Role of tropical synoptic-scale disturbances in modulating the strength of east Pacific Hadley cell

This study examines how tropical synoptic-scale disturbances can modulate the variations in the strength of East Pacific Hadley cell (EPHC). The East Pacific is characterized by relatively colder sea surface temperatures and a meridional overturning circulation consisting of both a shallow meridional overturning circulation (1000–800 hPa) and a deeper meridional overturning circulation reaching 250-200 hPa. The shallow convergence field over the east Pacific is mainly driven by meridional sea surface temperature gradients. However, sometimes deep convection and a deeper meridional circulation is also observed over the east Pacific domain, the maintenance of which remains unclear.

Previous studies have identified the presence of distinct westward propagating synoptic-scale disturbances over the domain, which may trigger deep convection through low-level meridional convergence. The Mixed Rossby Gravity (MRG) waves, characterized by cross-equatorial meridional flow and anti-symmetrically distributed convection are capable of modulating meridional convergence and convection over east Pacific. The study explores the impact of MRG waves on the variability of the East Pacific Hadley cell strength. The convergence associated with the MRG waves is found to induce deep convection over the East Pacific, consequently leading to the strengthening of the HC over this region. The EPHC is observed to be stronger during years of strong MRG activity and weaker during years of weak MRG activity. The study highlights that the variations in strength of East Pacific HC during boreal summer are linked to the fluctuations in MRG wave activity in this region