Version 15 (modified by Jin Lee, 3 years ago) (diff)


Impact Of a Single Observation from IASI


The vertical profile of analysis increments from assimilating a single AHI CSR channel observation had complicated structure. For example when a channel observation whose weighting function was mostly in lower troposphere was assimilated the resulting analysis increments were not confined vertically to the peak of the weighting function. To better understand vertical spreading of analysis increments a single-observation test using IASI channel obs is attempted. As the weighting functions of IASI channels peak sharply the analysis increments should be more confined vertically.

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,

  1. Ensemble and hybrid VAR are switched off (glu_var_anal_n108 job 01)
  1. Turned off VarBC (glu_var_anal_n108 job 02)
  1. Set up 3DVAR task
    1. 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 (glu_var_anal_n108 job 03)
  1. Selected a single FOV which passed to VAR a.following the changes in u-aj977 Ops_ExtractAndProcess for AHI CSR selected smaller number of IASI observations
    1. turned on SatRad NetCDF write: using this selected a FOV that passed to VAR
    2. then a single FOV was selected using extractcontrolnl: this passed QC and thinning and was the only FOVS in varobs; the FOV had a coordinates of 83.77021 degE, -28.4431 degN (N.B. SatRad 1DVAR identified a cloud with CTP=686 hPa)
  1. Assimlated the single FOV using 3DVAR
    1. following the changes in the Var_AnalysePF tasks of u-aj977 assimilated a single IASI FOV
    2. a gridpoint nearest the FOV was selected: cubes[2].coord('longitude').points[148]=83.53125 and cubes[2].coord('latitude').points[164]=-28.3125
    3. the max in the vertical profile of analysis increment for theta and u occurs near the model top; for qT it is below tropopause
  1. Selected a single channel observation
    1. changed /home/548/jtl548/da/suite/nwp_input/ops_var/Data/SatRad_coeffs/bom/users/u-am568/aps3_r00_my00.default@38138/ to allow only MetDB channel 70 to be selected (glu_ops_process_background_iasi job 14)

Note I could have changed but decided to change OPS channel selection file as I could make sure that no other channels were selected


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