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What contributes to the interannual variability in tropical lower stratospheric temperatures?
  • Alison Ming,
  • Peter Hitchcock
Alison Ming
University of Cambridge

Corresponding Author:[email protected]

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Peter Hitchcock
Cornell University
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Abstract

The interannual variability in mid and lower stratospheric temperatures for the period 1984–2019 is decomposed into dynamical and radiative contributions using a radiative calculation perturbed with changes in dynamical heating, trace gases and aerosol optical depth. The temperature timeseries obtained is highly correlated with the de-seasonalised ERA5 temperature (r2>0.6 for 1995 to 2019 in the region 15 to 70 hPa). Contributions from ozone and dynamical heating are found to be of similar importance, with water vapor, stratospheric aerosols, and carbon dioxide playing smaller roles. Prominent aspects of the temperature timeseries are closely reproduced, including the 1991 Pinatubo volcanic eruption, the year-2000 water vapour drop, and the 2016 Quasi-biennial oscillation (QBO) disruption. Ozone below 20 hPa is primarily controlled by transport and is positively correlated to the upwelling. This ozone-transport feedback acts to increase the temperature response to a change in upwelling by providing an additional ozone-induced radiative temperature change. This can be quantified as an enhancement of the dynamical heating of about 20% at 70 hPa. A principle oscillation pattern (POP) analysis is used to estimate the contributionof the ozone QBO (±1 K at 70 hPa). The non-QBO ozone variability is also shown to be significant. Using the QBO leading POP timeseries as representative of the regular QBO signal, the QBO 2016 disruption is shown to have an anomalously large radiative impact on the temperature due to the ozone change (>3 K at 70 hPa).