Assimilation of S-NPP VIIRS Land Surface Temperature into NCEP Real-Time Mesoscale Analysis (RTMA) System over Alaska

The NCEP Real-Time Mesoscale Analysis (RTMA) provides hourly 2.5 km analyses of near-surface sensible weather elements and cloud fields on domains for CONUS, Hawaii, Alaska (3 km), Puerto Rico, and Guam. The RTMA uses a one-hour model forecast as the background, and assimilates mostly conventional observations into its 2DVar analysis. Over the oceans, it also assimilates scatterometer winds and low-level satellite drift winds. Over CONUS, the RTMA system has ample access to a fairly dense network of conventional surface observations, especially in non-mountainous regions. Alaska, however, has comparatively sparse coverage of in-situ observations which complicates the creation of a quality analysis. The current RTMA system does not assimilate satellite radiance data, which could be explored to improve the RTMA surface temperature analyses in these otherwise data void regions. With the current 2D framework of RTMA, the direct assimilation of satellite radiance observations cannot be realized. Therefore, the assimilation of satellite retrieval products presents an alternative way to utilize satellite observations to fill in the gaps in these data void regions of Alaska.

The Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the Joint Polar Satellite System (JPSS) is leveraged to produce a Land Surface Temperature (LST) product from two window channels. The LST has a moderate spatial resolution of 750 m at nadir during the satellite over-pass times at both day and night. VIIRS scans Alaska twice a day with full coverage around 12 and 22 UTC, and twice a day with half coverage around 08 and 14 UTC. It will potentially make up the in-situ data sparse issue if it can be assimilated properly. Here, we focus on directly assimilating LST in the RTMA with appropriate errors to improve the 2m temperatures analysis over the Alaska RTMA domain.

Results from the VIIRS LST product evaluation will be presented at the meeting, the method of assimilating LST into RTMA will be explained, and the preliminary impact of the assimilation VIIRS LST will also be discussed.