Harmonisation of the usage of microwave sounder data over land, coasts, sea ice and snow. First year report

The usage of microwave sounder data from different instruments has been made more consistent by harmonising the use of similar channels over land, sea ice and snow. This includes the introduction of MHS channel 4 over snow-covered land, ATMS channels 7, 8, 20, 21 and 22 over sea ice, ATMS channels 6, 18 and 19 over cold sea. In addition, the 118GHz channels of MWHS2 (channels 2 to 6) have been activated over land. Corresponding channels on other instruments are already used in these areas with a dynamic emissivity retrieval used to improve the accuracy of the observation operator for surface sensitive channels.

Results show small improvements to the first guess fits to independent observations including lower peaking temperature sounding channels from AMSU-A. This indicates the change is improving the accuracy of short range temperature forecasts in the troposphere. Also, geopotential height analysis increments are smaller and there are some significant benefits to forecasts out to 3 days, especially at high latitudes.

In addition, the usage of microwave sounder data in the all sky system has been extended to near coastal regions. Currently there is a strict quality control check which rejects all microwave sounder data in near coastal areas (land-sea mask value between 0 and 0.95) resulting in 14% of available MW sounder data not being assimilated in the all sky system. Relaxing this check results in significantly improved first guess fits to independent humidity sensitive and wind observations as well as modest improvements to geopotential height forecasts out to 5 days.