Tuesday, 15 January 2002: 4:15 PM
Assimilation of Scatterometer and In Situ Winds for Regularly Gridded Products
An objective technique is used to create a new monthly climatology for surface fluxes and related fields. The wind (pseudostress) products are improvements over our previous product: the subjectively analyzed FSU winds. Fields of turbulent surface fluxes and the variables needed to calculate these fluxes are also generated. The new objective method is an extension of a technique used to create daily grid scatterometer vector wind observations obtained a polar-orbiting satellite. The problems related to gridding daily ship data are analogous to those of gridding daily scatterometer observations. In both cases, there are large gaps in the observational coverage and observational errors and uncertainty should be considered. Furthermore, observational tracks from different times intersect, often with substantial changes in the wind pattern occurring between the observations. Simple averaging would result in spurious wind curl and divergence, which generates spurious Rossby and Kelvin waves when these fields are used to force ocean models. Despite these problems, in-situ observations have demonstrated value in producing long time series of monthly products. Our gridding technique developed for scatterometer observations deals with these problems more effectively the previous techniques. Our previous objective techniques considered observations from only one type of platform. The new objective technique treats various types of data sources (volunteer observing ships, buoys, and scatterometers) as independent. Two products are produced: one based solely on in-situ observations, and another that also includes scatterometer observations. Physical differences between in-situ and satellite winds are considered to improve the product. Comparisons are made between the new FSU fields (based on volunteer observing ships and buoy observations), the old subjective FSU fields, individual TAO buoys, the NCEP reanalysis, and fields based solely on the SeaWinds scatterometer observations.