Effects Of Winter And Spring Snow Cover On The Qinghai-Tibet Plateau On The Frequency Of Rapidly Intensifying Tropical Cyclones In The Northwest Pacific

The rapid intensification(RI)plays a key role in the predication of tropical cyclones(TCs)intensity change and remains a great challenge.Previous studies have focused on the impact of sea surface temperature anomalies(SSTAs)teleconnection on rapidly intensifying TCs(RITCs)activity.However,none of studies date on land conditions affecting RITCs.As the most sensitive regions of land surface,Tibetan Plateau(TP)exert enormous effect on local and global climate and weather events via thermodynamic forcing.Based on snow depth data,this study investigates the relationship between boreal winter-spring snow depth over the eastern TP(TPSD)and boreal summer-autumn RITC frequency,and the physical mechanism is mentioned so that revealing the modulation of RITCs by TPSD from the views of SST feedback over the Indo-Pacific.Serval conclusions are proposed as follows:1)Study indicates an enhanced relationship in recent years between winter-spring TPSD and the frequency of RITCs over the western North Pacific(WNP)during the following peak TC season.The correlation between TPSD and RITCs is significant during 2000–2014 but was insignificant during 1979–1999.Large-scale environmental factors in response to TPSD suggest a pathway modulating RITCs,in which changes in low-level relative vorticity and vertical motion are identified to key roles.Correlation maps of two types of genesis potential indices and composite characteristics of TCs activity provide possible evidence that TPSD modulating TC genesis location and prevailing track can also determine the RITC frequency.Enhanced response of SSTAs similar to the pattern of Pacific Meridional Mode(PMM)and transition of tropical Indian ocean(TIO)SST diploe mode are considered as the essential roles in the connection between TPSD and RITCs.2)Study proposes a chain process that TPSD-modulating westerly jet motivates the PMM-like SSTAs and thus effects RITC frequency: During 2000-2014 when TPSD increases,there is an enhanced low-level anomalous anticyclone over the subtropical eastern Pacific mainly due to the combined effect of advection and dynamics of the climatological prevailing westerly jet.Northeasterly wind anomalies are observed on the flank of the anticyclonic circulation anomaly,favoring anomalously cool sea surface temperature.These anomalies lead to an anomalous pattern similar to the PMM,via a wind–evaporation feedback and cold advection.A Gill-type Rossby response to the PMM-like negative phase results in an anticyclonic circulation anomaly over the WNP,suppressing RITCs during 2000–2014.A nearly opposite circulation anomaly occurs when TPSD is lower during 2000–2014.There is a weak relationship between TPSD and RITCs,due to the lack of a link between TPSD and the PMM-like pattern from 1979 to 1999.Decadal changes in the relationship between TPSD and RITCs are mainly due to the meridional displacement of the prevailing westerly jet,which may be in response to decadal-to-multidecadal variability of SST anomalies.These changes then result in changes in the relationship between January–March TPSD and the PMM-like pattern.3)Study reveals an important influence of TPSD on seasonal evolution in the TIO SST modes,involving changes in RITC frequency associated with TIO SST.Higher TPSD hampers the westward extension of the South Asian High and thus intensifies ascending motion over the tropical Indian Ocean via changes in the tropical zonal circulation.The associated ascending motion promotes basin-wide tropical Indian Ocean cooling in spring through a Gill-type response.In the summer following a high winter-spring TPSD,a weaker monsoon circulation warms the western tropical Indian Ocean,thus favoring a positive phase of the Indian Ocean Dipole.This evolution of TIO SST associated with abnormal TPSD potentially weakens the relationship between RITC frequency and spring tropical Indian Ocean SST.When the effect of TPSD is removed via partial correlation analysis,we find a significant relationship between spring tropical Indian Ocean SST and rapidly-intensifying tropical cyclones as well as corresponding large-scale environmental factors.More comprehensive of understanding the basin-wide TC intensity climatology is performed to be obtained from the perspective of land-ocean-atmosphere interactions in this study that not only provides a potential implication for seasonal prediction of TC intensity changes but also highlights the importance of air-sea couple in TP thermal forcing.