Connections between Upper Tropospheric and Lower Stratospheric Circulation Responses to Increased CO2

There are myriad ways atmospheric circulation responds to increased CO2. In the troposphere, the re-gion of the tropical upwelling narrows, the Hadley cells expand, and the upper-level subtropical zonal winds that com-prise the subtropical jet strengthen. In the stratosphere, the tropical upwelling narrows and strengthens, enhancing the Brewer-Dobson circulation. Despite the robustness of these projections, dynamical coupling between the features re-mains unclear. In this study, we analyze output from the NASA Goddard Institute for Space Studies (GISS) ModelE coupled climate model to examine any connection between the upper tropospheric and lower stratospheric circulation by considering the features' seasonality, hemispheric asymmetry, scaling, and transient response to a broad range of CO2 forcings. We find that a narrowing and strengthening of upper tropospheric upwelling occurs with a strengthening of the subtropical jet. There is also a narrowing and strengthening of lower stratospheric upwelling that is related to an equatorward shift in critical latitude for wave breaking and the associated strengthening of the subtropical lower stratosphere's zonal winds. However, the stratospheric responses display different seasonal, hemispheric, and tran-sient patterns than those in the troposphere, indicating independent circulation changes between the two domains.

Automated summary

There are multiple responses of atmospheric circulation to increased CO2. In the troposphere, the tropical upwelling region narrows, the Hadley cells expand, and the subtropical jet strengthens. In the stratosphere, the tropical upwelling region narrows and strengthens, enhancing the Brewer-Dobson circulation. However, the dynamical coupling between these features remains unclear, indicating independent circulation changes between the stratosphere and troposphere.