GPSRO Usage at CMA

Deterministic models assimilating RO 

  • GRAPES (Global/ Regional Assimilation and PrEdiction System) of CMA
    • GRAPES forecast model:
      • Non-hydrostatic equations
      • Terrain-following coordinate
      • Arakawa-C(horizontal) and Charney-Phillips(vertical) grid
      • Model top at 32.5km
      • 37 vertical levels
      • Resolution 0.5°x 0.5 °(720*360)
      • Run four times per day (twice a day to 144 hours)
    • GRAPES-Var system:
      • Configuration of coordinate and grid is same to the forecast model
      • Resolution 1.125°x 1.125 °
      • Incremental digital filter initialization

Data assimilation method

  • 3D-Var with a 6-hour time window (T±3h)

RO quantity assimilated

  • Refractivity, 1D operator
  • No tangent point drift
  • QC in preprocessing refers to that of Mete. France
  • Vertical thinning: 1 datum per analysis vertical layer
  • No horizontal thinning
  • Background check

Observation error characteristics

  • Obs. Error is dependent on latitudes (low, high and mid) and height


  • Analysis and forecast score show that RO data is one of the most important data at GRAPES.
  • Adjoint sensitivity studies are not possible with the GRAPES now