Different Effects of Two ENSO Types on Arctic Surface Temperature in Boreal Winter

Abstract

The present work investigates different responses of Arctic surface air temperature (SAT) to two ENSO typesbasedonreanalysisdatasetsandmodelexperiments.WefindthateasternPacific(EP)ENSOeventsare accompaniedbystatisticallysignificantSATresponsesovertheBarents–KaraSeasinFebruary,whilecentral Pacific (CP) events coincide with statistically significant SAT responses over northeastern Canada and Greenland.TheseimpactsarelargelyofoppositesignforENSOwarmandcoldphases.DuringEPElNiñoin February, the enhanced tropospheric polar vortex over Eurasia and associated local low-level northeasterly anomalies over the Barents–Kara Seas lead to anomalously cold SAT in this region. Simultaneously, the enhanced tropospheric polar vortex leads to enhanced sinking air motion and consequently reduced cloud cover.Thisinturnreducesdownwardinfraredradiation(IR),whichfurtherreducesSATintheBarents–Kara Seas region. Such a robust response cannot be detected during other winter months for EP ENSO events. DuringCPElNiño,theFebruarySATsovernortheasternCanadaandGreenlandareanomalouslywarmand coincide with a weakened tropospheric polar vortex and related local low-level southwesterly anomalies originatingfromthe AtlanticOcean.The anomalous warmthcan be enhancedby thelocal positivefeedback. Similar SAT signals as in February during CP ENSO events can also be seen in January, but they are less statisticallyrobust.WedemonstratethatthesecontrastingArcticFebruarySATresponsesareconsistentwith responses to the two ENSO types with a series of atmospheric general circulation model experiments. These results have implications for the seasonal predictability of regional Arctic SAT anomalies. ! 2019 American Meteorological Society.