Abstract

The tropical lower stratosphere is the primary region by which air enters the stratosphere from the troposphere and this region exerts a strong control on the properties of the upwelling air and hence the wider stratosphere. In this talk, I will focus on the large inter‐annual variability in temperatures. To understand how this variability arises, the temperature changes are 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 a de‐seasonalized reanalaysis dataset (ERA5). Ozone and dynamical heating contributions are found to be equally important, 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 vapor drop, and the 2016 Quasi‐biennial oscillation (QBO) disruption. Below 20 hPa, ozone 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 Principal Oscillation Pattern (POP) analysis is used to estimate the contribution of 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 temperature due to the ozone change ( > 3 K at 70 hPa).