# Presentation: 142963

## Studying the Subvortex in the Lowermost Stratosphere Using New Trace Gas Measurements from Aura MLS

**Michelle Santee** **& Gloria Manney**
- Jet Propulsion Laboratory, California Institute of Technology
- Aura Science Team Meeting
- 3 October 2007
- Pasadena, CA

## Introduction and Overview

- The **Microwave Limb Sounder (MLS)** provides daily global profiles of several key species useful for studying the upper troposphere (UT) and lowermost stratosphere (LMS):
- H2O
- CO, O3
- HNO3    New in UTLS in Version 2.2 (v2.2) MLS data
- We use v2.2 MLS data and GMAO GEOS-5 analyses to explore:
- Chemical processing in and springtime dispersal of chemically-processed air from the subvortex (~350-400 K)
- “Subvortex”  ≡  the portion of the polar vortex at levels where lower latitudes are in the troposphere
- Mixing of stratospheric and tropospheric air in the UTLS, particularly in the region between the subvortex and the tropopause transport barriers
- Seasonal evolution and interannual and interhemispheric variability in trace gases in the LMS (v1.5 MLS data)

## MLS Data in the LMS During a NH Stratospheric Warming

- Many features are persistent throughout the LMS; in particular, two troposphere-to-stratosphere transport events near 0° longitude in each hemisphere are evident down to at least 350 K
- Because of differences in tracer gradients, some features show up better in different species at different levels

## MLS HNO3 Data in the SH Late-Winter Subvortex

- MLS HNO3 shows denitrification in the SH subvortex down to 350 K
- MLS O3 also shows chemical loss in subvortex
- Dispersal of chemically-processed air from the subvortex may significantly affect midlatitude LMS composition

## Synoptic Subvortex/UTLS Structure in SH Spring/Summer

- In SH winter, the major transport barrier is the subvortex; by mid-December, it is the subtropical jet / tropopause

- Wind Speed

- HNO3

- O3

## MLS UTLS Time Evolution and Transport Barriers: 370 K

**MLS UTLS Time Evolution and Transport Barriers: 370 K**

- v1.5 MLS data until March 2007, v2.2 data thereafter
- Effective diffusivity (Keff) gives a measure of the degree of mixing:  low values indicate transport barriers, high values indicate strong mixing
- The tropopause and subvortex transport barriers, their seasonal patterns, interannual and interhemispheric variability, and evidence of mixing and stratosphere-troposphere exchange are clearly seen in MLS O3 data

- O3

- Keff

## Summary

- The release of MLS v2.2 data provides new opportunities for comprehensive studies of the LMS, particularly the subvortex:
- v2.2 HNO3 extends into the UTLS and exhibits strong gradients across the subvortex boundary and the tropopause
- MLS O3, CO, and H2O are also very useful for studying this region
- Specifically, we used MLS v2.2 data and GEOS-5 analyses to examine:
- Quasi-isentropic troposphere-to-stratosphere and stratosphere-to-troposphere exchange events
- Dispersal of chemically-processed air from the subvortex
- Mixing of stratospheric and tropospheric air in the UTLS
- Seasonal evolution and interannual and interhemispheric variability of the subtropical jet / tropopause and subvortex transport barriers
- Observed changes in trace gases are consistent with the evolution of transport barriers as diagnosed from meteorological analyses