ThesynopticsituationandmesoscalestructureofanexplosiveextratropicalcycloneovertheNorthwesternPacificinMarch2007areinvestigatedthroughweatherstationobservationsanddatareanalysis.Thecycloneislocatedbeneaththepolewardsideoftheexitofa200hPajet,whichisastrongpergentregionaloft.Atmid-level,thecycloneliesonthedownstreamsideofawell-developedtrough,whereastrongascendingmotionfrequentlyoccurs.Cross-sectionanalyseswithweatherstationdatashowthatthecyclonehasawarmandmoistcore.A'nose'ofthecoldfront,whichischaracterizedbyalow-levelprotrudingstructureintheequivalentpotentialtemperaturefield,formswhenthecyclonemovesoffshore.This'nose'structureishypothesizedtohavebeencausedbytheheatingeffectoftheKuroshioCurrent.Twolow-leveljetstreamsarealsoidentifiedonthewesternandeasternsidesofthecoldfront.Thewesternjetconveyscoldanddryairat800-900hPa.Thewindinthenorthernpartisnortheasterly,andthewindinthesouthernpartisnorthwesterly.Bycontrast,theeasternjetcarrieswarmandmoistairintothecyclonesystem,ascendingnorthwardfrom900hPato600-700hPa.Thesouthernpartisdominatedbythesoutherlywind,andthewindinthenorthernpartissouthwesterly.Theeasternandwesternjetssignificantlyincreasetheairtemperatureandmoisturecontrastinthevicinityofthecoldfront.Thisincreasecouldplayanimportantroleinimprovingtherapidcyclogenesisprocess.
