Version 11 (modified by Jin Lee, 2 years ago) (diff)


Impact Of a Single Observation from IASI


This test is a part of the H-8 AHI trial. As the weighting functions of IASI channels peak sharply the analysis increments can be better understood.

Experimental Set-up

Following set of configurations were used for this test,

  • 3DVAR
  • non-hybrid and no ensemble cycles
  • Resolution of PFM is N108
  • no VarBC

Note 1. N108 PFM resolution differs from the screen 3DVAR resolution

Experiment was done using suite ID u-am568 (copy of u-aj730/trunk@40220). I made following modifications to progressively arrive at the target configuration outlined above,

  • ensemble and hybrid VAR are switched off (job #1)
  • turned off VarBC (job #2)
  • copied screen 3DVAR app config file then made following changes
    • point to locations of LS, varobs and varcx
    • turned on 3DVAR - it appears all observations supplied are used, so this is FGAT 3DVAR (job #3)
  • following the changes in u-aj977 Ops_ExtractAndProcess for AHI CSR selected smaller number of IASI observations
    • turned on SatRad NetCDF write
    • then a single FOV was selected using extractcontrolnl: this passed QC and thinning and was the only FOVS in varobs; 83.77021 degE, -28.4431 degN
  • following the changes in the Var_AnalysePF tasks of u-aj977 assimilated a single IASI FOV
    • a gridpoint nearest the FOV was selected: cubes[2].coord('longitude').points[148]=83.53125 and cubes[2].coord('latitude').points[164]=-28.3125
    • the max in the vertical profile of analysis increment for theta and u occurs near the model top; for qT it is below tropopause
  • Changed to assimilate a single channel obs: MetDB ch70


  • Under [namelist:var_minimisenl] of gl_var_anal_low app maxiterations is 20. Perhpas this needs to be increased to 40 as in 4DVAR (?)