On Interdecadal Variation Of The Relationship Between The Intense Tropical Cyclone Activity Over The Western North Pacific And ENSO

The interdecadal change of the interannual relationship between the intense tropical cyclone (TC) frequency over the western North Pacific (WNP) and the El Nino-Southern Oscillation (ENSO) is studied based on the TC Best Track and global reanalysis data. The results show that during 1983-2014 (the recent period), the frequency of intense TC and the November-January (NDJ) Nino3.4 are closely correlated, whereas during 1950-1971 (the prior period), their correlation is not statistically significant.Compare to the prior period, the difference of genesis frequency, genesis location and lifespan of intense TCs between the El Nino developing years and La Nina developing years has been significantly enlarged in the recent period, moreover the the difference mainly generate in the southeastern quadrant of WNP. In the recent period,more intense TCs formed in the southeastern quadrant in El Nino developing years,and less intense TCs formed in the southeastern quadrant in La Nina developing years.That indicating the impact on WNP intense TC of ENSO is enhanced, specifically in El Nino developing years.The westward shift of positive SSTA over the tropical Pacific in the recent El Nino developing years is a key factor that enhanced the relationship between the Nino3.4 index and annual intense TC frequency. The enhancement of positive(negative) SSTA induce positive (negative) MPI, at meantime the westward shift of positive (negative) SSTA cause the upward (ascending) motion shift westward to the centre of tropical Pacific. The westward shift of anomalous upward (ascending) motion increases (decreases) relative humidity and decreases (increases) vertical wind shear anomalies in the southeastern quadrant of the tropical WNP in the El Nino (La Nina)developing years during the recent period are favorable (unfavorable) to TC genesis in the southeastern quadrant of the tropical WNP and enhanced the interannual relationship between the intense TC frequency and ENSO in the recent period. This is because the TCs forming in the southeastern quadrantare more likely to move over the warm tropical ocean and intensify into intense TCs.