All-Sky Assimilation of Microwave and Infrared Humidity Sounding Radiances at the Met Office

All-sky radiance assimilation of microwave temperature sounding radiances from AMSU-A channel 4 and 5 is going to be implemented in the Met Office operational data assimilation system later this year. This decision is based on results from trial experiments including RMSE reductions in 500 hPa geopotential height forecasts of about 1% up to day 2.

Our next goal is to be able to assimilate microwave humidity sounding radiances (e.g., from MHS) in all-sky conditions. To this end, the 1D-Var pre-processing of MHS was upgraded to allow the estimation of both liquid water path (LWP) and ice water path (IWP) using RTTOV-SCATT. The symmetric error model for MHS was devised as a bilinear function of LWP and IWP. Care was taken to assess the effects of the cloud overlapping assumptions in RTTOV-SCATT on the cloud liquid and ice water jacobians from RTTOV-SCATT. This presentation will discuss our latest trial results when MHS channel 3, 4 and 5 are assimilated against control.

We will also present our plans and first tests (e.g., single ob experiments) on the assimilation of humidity-sensitive radiances from infrared sounders (e.g., IASI) simulated with RTTOV version 12 from profiles of temperature, humidity, cloud liquid and ice water and cloud fraction as well as surface fields.