SST and NWP

SST and sea-ice can have an important role in determining the behaviour of the overlying atmosphere. Consequently, NWP model systems need to be updated regularly to ensure an accurate forecast. Daily analyses of both the SST and sea-ice extent and concentration are required by many operational NWP system. SST often provides the forcing for shower formation, affects the formation and subsequent evolution of tropical cyclones, convection and thunderstorms, cyclogenesis itself, sea fog and sea breezes. As the SST it hanges relatively slowly with respect to the atmosphere, it provides a good basis for seasonal forecasting techniques. SST is also used to help upper air forecasters at the World Aviation Forecst Centre (WAFC) monitor areas more likely to develop Culmulonimbus activity which can produce a significant threat to aircraft.

Sea-ice also has a significant impact on the exchange of energy between the atmosphere and the underlying surface, with a dramatic effect on the surface temperature. It is difficult to retrieve SST from space in the marginal ice zone due to the rapid development and retreat of sea ice depending on the season. Sea ice can also affect satellite radiance retrievals and an incorrect distribution of sea-ice may influence the model tropospheric state.

High resolution SST data products preserve SST gradients better and have been shown to significantly alter the surface wind stress field. The figure to the left provides a useful overview of SST observations from the AVHRR and AMSR-E satellite systems compared to Reynolds OIv2 and the NCEP RTG_SST. Notice how well the near all-wether capability microwave SST observations preserve the gradinet of SST compared to the analysis systems that rely on cloudy infrared and limited in situ sources. Recently, the ECMWF NWP model has has be demonstated to have a sensitivity to the spatial resolution of the SST fields used as the bottom boundary condition. A PDF of the paper available from the BAMS pages at http://www.ametsoc.org/pubs/bams DOI:10.117/BAMS-86-81079.

The GHRSST-PP is working together with mant National Meterological services to ensure that SST data GHRSST-PP data products and services are tailored to requirements, provided on an operational bases and provide an improved service in termns of data quality and access. Never before have so many Satellite SST data set been avaialble to the community in this way. This frees up time to concentrate on applying the data rather than gaining access to it in the first place.

An important element of the GHRSST-PP R/GTS is operational uptake of products. Tnhis can only take place if NWP systemns are able to demonstrate a useful improvement to their forecast skill. This is a challenging and costly area, but one that is a pre-requisite for the GHRSST-PP to be assessed by if it is to gain operational support.