The Reason And Influence Of Arctic Rapid Tropospheric Warming

Here we use atmospheric data from NCEP/NCAR Reanalysis to define Arctic rapid tropospheric warming(RTW)events that in one day,which the Arctic average 1000hPa air temperature is over 3σ(above the 1948-2015 winter mean)warmer in situ winter(December-February).As a result of synthetic analysis,maximum temperature increase is over 13℃ at the North Pole in one day.We first make a case analysis of the tropospheric warming that occurred on 29 December 2015 and analyze the causes and process of the synoptic scale warming events of Arctic troposphere in the winter.With 6-h and daily reanalysis data from NCEP/NCAR,we studied the mechanisms for the sudden Arctic warming on 29 December 2015.The signal area average method and heat flow equation for temperature estimation were used in this study.It revealed that there was a sudden warming in the Arctic on 29 December 2015 and the maximum temperature increase was over 25℃ or more.There existed strong southerly winds with speeds larger than 20 m s-1 over the warming area during the same period,which was driven by the combined effects of a strong cyclone and anti-cyclone.The strong moist southerly winds brought warm temperature to the Arctic region and enhanced cloud cover over the sudden warming area.The temperature advection turned from cold pattern to warm pattern from 28 December to 29 December,which corresponded to the rapid increase in temperature and indicated that warm temperature advection played a vital role in the sudden Arctic warming.The enhanced cloud cover led to deceases in the upward long-wave radiation flux in the dark night,contributing to the temperature rise.For the sudden warming,the contributions of temperature advection,vertical term,and non-adiabatic effect were 20.4%,-9.9%,and 89.5%,respectively.Therefore,the temperature advection and non-adiabatic effect were responsible for the sudden Arctic warming,and the non-adiabatic effect was a more important factor.We find that the main energy sources of the RTW events are from the Atlantic Ocean,the Pacific Ocean and the Eurasian continent,and 65%of warming events originate from the Atlantic Ocean.We find the temperature increase is nearly entire tropospheric,not just the near-surface.The spatial distribution of rapid tropospheric warming reaches 500hPa,and it increases the local geopotential thickness.Further the rapid Arctic warming has contributed to split the tropospheric polar vortex into two pieces.The RTW events of different energy sources have different vertical distributions of warming.Therefore,different polar vortex splitting is induced.The splitting of the polar vortex means the movement of the cold air mass.As for the Atlantic pattern,the north wind anomalies from the polar region irrupt Northwest Eurasian continent and North America.In the case of the Pacific pattern,the temperature negative anomalies are located in the west of Canada and America,reaching the middle latitude.In the last pattern,the cold air mass after the trough sweep the east of North America.The different energy sources of RTW events lead to different regions of the polar cold air mass invasion.