Impacts of the Boreal Spring Indo-Pacific Warm Pool Hadley Circulation on Tropical Cyclone Activity over the Western North Pacific

• Published in: Journal of climate 2018-02, Vol.31 (4), p.1361-1375
• Main Authors: Guo, Yi-Peng, Tan, Zhe-Min
• Format: Article
• Language: English
• Subjects: Annual variations; Anomalies; Atmospheric sciences; Circulation; Climate; Cyclones; Cyclonic activity; Cyclonic circulation; Empirical analysis; Gravitational waves; Hadley circulation; Hurricanes; Interannual variability; Laboratories; Monsoon trough; Monsoon winds; Monsoons; Orthogonal functions; Precipitation; Precipitation anomalies; Relative vorticity; Sea level; Sea level anomalies; Sea level pressure; Sea surface; Sea surface temperature; Spring; Summer; Surface temperature; Tropical circulation; Tropical circulation anomalies; Tropical climate; Tropical cyclone activity; Tropical cyclones; Variability; Vertical wind shear; Vorticity; Wind; Wind shear; Wind speed
• ISSN: 0894-8755; 1520-0442
• DOI: 10.1175/JCLI-D-17-0422.1

This study investigated the impacts of the interannual variability in the boreal spring regional Hadley circulation over the Indo-Pacific warm pool (IPWP) on the tropical cyclone (TC) activity over the western North Pacific (WNP). The principal modes of the interannual variability in the IPWP Hadley circulation were calculated using empirical orthogonal function (EOF) analysis. The leading mode (EOF-1) features cross-equatorial southerly wind anomalies over the Indian Ocean and Maritime Continent and has an evident impact on WNP TC activity during summer. In the summer following a positive phase of the EOF-1, a cyclonic circulation anomaly, with upward motion, positive relative vorticity anomalies, and weak sea level pressure, dominates the WNP, and this favors increased TC genesis. However, large positive vertical wind shear anomalies over the South China Sea and Philippine Sea inhibit the TC intensification. A positive wind–sea surface temperature (SST)–precipitation feedback was found to facilitate the ability of the signal of the EOF-1 to persist until the summer. The westerly wind anomalies converge around 110°N over the WNP, thus increasing precipitation, and this increased precipitation enhances the westerly wind anomalies via a Gill-type response. The strengthened westerly wind anomalies increase total wind speeds, which in turn cool the SST in the Bay of Bengal and the South China Sea, and warm the SST in the eastern WNP, increasing the zonal SST gradient. Consequently, this increased zonal SST gradient further enhances the westerly wind anomalies, strengthens the monsoon trough, and increases the WNP precipitation further. Therefore, the WNP precipitation anomalies are sustained into the summer.