| The surface air temperature over the Arctic increases faster than the rest of the globe,a feature called ‘Arctic Amplification(AA)’.The warming phenomenon also extends to the troposphere.Although there are numerous studies existing,the quantification of Arctic warming is still a challenge.This thesis,with combination of observation and multi-model coordinated experiments,investigates the both Arctic surface warming and the troposphere warming and the potential mechanisms during1982 and 2014.The main conclusions are as follows:(1)The Arctic air temperature decreases with height.Change of sea surface temperature is climatologically main driver for the mid(500 h Pa)and low(850 h Pa)tropospheric warming over the Arctic for all seasons,and in particular,for autumn(September to October,SO),early winter((November to December,ND)and late winter(January to February,JF),.(2)The mid-and-lower Arctic troposphere is colder before 1998 and warmer after1998,leading to a significant warming trend.However,the upper Arctic troposphere(200 h Pa)showed no significant warming trend during 1982 to 2014,but with strong interannual variability.(3)The Arctic troposphere warming mainly appears on 1000-300 h Pa.The warming trend of Arctic mid-and-lower troposphere is seasonally different.During the SO,ND and JF,sea ice change and the external forcings mainly affect the warming trend of the near-surface,and has a weaker influence on the temperature trends in the mid-and-upper troposphere.On the contrary,sea surface temperature can significantly affect the warming trend of the middle and lower troposphere in each period,while the temperature trend of 200h Pa is relatively weak.Correspondingly,there is a weakening of zonal wind during 50°N-70°N.(4)The change of sea surface temperature can force the convergence of Eliassen-Palm(E-P)flux over mid-latitudes and result in the weaken zonal wind during the ND and JF.At the same time,the increased polar-ward eddy heat flux contributes to the Arctic warming.In particular,the sea surface temperature in the tropical eastern Pacific and the central North Pacific(45°N-60°N)are the sources to trigger anomalous polar-ward planetary wave and therefore the changes in atmosphere circulation over the Arctic and the Arctic warming. |
