Characteristics of the linkage between the boreal winter Hadley cell and various tropical sea surface temperature meridional structures

Abstract

AbstractThis paper investigates the asymmetric response of the boreal winter Hadley cell (HC) to the meridional structures of the tropical sea surface temperature (SST) over the period 1979–2016. The variations in the zonal‐mean SST and HC are decomposed into equatorially symmetric (i.e. SES for SST, HES for HC) and equatorially anti‐symmetric (i.e. SEA for SST, HEA for HC) components. The response of the HEA to a given amplitude variation in SEA is stronger (by around three times) than that of the HES to the same amplitude variation in SES; this response ratio for the boreal winter is smaller than that for the annual mean. The variations in boreal winter HEA and HES are both related to the canonical El Niño, but in different regions; that is, the HEA is connected to the tropical Northwest Pacific SST, whereas the HES is linked to the SST over the tropical Eastern Pacific. During the period 1979–2016, warming of the tropical Northwest Pacific SST weakened the HEA and contributed to the decreased response ratio of the boreal winter HC to tropical SST. This point is further supported by examining the situation over the period 1958–2001, during which an interdecadal variation of tropical Northwest Pacific SST modulated the linkage between the boreal winter HC and SST. This observation shows that the warming of Northwest Pacific SST contributes to the decreased sensitivity of the boreal winter HC to SST, raising the possibility that global warming may affect the relationship between the HC and SST.Key FindingsThe ratio of the Hadley circulation to different SST meridional structures is reduced during boreal winter. The result raises the possibility that the contribution of global warming in impacting the relationship between the Hadley circulation and SST.