jonathan petters february 20, 2009 naval research lab marine meteorology division
DESCRIPTION
Dynamical impacts of surface and atmospheric radiative heating on cloud systems. Jonathan Petters February 20, 2009 Naval Research Lab Marine Meteorology Division. Howard W. Barker, Eugene E. Clothiaux, Jason N.S. Cole, Jeffrey W. Frame, Jerry Y. Harrington, Paul M. Markowski - PowerPoint PPT PresentationTRANSCRIPT
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Jonathan PettersFebruary 20, 2009
Naval Research Lab Marine Meteorology
Division
Dynamical impacts of surface and atmospheric radiative heating on
cloud systems
Howard W. Barker, Eugene E. Clothiaux, Jason N.S. Cole, Jeffrey W. Frame, Jerry Y. Harrington, Paul M. Markowski
This work funded by the Department of Energy Atmospheric Radiation Measurement Program (DOE ARM)
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Cloud
Shadow
Cloud
Shadow
From Sun
Atmospheric Solar Radiative Transfer
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Cloud
To Sun
Atmospheric Solar Radiative Transfer -Modeled
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Cloud
To Sun
Diff use
Direct
I nfinitely Long Layers
Each model column is its own plane-parallel atmosphere!
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Cloud
To Sun
Cloud
Shadow Shadow
Independent Column Approximation (ICA) – leads to radiative heating errors in the atmosphere and surface
hotspotscloudside heating
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Errors in surface heating due to ICA - Cumulonimbus?
Markowski et al. (1998)
Surface cooling of ~3K observed under anvil shadow
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Surface solar irradiance – model supercell (ARPS) - ICA
Frame, Petters, Markowski and Harrington (2009)
- Solar zenith - Solar zenith angle of 47°angle of 47°- azimuth just - azimuth just S of WS of W
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Surface solar irradiance – same supercell – Monte Carlo
Frame, Petters, Markowski and Harrington (2009)
- Solar zenith - Solar zenith angle of 47°angle of 47°- azimuth just - azimuth just S of WS of W
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How might we rectify these surface heating errors?
Tilt model columns (titled ICA -> TICA)
To Sun
Anvil
CbCloud Shadow
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Frame, Petters, Markowski and Harrington (2009)
Use of TICA lessens error
ICA – Monte CarloICA – Monte Carlo TICA – Monte CarloTICA – Monte Carlo
Surface solar irradiance
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Use of TICA in Supercell – Dynamical impact?
For stationary storms and storms moving slowly in the direction of anvil shadow, cooling of surface under anvil shadow can lead to weakening.
Frame, PhD Dissertation (2008)
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Anvil
CbCloud
Cloud shading in Cb – Dynamical impact?
No radiation = no shadow!
Little vertical wind shear near surface
Frame, PhD Dissertation (2008)
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Anvil
CbCloud
Cloud shading in Cb – Dynamical impact?
shadow Added vertical wind shear near surface
Cooling under anvil -> stabilize surface layer -> less vertical mixingFrame, PhD Dissertation
(2008)
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Lemon and Doswell (1979)
With anvil shadowing, rear-flank gust front accelerates, can undercut mesocyclone, leading to weakening of storm
Anvil
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To Sun
Anvil
CbCloud
Shadow
Use of TICA improves atmospheric heating calculations as well
Not important here! Where then?
cloudside heating
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Photo: Alexei KorolevNorth of Barrow, AK
Quite homogeneous cloud field
Errors due to use of ICA in such a cloud field not likely to be large
Stratocumulus! Radiatively driven
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Photo: Amy M DobrzynBloomsburg, PA
Inhomogeneous Sc field
Errors due to use of ICA in modeling such a cloud field important (?)
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DayNight
What do we know about the impact of solar heating on
stratocumulus?
Can be thin, broken, light drizzle
Can be thick, overcast, heavy drizzle
Examine further with ICA treatment of radiation first!
Stabilizes cloud layer with respect to subcloud
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Regional Atmospheric Modeling System (RAMS)Eddy-resolving mode (2-D)Input sounding –
ASTEX (Jiang et al. 2002)30 m vertical resolution, 50 m horizontal resolution (64X70X70)2 second model and radiative timestepno surface fluxes
Experimental Platform
Find model Sc cloud fields sensitive to changes in solar heating
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No Sun
Sun at 45°
Overhead Sun
No drizzle allowed
Solar forcing thins model cloud layer significantly
CDNC – cloud droplet number concentration
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Drizzle production lessens as solar forcing increases
No Sun
Sun at 45°
Overhead Sun
Same as above
Drizzle allowed
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Increased CDNC -> reduced liquid water path when sun is overhead
No drizzle allowed, change CDNC
No Sun
Sun at 45°
Overhead Sun
Same as aboveHigh CDNC
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Difference in integrated radiative heatinghigh CDNC – low CDNC
Less heating
More heating
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No Sun
Sun at 45°
Overhead Sun
Same as aboveHigh CDNC
Sensitivity to small changes in solar forcing when sun is overhead – broken Sc commonly observed when sun is overhead too
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Good candidate for study – broken cloud field sensitive to small changes in solar forcing
Testing importance of atmospheric radiative heating
errors in Sc
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Finding a candidate model Sc field
CDNC = 50/cc
Overhead Sun
Drizzle
Calculate radiative fluxes through cloud without ICA offline, note changes in integrated shortwave heating
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Monte Carlo radiative transfer model coupled with RAMS
Accurately represents horizontal transport of radiation through model domain
Simulate broken Sc cloud fieldWith ICA treatment of radiationWithout ICA treatment of radiation
Observe/analyze dynamical impact (if any)
Testing importance of atmospheric radiative heating
errors in Sc
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Summary
Modeling of radiative transfer leads to errors in computed radiative heating in numerical atmospheric models
Errors in surface heating can lead to changes in model supercell evolution
Errors in atmospheric heating might impact stratocumulus evolution – analysis continues!
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Thank You!Questions/Comments?
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Finding a candidate model Sc field
CDNC = 50/cc
Sun at 45°
Drizzle
Calculate radiative fluxes through cloud without ICA offline, note changes in integrated shortwave heating
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Supercell Schematic and Pic
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