Normal mode Rossby waves and their effects on chemical composition in the late summer stratosphere

D Pendlebury,M Pritchard,C Mclandress,T G Shepherd

doi:10.5194/acp-8-1925-2008

Abstract

Abstract. During past MANTRA campaigns, ground-based measurements of several long-lived chemical species have revealed quasi-periodic fluctuations on time scales of several days. These fluctuations could confound efforts to detect long-term trends from MANTRA, and need to be understood and accounted for. Using the Canadian Middle Atmosphere Model, we investigate the role of dynamical variability in the late summer stratosphere due to normal mode Rossby waves and the impact of this variability on fluctuations in chemical species. Zonal wavenumber 1, westward travelling waves are considered with average periods of 5, 10 and 16 days. Time-lagged correlations between the temperature and nitrous oxide, methane and ozone fields are calculated in order to assess the possible impact of these waves on the chemical species. Using Fourier-wavelet decomposition and correlating the fluctuations between the temperature and chemical fields, we determine that variations in the chemical species are well-correlated with the 5- and 10-day waves between 30 and 60 km, although the nature of the correlations depend strongly on altitude. Interannual variability of the waves is also examined.

Highlights

The Middle Atmosphere Nitrogen TRend Assessment (MANTRA) campaign measures stratospheric chemical species relevant to ozone depletion from balloon-borne instruments during late summer over Vanscoy, Saskatchewan (52◦ N, 253◦ E) from 10 to 50 km
In order to keep the balloon within the telemetry range for a full day of measurements, the timing of the balloon launch is set to coincide with the turnaround of the stratospheric zonal-mean zonal winds
While quasistationary planetary waves, which are the largest source of large-scale variability in the Northern Hemisphere stratosphere, are filtered out by the background wind during the summer, some large-scale variability exists due to other planetary waves

Summary

Introduction

The Middle Atmosphere Nitrogen TRend Assessment (MANTRA) campaign measures stratospheric chemical species relevant to ozone depletion from balloon-borne instruments during late summer over Vanscoy, Saskatchewan (52◦ N, 253◦ E) from 10 to 50 km. We use the first data set to examine the time evolution of the 5-, 10- and 16-day waves over the summer, and to determine the relationship of the waves in the dynamical fields to the chemical fields nitrous oxide (N2 O), methane (CH4 ), and ozone (O3 ).

Results

Conclusion