简介：BasedontheJointTyphoonWarningCenter(JTWC)best-trackdatasetbetween1965and2009andthecharacteristicparametersincludingtropicalcyclone(TC)position,intensity,pathlengthanddirection,amethodforobjectiveclassificationoftheNorthwesternPacifictropicalcyclonetracksisestablishedbyusingk-meansClustering.TheTClifespan,energy,activeseasonandlandfallprobabilityofsevenclustersoftropicalcyclonetracksarecomparativelyanalyzed.Thecharacteristicsoftheseparametersarequitedifferentamongdifferenttropicalcyclonetrackclusters.Fromthetrendofthepasttwodecades,thefrequencyofthewesternrecurvingcluster(accountingfor21.3%ofthetotal)increased,andthelifespanelongatedslightly,whichdiffersfromtheotherclusters.TheannualvariationofthePowerDissipationIndex(PDI)ofmostclustersmainlydependedontheTCintensityandfrequency.However,theannualvariationofthePDIinthenorthwesternmovingthenrecurvingclusterandthepelagicwest-northwestmovingclustermainlydependedonthefrequency.

简介：BasedontheMulti-ScaleStandardizedPrecipitationIndex(MSPI),extremeseveredroughteventsinChinaduring1961-2010wereidentified,andtheseasonal,annual,andinterdecadalvariationsoftheclusteringextremedroughteventswereinvestigatedbyusingthespatialpointprocesstheory.Itisfoundthatseveredroughtspresentatrendofgradualincreaseasaresultofthesignificantincreaseandclusteringtendencyofseveredroughtsinautumn.Theperiodicityanalysisoftheclusteringextremedroughtsindifferentseasonssuggeststhatthereisaremarkableinterdecadalchangeintheoccurrenceofclusteringextremedroughtsinwinter.Meanwhile,itisrevealedthattheclusteringextremedroughteventsexhibitgreatlydifferentannualmeanspatialdistributionsduring1961-2010,withscatteredandconcentratedclusteringzonesalternatingonthedecadaltimescale.Furthermore,itisfoundthatthedecadal-meanspatialdistributionsofextremedroughteventsinsummerarecorrelatedoutofphasewiththoseoftherainybandsoverChinainthepast50years,andagooddecadalpersistenceexistsbetweentheautumnandwinterextremedroughts,implyingasalientfeatureofconsecutiveautumn-winterdroughtsinthis50-yrperiod.ComparedwithotherregionsofChina,SouthwestChinabearsthemostprominentcharacteristicofclusteringextremedroughts.