The Roles of Greenhouse Gas, Solar Cycle Forcing, and Atmospheric Coupling on the Interannual Variability of Temperature near the Mesopause Region

The Solar Occultation for Ice Experiment (SOFIE) on the Aeronomy of Ice in the Mesosphere (AIM) mission has been observing the upper atmosphere since its 2007 launch. Among its data products, SOFIE measures Polar Mesospheric Cloud (PMC) ice properties and the temperature of the air in which the ice forms. SOFIE has shown that over the course of the AIM mission, the northern hemisphere, July temperature at PMC altitudes has generally decreased, while PMC ice mass for the same period has generally increased. While this inverse relationship is as expected, the trends are opposite to expectations as solar activity has generally increased during the period of AIM observations. This suggests that another forcing is overwhelming the effects of solar activity, at least for this particular solar cycle. Candidate forcings include both interhemispheric and intrahemispheric coupling, as well as cooling due to greenhouse gas increases. In this talk, we examine observations from SOFIE, the Sounding of the Atmosphere by Broadband Emission Radiometry (SABER), and the Halogen Occultation Experiment (HALOE) to look at the decadal variation of polar mesosphere temperature at PMC altitudes and disentangle the relative effects of solar cycle and other forcings. We show that intrahemispheric coupling is the largest driver of temperatures at PMC altitudes during the SOFIE era and that greenhouse gas forcings play a role over longer time periods.