Assimilation of MWHS data over Land

ECMWF have been assimilating the FY-3B MWHS (Microwave Humidity Sounders) data over sea in the operational forecasting system since the September 24^th, 2014. It is more difficult to assimilate microwave observations over land and sea ice than over the open ocean due to higher uncertainty in land surface temperature, surface emissivity and less effective cloud screening. We compare approaches in which the emissivity is retrieved dynamically from MWHS channel 1 (150GHz (V)) with the use of an evolving emissivity atlas from 89 GHz observations from the Microwave Humidity Sounders (MHS) on NOAA and EUMETSAT satellites.

The assimilation of the additional data over land improves the fit of short-range forecasts to other observations, notably ATMS humidity channels, and the forecast impacts are mainly neutral to slightly positive over the first 5 days. The forecast impacts are better in boreal summer and the Southern Hemisphere. These results suggest that all of the techniques tested allow for effective assimilation of MWHS/FY-3B data over land.