Abnormal Response Of Arctic Sea Ice To Two Types Of ENSO In Autumn And Possible Mechanisms

Based on the monthly Hadley Center sea surface temperature data,Hadley Center Arctic sea ice concentration data,and the National Centers for Environmental Prediction(NCEP)/the National Center for Atmospheric Research(NCAR)reanalysis data during the period of 1961-2016,we analyzed the abnormal response of Arctic sea ice to two types of ENSO in autumn,and the possible mechanisms of such a abnormal response are furtherly discussed.The main conclusions are as follows:(1)Sea ice in the Kara Sea(60-90°E,70-80°N)has always been a significant negative anomaly in both EP El Nino and EP La Nina years.The physical process in the fall of EP El Nino that causes the sea ice anomaly in the Kara Sea is mainly located in the Pacific region.The suppressed convection near the western Pacific Warm Pool stimulates the negative PJ wave train,and the anomalous anticyclone forms in the high latitudes.The circulation forms a warm advection to the Kara Sea from the warmer mid-high latitudes,resulting in an unusually low sea ice.In the autumn of EP La Nina,was mainly an obvious westerly wind anomaly in the open seas of the Atlantic Ocean.Individual cases analyses show that there was a clear westerly jet center over the North Atlantic Ocean in the autumn of EP La Nina and a quasi-positive pressure response to the low-level westerly winds.It is favorable for the warm water in the open seas of the North Atlantic to be transported to the Kara Sea area,accelerating the ice melting process.(2)The linear correlation between the occurrence of CP ENSO events and the sea ice anomalies during the same period of autumn are not significant。By diagnosis and analysis of sea ice anomalies and variations in individual CP ENSO cases,the variations of sea ice concentration in the Chukchi Sea area are small in the autumn of CP El Nino,and the negative sea ice anomalies response are relatively stable.However,the abnormal sea ice responses in the cases of CP La Nina are unstable.Further analysis of circumfluence field,PNA-like phase can be stimulated in the extratropical area in CP El Nino year,but this is mainly manifested in the mature winter of CP El Nino.Anomalous circumfluence field in the autumn which is concerned in this paper,the response of PNA-like phase in high latitudes has not passed the test,which means that large-scale circulations in high latitudes in the autumn have relatively complex changes,and the abnormal changes in individual years are inconsistent.Therefore,the consistency of the reduction of sea ice in the Chukchi waters in the autumn and the connection with CP El Nino are not stable.(3)The AM2.1 atmospheric model and CCSM4-amip model(1979-2010)were introduced to verify the possible mechanisms of Arctic sea ice anomaly response in the two types of ENSO.The AM2.1 atmospheric model shows a“+”“-”“+”triple wave train in the extratropical area,which is a representation of the significant sea ice anomalies in the Kala Sea area during the autumn of EP El Nino.AM 2.1 model simulates the autumn anomalous circulation pattern in the high latitudes of EP La Nina,but there are still in the numerical differences between observations.The CCSM4-amip model is a representation of the circulation anomalies in the high latitudes of the EP La Nina region in the autumn.There is a significant large-value westerly jet center in the North Atlantic waters,which is conducive to warm water transportation in the open seas of the high latitudes of the North Atlantic to the Kara Sea area;AM 2.1 model does not reproduce well for CP El Nino,which may be related to the signal instability of the CP El Nino years.It may be difficult to stimulate the climate anomalies in sensitivity tests for CP El Nino.However,in the CCSM4-amip model,the anomalous modes of the height field in the extratropical regions in the autumn for CP El Nino are reconstructed.The main manifestation is PNA-like phase.The response in the high latitudes was weak,and does not pass the significant test.The results of the circumfluence field is the same.It is further verified that the connection between Arctic sea ice anomalies and CP El Nino is unstable.