The Role of Asian Summer Monsoon Circulation on Tropopause Variability

A dynamical relationship that connects the extratropical tropopause potential temperature and the near surface distribution of equivalent potential temperature was proposed in a previous study. And this relationship has been found to work successfully in explaining both the annual cycle of the extratropical tropopause and inter-annual variability in northern summer in reanalyses.

In order to better understand the observed strong moisture-tropopause linkage in northern summer, a set of idealized aquaplanet model experiments has been used. While the control experiment prescribes a zonally symmetric sea surface temperature (SST), the perturbation experiment further includes a subtropical planetary-scale SST perturbation, which mimics the land-ocean heating asymmetry. It's found that as a monsoon-like SST perturbation is introduced, the near surface fluctuation of equivalent potential temperature is positively correlated with the tropopause potential temperature. Furthermore, the planetary-scale eddies associated with monsoon-like circulation also play a significant role in determining the thermal stratification in this region. This result clearly demonstrates the importance of Asian summer monsoon circulation in regulating the extratropical tropopause variability in inter-annual time scale.