Studies of the extratropical upper troposphere and lower stratosphere using new trace gas measurements from Aura MLS (Invited Speaker)

The two-way exchange of air masses between the upper troposphere (UT) and the lower stratosphere (LS) plays a critical role in ozone photochemistry and the radiative balance in the UT/LS region. The Microwave Limb Sounder (MLS) on NASA's Aura satellite, launched in July 2004, provides daily global profiles of several key species that are useful for studying the extratropical UT/LS. In addition to CO, O3, and H2O, recently-released MLS version 2.2 (v2.2) data processing algorithms are now producing the first daily global measurements of HNO3 in the UT/LS. We will use v2.2 MLS data to explore a number of issues related to extratropical stratosphere-troposphere exchange (ET-STE). For example, chemical processing in and dispersal of chemically processed air from the "subvortex" (the portion of the polar vortex at levels where lower latitudes are in the troposphere) in the spring will be investigated, including mixing in the lowermost stratosphere in the region between the subvortex and tropopause transport barriers, as well as possible transport of processed air into the troposphere. Examples of short-time-scale quasi-isentropic ET-STE will be shown, including intrusions of low-latitude, UT air into the LS. In addition, the seasonal evolution of and interannual and interhemispheric variability in trace gases in the lowermost stratosphere in MLS data will be described. Correlations of trace gases across the tropopause will be shown. Finally, comparisons of the MLS data with model simulations will also be discussed.