Numerical Simulation And Diagnosis Of The Impacts Of The Antarctic Sea-ice On Southern Hemisphere Atmospheric Circulation And Climate

Antarctic sea ice zone,accounting for more than half of the total Southern Hemisphere snow and ice area,is an important component of the global cryosphere.It is also one of the major characteristics of the Antarctic marine environment.For the Antarctic sea ice's important impact on the global atmospheric circulation and climate,it is very necessary to understand the patterns and trends of the changes in Antarctic sea ice,and to stimulate and diagnose the process that the Antarctic sea ice impacting on the global atmospheric circulation.First of all,changes of Antarctic sea ice and its impact on the Southern Hemisphere atmospheric circulation,atmospheric circulation in East Asia are reviewed.Then we modeled the impacts of the overall changes in the Antarctic sea ice and anomaly of Antarctic dipole on southern hemisphere atmospheric circulation and climate,East-Asian atmospheric circulation, Asian climate,Indian climate and Pacific climate,using the NCAR/CAM3.0 global climate model.We focused on\the impact of Antarctic dipole on atmospheric circulation in the middle and high latitude of southern hemisphere,and explored the possible mechanism.The main conclusions are as follows:1.The numerical experiments about the impact of the Antarctic sea-ice's positive anomalies on the global atmospheric circulation and climate show that:the atmospheric circulation in NCAR/CAM3.0 model is sensitive to the Antarctic sea-ice,the areas which has strongest and the most direct response is the high latitudes in southern hemisphere,mainly Performancing in the atmospheric circulations,such as the low pressure zone around the southern oceans,Australia high and Mascarene high.The northwest Pacific subtropical high pressure also has a strong response to the Antarctic sea-ice changes.Antarctic sea-ice changes's effect on the January atmospheric circulation in china is relatively weaker than its effect in July,the impact on January atmospheric circulation and climate is mainly located in the southern hemisphere.2.The numerical simulation about the impact of Antarctic Dipole anomaly on atmospheric circulation and climate in the middle and high latitudes of southern hemisphere shows that:the surface heat flux has the first respond to the abnormal changes in the Antarctic Dipole.anomaly low(positive phase) of sea ice,corresponding to the surface heat flux increase(decrease) in the same region,which will lead directly to the lower troposphere's temperature decreased(increased).Further research also showed that the Antarctic dipole anomalies can affect the upper troposphere,which may be caused by the rising airflow of the Ferrel circulation,the rising flow can carry the lower tropospheric heat flux and temperature's anomaly response to the upper atmosphere.Cohpained with the analysis of air circulation, geopotential height and pressure field in high and low level of the troposphere field,we found that the effect of the Antarctic Dipole anomaly in the lower troposphere can only reach about 50°S,while in the upper troposphere the effects can go up to about 20°S through the interaction among the atmospheric activity centers.In addition,the areas that has strongest respose to sea ice anomalies of precipitation in the Southern Hemisphere is the 30-35°S latitude belt,the numerical simulation results show that the remote respose of the precipitation in this latitude belt is forced through the effect of the Antarctic Dipole anomalies on the strength of the Ferrel circulation.The sea-ice abnormal changes in dipole negative(positive) phase would strengthen(weaken) the Ferrel circulation's strength in the same longitude belt, and the precipitation in its sinking branch will be less(more).3.There was a significant negative correlation between Ross sea ice's change in April and Mascarene high pressure in the Indian Ocean in May,and there is a close relationship bwtween the spring Mascarene high and the East Asian summer monsoon climate.Ross Sea ice anomalies could affect the Mascarene high by changing the strength of the Antarctic Oscillation.Specific process as follows:Ross Sea ice's anomaly less(more) in April will make the Circumpolar low pressure zone deeper(shallower),make the Antarctic Oscillation strengthening(weakening).The strength of the Antarctic Oscillation will directly decide the strength of Mascarene high changes in May,so that make it strengthening(weakening),and make the cross-equatorial flow to strengthen(weaken),and finally affect the precipitation in China in June.On average,spring Mascarene high pressure will have an significant effect on the East Asian summer monsoon circulation and precipitation ahead a month.So,Ross Sea ice's change in April can be regarded as a precursor of the onset and the strength of the East Asian summer monsoon.