Post on 23-Feb-2016
description
Robert G. Ellingson and the ARESE II Science Team
Department of MeteorologyUniversity of Maryland
College Park, MD
ARESE II: Description and Initial Results
(ARM Enhanced Shortwave Experiment)
Motivation• Knowledge of the amount and location of solar energy
absorption is key to understanding the general circulation of the ocean and atmosphere and to our understanding and prediction of climate change.
• Measurements of the amount of solar radiation absorbed within clouds have yielded conflicting results. Many studies show much more absorption than can be explained by theory.
• If excess or enhanced absorption is true - we must:• reexamine our knowledge of the basic physics • modify climate models, AND • change remote sensing techniques.
The ARESE Experiments - Objectives
• Directly measure the absorption of solar radiation by the clear and cloudy atmosphere and
• investigate the causes of any absorption in excess of model predictions.
ARESE I - 25 September - 1 November 1995ARESE II - 15 February - 15 April 2000
ARESE I - A Thumbnail Sketch
• Used three aircraft platforms, as well as satellites and the ARM central and extended facilities in North Central Oklahoma
• Measured solar radiative fluxes at different altitudes and at the surface with spectral broadband, partial bandpass, and narrow bandpass filters
• Measurements obtained from aircraft flying in stacked formation over horizontal legs extending over several hundred kilometers
25 September - 1 November 1995
ARESE I - broadband absorptance increases with cloud fraction
Courtesy of R. Cess - SUNY Stonybrook
10 km10 km
Fluctuations of cloud liquid water
aerosol & water vapor
are assumed to be
horizontally homogeneous
Flight patterns : to fly over the CF with REVISIT times of
4 -5 min ., about 10 ind. samples/h., or 30 per 3 h. flight.
Central Facility
1 min 3 min 3 min 1 min
A schematic plot of the Observing System Simulation
with one aircraft above clouds and ground-based
radiometers
ARESE-II Conducted During Feb -Apr ‘00
Simulation by A. Marshak
ARESE-II was coordinated with an ARM Cloud IOP - insitu measurements of cloud microphysics
• Major Features• Unique sampling strategy - single
aircraft overflying SGP CART site on only overcast days
• Multiple independent instruments making same measurements with different technologies (aircraft and ground)
• Extensive pre- and post- experiment calibrations
• Long duration during a period of climatologically high frequency of extensive overcast (~ 6 cases)
• Science Team with considerably different pre-experiment views
The ARESE-II Measurement Strategy Differed Significantly From ARESE-I
• Used single aircraft (Twin Otter) repeatedly overflying surface instruments
• Single aircraft reduced cost, makes long deployment possible
• ARESE-I showed thick stratus approach uniform case
• 2 years CART data 4-6 uniform stratus cases in 6-week period
• Consistent with simulations by R. Cess and by A. Marshak
One of 2 flight patterns(6 min revisit, 83% duty cycle)
Ingress
Central facility
Continue on
Blue=data flight legRed=data not valid
DHC-6 Twin-Otter
Photos courtesy of Tim Tooman
Conditional Sampling(theory)
from Marshak et al., 1999: On the Removal of the Effect of Horizontal Fluxes in Two-Aircraft Measurements of Cloud Absorption. Quart. J. Roy. Meteor. Soc., 558, 2153-2170.
Atrue(x) =(1−ϖ0)σ (x) I(Ω,x,z)dΩdz4π∫
zbase
ztop
∫ Aapp(x) =[1−R(x)]−[T(x)−0] =
1− ΩI(Ω,x,ztop)dΩ− ΩI(Ω,x,zbase)dΩ2π −∫
2π +∫
H(x) =Aapp(x) −Atrue(x)
Uε = x:H500nm(x) ≤ε{ }
x: Atrue(x)∩ Aapp(x) ≠∅{ }= x:H500nm≈0{ }
x:HBroadBand(x) =0{ }?
-1
-0.5
0
0.5
1
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4
Aapp
(x)
Atrue
(x)
-1
-0.5
0
0.5
1
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4
all x∈[0,L]x∈U
ε,ε=0.01
Aapp
(x)
Atruε
(x) Courtesy ofAlexander Marshak
Extensive Spectral and Broadband Calibrations Were Performed Before and After ARESE II
• Spectral calibrations at Ponca City airport using lamps traceable to the ARM working standard
• Broadband calibrations at Blackwell-Tonkawa airport• Broadband calibrations at SGP site• Surface measurements at SGP 19 February through 6
April 2000
ARESE II Broadband Calibration Facility at Blackwell-Tonkawa Airport
Photos courtesy of Joe MichalskyPNNL/SUNY
Direct Measurement Uncertainty
3 W/m2
Diffuse Measurement Uncertainty
5 W/m2
But ...Slide courtesy of Joe MichalskyPNNL/SUNY
The Twin Otter Payload Was Significantly Enhanced Over ARESE I
3 sets of spectral and broadband nadir and zenith viewing radiometersScripps, RAMS total solar broadband hemispheric (224-3910 nm) ValeroScripps, RAMS fractional solar broadband hemispheric (680-3300 nm)Scripps, RAMS total direct-diffuse hemispheric; seven bands(495-505; 400-450; 450-500; 500-550; 550-600; 600-650; 650-700 nm)
NASA ARC SSFR (300-2500 nm in ~300 channels) PilewskieCSU SSP2 (400-2500 nm in ~100 channels) StephensMRI, CM21 broadband hemispheric (3350-2200 nm) AsanoSNL, CM22 broadband hemispheric (3350-2200 nm) ToomanCloud and meteorological measurementsJPL/UMASS ACR nadir viewing radar SekelskyBNL total temperature ToomanBNL static pressureBNL chilled mirror hygrometer
QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.QuickTime™ and aQuickDraw decompressorare needed to see this picture.
ARESE II Summary• High quality data obtained on several clear and overcast days
(03/03, 03/17, 03/18, 03/21, 03/29 {best ones})• b1 data released by instrument PIs to ARESE II Science Team
in Sept 2000 (some data in better state than others)• ARESE II ST data discussion meeting 24-26 Oct 2000• Reprocessing with common calibration Nov-Dec 2000• ARESE II ST meeting 8-9 Feb 2001 - preliminary findings• Data released to science community 17 March 2001• Publication of ARESE II Science Team papers in progress
For additional information see the ARM UAV Homepagehttp://armuav.atmos.colostate.edu/
Looking for the Right Stuff
March 29, 2000 - An Excellent Example
NCEP Forecasts Are A Must!!!!
What Did We See From Space?
Alti
tude
(km
AG
L)
CART MMCR Reflectivty
Otter Cloud Radar
1800 20001900Time (UTC)
0
3
5
Alti
tude
(km
MSL
)
Flight Track
Latit
ude
(°N
)(°E )
What Did We See From the Aircraft and Ground?
Diffuse Field Camera
Image courtesy of Tim Tooman
Spectral Distribution of Fluxes From the SSFR
SSFR Upwelling Fluxes - 03/29/00W
avel
engt
h (n
m)
Time (hours)
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
400
600
800
1000
1200
1400
1600
18.5 20.519.5
Preliminary SSFR Data From 29 March 2000
Wavelength (nm)
400 600 800 1000 1200 1400 1600
Alb
edo
Irra
dian
ce (W
m-2 n
m-1)
Nadir irradiance
Albedo
1930 UTC
Data courtesy of Peter Pilewskie, NASA Ames
Broadband Fluxes
500
600
700
800
18.5 19 19.5 20 20.5
RAMSCM22
Time (GMT)
900
1000
1100
1200RAMSCM22
Downwelling Flux
Upwelling Flux
March 29, 2000
ARMARMAtmospheric Radiation MeasurementAtmospheric Radiation Measurement
Defined as the layer absorption divided by the downwelling solar flux at the top of layer (aircraft level)
Absorptance
Slide courtesy of Tom Ackerman
Conditional Sampling(March 29)
-0.1
0
0.1
0.2
0.3
0.4
0
0.02
0.04
0.06
0.08
0.1
18.5 19 19.5 20 20.5
500nm_abs_329liq
absorptance liq (cm)
GMT (h)
-0.1
0
0.1
0.2
0.3
0.4
0
0.02
0.04
0.06
0.08
0.1
18.5 19 19.5 20 20.5
500nm_abs_329BB_abs_329 liq
absorptance liq (cm)
GMT (h)
-0.1
0
0.1
0.2
0.3
0.4
0
0.02
0.04
0.06
0.08
0.1
18.5 19 19.5 20 20.5
500nm_abs_329BB_abs_329500nm_abs_329
liq
absorptance liq (cm)
GMT (h)
-0.1
0
0.1
0.2
0.3
0.4
0
0.02
0.04
0.06
0.08
0.1
18.5 19 19.5 20 20.5
Conditional sampling and LWP3_29_00
500nm_abs_329
BB_abs_329
500nm_abs_329
BB_abs_329
liq
absorptance liq (cm)
GMT (h)0
2
4
6
8
10
12
14
0.205 0.21 0.215 0.22 0.225 0.23 0.235 0.24 0.245
BB absorptionHistogram
March 29, 2000
frequ
ency
BB absorption
-0.1
0
0.1
0.2
0.3
0.4
18.5 19 19.5 20 20.5
500nm_abs_329
BB_abs_329
500nm_abs_329
BB_abs_329 CART siteoverpass
absorptance
GMT (h)
Courtesy ofAlexander Marshak
Analysis courtesy of Bob Cess using data from 10/00
Analysis courtesy of Bob Cess using data from 10/00
0.0
0.1
0.2
0.3
0.4
0.0 0.1 0.2 0.3 0.4
02270303032003210329
TSBR absorptance
ARESE II: absorptance
Pope, Valero et al. 2001
These data are from the five days for which absorptance measurements from the CM22 radiometers and the TSBR radiometers can be compared.
There are two clear days, 0227 and 0320, with low absorptance values, and three cloudy days with higher absorptances. Agreement between the two types of radiometers is very good. (A 3% difference in the upwelling at 7 km on 0303 accounts for the offset in absorptance on that day.)Conclusion: The two different types of radiometers yield the same measured absorptance in both clear and cloudy conditions.Results courtesy of Pope et al.
Preliminary Comparisons of Model Calculations with
Observations
ARMARMAtmospheric Radiation MeasurementAtmospheric Radiation Measurement
ARESE2 March 2000, Cloudy-sky Flights
0
50
100
150
200
250
300
March 3 March 21 March 29
TSBRCM22SBDART
Results courtesy of Ackerman et al.
Bars represent leg to leg variability
Absorptance in ARESE II Flights
0.00
0.05
0.10
0.15
0.20
0.25
0.30
27-Feb 20-Mar 3-Mar 21-Mar 29-Mar
TSBR CM22 CM21 Model
Clear cases
(Bars indicate leg to leg variability)
Results courtesy of Ackerman et al.
Ignore CM21 results shown here
0.00
0.05
0.10
0.15
0.20
0.25
0227 0303 0317 0320 0321 0329 0403
ARESE II – day averages
date
range of modelvalues
Pope, Valero et al. 2001
Day averages of absorptance (from TSBR measurements) show values of 0.10 to 0.12 for the clear days and values of 0.20 to 0.23 for the cloudy days. A standard model gives absorptance values ranging from 0.10 for clear sky to 0.15 for cloudy sky (optical depth 60).
Conclusion: observed cloudy-sky absorptances are significantly greater than model predictions.
Results courtesy of Pope et al.
MMCR
AOS
MWR
MPLBLC
MFRSRMFR
SMOS
TOMSBBSS
SSPSSFR SB3D
MIE SBMOD
RAMS
CM21/22s
TDDR
SHORTWAVEABSORPTIONCOMPARISON
aerosol
surface
atm.
cloud
model obs. obs.
O’Hirok and Gautier, 2001
CLOUD RECIPE
Ø COMPUTE MMCR MODE 1 and 3
Ø COMPUTE CLOUD BASE
Ø MASK REFLECTANCE FIELD (min. threshold)
Ø COMPUTE ICE WATER CONTENT [Frisch et al. 1995, Platt, 1997]
Ø COMPUTE DRIZZLE [Liu and Illingworth, 2000]
Ø DERIVE CLOUD OPTICAL THICKNESS FROM MFRSR
Ø COMPUTE MEAN RE FROM TAU AND LWP (MWR)
Ø DERIVE LWC FROM MMCR AND LWP [Dong et al. 2000]
Ø DERIVE N FROM LWC AND MEAN RE –
Ø COMPUTE RE AT ALL CELLS –
Ø CONVERT TIME CONSTANT TO SPATIAL CONSTANT (wind)
Ø INTERPOLATE ONTO 1000 COLUMN x 150 LAYER GRID
Ø BAKE AT 350° FOR ONE HOUR AND ENJ OY
O’Hirok and Gautier, 2001
17:30 21:30 UTC0 75 km
03/29/2000
120
0
60
9
0
structure
within 2.5 km of cart site
optical thickness
km
t = 55re = 7.5
O’Hirok and Gautier, 2001
visible near-ir total
0.1
0.2
0.3
0.4
0.5
0.0
ModelRAMSCm22
Absorptance
March 03 2000
+/-5%
+/-10%
O’Hirok and Gautier, 2001
0.1
0.2
0.3
0.4
0.5
0.0
ModelRAMSCm22
Absorptance
March 21 2000
+/-5%
+/-10%
visible near-ir total O’Hirok and Gautier, 2001
visible near-ir total
0.1
0.2
0.3
0.4
0.5
0.0
ModelRAMSCm22
Absorptance
March 29 2000
+/-5%
+/-10%
O’Hirok and Gautier, 2001
ref rnd ipa re x2 drz ice x4
0.06
0.03
0.4
0.3
0.25
0.15
RAMSCm22
visible absorptance
near-ir absorptance
total absorptance
March 29 2000 model sensitivity
O’Hirok and Gautier, 2001
Summary conclusions to date
• Ackerman et al. - Differences between modeled and observed absorption on cloudy days are order 10%
• Pope et al. - observed cloudy-sky absorptances are significantly greater than model predictions.
• O’Hirok and Gautier - major differences between observations and calculations are in the near IR, but total differences are within the order 10% range.
Common to all
• Observed absorption is greater than calculated
• Smaller absorption and smaller discrepancies than ARESE I
Problems and Paths Forward• Apparent disagreement between different models -
use ICRCCM as an arbiter
• Causes of the discrepancies not yet identified - expanded use of the spectral data and extensive examination of all the data by the ARM Science Team and the general science community
• The data are there - Have at them!!!
ARESE-II has a broad-based Science Team
Ackerman, Tom (PNNL) Marshak, Sasha (Univ Maryland)
Asano, Shoji (Tohoku Univ) Michalsky, Joe (SUNY Albany)
Cahalan, Bob (NASA GSFC) Minnis, Pat (NASA LRC)
Cess, Bob (SUNY, Stony Brook) Sekelsky Steve (Univ Mass)
Ellingson, Bob* (Univ Maryland) Stephens, Graeme (CSU)
Gautier, Catherine (UCSB) Tooman, Tim (SNL)
Long, Chuck (PSU) Valero, Francisco (Scripps)
Mace, Jay (Univ Utah) Vitko, John (SNL)
Marchand, Roger (PNNL) Wiscombe, Warren (NASA GSFC)
* Mission Scientist
Pre- and Post- ARESE II Boadband Calibrations Data
courtesy of Joe MichalskyPNNL/SUNY
Pre-
Pre-
Post-
Post-