IMPORTANCE OF BOUNDARY LAYER PROCESSES FOR SURFACE FLUXES Erica McGrath-Spangler PhD Defense 20...

IMPORTANCE OF BOUNDARY LAYER PROCESSES FOR SURFACE FLUXES

Erica McGrath-Spangler

PhD Defense20 October 2011

Acknowledgements

• Dr. Scott Denning• Drs. Dave Randall, Colette Heald, Dusanka

Zupanski, and Jennifer Hoeting• Denning group members• Data providers• Family and Friends

Outline• Introduction and Motivation•PBL Top Entrainment• Idealized Experiment• Case Study•PBL Depth from Space•Conclusions and Future Work

Introduction and Motivation

• Planetary boundary layer (PBL) • Turbulent layer closest to the Earth’s surface

• Determines surface fluxes of heat, moisture, momentum• Interacts with clouds, radiation, convection,

aerosols, pollutants• Transport of water vapor and momentum• Scalar quantities (CO2, H2O, heat) diluted by

depth of the PBL

Stull, 1988; Beljaars and Betts, 1993

PBL top

Free Atmosphere

Potential Temperature

CO2

Entrainment Zone

Idealized

• Response of CO2 mixing ratio to a surface flux is inversely proportional to the depth of the PBL• A deeper PBL will dilute

a flux signal relative to a shallower PBL• In models, need to get

the depth of the PBL right in order to get the CO2 mixing ratio correct

Shallow PBLHigh CO2

Deep PBLLow CO2

Another way to look at this

Full Glass => Deep PBL ½ Glass => Shallow PBL

Full Glass => Deep PBL

CO2 Flux CO2 Flux

½ Glass => Shallow PBL

Full Glass => Deep PBL ½ Glass => Shallow PBL

Small Impact Large Impact

Air Parcel

Air Parcel

Air Parcel

Inverse Modeling

Wind Wind

SourcesSinks

Sample Sample

Changes in CO2 in the airtell us about sources and sinks

But what if we don’t know the vertical

transport??

• The PBL depth is hard to observe• 1-2 km above the ground• Wind profilers and aircraft are

expensive • Limited spatially and temporally

• Radiosondes launched at the wrong times within the US (0 and 12 UTC)• Measure only one point in space/time

and may differ from average by up to 40%

Angevine et al., 1994

What happens when we try to model PBL depth?

• Sunny, midday PBL depths• June, July, and August• 2006-2010• Qualitatively similar• Very different

quantitative results!

500

1000

1500

2000

2500

3000

• Different methods exist to evaluate the PBL depth• Turbulent Kinetic Energy• Heat Diffusivity• Temperature profiles• Bulk Richardson number• PBL processes are often small-scale and not

resolvable by the models• Parameterizations exist, but these are based

on empirical data from idealized experiments

• Overshooting thermals produce entrainment of free tropospheric air into the PBL

• Parameterize the effects

PBL top

Free Atmosphere

Potential Temperature

CO2

Entrainment Zone

e.g. Stull 1988

Overshooting Thermals

Atmosphere

Land

Land-Atmosphere


Entrainment

Atmosphere

Land

Land-Atmosphere


Weaker Capping Inversion Deeper PBL Warmer, Drier PBL

Atmosphere

Land

Land-Atmosphere

Entrainment



Dilution of Surface Fluxes

Atmosphere

Land

Land-Atmosphere

Entrainment




Higher Daytime CO2

Atmosphere

Land

Land-Atmosphere

Entrainment




Higher Daytime CO2

Stomatal Closing Decreased Cloud Cover

Atmosphere

Land

Land-Atmosphere

Entrainment




Higher Daytime CO2

Decreased Cloud Cover

Decreased CarbonAssimilation

Atmosphere

Land

Land-Atmosphere

Decreased Latent Heat,Increased Sensible Heat

Greater Surface Heat Flux

Stomatal Closing

Entrainment




Higher Daytime CO2



Changes in Surface Pressure,Precipitation Patterns, WindVelocity, etc

Atmosphere

Land

Land-Atmosphere



Stomatal Closing

Entrainment




Higher Daytime CO2





Changes in Surface Pressure,Precipitation Patterns, WindVelocity, etc

Changes in Large-ScaleWeather and Climate

Atmosphere

Land

Land-Atmosphere

Stomatal Closing

Entrainment

Idealized Experiment

• Simple Biosphere 3 – Regional Atmospheric Modeling System (SiB-RAMS)• Idealized experiment• Horizontally homogeneous• Cyclic boundary conditions• No cloud formation• 5x5 grid over WLEF tower in N. Wisconsin

McGrath-Spangler et al., 2009

Potential Temperature H2O Mixing Ratio

Hei

ght

Hei

ght

Kelvin g/kgMcGrath-Spangler et al., 2009

Controlα = 0.2

Controlα = 0.2

• Deeper PBL dilutes CO2 fluxes•Warmer, drier

conditions impact physiological stress factors• Shifts Bowen ratio• Changes

photosynthesis

CO2 Concentration

Local Time

ppm

McGrath-Spangler et al., 2009

Controlα = 0.2

Case Study

• July – September 1999• Fully 3D Model• Nudged lateral boundary conditions• North America domain with 40 km grid

intervals• Initialized from reanalysis

McGrath-Spangler and Denning, 2010

7 ppm

McGrath-Spangler and Denning, 2010

PBL Depth from Space• Cloud-Aerosol LIDAR and

Infrared Pathfinder Satellite Observations (CALIPSO)• Launched April 2006, First light

June 2006• Part of the Afternoon

(A-train) constellation of satellites

e.g. Winker et al., 2007

• CALIOP LIDAR is sensitive to aerosols and clouds• Lidar measures the scatter of a laser beam off of

objects such as aerosols, clouds, and the ground• CALIOP has a horizontal resolution near the

surface of 0.33 km and a vertical resolution of 30 m• Emits light at 1064 nm (infrared) and polarized

light at 532 nm (green)• First satellite lidar optimized for aerosol and

cloud measurements• CALIOP acquires 1.7 million laser shots every 24

hours

e.g. Winker et al., 2007; 2009

PBL from SpaceRocky MountainsOcean Mexican Plateau

Altit

ude

(km

)

•Method initially developed by Jordan et al. (2010) • Identifies a local maximum in LIDAR 532 nm

backscatter collocated with a maximum in the variance in the backscatter• Entrainment zone has mixing of aerosol-

laden PBL air mixing with clean, free tropospheric air or capped by boundary layer clouds

• Search only between 250 m and 5 km AGL• Remove surface noise• Remove unclear aerosol signatures

• Reject profiles attenuated by thick clouds• Identified by high values in the 1064 nm

backscatter• Boundary layer clouds accepted

• Accept only easiest to retrieve

Backscatter

Variance

Retrieved PBL

km-1 sr-1

Hei

ght (

km)

CALIPSO 532nm Total Attenuated Backscatter

km-1 sr-1

CALIPSO 532nm Total Attenuated Backscatter

Hei

ght (

km)

Backscatter

Variance

Latitude, Longitude

PBL DepthSurface

Yucatán Peninsula Little Rock, AR Winnipeg, Manitoba

CleanProfile

5000 10002500 7500 12500

PBL Height (m)

25 50 75

• Success decreased by cloud cover and unclear aerosol signature• Greatest success over

water• Reduced success over

highly convective regions• Florida and the Gulf

Coast• Rocky Mountains and

Mexican Plateau

• Success ranges from 15% to near 100%

1000 1500 2000 2500

• Deeper PBL over land• Shallow PBL off

California coast• Shallow PBL over

Midwest farmlands• Deeper PBL over

Rocky Mountains and Mexican Plateau• Deeper PBL over

Canada - stomatal control and longer day length

100 400 700 1000

• Lowest variability over water• Highest variability

along Rocky Mountains and boreal North America• Standard deviation of

almost 1 km here in Colorado!

• MERRA reanalysis• At times and

locations of satellite overpass• Above 55°N,

daytime PBL not yet developed

500 1000 1500 2000 2500 3000

MERRA is deeper CALIPSO is deeper25 50 75 100 125 150 175

• Compares MERRA reanalysis to CALIPSO• Over much of US,

CALIPSO and MERRA give similar results• Over SW US, MERRA

deeper• Off California coast and

boreal Canada, CALIPSO deeper• Boreal MERRA PBL not fully

developed by time of overpass

• Off CA coast, CALIPSO detects stratocumulus cloud top

Relevance to Inversions• If observed PBL is shallower than simulated, inversion

adjustment should be decreased• Model CO2 is too high, inversion increases photosynthesis• Decrease PBL depth, photosynthesis is more concentrated so in

new inversion, increase photosynthesis less• Southwestern United States

• If observed PBL is deeper than simulated, inversion adjustment should be increased• Model CO2 is too high, inversion increases photosynthesis• Decrease PBL depth, photosynthesis is more dilute so in new

inversion, increase photosynthesis more• Boreal Canada

Conclusions and Future Work

• PBL depth is important for carbon budget studies, especially inversion studies• Inaccurate PBL depths produce inaccurate

CO2 mixing ratios, even for perfect surface fluxes•Millions of satellite observations can be used

to determine PBL depth and constrain model simulations• Initial estimates are qualitatively reasonable

• Success of the retrieval is greatest over subtropical oceans• General success over land is about 50%• Decreased success over mountainous United

States and convective regions• Underprediction of PBL depths by reanalyses

over oceans• Overprediction by reanalyses over SW United

States

Zupanski et al. 2007

Atmospheric CO2

FoutFin

Future Work• Data Assimilation• Optimize entrainment fluxes using well-observed

variables (T, Td, etc.) and space-borne measurements of PBL depth• Use CO2 observations to optimize CO2 fluxes

FT(x,y,t) = βRESP(x,y)*Fin(x,y,t) – βGPP(x,y)*Fout(x,y,t)

• CALIPSO PBL Depth• Compare to and evaluate against other

observations• Extend analysis spatially and temporally• Compare CALIPSO PBL depth to aerosol

distributions in models

Thank you.

Questions?

References• Angevine, W. M., A. B. White, and S. K. Avery (1994), Boundary-layer depth and entrainment zone characterization with a boundary-layer

profiler, Boundary-Layer Meteorology, 68(4), 375-385.

• Beljaars, A. C. M., and A. K. Betts (1993), Validation of the boundary layer representation in the ECMWF model, paper presented at Seminar Proceedings on Validation of Models over Europe, ECMWF, Reading, England.

• Corbin, K. D., A. S. Denning, E. Y. Lokupitiya, A. E. Schuh, N. L. Miles, K. J. Davis, S. Richardson, and I. T. Baker (2010), Assessing the impact of crops on regional CO2 fluxes and atmospheric concentrations, Tellus B, 62(5), 521-532.

• Jordan, N. S., R. M. Hoff, and J. T. Bacmeister (2010), Validation of Goddard Earth Observing System-version 5 MERRA planetary boundary layer heights using CALIPSO, J. Geophys. Res., 115(D24), D24218.

• Lokupitiya, E., S. Denning, K. Paustian, I. Baker, K. Schaefer, S. Verma, T. Meyers, C. J. Bernacchi, A. Suyker, and M. Fischer (2009), Incorporation of crop phenology in Simple Biosphere Model (SiBcrop) to improve land-atmosphere carbon exchanges from croplands, Biogeosciences, 6(6), 969-986.

• McGrath-Spangler, E. L., A. S. Denning, K. D. Corbin, and I. T. Baker (2009), Sensitivity of land-atmosphere exchanges to overshooting PBL thermals in an idealized coupled model, Journal of Advances in Modeling Earth Systems, 1(Art. #14), 13 pp.

• McGrath-Spangler, E. L., and A. S. Denning (2010), Impact of entrainment from overshooting thermals on land–atmosphere interactions during summer 1999, Tellus B, 62(5), 441-454.

• Okamoto, H., et al. (2007), Vertical cloud structure observed from shipborne radar and lidar: Midlatitude case study during the MR01/K02 cruise of the research vessel Mirai, J. Geophys. Res., 112(D8), D08216.

• Stull, R. B. (1988), An introduction to boundary layer meteorology, 666 pp., Kluwer Academic Publishers, Norwell, MA.

• Winker, D. M., W. H. Hunt, and M. J. McGill (2007), Initial performance assessment of CALIOP, Geophys. Res. Lett., 34(19), L19803.

• Zupanski, D., A. S. Denning, M. Uliasz, M. Zupanski, A. E. Schuh, P. J. Rayner, W. Peters, and K. D. Corbin (2007), Carbon flux bias estimation employing maximum likelihood ensemble filter (MLEF), J. Geophys. Res.-Atmos., 112(D17).

IMPORTANCE OF BOUNDARY LAYER PROCESSES FOR SURFACE FLUXES Erica McGrath-Spangler PhD Defense 20...

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