Assimilation of GOME Measurements with a 3D Variational Analysis

Abstract

During the past three years a 3D variational data assimilation system (3Dvar) has been developed for the Canadian global spectral forecast model that is used for global data assimilation and medium- and long- range forecasts at the Canadian Meteorological Centre. One key advantage of 3Dvar is that it provides a framework for assimilation of observations that are indirectly (even nonlinearly) related to model variables, which is often the case for satellite data.
The 3Dvar system has been used to assimilate total ozone measurements retrieved from TOVS radiances. The assimilation cycle used the global model in hybrid coordinates to passively advect ozone. The full model was used at a lower triangular truncation of T42 with 29 levels in the vertical and a model top at 1 hPa, whereas the operational model uses T199, 21 sigma levels and a top at 10 hPa. Two assimilation cycles were performed. The first one was for July 1995 using a priori statistics in the 3Dvar scheme. The 24 and 48 hour forecassts issued from this cycle were used to estimate the forecast error statistics using a lagged forecast method. The impact of the new statistics on the quality of the analysis was assessed by doing another analysis cycle over a second period of one month (July 1996). The results show a systematic improvement in the resulting analyses and forecasts.
We are now in a position to carry out further analysis cycles at higher resolution to assess the impact of directly assimilating the ERS-2 GOME data which we expect to improve the quality of our stratospheric ozone analyses and forecasts. Latest results will be presented at the symposium.

Keywords: Atmosphere, Ozone, GOME, 3Dvar

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry