Influence of El Niño decaying pace on low latitude tropical cyclogenesis over the western North Pacific

Abstract

The modulation of El Niño decaying pace on tropical cyclones (TCs) activities at low latitude (within 10°) over the western North Pacific (WNP) is investigated in this study. During rapidly decaying El Niño events, fewer TCs occur near the equator and the averaged genesis location is more westward. More TCs are found in the southeast of WNP during slowly decaying phase of El Niño events. The distinctive differences of TC genesis frequency and their respective meridional positions are related to the modulation of El Niño to large‐scale environmental flows. Both dynamical and thermodynamical conditions, such as low‐level vorticity, mid‐level relative humidity and vertical motion, are favourable for TC genesis in the southeast of WNP during slowly decaying El Niño events. The differences of sea surface temperature, vertical wind shear, and TC heat potential between the two El Niño events are similar to the spatial distribution of TC genesis at low latitude. Disturbances in southeastern WNP in slowly decaying El Niño events are more likely to develop into TCs due to the stronger zonal convergence and meridional shear of zonal wind. These findings may help to better understand the interaction between low‐latitude TCs and El Niño. The higher frequency of low‐latitude TC genesis and their more eastward TC genesis position in slowly decaying El Niño events may in turn slow down the transition speed of El Niño.