Dynamical influence on stratospheric ozone and water vapor

Abstract

Influence of the some of the the most important processes contributing ozone variability (stratospheric aerosol loading, Brewer-Dobson circulation, QBO,solar variability, changes in stratospheric chlorine loading) is studied using updated meteorological and total ozone data sets. Accumulated winter eddy heat flux has been proposed as a newproxy for the attribution of dynamical influence on ozonechange. A compact relationship between winter ozone gain and eddy heat flux has been demonstrated. It is shown that eddy heat flux not only controls high-latitude winter ozone gain but also chemical ozone loss due to heterogeneous chemistry. Influence of 11-year solar cycle on the stratospheric temperatures is confirmed using long term meteorological data (1958-2005) from NCEP and ECMWF. It has been observed that polar stratospheric temperatures and solar flux show strong coupling during westerly phase of QBO. Regressionanalysis (1979-2005) shows that mid-winter polar stratospheric temperatures are generally higher during solar maxima but lower during early winter months. The opposite is true during solar maxima. A new multivariate regression model has been used to study long term ozone trends as well changes in ozone trends due to changes in stratospheric halogen loading. Using WFDOAS GOME [1995-2003], SBUV V8 [1979-2003] and TOMS/SBUV merged [1979-2005] total ozone data sets, detailed analysis has been carried out. Largest negative ozone trends are observed at high latitudes during winter season beyond 50 circ latitudes. In tropical latitudes ozone trends are quite small. Solar variability contributes up to 6-8 DU ozone change whereas QBO explains most of the ozone variability in tropical latitudes. It is also shown that the increase in planetary wave drivingand solar cycle maxima contributed significantly to the observed increase in NH mid-high latitude total ozone since the late 90s. Replacing linear trend term with EESC, regression model shows that changes in ozone trends due to decline in halogen loading are up to 4 DU/decade in NH and 8 DU/decade in SH.Influence of planetary wave driving on tropical lower stratospheric water vapor has been studied using SAGE V6.2 (1984--2005) and HALOE V19 (1991--2005) water vapor data. A compact relationship between global eddy heat flux (averaged from both hemisphere) at 50 hPa and tropical lower stratospheric water vapor (averaged between 16--20km) have been demonstrated. Some years, such as 1991, 1997 show departure from the observed relationship indicating that water vapor variability in the tropical lower stratosphere can not be solely attributed to the strength of Brewer-Dobson circulation. It is also shown that decrease instratospheric water vapor since 2000, is related to increase in planetary wave driving from both hemisphere. Regression analysis shows that such a increase in wave driving contributed up to 0.7 K cooling in the tropical lower stratosphere.