简介:AtmosphericInfraredSounder(AIRS)datashowthattheSaharanairlayer(SAL)isadry,warm,andwell-mixedlayerbetween950and500hPaoverthetropicalAtlantic,extendingwestwardfromtheAfricancoasttotheCaribbeanSea.TheformationsofbothHurricaneIsabelandTropicalDepression14(TD14)wereaccompaniedwithoutbreaksofSALairduringtheperiod1-12September2003,althoughTD14failedtodevelopintoanamedtropicalcyclone.TheinfluenceoftheSALontheirformationsisinvestigatedbyexaminingdatafromsatelliteobservationsandnumericalsimulations,inwhichAIRSdataareincorporatedintotheMM5modelthroughthenudgingtechnique.AnalysesoftheAIRSandsimulationdatasuggestthattheSALmayhaveplayedtworolesintheformationoftropicalcyclonesduringtheperiod1-12September2003.First,theoutbreaksofSALairon3and8Septemberenhancedthetransverse-verticalcirculationwiththerisingmotionalongthesouthernedgeoftheSALandthesinkingmotioninsidetheSAL,triggeringthedevelopmentoftwotropicaldisturbancesassociatedwithHurricaneIsabelandTD14.Second,inadditiontothereducedenvironmentalhumidityandenhancedstaticstabilityinthelowertroposphere,theSALdryairintrudedintotheinnerregionofthesetropicaldisturbancesastheircyclonic?owsbecamestrong.ThiseffectmayhavesloweddowntheformationofIsabelandinhibitedTD14becominganamedtropicalcyclone,whiletheenhancedverticalshearcontributedlittletotropicalcycloneformationduringthisperiod.The48-htrajectorycalculationsconfirmthattheparcelsfromtheSALcanbetransportedintotheinnerregionofanincipienttropicalcyclone.