Robert Tubbs, Met Office, Exeter
Improvements to the Use of Infrared Data from Geostationary Satellites in Met Office Global and Regional Models
Abstract: The Met Office regional UKV NWP system assimilates infrared radiances in clear regions and above low cloud for channels which are not significantly affected by the cloud. Infrared radiance data and NWP forecast temperature and humidity information are also used to derive cloud-top pressure information which is assimilated as humidity increments. Both these approaches utilise the 3-hourly 3D-Var data assimilation within the UKV NWP system. The presentation will discuss improvements currently being tested including a switch to calculating cloud-top pressure information in real time during the data assimilation cycle using the latest UKV model background fields, rather than using cloud-top pressure values calculated offline.
The global NWP system currently assimilates infrared radiances, in cloud-free regions only, from five geostationary imagers. For four of these five instruments, only the high-peaking water vapour channel radiances are assimilated, whereas for the SEVIRI imager onboard Meteosat Second Generation (MSG), a combination of water vapour and window channel radiances is assimilated. This presentation will discuss the introduction of Advanced Himawari Imager (AHI) radiances into the global assimilation system, showing results from the testing of various configurations including: (i) the use of the highest-peaking channel only (a like-for-like replacement for its predecessor, MTSAT); and (ii) the fuller use of the available infrared wavelengths, including water vapour, window and carbon dioxide channels. Results from testing the introduction into the global model assimilation system of high-peaking absorption channel radiances over low cloud will also be presented.