Understanding the variability and trend of the regional Hadley Cell over Asia-Pacific

The zonal mean Hadley Cell (HC) has been reported to be expanding poleward in the last few decades. However, there has been no consensus on whether the zonal mean HC is strengthening or weakening. The features of longitudinally averaged HC are collectively modulated by various regional HCs, controlled by the regional differences in land-ocean distribution and topography. However, there have not been many studies exploring the variability and trend of regional HCs in a detailed manner. In this study, we examine the variability and long-term trend of the regional HC over the Asia-Pacific and explore the different factors contributing to the regional HC variability. Moist convection can regulate regional HCs on synoptic time scales through equatorial wave dynamics. The ocean–atmosphere coupled variability associated with the El Niño-Southern Oscillation (ENSO), and the modulation of tropical convection and equatorial waves are considered to exert a dominant control on the regional HC variability in the interannual timescale. In addition to the tropical forcing, the regional HC variability is also affected by fluxes transported by the midlatitude eddies from the subtropics to the tropics. In this study, we will be quantifying the relative role of these tropical and extratropical forcings in modulating the variability of regional HC over Asia-Pacific.