GPSRO Usage at JMA

Deterministic models assimilating RO

Global Spectral Model (GSM)

• Spectral model
• Horizontal resolution: TL959 (0.1875°(20 km) Reduced Gaussian Grid)
• Vertical resolution: 100 vertical levels, sigma-p hybrid coordinate, lid at 0.01 hPa

Meso-scale Model (MSM)

• Grid model
• Horizontal resolution: 5 km
• Vertical resolution: 48+2 layers up to 21.8 km

Data assimilation method

Global Analysis (GA)

• 4D-Var, 6-hr data assimilation window, increment resolution TL319 (~55 km)
• Analysis times (T): 00, 06, 12, 18 Z
• Time window: T ± 3 hrs
• Data cut-off time (time after the start of the assimilation window):
  • Early analysis: 5 hrs 20 mins
  • Cycle analysis: 14 hrs 50 mins (T=00,12), 10 hrs 50mins (T=06,18)

Meso-scale Analysis (MA)

• 4D-Var, 3-hr data assimilation window, Horizontal resolution of inner model: 15 km
• Analysis times (T): 00, 03, 06, 09, 12, 15, 18, 21 Z
• Time window: (T-3hrs) – T
• Data cut-off time (time after the start of the assimilation window):3hrs50mins

RO quantity assimilated

Global Analysis (GA)

• Bending angle
• 1D operator
• Tangent point drift included
• No vertical thinning
• No bias correction applied

Meso-scale Analysis (MA)

• Refractivity
• 1D operator
• Tangent point drift included
• No vertical thinning
• No bias correction applied

Observation error characteristics

Global Analysis (GA)

Observation error depends on impact height only:

• 1% of observed bending angle for h > 10 km,
• linear variation from 20% at h=0 km to 1% at h=10 km,
• lower limit of 3*10^-6 rad

Meso-scale Analysis (MA)

Observation error depends on geometric height only:

The refractivity errors are calculated using a linear interpolation between these points:

Impact

An adjoint sensitivity study has not been conducted yet using the latest JMA global model.