A Missing LinkCoupling clouds to radiation

Greg Thompson, NCAR-RAL & DTC25 Jun 2013

With excellent assistance from:Mukul Tewari, NCAR-RALShaowu Bao, Ligia Bernadet NOAA-ESRL/GSDSam Trahan, NCEP-EMC

Short Term Explicit Prediction

STEP

Supported by

• OU-CAPS ARW ensembles• SPC/NSSL Hazardous Weather Testbed• old MCS decaying cloud mostly composed

of snow was essentially transparent• next day’s convection triggered much too

early since minimal cloud cover seen by radiation

• caused by cloud ice versus snow categorization

Motivation…

DTC/NOAA/NCAR

HWRF

• Implement/test Thompson microphysics scheme in HWRF

• existed but essentially untested in HWRF• scheme was recently implemented in

COAMPS (Yi Jin, NRL)• initial tests in COAMPS improved

hurricane forecasts compared to legacy scheme

Case: large winter cycloneVisible satellite image 17:45UTC 01 Feb 2011

Clear-sky, snow cover

Lake-effect snow

Clear-sky, forest, snow

Deep, snowing cloud

Deep, mixed-phase cloud

Thin/partial cloud, mostly ice-phase

Shortwave reaching groundHWRF Test0: Ferrier microphysics & GFDL radiation

minimal lake-effect

broad, thin ice cloud

missing all clouds

0-15 W/m2 ?

Clouds too opaque?

Shortwave reaching groundHWRF Test1: Thompson microphysics & GFDL radiation

GFDL/Goddard radiation schemes essentially ignore snow, only care about cloud ice. There is near blizzard-like conditions here correctly predicted in the model and yet no reduction of shortwave reaching the ground.

Shortwave reaching groundHWRF Test2: Thompson microphysics & RRTMG radiation-uncoupled

RRTMG has internal assumptions about size of cloud droplets, ice, and snow; NOT coupled with what is known in microphysics scheme(s).

RRTMG does significantly better with all clouds, but still can be improved.

Shortwave reaching groundHWRF Test3: Thompson microphysics & RRTMG radiation-coupled

Properly connecting effective radii of cloud water, ice, and snow (passing from microphysics to RRTMG).

Deepest clouds become slightly less opaque?

Thin, mostly ice clouds become slightly more opaque?

Current code issuesRRTMG: Combined cloud ice and snow variablesGFDL & Goddard: only Qice, neglect Qsnow

Ramifications of adding ice and snow!

Look at Slide#10, table of look-up values of assumed ice radius. Dependence on temperature. Therefore, if there exists 0.5g/kg of snow (typical in deep synoptic winter storm) plus 0.1-0.2 g/kg of cloud ice, up near tropopause/anvil level, then this combined mass will have a very small diameter (massive impact to radiation) as compared to using larger ice crystal size or lower mass of the small crystals.

Current code issuesCloud water radii

Current code issuesCloud ice radii

New treatment ice/snow pathFor ice, go back to ice content only; for snow, reduce mass by inversely scaling with diameter

Modifications to WRF (v3.4.1)

Registry (.EM_COMMON, NMM, NMM_NEST, HWRF)

dyn_em/start_em.Fdyn_em/solve_em.Fdyn_nmm/module_PHYSICS_CALLS.Fphys/module_physics_init.Fphys/module_microphysics_driver.Fphys/module_mp_thompson.F

dyn_em/module_first_rk_step_part1.Fphys/module_radiation_driver.Fphys/module_ra_rrtmgsw.Fphys/module_ra_rrtmglw.F

added new 3D variables: re_cloud, re_ice, re_snowadded new switch variables: has_reqc, has_reqi, has_reqspass new top-level variables to physics_init routine pass the top-level variables to micro_driverpass variables into one or more microphys routinescalculate effective radii for cloud, ice, snow

pass the top-level variables to radiation_drivercalculate cloud optical depth from new radiionly if has_reqX=1, otherwise, unaltered code!

Also possible to do similar for nearly all other microphysics choices, especially Morrison, Milbrandt, WSM6, WDM6, etc.

Thus far (May 2013), fixed code coupling Thompson MP & RRTMG schemes only submitted to MMM for version 3.5.1 release ~Aug2013. This altered code is a member of OU-CAPS spring experiment ensembles (“arw_25”).

Should be part of v3.5.1 release (late Summer 2013)

Proof it is working (cloud drop size)Radiative effective radius: cloud droplets(k=16 from bottom)

Radiative effective radius: cloud ice(k=44 from bottom)

Proof it is working (cloud ice size)

Radiative effective radius: snow(k=37 from bottom)

Proof it is working (snow size)

Shortwave reaching groundHWRF Test2: Thompson microphysics & RRTMG radiation-uncoupled

RRTMG has internal assumptions about size of cloud droplets, ice, and snow; NOT coupled with what is known in microphysics scheme(s).

RRTMG does significantly better with all clouds, but still can be improved.

Shortwave reaching groundHWRF Test3: Thompson microphysics & RRTMG radiation-coupled

Properly connecting effective radii of cloud water, ice, and snow (passing from microphysics to RRTMG).

Deepest clouds become slightly less opaque?

Thin, mostly ice clouds become slightly more opaque?

Microphysics & RadiationTest3 minus Test2

showing RRTMG coupled versus uncoupled

Previous slides showed sensitivity with WRF-NMM, this graphic created from WRF-ARW with 4-km grid spacing changing only the coupling of RRTMG with Thompson microphysics.

Deepest clouds become slightly less opaque?

Thin, mostly ice clouds become slightly more opaque?

Aerosols, Microphysics & RadiationPreview of next steps

Cloud droplet number concentration difference from run with 10X aerosols minus 1X aerosolsHigher aerosol concentration leads to more numerous cloud droplets. [Single model vertical level, k=10, shown as example.]

Aerosols, Microphysics & RadiationPreview of next steps

Cloud droplet radiative effective size difference from run with 10X aerosols minus 1X aerosolsHigher aerosol concentration leads to more numerous cloud droplets that causes overall decrease in effective size. [Single model vertical level, k=10, shown as example.]

Aerosols, Microphysics & RadiationPreview of next steps

Cloud albedo (shortwave, upward, top-of-atmos difference from run with 10X aerosols minus 1X aerosolsSmaller cloud droplet size produced by having more aerosols leads to larger cloud albedo (Twomey, 1974) illustrating the first aerosol indirect effect.

See Poster#84

Testing:

• Hurricane Earl (2010), Hurricane Sandy (2012)

• ~28 days May/Jun 2013 in OU-CAPS ensemble members

• DTC project to test in HFIP re-runs

Next steps:

Thank you, especially:Mukul, Ligia, Laurie, Shaowu

• Compute water/ice sizes in other microphysics schemes to couple directly with RRTMG

• Compare WRF output to SurfRad (other) radiation measurements

• Using coupled “aerosol-aware” Thompson microphysics, investigate aerosol indirect effects