Abstract
Abstract. We describe a sequential assimilation approach useful for assimilating tracer measurements into a three-dimensional chemical transport model (CTM) of the stratosphere. The numerical code, developed largely according to Kha00, uses parameterizations and simplifications allowing assimilation of sparse observations and the simultaneous evaluation of analysis errors, with reasonable computational requirements. Assimilation parameters are set by using χ2 and OmF (Observation minus Forecast) statistics. The CTM used here is a high resolution three-dimensional model. It includes a detailed chemical package and is driven by UKMO (United Kingdom Meteorological Office) analyses. We illustrate the method using assimilation of Upper Atmosphere Research Satellite/Microwave Limb Sounder (UARS/MLS) ozone observations for three weeks during the 1996 antarctic spring. The comparison of results from the simulations with TOMS (Total Ozone Mapping Spectrometer) measurements shows improved total ozone fields due to assimilation of MLS observations. Moreover, the assimilation gives indications on a possible model weakness in reproducing polar ozone values during springtime.
Highlights
The analysis of the change in the ozone distribution, and of atmospheric chemistry in general, is severely hampered by a lack of consistent data sets
This methodology represents a powerful tool for the understanding of chemical and dynamical atmospheric processes
The STRATAQ model (Grassi et al, 2002) is a threedimensional chemistry transport model of the stratosphere that extends from 0.6 km to about 52 km in altitude with a vertical resolution varying from about 1 km below 20 km and up to 2.5 km in the higher stratosphere
Summary
The analysis of the change in the ozone distribution, and of atmospheric chemistry in general, is severely hampered by a lack of consistent data sets. This prevents one from gaining insights into the role of chemistry and dynamics in determining the ozone distribution. These issues are usually studied by comparing observations with results from numerical modelling. The resulting system, described below, was used to assimilate UARS MLS ozone observations for a three-week period during the 1996 antarctic spring. The results are presented while in the final section results are discussed and summarized
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