Radiative Linkages Between Meridional Asymmetries in the Seasonal Cycles of Observed Tropical Lower Stratospheric Ozone and Temperatures

Observed seasonal cycles of ozone concentrations and temperatures in the tropical lower stratosphere show a hemispheric asymmetry: Their amplitudes are substantially larger in the northern hemisphere (NH) tropics than the southern hemisphere (SH) tropics. These seasonal cycles primarily have common origins in the mechanical forcing of tropical stratospheric upwelling. However, ozone’s seasonal cycle also induces radiative effects that feed back upon and contribute to the seasonal temperature asymmetric structure. This study investigates seasonal ozone radiative heating asymmetry using Aura Microwave Limb Sounder (MLS) observations of ozone and Global Positioning Satellite (GPS) occultation measurements of temperature in the tropical lower stratosphere. Radiative heating is calculated with an offline broadband radiative transfer model. We analyze the partitioning of ozone radiative heating between longwave instantaneous, longwave adjusted, and shortwave effects. Furthermore, we assess the importance of the vertical structure in the ozone seasonal cycle for the amplitudes of seasonal ozone radiative heating in the tropical lower stratosphere. An upper bound on the temperature adjustments associated with the ozone seasonal cycle is determined and compared with the observed hemispheric asymmetry in the seasonal cycle of temperature. Results show that ozone seasonal radiative heating is about a third larger in the NH than the SH. Additionally, the NH radiative signal is more sensitive to the overlying seasonal cycle structure than the SH. These radiative linkages suggest that future long-term trends in the seasonal cycles of stratospheric ozone are important for the future evolution of lower stratospheric seasonal temperatures. Results further suggest that modeling stratospheric ozone appropriately will be essential for capturing for the spatial structure of the lower stratospheric radiative heating budget.