Background

In the current operational system, snow analysis is based on 2D-OI separated from the SEKF (for soil moisture analysis) and the 1D-OI (for soil temperature and snow temperature). As a first step towards a unified land data assimilation system (de Rosnay et al., 2022), snow analysis has been implemented in the SEKF. This page shows details of the changes and the first result.

Branches

dako_CY48R1.1_SEKF_snow

• ifs-scripts: https://git.ecmwf.int/users/dako/repos/ifs-scripts/browse?at=refs%2Fheads%2Fdako_CY48R1.1_SEKF_snow
• ifs-source: https://git.ecmwf.int/users/dako/repos/ifs-source/browse?at=refs%2Fheads%2Fdako_CY48R1.1_SEKF_snow
• ifs-suites: https://git.ecmwf.int/users/dako/repos/ifs-suites/browse?at=refs%2Fheads%2Fdako_CY48R1.1_SEKF_snow

Configurations to analyse snow water equivalent in the SEKF

• Input increments from the 2D-OI for snow depth (arpifs/obs_preproc/obsgen.F90)
• Calculate and input additional EDA Jacobians related to snow (gen/fetchmars, arpifs/sekf/sekf_geteda_jacobians.F90)
  • Covariances between soil moisture and snow depth are set to 0
  • Covariances between snow water equivalent and 2m temperature, relative humidity, soil moisture are also set to 0 (consider snow depth only)
  • Jacobians between snow water equivalent and snow depth are set to 1/rsn (based on the relationship in the model)
• Analyse snow water equivalent using the 2D-OI increments and Jacobians (arpifs/sekf/sm_ekf_main.F90)

Result

Future work

• Input snow observations directly in the SEKF (the same task as soil moisture analysis using 2m temperature and relative humidity)
  • Need to implement a localization in observation space
  • Each QC should also be implemented in the SEKF
• Consider flow dependent background errors