Impact Of a Single Observation from IASI

Aim

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 u-aj977 Var_AnalysePF only assimilated IASI

ToDo

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