Sensitivity of Extreme Rainfall in Taiwan to SST Over the South China Sea Through Modulation of Marine Boundary Layer Jet: A Mei-Yu Front Event During 1-4 June 2017

Water vapor transport from the South China Sea (SCS) by the marine boundary layer jet (MBLJ) can be an important moisture source for heavy rainfall events in Taiwan during the mei-yu season. However, the variability in the MBLJ due to sea surface temperature (SST) changes and its impact on extreme rainfall events have yet to be well understood. This study investigates how varying the SST over SCS modifies the structure of MBLJ and further impacts an extreme mei-yu rainfall in Taiwan during 1-4 June 2017. Results show that SST over the SCS can affect rainfall in Taiwan through its modulation of the MBLJ. Increasing SST leads to a southward shift of the mei-yu rainfall. This is attributed to the weakening of the MBLJ and the enhanced convection at the leading edge of the mei-yu front. The opposite effect is observed when the SST is decreased but with a smaller impact. The marine boundary layer jet (MBLJ) is a strong airflow in the lower atmosphere that can transport moisture to Taiwan and lead to heavy rainfall during the mei-yu season. This study conducts numerical simulations to investigate the impact of varying sea surface temperature (SST) over the South China Sea (SCS) on the MBLJ and how it affects rainfall in Taiwan. Based on the simulation results of an extreme mei-yu rainfall in Taiwan during 1-4 June 2017, we found that when SST over the SCS increased, the MBLJ weakened. Hence, the mei-yu front can move forth south and lead to a southward shift in rainfall location. On the other hand, decreasing the SST has the opposite effect but with a relatively smaller impact. Varying sea surface temperature (SST) over the South China Sea (SCS) can modulate the marine boundary layer jet (MBLJ) and affect an extreme rainfall event in Taiwan (2017)SST modulates MBLJ by adjusting vertical mixing in the boundary layerThe warm (cold) SST perturbation leads to a weak (strong) MBLJ, and the mei-yu rainband over Taiwan is shifted southward (northward)