This study investigates the role of the winter residual circulation in shaping Northern Hemisphere summer mesopause conditions. In a recent study carried out with the Kühlungsborn Mechanistic general Circulation Model (KMCM), it was shown that the interhemispheric coupling mechanism has a net cooling effect on the summer polar mesospheres. In this study, the comprehensive Whole Atmosphere Community Climate Model (WACCM) is used to reconfirm the hypothesis that the summer polar mesosphere will be much warmer without a gravity wave driven residual circulation in the winter. We reaffirm that it is the equatorial temperature response in the mesosphere that is the crucial step in interhemispheric coupling.

The role of the summer stratosphere in shaping the conditions of the NH summer polar mesosphere is also investigated. Without GWs in the winter, it is the summer stratosphere that controls the temperature in the summer mesopause region. It is found that if there are no GWs in the winter hemisphere, a weaker Brewer-Dobson circulation would lead to a cooling of the summer mesosphere region instead of the warming of this region associated with interhemispheric coupling.