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A Missing Link Coupling clouds to radiation

A Missing Link Coupling clouds to radiation. Greg Thompson, NCAR-RAL & DTC 25 Jun 2013. With excellent assistance from: Mukul Tewari , NCAR-RAL Shaowu Bao , Ligia Bernadet NOAA-ESRL/GSD Sam Trahan, NCEP-EMC. Supported by. STEP. HWRF. Short Term Explicit Prediction. DTC/NOAA/NCAR.

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A Missing Link Coupling clouds to radiation

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  1. A Missing LinkCoupling clouds to radiation Greg Thompson, NCAR-RAL & DTC 25 Jun 2013 With excellent assistance from: MukulTewari, NCAR-RAL ShaowuBao, LigiaBernadet NOAA-ESRL/GSD Sam Trahan, NCEP-EMC

  2. Supported by STEP HWRF Short Term Explicit Prediction DTC/NOAA/NCAR • 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 • 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 Motivation…

  3. Clear-sky, snow cover Clear-sky, forest, snow Case: large winter cyclone Lake-effect snow Deep, snowing cloud Thin/partial cloud, mostly ice-phase Visible satellite image 17:45UTC 01 Feb 2011 Deep, mixed-phase cloud

  4. broad, thin ice cloud Shortwave reaching ground minimal lake-effect missing all clouds Clouds too opaque? HWRF Test0: Ferrier microphysics & GFDL radiation 0-15 W/m2 ?

  5. 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 ground HWRF Test1: Thompson microphysics & GFDL radiation

  6. RRTMG has internal assumptions about size of cloud droplets, ice, and snow; NOTcoupled with what is known in microphysics scheme(s). Shortwave reaching ground RRTMG does significantly better with all clouds, but still can be improved. HWRF Test2: Thompson microphysics & RRTMG radiation-uncoupled

  7. Properly connecting effective radii of cloud water, ice, and snow (passing from microphysics to RRTMG). Shortwave reaching ground Thin, mostly ice clouds become slightly more opaque? HWRF Test3: Thompson microphysics & RRTMG radiation-coupled Deepest clouds become slightly less opaque?

  8. Current code issues RRTMG: Combined cloud ice and snow variables GFDL & 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.

  9. Current code issues Cloud water radii

  10. Current code issues Cloud ice radii

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

  12. Modifications to WRF (v3.4.1) Should be part of v3.5.1 release (late Summer 2013) added new 3D variables: re_cloud, re_ice, re_snow added new switch variables: has_reqc, has_reqi, has_reqs pass new top-level variables to physics_init routine pass the top-level variables to micro_driver pass variables into one or more microphys routines calculate effective radii for cloud, ice, snow pass the top-level variables to radiation_driver calculate cloud optical depth from new radii only if has_reqX=1, otherwise, unaltered code! dyn_em/module_first_rk_step_part1.F phys/module_radiation_driver.F phys/module_ra_rrtmgsw.F phys/module_ra_rrtmglw.F 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”). Registry (.EM_COMMON, NMM, NMM_NEST, HWRF) dyn_em/start_em.F dyn_em/solve_em.F dyn_nmm/module_PHYSICS_CALLS.F phys/module_physics_init.F phys/module_microphysics_driver.F phys/module_mp_thompson.F

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

  14. Proof it is working (cloud ice size) Radiative effective radius: cloud ice (k=44 from bottom)

  15. Proof it is working (snow size) Radiative effective radius: snow (k=37 from bottom)

  16. RRTMG has internal assumptions about size of cloud droplets, ice, and snow; NOTcoupled with what is known in microphysics scheme(s). Shortwave reaching ground RRTMG does significantly better with all clouds, but still can be improved. HWRF Test2: Thompson microphysics & RRTMG radiation-uncoupled

  17. Properly connecting effective radii of cloud water, ice, and snow (passing from microphysics to RRTMG). Shortwave reaching ground Thin, mostly ice clouds become slightly more opaque? HWRF Test3: Thompson microphysics & RRTMG radiation-coupled Deepest clouds become slightly less opaque?

  18. 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. Microphysics & Radiation Test3 minus Test2 showing RRTMG coupled versus uncoupled Thin, mostly ice clouds become slightly more opaque? Deepest clouds become slightly less opaque?

  19. Higher aerosol concentration leads to more numerous cloud droplets. [Single model vertical level, k=10, shown as example.] Aerosols, Microphysics & Radiation Preview of next steps Cloud droplet number concentration difference from run with 10X aerosols minus 1X aerosols

  20. Higher 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 & Radiation Preview of next steps Cloud droplet radiative effective size difference from run with 10X aerosols minus 1X aerosols

  21. Smaller cloud droplet size produced by having more aerosols leads to larger cloud albedo (Twomey, 1974) illustrating the first aerosol indirect effect. Aerosols, Microphysics & Radiation Preview of next steps Cloud albedo (shortwave, upward, top-of-atmos difference from run with 10X aerosols minus 1X aerosols See Poster#84

  22. 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

  23. Next steps: • 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 Thank you, especially: Mukul, Ligia, Laurie, Shaowu

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