Extratropical Lower Stratospheric and Tropospheric Ozone in High Resolution Analyses by the GEOS-5 Ozone Assimilation System

The magnitude and distribution of ozone in the upper troposphere and lower stratosphere is a critical component of Earth's radiative budget. In addition, ozone of stratospheric origin in the troposphere is important to the oxidizing capability of the troposphere and tropospheric chemistry. Total column ozone from the Ozone Monitoring Instrument (OMI) and stratospheric ozone profiles from the Microwave Limb Sounder (MLS) onboard the Aura satellite have been assimilated into the Goddard Earth Observing System version 5 (GEOS-5) data assimilation system, providing 6-hourly, global analyses of atmospheric ozone. The tropospheric profiles of ozone are not directly constrained by the data. Two analyses spanning a complete seasonal cycle have been produced with different horizontal resolutions of the assimilation system. A 2° x 2.5° latitude-longitude grid is used in the low-resolution experiment and the high-resolution case is 0.25° x 0.3125°. In this study we examine the impact of increased resolution on the magnitude, distribution, and budget of ozone in the analyses extratropical troposphere and lower stratosphere.

First, a statistical evaluation will be presented comparing the analyses tropospheric column ozone and profiles from the troposphere to lower stratosphere with ozonesonde observations. Second, we will examine the impact of higher resolution on the structure and transport of ozone in stratospheric intrusions into the troposphere that are significant sources of extratropical stratosphere-troposphere exchange. We will show that the structural integrity of the intrusions is better maintained to lower altitudes in the high-resolution analysis with less artificial mixing in the upper troposphere. Finally, net hemispheric STE estimates and the net upper and lower tropospheric burdens will be compared for the two analyses.