A STUDY ON ASSIMILATING POTENTIAL VORTICITY DATA

The correlation that exists between the potential vorticity (PV) field and the distribution of chemical tracers such as ozone suggests the p ossibility of using tracer observations as proxy PV data in atmospheri c data assimilation systems. Especially in the stratosphere, there are plentiful tracer observations brit a general lack of reliable wind ob servations, and the correlation is most pronounced. The issue investig ated in this study is how model dynamics would respond to the assimila tion of PV data. First. numerical experiments of identical-twin type w ere conducted with a simple univariate nuding algorithm and a global s hallow water model based on PV and divergence ( PV-D model). Ail model fields are successfully reconstructed through the insertion of comple te PS' data alone if an appropriate value for the nudging coefficient is used, A simple linear analysis suggests that slow modes are recover ed rapidly, at a rate nearly independent of spatial scale. In a more r ealistic experiment. appropriately scaled total ozone data from the NI MBUS-7 TOMS instrument were assimilated as proxy PV data into the PV-D model over a 10-day period, The resulting model PV field matches the observed total ozone field relatively well on large spatial scales, an d the PV, geopotential and divergence fields are dynamically consisten t. These results indicate the potential usefulness that tracer observa tions, as proxy PV data, may offer in a data assimilation system.