Penn State

K. Davis, K. Craig, A. Desai, S. Kang, B. Reen, S. Richardson, N. Seaman and D. Stauffer

Department of MeteorologyThe Pennsylvania State University

University Park, PA

Mesoscale variability in convective boundary layer

structure observed during IHOP:

Causes and implications for convective initiation

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Acknowledgements and Collaborators

• DIAL groups– NASA Langley, LASE, Browell, Ismail et al– CNRS France, LEANDRE, Flamant et al– DLR Germany, DLR DIAL, Ehret et al

• University of Wyoming King Air team– Field crew– LeMone et al, NCAR

• Land surface modeling/fluxes– ALEXI project, U. Wisconsin, J. Mecikalski– NOAH LSM, Chen and Manning, NCAR

• Add ground-based profiling groups, NAST• NCAR-ATD

– ISFF group– Parsons, Weckwerth, Tignor, Baeuerele, many others

• UCAR/JOSS• NSF Atmospheric Sciences Division (IHOP)• NASA Land Surface Hydrology program (SGP97)

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overview

• Goals/background

• Products we propose to create

• Preliminary results– Large scale ABL heterogeneity– Small scale ABL heterogeneity– Attempt to model ABL heterogeneity

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Background – land surface processes and ABL development

• Modeling studies have suggested that land surface conditions are critical to properly predict moist convection in the Great Plains (Avissar et al). RAMS, cloud fields

• Surface observations have shown little climatological connection between surface energy balance heterogeneity and mesoscale flow (Shaw, Doran et al). OK surface met data

• ABL observations are often absent or scarce in previous studies. The ABL is critical to this question.

• Where available, ABL observations have shown only modest mesoscale flow in the presence of strong but fairly small scale (10-20 km) flux heterogeneity (Sun et al, Ehret et al). BOREAS - DLR

• Larger-scale (~250 km) ABL heterogeneity has been observed and tentatively linked to the surface energy budget (Desai et al, Reen et al). SGP97 – LASE

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Goals• Building blocks

– Document mesoscale heterogeneity in the atmospheric boundary layer (ABL). DIAL, DOW, HRDL, UWKA

– Map the surface energy budget over the same mesoscale region. ALEXI, NOAH, ISFF, UWKA

• Role of the land surface– Examine the degree to which land surface heterogeneity is responsible

for ABL heterogeneity. MM5, observations– Examine the potential for land-atmosphere interactions to focus the

initiation of moist convection. MM5, observations• Data assimilation

– Examine the degree to which improved ABL and land surface data improve model predictions of ABL development and moist convection. MM5, observations

• Model development– Evaluate the ability of ABL and land surface models to simulate the

structures observed during IHOP. MM5, observations, ABL and LS model choices

• New area of focii?– Mesoscale rolls – appeared on many BLH day, possibly important for CI– Microscale structure of the entrainment zone

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Methods (to date)• Airborne lidar. 200-300 km scale.

– Backscatter for ABL depth. ~10m x 10m resolution.– Differential absorption lidar (DIAL) for ABL H2O mixing ratio– Doppler lidar for turbulent vertical winds

• U. Wyoming King Air. 60 km scale.– Turbulent variables, fluxes

• Surface flux towers– Spaced along King Air flight tracks

• Remote sensing, land surface models. IHOP domain– Map surface energy budget

• Mesoscale model. IHOP domain.– Determine the degree to which the surface energy budget

governs mesoscale heterogeneity in the ABL.• Collect observations for at least 10 days over the same

region. Go beyond case studies. All BLH days.

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Completed Missions

• 12 BLH missions with joint airborne H2O lidar and flux aircraft operations.

• No cases that led directly to deep convection.

• Dates spanning 19 May through 22 June, 2002.

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Expected Products

• High-resolution ABL depth and water vapor maps for all BLH missions (joint with lidar groups). Add ground-based profilers, NAST?

• Surface energy balance maps for all BLH missions (joint with NCAR, UWisconsin).

• MM5 reanalysis fields for all BLH missions, including airborne lidar data assimilation.

Suitable to submit to JOSS as merged “data” products? Would IHOP scientists use these products?

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Preliminary findings

• Surface energy budget heterogeneity was extreme Kang– Persistent, climatological east-west gradient– Local variations due to recent precipitation

• ABL heterogeneity was evident– East-west gradient was realized in different ways

depending on atmospheric environment Craig– Some local heterogeneity was also persistent over

time, suggesting land-surface origins Kang, Craig• Comparisons of ABL-LSM schemes within MM5

show a great deal of variability among model formulations. Reen

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East – West moisture gradient and its impact on the ABL

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Station7(E)

Station1(W)

Station4(C)

Persistent west to east soil moisture gradient

Station 1 = west. Station 4 = central. Station 7 = east.

Intense rainfall associated with frontal passage.

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station1 station2 station3

East – west soil moisture gradient is reflected in U. Wyoming King Air flux measurements

WEST: L=125 W m-2

Line represents 10kmUWKA latent heatflux measurements.

EAST: L=300 W m-2

Apparent error ineastern flux towers on this date.

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19 May 12 UTC 29 May 12 UTC

SOUNDINGS (Dodge City)

Strong capping inversionStrong surface energy balance gradient

Weak capping inversionStrong surface energy balance gradient

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19 May 2002

1845-1926 UTC

29 May 2002

1839-1913 UTC

LEANDRE FLIGHT TRACKS

Strong capping inversionStrong surface energy balance gradient

Weak capping inversionStrong surface energy balance gradient

Penn StateWest East35 km

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LEANDRE: 19 May 2002

35 kmWest East

Penn StateWest East37 km

LEANDRE: 29 May 2002P

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LEANDRE: 29 May 2002

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LEANDRE H2O VAPOR

29 May 2002

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LASE: 30 May, 2002.An additional view of CBL heterogeneity with a weak capping inversion.

CBL depth via lidar backscatter, and CBL H2O content via DIAL.

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Visible Satellite: 30 May 2002, 2007 UTC

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Smaller scale heterogeneity: Along the UW King Air flight track

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station7 station9station8

Eastern soil moisture conditions remain fairlyhomogeneous throughout the study.

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station2

station1

station3

Western soil moisture conditions become quiteHeterogeneous, especially around 27 May.

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station1 station2

station3

U Wyoming King Air flux latent heat flux observations (line) reflect the south to north soil moisture gradient along the

“Homestead track”

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DLR lidar shows the context of the UW King Airobservations along this N-S gradient.

Is the ABL heterogeneity closely tied to soil conditions?

Pattern was repeated on multiple DLR Falcon passes over 3 hours.

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Case study: Southern Great Plains 97 Experiment, 12-13 July, 1997

Desai et al, in prep; Reen et al, in prep

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Attempts to model coupled land surface - ABL development using MM5:

SGP97 example

•Spatial variability is difficult to reproduce. Role of the surface energy balance is not entirely clear.•Different ABL-LSM schemes give very different mean ABL heights and mixing ratios.

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Good ideas?

• Centrally choreographed instrument intercomparison work

• Centrally choreographed data assimilation efforts

• Central guidance on the creation(?) of a project reanalysis product