Preliminary findings/fixes about GSI/WRF_ARW interface

1. Preliminary findings/fixes about GSI/WRF_ARW interface Hui-Chuan Lin

2. The discussion is based on the release V1 version https://gsi.fsl.noaa.gov/svn/comgsi/branches/release_V1 • Key problems to fix: • The calculations of 3-D pressure and 3-D geopotential height • They should be based on WRF_ARW formulations. • 3-D pressure is used in many places: interpolation, qsatg (affects change of moisture variable), tropprs (affects deflation of moisture jacobian for radiance and IR quality control), etc. • Psfc increment to 3-D pressure increment • 3-D pressure after first outer loop. • 3-D pressure increment is used in computing q increment when qoption=2

3. Basic features of WRF_ARW formulations WRF_ARW vertical coordinate is defined with dry hydrostatic pressure. Some variables are defined as perturbations from a hydrostatically-balanced reference state. Total pressure  PB  P Total geopotential  PHB  PH Total   MUB  MU • WRF_ARW prognostic variables: • U, V, W • MU (perturbation dry air mass in column) • PH (perturbation geopotential) • T (potential temperature) • scalars

4. WRF_ARW to GSI • Geopotential is simply PHB+PH • Pressure can be PB+P (when they are available in the file) or • can be diagnosed from PH using the following relations: • Compute base state using T00, P00, TLP, TISO, terrain height • Compute density using (2.45) • Compute full pressure using (2.21)

5. GSI to WRF_ARW Compute  increment from Psfc increment and q increment TL of (i) to compute 3-D pressure perturbation increment from  increment Compute density from total t, total p, total q Compute total geopotential using (2.30) (i) For WRF_ARW, the transformation of surface pressure increment to 3-D pressure increment is not as straightforward as for WRF_NMM.

6. GSI analysis increments (after change of variables) • Psfc • u • v • Tv • Q • WRF_ARW output variables to be updated after GSI analysis • U • V • W • MU • PH • T • QVAPOR • P • PSFC • T2 • TH2 • Q2 • U10 • V10 • TSK • SST updated should be updated, but not updated in the current GSI diagnostic variables not clear yet • Progress made since last GSI developers’ meeting: • Formulations consistent with WRF_ARW definitions are used in the fixed GSI/WRF_ARW interface • PH: geopotential perturbation • P: pressure perturbation • PSFC: surface pressure • are updated in the fixed code

7. based on releave_V1 • netcdf interface only, so far • Subroutines that need modifications • convert_netcdf_mass (wrf_inout to sigf06) • read_wrf_mass_netcdf_guess (sigf06 to guess fields) • wrwrfmassa_netcdf (guess+increment to siganl) • update_netcdf_mass (siganl to wrf_inout) • getprs_tl • getprs_ad (not done yet) • ...... (init_reg_glob_ll, update_guess, create_ges_bias_grids, • destroy_ges_bias_grids, load_prsges, load_geop_hgt) • Files that are modified • read_wrf_mass_guess.F90 • gridmod.f90 • update_guess.f90 • getprs.f90 • guess_grids.f90 • wrwrfmassa.F90 • wrf_netcdf_interface.F90

8. Middle East domain experiment • 30 km grid-spacing, 232 x 174 • Model Top: 10 hPa, 57 vertical levels, • Cool-Start 2008102206 ~ 2008102500 (3 days)