Abstract

Interhemispheric coupling (IHC) is a positive correlation between temperatures in the polar winter stratosphere and polar summer upper mesosphere and lower thermosphere. Over the two decades since its discovery through observations of polar mesospheric clouds, several plausible mechanisms of the IHC have been proposed. However, a consensus on the IHC mechanism has yet to be fully reached. One of the most uncertain aspects of the mechanism is the role of gravity waves (GWs). Since most GWs were parameterized in models used in the previous studies, their contribution to the IHC was not necessarily realistic when assumptions used in the parameterizations did not hold. We perform hindcast simulations of the whole neutral atmosphere over seven boreal winters using a GW-permitting general circulation model. The model is initialized through spectral nudging to state-of-the-art reanalysis covering the whole neutral atmosphere. The IHC is analysed as a sequential development of anomalies from the climatology including GW forcing. As a result, it is revealed that consequential interplay of GWs and quasi-two-day waves in the summer mesosphere is the key driver of the IHC . The mechanism applies to multiple cases associated with sudden stratospheric warming and vortex intensification. In addition, we will discuss the model representation of GWs in the summer polar mesosphere, which play a crucial role in the IHC , by comparing resolved waves from the high-resolution hindcasts with GW parameterizations and assimilation increments in the reanalysis. The outputs from hindcasts are highly useful in elucidating global and climatological behaviour of GWs in the whole neutral atmosphere.