfrom the North Africa/Middle East/Afghanistan re-gion coupled with black carbon from local emissionsover northern India can increase monsoon rainfallover northwestern India and the Bay of Bengal.The rainfall increase appears to be spurred by anelevated heat source over the Tibetan Plateau, in-duced by shortwave absorption by dust and blackcarbon aerosols, which are lofted by orographicallyforced ascent against the southern slope of theHimalayas. The net atmospheric heating due toaerosol absorption causes the air to warm and rise,increasing moisture convergence in the mid-tropo-sphere, and providing a positive feedback to theaerosol heating.

The figure on page 8 shows that the anomalouswarming in the upper troposphere over the Ti-betan Plateau begins in March (panel a), becomeswell established in April and May (panels b and c),which correspond to the pre-monsoon dry seasonwith heavy atmospheric loading, and maximum resi-dence time of dust and black carbon from industrialpollution and biomass burning. The warming forcesan anomalous local meridional overturning with ris-ing motion over northern India, and subsidenceover southern India, which becomes very pro-nounced in May and June (panels c and d). Thisoverturning persists into July and August (not shown),resulting in an overall increase in rainfall over northernIndia, and suppressed rainfall in southern India andthe northern Indian Ocean.

The increased rainfall over northern India andthe reduction in southern India is only a part of alarge-scale response of the entire Asian monsoonto aerosol-induced forcing featuring extensive rain-fall reduction in southern China, the East China

February 20058

Sea, an east-west oriented band of enhanced rainfallalong 30–35o N in central China, southern Korea andJapan, and reduced rainfall over northeastern China(see panel a in the top right figure on page 20). Thesuppression of rainfall over southern China is due tosurface cooling spurred by industrial pollution mainlyfrom sulfate and black carbon. In contrast to theIndian monsoon region, the absorption heating due toblack carbon over southern China remains largelywithin the lower troposphere due to the lack oforographic forced ascent, and consequentially is notefficient as an atmospheric heat source to initiate newconvection. As a result, the stabilizing influence dueto the semi-direct effect of aerosols prevails, as isevident in the wide-spread suppression of rainfallover southern China.

Panel b in the figure on page 20 shows that theaerosol-induced rainfall anomaly is associated withthe development of a large-scale surface pressureand wind anomaly pattern, represented by an east-ward extension and strengthening of the westernsubtropical high, which appears to be connected toa large-scale anticyclonic circulation anomaly oversouthern India and the Indian Ocean. The increasein low level westerlies over northern India and theBay of Bengal indicates a strengthening of theIndian monsoon. The climatological southwesterlyflow over the northern South China Sea is replacedby low level easterlies. Anomalous southwesterliesare found over central China, South Korea andJapan, signalling a northward shift and weakeningof the Mei-Yu rainfall regime over East Asia. Analy-ses of further experiments with various combinationsof aerosol forcing (not shown), suggest that theanomaly patterns are due to the combined effectsof dust and black carbon aerosols, with dust play-ing a primary role in instigating these patterns.

Our results suggest a plausible and testable hy-pothesis regarding the different impacts of aerosolson the Asian monsoon that needs to be validated withfurther model experiments and observations. How-ever, the validation process will be challenging for anumber of reasons. First, state-of-the-art climatemodels either do not include aerosol-cloud interactionprocesses, or include them as simple, empiricalparameterizations. Our present experiments deal withdirect effects only. Second, the present bootstrappingstrategy of using dynamics for aerosol chemistrytransport, and then separately using a chemistry trans-port model to force dynamics has obviousinconsistencies and limitations. Ultimately, coupledchemistry-dynamic models have to be developed tosimulate the full feedback between dynamics andaerosol forcing. Third, the lack of long-term globalobservations of aerosol emission, composition, anddistribution makes it very difficult to define aerosolforcing functions, and to validate model results. Atpresent, satellite observations from satellites [e.g.,Total Ozone Mapping Spectrometer (TOMS), Mod-erate Resolution Imaging Spectroradiometer (MODIS),POLarization and Directionality of the Earth’sReflectances (POLDER), and the Multi-Angle Imag-ing Spectroradiometer (MISR)] have been providingtantalizing signals of the direct and indirect effects onthe water cycle. The Aerosol Robotic Network(AERONET) has provided valuable aerosol data forcharacterization and calibration of satellite observa-tions (Holben et al., 1998). However, these observationsstill fall short of the requirement of global, coincidentobservations of aerosols, clouds and rain with hightemporal and spatial (horizontal and vertical) resolu-tions. Current efforts in assembling and integratingmulti-platform local and global data for model valida-tion such as the Coordinated Enhanced Observing

Vertical cross section of temperature andwind averaged over the Indian subconti-nent in the fvGCM-GOCART simulations,showing the anomalous meridional over-turning, and upper tropospheric tempera-ture as a result of aerosol-induced heating.

9February 2005

NEW GEOSTATIONARY DATA SETFOR CLIMATE SCIENCE

Ken Knapp, John J. BatesNational Climatic Data Center

The National Oceanic and Atmospheric Admin-istration (NOAA) National Climatic Data Center(NCDC) is developing a new data set for climatescience. Originating from the International SatelliteCloud Climatology Project (ISCCP), the data areobservations from all channels on the GeostationaryOperational Environmental Satellite (GOES) series,the European Meteorological satellite (Meteosat) seriesand the Japanese Geostationary Meteorological Sat-ellite (GMS) series. The period of record covers1983 through the present.

The ISCCP Sector Processing Centers (SPCs)began providing geostationary and polar-orbiting sat-ellite imagery in 1983. The geostationary data providedto ISCCP for cloud analysis are images subsampledin time and space (up to 3 hours and 32 km,respectively). However, ISCCP archived a versionof the geostationary data called B1 at 3-hour and10-km resolutions. Until now, the volume of thehigher resolution B1 data was too large to be incor-porated into processing.

The B1 data set consists of spectral radiancesfrom satellite sensors and the corresponding bright-ness temperature or albedo for infrared and visiblewavelengths, respectively (i.e., no retrievals of geo-physical parameters are available). Observations atvisible (near 0.6 µm) and infrared window (near 11µm) wavelengths are available for every satellite,while information at other wavelengths is included.

These spectral observations are available overmost of the globe, except at the poles where geo-stationary observations are not possible. The B1data set will include observations from future satel-lites as well, including Meteosat-8 and the Japan’supcoming MTSAT-1R. Thus, the B1 data set willrepresent one of the most comprehensive satelliteclimate data sets available.

Currently, the data set is available to interestedusers for testing. It is hoped that through intenseuse by scientists, data set errors or deficiencies canbe found and fixed before the complete data set isreleased to the general public later in 2005. Scien-tists and students interested in using the B1 datashould contact [email protected] for informa-tion on how to retrieve the data.

Period (CEOP) must be supported, while new fieldcampaigns and monitoring programs are being plannedand incorporated into the global integrated database.Observational and model efforts on monsoon andwater cycle dynamics research should be coordinatedto improve physical parameterization in models.

An organized international effort on a aerosol-monsoon water cycle process study that is jointlysponsored by GEWEX and the Climate Variabilityand Predictability (CLIVAR) Project under the aus-pices of the WCRP emerging banner CoordinatedObservations and Prediction of the Earth System(COPES) will go a long way in meeting these require-ments and challenges.

References

Chin, M., P. Ginoux, S. Kinne, and co-authors, 2002. Tropo-spheric Aerosol Optical Thickness from the GOCART Modeland Comparisons with Satellite and Sun Photometer Measure-ments, J. Atmos. Sci., 59, 461-483.

Climate Change 2001. The Scientific Basis – Contribution ofWorking Group I to the Third Assessment Report of the IPCC,Ed. J. T. Houghton et al, Cambridge University Press, 867 pp.

Holben, B., and coauthors 1998. AERONET – a federatedinstrument network and data archive for aerosol characteriza-tion, Remote Sensing Environ., 66, 1-16.

Ramanathan, V., P. J. Crutzen, J. T. Kiehl, D. Rosenfeld, 2001.Aerosols, climate and the hydrologic cycle, Science, 294, 2119-2124.

Rosenfeld, D., 2000. Suppression of rain and snow by urbanand industrial air pollution. Science, 287, 1793-1796.

Sud, Y. C. and G. K. Walker, 1999. Microphysics of clouds with therelaxed Arakawa-Schubert scheme (McRAS). Part II: Implementationand performance in GEOS II GCM, J. Atmos. Sci., 56, 3221-3240.

GEWEX AMS HONOREES

The following GEWEX scientists received awardsat the 85th Annual Meeting of the American Meteo-rological Society.

Graeme L. Stephens, The Jule G. Charney Award"for pioneering advances in understanding and mea-suring radiation processes and their role in climate"

William B. Rossow, The Verner E. Suomi Award"for tireless efforts using multi-satellite observationsto study clouds and their role in radiation andclimate"

Dennis P. Lettenmaier, The Walter Orr RobertsLecturer in Interdisciplinary Sciences Award"for significant research contributions and leader-ship in fostering effective interchange of knowledgebetween atmospheric and hydrologic scientists"

Robert A. Schiffer and William B. Rossow werehonored as new AMS Fellows.

February 200510

MEASURING PRECIPITATION IN HIGHPLACES—SPACE-TIME VARIABILITY

IN THE HIMALAYAS

Ana P. BarrosDuke University, North Carolina, USA

A hydrometeorological network was installed inthe Marsyandi River Basin in Central Nepal toobtain high-frequency (one-half hourly) measure-ments of rainfall, snow depth, snow water content,temperature, relative humidity, wind direction andspeed along three upwind ridges and adjacent val-leys, and then into the rainshadow behind theAnnapurna Range that stretches into the TibetanPlateau (Barros et al., 2000; see figure below).The first phase of the hydrometeorological networkwas installed during the pre- and post-monsoonseasons in 1999 with National Aeronautics andSpace Administration (NASA) Tropical RainfallMeasuring Mission (TRMM) funding to augmentthe existing operational network operated by theNepalese Department of Hydrology and Meteorol-ogy. Especially noteworthy was the installation ofsix 10-m towers roughly spaced at 1,000-m eleva-tion difference from each other up to 4,500 m.Five stations were added in the pre-monsoon sea-

son of 2000, and one of the network towers at3,300 m altitude was equipped with radiation sen-sors [solar, longwave, Photosynthetically ActiveRadiation (PAR)], soil temperature, soil heat flux,and soil moisture probes at three different depths,as well as standard relative humidity, surface pres-sure and air temperature, and wind speed anddirection sensors at 2- and 10-m levels. Streamflowmeasurements were conducted for selected head-water catchments within the area of the network.

The Marsyandi network was designed to monitorthe space-time variability of precipitation at hightemporal and spatial resolution with the objectiveof understanding orographic precipitation phenom-ena in the Himalayas, and it has served the sciencecommunity well. A comprehensive compilationand analysis of observations from the networkrevealed the large complexity of the relationshipbetween elevation and precipitation in the CentralHimalayas (Barros et al., 2004): (1) weak altitudinalgradients of annual rainfall between 1,000 and 4,500m; (2) strong ridge-to-ridge zonal (east-west) gradi-ents of monsoon rainfall (~1,500 mm/5 km); (3)strong ridge-valley gradients during rainstorms, es-pecially in the case of deep valleys (elevation differences>1,000 m) and steep hillslopes (70%); and (4)strong altitudinal gradients in rainfall intensity andduration (convective versus stratiform), with longer(shorter) durations and lower (higher) intensities athigher (lower) elevations along the ridges. Highelevations [>3000-m mean sea level (MSL)] canreceive up to 40% of their annual precipitation assnowfall during the winter; with the highest altitudestations (~4000-m MSL and above) having themost total winter precipitation (Lang and Barros,2002 and 2004).

Analysis of TRMM Precipitation Radar (PR) andinfrared imagery data along the Himalayas suggestsorographic precipitation processes include cells oflocalized shallow convection embedded in bandsof stratiform rainfall from the foothills up to 5,000m (Lang and Barros, 2002; Barros et al., 2004).The diurnal cycle of rainfall in the central Himalayasexhibits both afternoon and evening peaks withnocturnal maxima and early morning peaks duringthe monsoon (Barros et al., 2000 and 2004, Barrosand Lang 2003). This late night/early morningrainfall maximum accounts for about one-third ofthe cumulative monsoon rainfall and routinely causesflash floods in headwater streams everywhere alongthe Himalayan range. While the large-scale spatialpatterns of precipitation and the amplitude of thediurnal cycle exhibit interannual and subseasonalvariability consistent with monsoon forcing (Barros

Topography of the Marsyandi River Basin. The largermap shows locations of the hydrometeorological stationsin the network. The inset shows the location of thenetwork relative to the Indian subcontinent. Numbersindicate distribution of stations.

11February 2005

et al., 2004), the spatial patterns exhibit remarkablespatial stationarity. Note the remarkable consis-tency in the spatial organization of precipitationfeatures from year to year (see figure above).

Based on the Monsoon Himalaya PrecipitationExperiment (MOHPREX) observations, Barros andLang (2003) estimated that contributions from dailyevapotranspiration (ET) to Precipitable Water (PW)can vary between 15% of daily rainfall at highelevations (>3,000 m) up to 35% in adjacent val-leys (<1000 m). These estimates are quantitativelyand qualitatively consistent with recent studies ofthe diurnal cycle of rainfall in mountainous regionselsewhere (e.g., Iwasaki, 2003; Yang et al., 2004).These studies show that evapotranspiration andmountain-valley moist transport have a strong influ-ence in the diurnal cycle of PW and ConvectiveAvailable Potential Energy (CAPE), thus ultimatelyaffecting the location and timing of the onset ofconvection in the daytime, and establishing condi-tions for the late evening convective activity. Whilesuch studies have been conducted for unfavorablesynoptic conditions and moderate topography (500-1,500-m elevation differences), it is remarkable thatthe diurnal cycle of rainfall in the Himalayas exhib-its similar features, and a nocturnal rainfall maximumthat occurs after midnight during the monsoon atall elevations independently of large-scale forcingconditions (Lang and Barros 2002; Barros andLang 2003). This behavior suggests the ubiquityof a dynamic link between the spatial variability ofevapotranspiration and soil moisture (e.g., surfacesensible and latent heat fluxes), topography and thespatial organization of monsoon rainfall by whichthe mountains modulate precipitation processes andlatent heating in the troposphere (Magagi and Barros,2004). Whether and how regional land-surfacecontrols have an impact on seasonal to interannualclimate variability that propagates beyond the northernIndian subcontinent needs to be further investigated.

Monsoon composite ofthe spatial organizationof nocturnal shallow pre-cipitation features from2 years of TRMM data.Note the remarkable spa-tial consistency coincid-ing with upwind ridgesalong the Himalayanrange. From Barros etal., 2004.

Acknowledgements: The Marsyandi network wasinstalled and maintained with support from theNASA TRMM Program and the National ScienceFoundation Continental Dynamics programs.

Editor's Note: Although this data system has provedto be very valuable for monsoon research, fundinghas not been made available for the author tomaintain the system.

References

Barros, A. P., M. Joshi, J. Putkonen, and D. W. Burbank,2000. A study of the 1999 monsoon rainfall in a mountainousregion in Central Nepal using TRMM products and raingaugeobservations. Geophys. Res. Lett., Vol. 27, No. 22, 3683-3686.

Barros, A. P., and T. J. Lang, 2003. Monitoring the Monsoonin the Himalayas: Observations in Central Nepal, June MonthlyWeather Review, Vol. 131, No. 7, 1408-1427.

Barros, A. P., G. Kim, E. Williams, and S. W. Nesbitt, 2004.Probing Orographic Controls in the Himalayas During the Mon-soon Using Satellite Imagery. Natural Hazards and EarthSystem Science, Vol. 4, 1-23.

Iwasaki, H., 2003. Diurnal Variation of Precipitable Water andConvective Activity with Dual Maxima in Summer Season aroundMt. Tanigawa in the northern Kanto District, Japan. Pro-ceedings of the International Workshop on GPS Meteorology:Ground-Based and Space Borne Applications, paper 3-31.

Lang, T. and A. P. Barros, 2002. An Investigation of theOnsets of the 1999 and 2000 Monsoons in Central Nepal,Monthly Weather Review, Vol. 130, No. 5, 1299-1316.

Lang, T. J. and A. P. Barros, 2004. Winter Storms in theCentral Himalayas. J. Japanese Meteo. Soc., Vol. 82, No. 4,829-844.

Magagi, R. and A. P. Barros, 2004. Latent Heating of RainfallDuring Onset of the Indian Monsoon Using TRMM-PR andRadiosonde Data. J. Applied Meteorology, Vol. 43, No. 2, 328-349.

Yang, K., T. Koike, H. Fujii, T. Tamura, X. Xu, and L. Bian,2004. The Daytime Evolution of the Atmospheric BoundaryLayer and Convection over the Tibetan Plateau: Observationsand Simulations. J. Met. Soc. Japan, Vol. 86(6), 1-20.

February 200512

SOUTH AMERICAN MONSOON SYSTEM

C. Roberto Mechoso1,Andrew W. Robertson2, Alice M. Grimm3,

and Carolina S. Vera4

1University of California, Los Angeles, USA2International Research Institute forClimate Prediction, New York, USA3Federal University of Paraná, Brazil

4CIMA/University of Buenos Aires, Argentina

We refer to the flow over South America dur-ing the warm season as the South American MonsoonSystem (SAMS) since it (1) shows the monsoon-type surface low pressure/upper-level anticycloneconfiguration and intense low-level inflow of mois-ture from the ocean; (2) is affected by large-scaleland-sea surface temperature contrasts, as well asby terrain elevations and land surface conditions(e.g., soil moisture); and (3) includes shifts inregional precipitation from low or relatively low tovery intense. SAMS provides a useful frameworkfor describing and diagnosing warm season climate.See the recent papers by Paegle et al. (2002) andVera et al (2004) for an extensive bibliography onSAMS.

SAMS is characterized by intense precipitationover central Brazil and Bolivia and the South Atlan-tic Convergence Zone (SACZ) to the southeast(see top right figure on page 1). The associatedupper-level anticyclone (Bolivian High) establishesclose to the Altiplano. The upper-level high andaccompanying low-level heat low are in spatial

quadrature in longitude with ascent on the easternside of the continent and subsidence on the westernside over the eastern Pacific, where extensive stra-tocumulus decks provide a radiative heat sink to thetropical atmosphere. Such a configuration allowsfor a largely Sverdrup-type balance between thevorticity source associated with diabatically forcedcontinental-scale vertical motion and advection ofplanetary vorticity. The monsoon circulation ex-tends poleward until the midlatitude dynamical regimetakes over.

The trade winds from the tropical Atlantic Oceanprovide the moisture source for the SAMS. Mois-ture transport intensifies locally along the easternscarp of the Andes, where the South Americanlow-level jet (SALLJ) develops throughout the yearwith its strongest winds over Bolivia.

The intraseasonal, as well as interannual andinterdecadal, variations of SAMS appear to be as-sociated with a continental-scale eddy (see figurebelow). In the cyclonic phase of the circulation, theSACZ intensifies with anomalous descent to thesouthwest and weakened low-level flow east of theAndes; the anticyclonic phase shows opposite char-acteristics. The vertical velocity distribution associatedwith the mode is consistent with a dipole defined bypersistent wet and dry anomalies over tropical andsubtropical eastern South America during the aus-tral summer. Two different convection “regimes” inAmazonia have been identified in recent field cam-paigns: (1) an intense mode consisting of a verticallydeveloped convection associated with a westerlywind regime, and (2) a weaker, monsoon-type mode,associated with an easterly wind regime.

Opposite phases of thedominant mode of vari-ability over SouthAmerica during thewarm season. Thick ar-rows indicate low leveljets. The area boundedby the dashed ellipsesare those in which en-hancement of mesoscaleconvective systems is ex-pected.

13February 2005

In the equatorial belt, El Niño and La Niña tendto be associated with anomalously dry and wetSAMS events, respectively. During El Niño con-vection is enhanced over the eastern tropical Pacificand subsidence increases over equatorial SouthAmerica, which disfavors convection. The El NiñoSouthern Oscillation (ENSO) can also influence theSAMS through the extratropics and the excitationof the Pacific South American Rossby wave trainsor teleconnection patterns and the subtropical eddy-circulation mentioned above, which also involve theSACZ and anomalies of the opposite sense overthe subtropical plains. No modulation of SAMSinvolving the snow pack has been proposed, to ourknowledge.

On seasonal to interannual time scales, predict-ability studies with global models generally indicatevery modest levels of seasonal-mean precipitationskill over most of the SAMS domain. One of thepossible reasons for the low predictability can bethe importance of regional atmosphere-land interac-tions. The successful simulation of land surfaceprocesses is one of the major current challengesfor numerical modeling of climate variability.

There are many unsolved questions on SAMS.These include the better understanding of the influ-ence on its evolution of the dynamical and thermaleffects of the Bolivian Altiplano, Amazonian defor-estation, and other land surface processes. Thereare also several aspects to clarify in reference tothe low-level jets, including the associated trans-ports of water vapor and development of convectivesystems.

Internationally organized research on the AmericanMonsoons has been accelerated in recent years byWCRP. The most relevant programs are the Cli-mate Variability and Predictability (CLIVAR) panelon the Variability of American Monsoon Systems(VAMOS); the GEWEX Hydrometeorology Panel(GHP) Continental-Scale Experiments: Large-scaleBiosphere Atmosphere Experiment in Amazonia(LBA) and the La Plata Basin (LPB) Project; andthe Coordinated Enhanced Observing Period (CEOP).These activities have greatly strengthened multina-tional scientific collaboration and coordination.

References

Nogués-Paegle, J., C. R. Mechoso, and co-authors, 2002. Progressin Pan American CLIVAR Research: Understanding the SouthAmerican Monsoon, Meteorologica, 27, 3-30.

Vera, C., W. Higgins, and co-authors, 2004. A Unified View ofthe American Monsoons, J. Climate (submitted).

RESULTS FROM THENAME 2004 FIELD CAMPAIGN

Wayne HigginsNOAA Climate Prediction Center,

Maryland, USA

The North American Monsoon Experiment (NAME)is an internationally coordinated process study todetermine the sources and limits of predictability ofwarm season precipitation over North America. NAMEis funded jointly by the GEWEX Americas PredictionProject (GAPP) and the Pan American Climate Stud-ies (PACS) Project. The NAME 2004 EnhancedObserving Period (EOP) was conducted during June–September 2004 with Intensive Observing Periods(IOPs) during a 6-week period (1 July–15 August2004). NAME 2004 collected an extensive set ofatmospheric, oceanic and land-surface observationsin the core region of the North American monsoon(see the figure at the bottom of page 20).

The IOPs were designed to address the follow-ing science questions: (1) How are low-levelcirculations along the Gulf of California/west slopesof the Sierra Madre Occidental related to the diur-nal cycle of moisture and convection? (2) What arethe relationships between moisture transport andrainfall variability? and (3) What is the typical lifecycle of diurnal convective rainfall?

While the general behavior of monsoon precipita-tion has been under investigation for many years,confident analysis of detailed spatio-temporal charac-teristics has been lacking due to deficiencies in theoperational precipitation monitoring network. Thisdeficiency was addressed, in part, during NAME2004 using strategic augmentations of the gauge-based observing network. Complementing nationalnetworks operated by the National Weather Service(NWS), the Mexican National Weather Service (ServicioMeteorólógico Nacional), and the Mexican ComisionNacional del Agua (CNA), hundreds of new raingauges were installed by NAME investigators in TierI to fill in data-sparse regions and to help amelioratea low-elevation bias in the existing observing net-work. Emphasis was placed on improving the samplingof precipitation within the complex terrain of theSierra Madre Occidental Mountains because prelimi-nary diagnostics have shown that rainfall during thesummer tends to initiate over the high terrain early inthe afternoon and then propagate or reform towardsthe Gulf of California (GOC) later in the evening.

February 200514

The NAME 2004 EOP atmospheric profilingprogram was aimed at gathering upper air data tostudy the dynamic and thermodynamic vertical struc-ture and temporal variability of the troposphere inthe core monsoon region, its relationship with large-scale systems, and the development of deepconvection and rainfall in the region. The opera-tional sounding systems of the southwestern UnitedStates and Mexico were enhanced to allow for anincreased frequency of balloon launches (4 to 6times per day, depending on the site) to bettercharacterize the diurnal evolution of the tropo-sphere. The enhanced operational soundings wereaugmented by additional soundings within the TierI region conducted by NAME Principal Investiga-tors and sponsoring agencies such as the Departmentof Defense at Yuma, Arizona, and the Salt RiverProject in Phoenix, Arizona. Enhanced operationalsoundings during IOPs were also made in theneighboring countries of Belize and Costa Rica.

During the EOP three NCAR Integrated Sound-ing Systems (ISSs), consisting of Global PositioningSystem (GPS) sounding systems, 915-MHz windprofilers, Radio Acoustic Sounding Systems (RASS)to measure virtual temperature profiles in the bound-ary layer, and surface meteorological stations. TheISSs were located at Puerto Peñasco, Sonora;Bahia Kino, Sonora, and Los Mochis, Sinaloa onthe eastern side of the Gulf of California. Thesesystems successfully sampled a number of aspectsof the monsoon system in real time includingmonsoon onset, GOC low-level jets and moisturesurges, the diurnal cycle of convection, land-seabreezes, influences of easterly waves and tropicalcyclones, and upper-level inverted troughs. Forexample, the ISSs successfully captured a majorinflux of moisture into the southwestern UnitedStates that occurred during NAME IOP-2 (12–15July 2004) in association with the passage of TropicalStorm Blas to the south of Tier I. This stormproduced several significant changes over Tier I,including changes in the midlevel flow from south-easterly to easterly, and an increase in surfacepressure over the southern Gulf, thereby enhancingthe north-south pressure gradient along the GOC.The Puerto Peñasco ISS documented the Gulfsurge on 13 July in real time. It was preceded bythe passage of two gust fronts exhibiting windshifts in the lowest 500 m of the atmosphere.Following that, a prominent moisture surge oc-curred with a peak wind exceeding 20 ms–1 near 1km AGL. A rise in the surface pressure of ~5 hPawas associated with this surge. The other ISSsites at Bahia Kino and Los Mochis also recordedsurges and significant surface pressure rises.

A radar network, consisting of the NCAR S-Pol polarimetric Doppler radar near Mazatlan, Sinaloaand two upgraded SMN Doppler radars in Guasave,Sinaloa and Cabo San Lucas, Baja California Sur,was operated during NAME 2004 to characterizemesoscale and convective-scale processes in TierI. The network provided improved observationsof the diurnal cycle of rainfall and storm morphol-ogy in the region. S-Pol was operated in twodifferent scanning modes to emphasize mesoscaleorganization of storms and to emphasize individualstorm structure. Both modes featured scans every15-minutes to produce accurate rainfall maps, andinformation on microphysical structure and evolu-tion of storms. After vigorous quality controlefforts, the SMN data will be merged with S-Poland NERN rain gauge data to create a griddedcomposite regional product that provides near-sur-face rainfall, reflectivity, and Doppler velocity every15 minutes during the EOP. Combined, theseradar products will be used to initialize and vali-date modeling work at multiple spatial scales, aswell as to validate satellite rainfall estimates.

The data set gathered during NAME 2004 willbe used to improve our ability to simulate andultimately predict monsoon precipitation months toseasons in advance. A driving hypothesis of NAMEis that we must develop proper simulations ofrelatively small (spatial and temporal) scale climaticvariability, especially the diurnal cycle, in the coreof the continental monsoon precipitation maximumin northwestern Mexico. A comprehensive model-ing strategy was developed that included the NAME2004 EOP as a critical component from the outsetto help guide progress. Details of the strategy,which includes climate model assessments, dataassimilation, model sensitivity and development, andprediction activities are available on the NAMEwebpage (www.joss.ucar.edu/name/).

The campaign generated an unprecedented dataset that is freely available to the climate community(www.joss.ucar.edu/name/catalog/). NAME model-ing and prediction studies will continue for the nextseveral years. By the end of the program in 2008,NAME will deliver an improved observing systemdesign for monitoring and predicting the NorthAmerican monsoon, more comprehensive under-standing of North American summer climate variabilityand predictability, strengthened scientific collabo-ration across Pan-America, and measurably improvedclimate models that simulate and predict monsoonvariability months to seasons in advance.

15February 2005

GEWEX RELEVANT PUBLICATIONSOF INTEREST

Ensemble Simulations of Asian–AustralianMonsoon Variability by 11 AGCMs

Reference: Bin Wang, In-Sik Kang and June-YiLee, 2004. Ensemble Simulations of Asian–AustralianMonsoon Variability by 11 AGCMs. Journal of Cli-mate: Vol. 17, No. 4, pp. 803–818.

Summary/Abstract: Ensemble simulations of Asian–Australian monsoon (A–AM) anomalies were evaluatedin 11 atmospheric general circulation models for theunprecedented El Niño period of September 1996–August 1998. The models’ simulations of anomalousAsian summer rainfall patterns in the A–AM region(30°S–30°N, 40°–160°E) are considerably poorer thanin the El Niño region. This is mainly due to a lackof skill over Southeast Asia and the western NorthPacific (5°–30°N, 80°–150°E), which is a strikingcharacteristic of all the models. The models’ defi-ciencies result from failing to simulate correctly therelationship between the local summer rainfall and theSST anomalies over the Philippine Sea, the SouthChina Sea, and the Bay of Bengal: the observedrainfall anomalies are negatively correlated with SSTanomalies, whereas in nearly all models, the rainfallanomalies are positively correlated with SST anoma-lies. While the models’ physical parameterizationshave large uncertainties, this problem is primarilyattributed to the experimental design in which theatmosphere is forced to respond passively to thespecified SSTs, while in nature the SSTs result inpart from the atmospheric forcing.

Seasonal Evolution and VariabilityAssociated with the

West African Monsoon SystemReference: Guojun Gu and Robert F. Adler, 2004.Seasonal Evolution and Variability Associated withthe West African Monsoon System. Journal of Cli-mate: Vol. 17, No. 17, pp. 3364–3377.

Summary/Abstract: In this study, the seasonalvariations in surface rainfall and associated large-scaleprocesses in the tropical eastern Atlantic and WestAfrican region are investigated. The 6-yr (1998–2003)high-quality Tropical Rainfall Measuring Mission(TRMM) rainfall, sea surface temperature (SST), watervapor, and cloud liquid water observations are ap-plied along with the NCEP–NCAR reanalysis windcomponents and a 4-yr (2000–2003) QuickScatterometer (Quik SCAT) satellite-observed surfacewind product. Major mean rainfall over West Africatends to be concentrated in two regions and is ob-

Model Study of Evolution and DiurnalVariations of Rainfall in theNorth American Monsoon

During June and July 2002

Reference: J. Li, X. Gao, R. A. Maddox and S.Sorooshian, 2004. Model Study of Evolution andDiurnal Variations of Rainfall in the North AmericanMonsoon during June and July 2002. Monthly WeatherReview: Vol. 132, No. 12, pp. 2895–2915.

Summary/Abstract: Rainfall evolution and diurnalvariation are important components in the North AmericanMonsoon System. In this study these componentsare numerically studied using the fifth-generation Penn-sylvania State University–National Center forAtmospheric Research (PSU–NCAR) Mesoscale Model(MM5) with high resolution (12-km grids) in contrastto most previous model studies that used relativelycoarse spatial resolutions (>25 km grids). The studyshows that, in general, the model results broadlymatched the patterns of satellite-retrieved rainfall datafor monthly rainfall accumulation. The rainfall timingevolution in the monsoon core region predicted bythe model generally matched the gauge observations.However, the differences among the three precipita-tion estimates (model, satellite, and gauge) are obvious,especially in July. The rainfall diurnal cycle patternwas reproduced in the monsoon core region of west-ern Mexico, but there were differences in the diurnalintensity and timing between modeled and observedresults. Furthermore, the model cannot capture thediurnal variation over Arizona. The simulations showthat the model has deficiencies in predicting precipi-tation over the Gulf of Mexico. The model cannotreproduce the low-level inversion above the marineboundary layers and thus does not generate enoughconvective inhibition to suppress the convection. Themodel also cannot produce realistic variations of day-to-day atmospheric conditions with only a singleinitialization at the start of the month.

served in two different seasons, manifesting an abruptshift of the mean rainfall zone during June–July. Theabrupt shift of the mean rainfall zone appears to bea combination of two different physical processes: (i)evident seasonal cycles in the tropical eastern AtlanticOcean, which modulate convection and rainfall nearthe Gulf of Guinea by means of SST thermal forcingand SST-related meridional gradient; and (ii) the in-teraction among the upper-tropospheric tropical easterlyjet (AEJ), upper-tropospheric tropical easterly jet (TEJ),low-level westerly flow, moist convection, and Afri-can easterly waves (AEWs) during July–September,which modulates rainfall variability in the interior ofWest Africa, primarily within the ITCZ rain band.

February 200516

GCSS SCIENCE PANEL MEETING

21–23 September 2004New York, USAChristian Jakob

Bureau of Meteorology Research CentreMelbourne, Australia

WORKSHOP/MEETING SUMMARIES

The meeting was hosted by the National Aero-nautics and Space Adminstration (NASA) GoddardInstitute for Space Studies (GISS). The goal of theGEWEX Cloud System Study (GCSS) is to im-prove the parameterization of cloud systems ingeneral circulation models (GCMs) and numericalweather prediction models through improved physicalunderstanding of cloud system processes. The maintools for achieving this are case studies in whichcloud resolving models and single column models(1D versions of full GCMs) are compared to ob-servations and with each other. A special focus ofthe meeting was to discuss how to increase GCSSinfluence in guiding the development of the repre-sentation of clouds in models.

The GCSS Science Panel approved the 3rd

Pan-GCSS Meeting on “Clouds, Climate and Mod-els” to be held 16–20 May 2005 in Athens, Greece.The meeting will host plenary sessions, as well asmeetings of all GCSS working group (WGs) andcross-WG activities. The plenary sessions willcover the following subjects: (1) Perspectives onthe importance of clouds in the climate system;(2) Methodologies and metrics in assessing mod-els; (3) The fundamental role of precipitation incloud systems; and (4) Progress in the representa-tion of clouds in large-scale models.

GCSS will aim at improving its alignment withGCM developments, and in that context, each GCSSWG is investigating how to more directly connectits specific process studies to GCM studies. GCSSwill also aim to involve a wider community, inparticular, the GCM evaluation community, as wellas broader parts of the data community, moredirectly into the GCSS process. The 3rd Pan-GCSSMeeting will be an excellent opportunity to fosterthis closer collaboration. To increase the visibilityof GCSS in the community, GCSS will publish anelectronic GCSS newsletter on a regular basis.

A new activity is the GCSS Pacific Cross-Section Intercomparison (GPCI), see adjacent articleon this page. This activity, which is led by J.Teixeira (Naval Research Laboratory), comparesand evaluates GCMs along a cross section of the

The GEWEX Cloud System Study (GCSS)Pacific Cross-Section Intercomparison (GPCI) Projectis a model evaluation project to compare and evaluatethe representation of clouds in climate and Numeri-cal Weather Prediction (NWP) models, both globaland regional, over the sub-tropical and tropicalPacific Ocean. The study consists of an analysisof two June/July/August periods (1998 and 2003)along an idealized cross section over the PacificOcean that encompasses both the ascending anddescending branch of the Hadley Circulation. Threemajor cloud types, namely stratocumulus, shallowcumulus and deep convective cloud systems, alloccur in a persistent and geographically separatedway, along the chosen cross section. These cloudsystems form a major focus of the process studiescarried out in GCSS using single-column versionsof the climate and NWP models, as well as cloudresolving models. GPCI will connect these processstudies to the simulation of cloud systems in thefull 3-dimensional models in a simplified and yetmeaningful way.

The main focus of the study is on processesrelated to the hydrological cycle within the HadleyCirculation. A special focus area will be theevaluation of the vertical humidity structure in boththe tropical and sub-tropical parts of the studyarea, using data that are becoming available from anew generation of satellite instruments, such as theAtmospheric Infrared Sounder (AIRS).

More details of the project, as well as instruc-tions on how to carry out the simulations and datarequirements can be found on the GCSS homepage(www.gewex.org/gcss.html). For questions and sug-gestions, please contact the lead scientist for theproject, Dr. Joao Teixeira ([email protected]).Results of an earlier version of the GPCI carriedout as part of the European Cloud System Study(EUROCS) can be found in Siebesma et al. (2004).

Reference

Siebesma, A. P., C. Jakob, G. Lenderink, and co-authors, 2004.Cloud representation in General Circulation Models over theNorthern Pacific Ocean: A EUROCS Intercomparison Study.Quart. J. Roy. Meteorol. Soc., 130, 3245-3267.

GCSS PACIFIC CROSS-SECTIONINTERCOMPARISON PROJECT

Christian Jakob1, Joao Teixeira2,Pier Siebesma3, and Roel Neggers4

1BMRC, Melbourne, Australia, 2UCAR/VSP,NRL, California, USA, 3KNMI, The

Netherlands, 4UCLA, California, USA

17February 2005

coast of California to the Inter-Tropical Conver-gence Zone, encompassing many major tropicaland subtropical cloud systems. An across-WG mi-crophysics effort is being established and the firstmeeting of the group will be held during the Pan-GCSS Meeting.

The WG on Boundary Layer Clouds (Chair:C. Bretherton – University of Washington) is con-tinuing its investigation of marine stratocumulusclouds and is currently focussing on the role ofdrizzle in such clouds. This study is likely to befollowed by an investigation into the role of pre-cipitation in small cumulus clouds. The WG onCirrus (Chair: S. Dobbie – University of Leeds) iscurrently devising a new case study for the group,most likely based on observations taken at the USDept. of Energy Atmospheric Radiation Measure-ment (ARM) Program Southern Great Plains (SGP)site. The WG on Extra-Tropical Layer Clouds(Chair: G. Tselioudis – NASA/GISS) is continuingtheir analysis of model performance during theMarch 2000 Intensive Observation Period at theARM SGP site in Oklahoma. New model evalua-tion techniques developed in this group show greatpromise in disentangling the causes for the modelerrors identified. The WG on Deep ConvectiveSystems (Chair: J. Petch – UK MetOffice) iscontinuing its work on the diurnal cycle of deepconvection and is preparing a new case study onthe transition from shallow to deep convectionover the tropical oceans using data from the Tropi-cal Ocean Global Atmosphere-Coupled OceanAtmospheric (TOGA-COARE) experiment. While geo-graphically separate, this study will have a closephysical relationship to that on the diurnal cycle. Inboth cases clouds grow gradually from shallow todeep convection, a process GCMs are currentlyonly poorly representing. The WG on Polar Clouds(Chair: J. Pinto – National Center for AtmosphericResearch) will focus on understanding and model-ling mixed-phase clouds that have been found tofrequently exist in the Arctic. The simulation ofsuch clouds is a challenge from both the cloud-dynamical and microphysical viewpoint. Data recentlycollected during the Mixed-Phase Arctic CloudExperiment (MPACE) will be a major source ofactivities for this working group.

Overall the work of GCSS is progressing well.The suggested small changes in focus, as well asthe more direct inclusion of the larger GCM andobservation communities, while building on ourstrengths in conducting detailed cloud process stud-ies, should make GCSS an even more relevantgroup in GEWEX and for the global researchcommunity.

WORKSHOP ON AMERICANMONSOON SYSTEMS

Montevideo, Uruguay17–18 September 2004

Jose MarengoCenter for Weather Forecasting and Climate

Studies-CPTEC/INPE, Brazil

The Third Workshop on Monsoon Systems as-sociated with the Coordinated Enhanced ObservingPeriod (CEOP) Inter-monsoon Model Study (CIMS)was held to: (1) provide a better understanding of thefundamental physical processes underpinning the di-urnal and annual cycles, and intraseasonal oscillationsin monsoon lands and adjacent oceanic regions, es-pecially in the Americas, and (2) to share experiencesand ideas on studies of processes and variability inthe American, Asian (Indian and Australasian) andAfrican monsoons.

Papers presented at the workshop included ob-servational studies on intraseasonal, interannual anddecadal timescale variability of the monsoon in theAmericas, the water and energy balances, the diurnalcycle, predictability of monsoons, teleconnections andregional forcing in the monsoon regions. A relativelynew aspect presented was the inclusion of aerosolsin monsoon development. Recent LBA studies havelinked the concentration of aerosols due to biomassburning in the Amazon to the physics of rainfall andthe onset of the rainy season in southern Amazonia(see article in the November 2004 issue of GEWEXNews). Conclusions from some of the workshoppapers are given below.

According to R. Mechoso, the core of the NorthAmerican Monsoon System (NAMS) is farther awayfrom the equator than the South American MonsoonSystem (SAMS) which is consistent with the seasonalchange in sea surface temperature (SST). Both SAMSand NAMS show intraseasonasl variations resemblingcontinental-scale models, in which precipitation inthe core monsoon region is negatively correlated withthat over the Northeast NAMS or Southeast SAMS,and they have stronger precipitation during El Niñoevents and weaker during La Niña, but low overallpredictability.

As introduced by H. Kim, the North AmericanMonsoon Model Assessment Project (NAMAP) pro-vided comparable control runs from six models forthe monsoon of 1990. These were used to assess theability of state-of-the-art regional and global modelsto simulate the seasonal evolution and diurnal cycle

February 200518

of atmospheric circulation, hydrometeorology, andland surface flux fields across the domain of theNAMS. Model simulations of the moist surges alongthe Gulf of California and the connection betweenTropical Easterly Waves (TEW) and moist surgesshow that they are related to the initiation and propa-gation of some of the Gulf surge events (H. Berbery).

In the SAMS region El Niño events impact pre-cipitation by enhancing or suppressing the mechanismsthat produce rainfall (A. Grimm). In the case of thesummer monsoon, the driving mechanism is the es-tablishment of a continental heat flow and a thermalcontrast between the continent and ocean that bringsabout circulation anomalies. These anomalies provideenhanced moisture convergence, which leads to moist-ening and destabilization of the troposphere and thus,to enhanced convection. A regional climate model,RegCM, has been used to assess the influence ofgiven conditions for soil moisture, topography, changesin parameterizations, and short-term changes in theAtlantic SSTs. RegCM simulations of seasonal ex-tremes and subseasonal statistics of rainfall for SouthAmerica (by A. Seth) showed that RegCM has po-tential for improving the location of ITCZ in a largerdomain. The results appear to be quite sensitive todomain size. As one of the components of theSAMS, J. Marengo discussed the South Americanlow level jet (SALLJ) and its importance in transport-ing moisture and aerosols from Amazonia to subtropicalSouth America. Recent work has shown that thefrequency and intensity of the SALLJ events exhibitconsiderable variability on intraseasonal, interannualand even longer time scales.

According to I. Cavalcanti, prediction of SAMSduring the summer must address climatological mon-soon features, changes during ENSO, the low frequencyand high frequency variability, the diurnal cycle andthe SACZ and SALLJ features. Y. Xue showed thatthe land surface processes, especially vegetation, af-fect summer monsoon simulations at continental andsynoptic scales. He concluded that vegetation affectsthe surface energy partitioning, modifies the heatgradients, circulation, and evaporation through non-linear and complex interactions.

According to R. Terra the diurnal phase of large-scale ascending motion and precipitation in CentralAmazon and the coastal region are almost in oppositephases, suggesting different diurnal convective desta-bilization mechanisms: Central Amazon is dominatedby surface heating over adiabatic cooling and for theCoastal Region convergence induced by coastal cir-culations plays a role. For NAMS, M. Lee showedthat large diversities in the diurnal cycle simulations

exist between GCMs in terms of amplitude and peakphase of rainfall. In general, models tend to reachtheir maximum phase of rainfall 2–3 hours earlier thanobserved over the deep convective region. T. Yasunarireported on the diurnal variability, elevated heat source,and water cycle variability in monsoon regions.

The La Plata Basin analyses of the National Cen-ters for Environmental Prediction (NCEP) reanalysesand the Eta/NCEP (H. Berbery) gave good agreementbetween the basin average time-mean model precipi-tation and the observed precipitation, although P-Eand moisture flux convergence (or observed streamflow)differ by about 0.28 mm/day, suggesting that themodel is somewhat high. According to I. Camillonithe Paraná and Uruguay basins are part of a regionin SE South America that has a strong precipitationsignal during ENSO events, and most of the extrememonthly discharge events occur during El Niño andnone during La Niña.

Both the European Center for Medium-RangeWeather Forecasts (ECMWF) and the Indian Na-tional Center for Medium Range Weather Forecasts(NCMRWF) model precipitation forecasts over Indiahave a tendency to over-predict the frequency ofprecipitation events in the light and moderate catego-ries and to under-predict events in higher categoriesduring the monsoon season (M. Basu). The magni-tude of bias is larger for the NCMRWF modelforecasts than the ECMWF model forecasts. Orog-raphy plays an important role in monsoons, especiallyin the Asian monsoon in the Himalayas (M. Bollasina).Furthermore, the phase of diurnal variation of precipi-tation in tropical Asia for the Indochina Peninsula andBangladesh depends on the distance from mountains(T. Satomura). According to W. Lau the mecha-nisms of aerosol-water cycle interaction include adirect effect, providing cooling effects due to thereflection of sunlight and a semi-direct effect withabsorbing aerosols reducing atmospheric convec-tion by surface cooling and heating in the lowertroposphere and enhancing low level heating andmoisture convergence, thus increasing convectionand rainfall. Aerosol transport and interaction withlarge-scale dynamics is also important for aerosol-atmospheric chemistry interaction. For the SoutheastAsia monsoon region and adjacent oceanic regions,monsoon rainfall is generally reduced in associationwith aerosol-induced reduction in land surface tem-perature. However, heating by absorbing aerosolsmay cause an early onset and intensification of theIndian monsoon with an enhanced rainfall anomalyoccurring over northern India and the Bay of Ben-gal (see page 7).

19February 2005

larly through modeling. Data exchange and coordi-nated modeling studies will be two key parts ofCOPAM. The new program functions will be: (1)promotion of coordinated/cooperative studies withinAsian monsoon countries; (2) modeling/predictionstudies of the Asian monsoon, hydro-climate andwater resources in Asia, including development,intercomparison and transfer models; (3) data collec-tion for hydro-climate and water-resources studies;(4) promotion of international workshops and trainingseminars; and (5) data archival. The WMO/WCRPdata policy (free and open exchange) for internationalresearch communities that was used in GAME will becontinued in COPAM. Components of the new pro-gram would consist of national and internationalprojects, a program promotion office/center, a coor-dinated modeling center, a data archiving andmanagement center, and regional centers. Relation-ships of the new project with the Global EarthObservation System of Systems (GEOSS) and theIntegrated Global Observing Strategy-Partnership(IGOS-P) Water Theme will be emphasized.

Following the GISP Meeting, the 6th Interna-tional Study Conference on GEWEX in Asia andGAME was held on 3–5 December with about 180participants from 14 countries. The presentationsconsisted of keynote talks, summary reports of sub-projects, talks on proposed programs, projects, andposter presentations. GAME was recognized as asuccess story and a future research program/projectto extend GAME’s fruitful results was strongly rec-ommended. The need for involvement of the operationalagencies, particularly, for modeling activities, wasemphasized. The model activity would include re-gional climate model development. It was agreed thatthe budgetary support should be from each domesticgovernment and that the scientific and operationalcommunity should propose a budget for research.GAME was focused on the land-atmosphere interac-tion. However, the ocean plays a major role in themonsoon activity, and the relationship of GEWEXand CLIVAR was discussed. The winter monsoonwas one of the identified themes. Thus far, much ofthe research is focused on the summer monsoon, butgreater precipitation is associated with the wintermonsoon in some regions, and many people stressedits importance. A kick-off workshop for the newprogram/project may be held in the Spring of 2005in Japan.

9th GISP MEETING AND6th GAME STUDY CONFERENCE

1–5 December 2004Kyoto, Japan

Kenji NakamuraGAME International Project OfficeHyARC, Nagoya University, Japan

The 9th GEWEX Asian Monsoon Experiment(GAME) International Science Panel (GISP) Meetingwas held at the Kyoto International Community House,Kyoto, Japan, 1–2 December with the support of theMinistry of Education, Culture, Sports, Science andTechnology of Japan, the World Climate ResearchProgramme, the Japan Aerospace Exploration Agency,and the Hydrospheric Atmospheric Research Center,Nagoya University.

The major focus of discussion was on the needfor and nature of a follow-on activity to the GAMEProject, which through its strong international col-laboration, has successfully clarified the basic processesof land-atmosphere interactions through regional ex-periments and monitoring. However, the mechanismsand the variations in the Asian monsoon are still notfully understood and the necessity for understandingthese was recognized. Every Asian country has seri-ous hydrometeorological problems (e.g., extremeweathers, floods, glacier retreats, permafrost degrada-tion) and many of these are closely related to themonsoon activity. Thus, many domestic projects withinternational collaboration will be continued or arebeing planned.

For the GAME follow-on, the basic scientificobjectives will remain the same: (1) understanding therole of the Asian monsoon on the hydrological cycle,and (2) improving prediction of the regional or basinscale hydrological cycle and water resources in mon-soon Asia. A third objective will be added,“understanding the impact of global warming andother anthropogenic forcing on the hydrological cycleand hydro-climate in monsoon Asia.” To attain theseobjectives, international collaboration is essential andthe gap between operational agencies and researchcommunities should be reduced.

It was concluded that the GAME follow-on ac-tivity should be within GEWEX or WCRP. Thetentative name of the project is the CoordinatedObservation and Prediction of Asian Monsoon Cli-mate (COPAM). The target time scale for COPAMstudies will be seasonal, interannual and long-termvariations. The new project will also contribute tosolving and mitigating local hydrological issues, particu-

GEWEX/WCRP MEETINGS CALENDARFor a complete listing of meetings, see the

GEWEX web site (http://www.gewex.org)

February 200520

EXPLICIT GCM VEGETATIONPARAMETERIZATION NEEDED

TO SIMULATE MONSOONS

AEROSOL-INDUCED RAINFALLAND SURFACE PRESSURE

ANOMALIES IN THE ASIAN MONSOON

Temporal evolution of the 10-day mean precipita-tion (mm day–1) averaged over 105–120 E fromMay through September. (a) CMAP; (b) GCM/Soil(c) GCM/Veg (after Xue et al., 2004a). See articleon page 5.

GEWEX NEWS

Published by the International GEWEX Project Office

Richard G. Lawford, DirectorDawn P. Erlich, Editor

Mail: International GEWEX Project Office1010 Wayne Avenue, Suite 450Silver Spring, MD 20910, USA

Tel: (301) 565-8345Fax: (301) 565-8279

E-mail: [email protected] Site: http://www.gewex.org

2004 NAME FIELD CAMPAIGNEXTENSIVE NEW DATA SET

Observing system enhancements for the NAME 2004Enhanced Observing Period. See article on page 13.

Spatial pattern of aerosol-induced seasonal mean(JJA) anomalies of a) rainfall, and b) sea levelpressure and 850-mb wind, based on the experi-ments with the NASA fvGCM-GOCART model. Seearticle on page 7.

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