The Impact Of The Mid-high Latitude Oceans On Climate Change Over North And Northeast China

The Ocean is a very important forcing source for atmospheric circulationanomaly change; and also plays an important role in climate prediction which ismainly based on the second kind predictability (the model sensitivity to inaccurateboundary conditions). Its influence on the atmospheric circulation anomaly changeand ocean thermal effect makes a great position in the studies of climate changetheory and climate prediction. Based on the National Center for EnvironmentalPrediction (NCEP) reanalysis data, Hadley Sea Surface Temperature (SST), China’s160meteorological stations monthly mean precipitation data and so on, this thesisanalysed: the east Asian cold high and the high altitude circulation field from autumnhigh latitude Sea Surface Temperature Anomaly (SSTA) change; the mechanism ofthe autumn high latitude SSTA effecting on East Asian cold air movement; and alsoverified it through Numerical Simulation experiment, utilizing Institute ofAtmospheric Physic’s9level Model (IAP-9L Model).The main results show that Barents Sea thermal change in autumn can be animportant reference to predict cold air movement over China in winter. As a goodindicator, positive SSTA over Barents Sea in autumn corresponds with higher winter500hPa geopotential height over the Ural Mountain and stronger1000hPa over theMongolian High. Cold air from the northerly wind component in front of theMongolian High easily has effect on the climate of Northeast and North China. Thenegative SSTA corresponds with higher winter500hPa geopotential height over NorthAtlantic Ocean-Norway Sea; but the cold air has little influence over North China.Comparison between positive SSTA and negative SSTA over the years shows thatthere are intra-seasonal change characteristics.There is also an interaction between North Atlantic SSTA and the atmosphericcirculation anomaly. Due to the continuity of the autumn SSTA in North Atlantic, the ‘positive-negative-positive (+-+)’ distribution of North Atlantic SSTA leads to largerDecember500hPa geopotential height over the Barents Sea. Under thebackground-wind and the sea surface wind anomaly (SSWA) actions, the feedbackmechanism and wind-evaporation-SSTA can benefit the ‘+-+’ SSTA lasting and thefeedback to atmospheric circulation anomaly. The negative SSTA moves easterly fromOctober to December, and the stronger evaporation, because of the same winddirection of the SSWA and background wind, produces stronger up-vertical movement.With the positive precipitation area moving easterly from Western Europe, the latentheat transport to the Barents Sea along with the southeast airflow in front of the lowtrough, promotes the development of the Ridge. Furthermore, the East Asian trough infront of the ridge becomes stronger from December to February, and then the anomalysurface cold high develops in front of the ridge and behind the trough, whichstrengthens the winter wind in North and East China.The autumn SSTA in Japan Sea and the Northwest Pacific ocean nearby hasinfluence on the winter climate change in Northeast China. The SSTA in Japan Seacould last from autumn to the end of winter, which shows significant continuityanomaly. In positive SSTA condition, the sea-land temperature difference becomeslarger as the land seasonal temperature declines. Due to the collective effects of thediabatic heating and the forcing wave by larger thermal difference between sea andland, the cyclonic circulation anomaly over ocean is strengthened and water vaporeasily transported from Okhotsk to NE China, thereby resulting to more precipitationand lower air temperature. In addition, the east part of the surface cyclone bringssoutherly abnormal airflow, which weakens the southward cold water transport fromOyashio, thereby keeping the Japan Sea SSTA positive. Such effect is notable inDecember. Comparing positive and negative SSTA years, intraseasonal changecharacteristics also exist.The subsequent effect of Northeast Asia anomaly lowering winter airtemperature could produce the climate anomaly in Northeast China (less precipitation).In autumn, the positive SSTA in the Barents Sea and Japan Sea enhances the wintercold air activity in Northeast Asia, resulting in higher Sea ice concentration in the northern part of Northeast Asia. Further, combining lower air temperature and highsnow in Northeast China, the Arctic zonal temperature gradient in spring and summerbecomes larger. Forced by high latitudinal zonal temperature gradient, there isanomaly in atmospheric circulation, the geopotential height difference between theBarents Sea and East Siberian Sea becomes larger, the anomalous anticyclone appearson ground of the Lake Baikal region and summer precipitation becomes lower inNortheast China (particularly in July and August). The relative study shows that theJanuary SSWA can influence the Arctic Ocean zonal temperature gradient throughEkman transport, thereby affecting the precipitation over eastern China in summer.This study shows that the Barents Sea and North Atlantic autumn SSTA haveinfluence on the winter climate change in Northeast China through the impact ofatmospheric circulation and SSTA distribution. Autumn SSTA in Japan Seasignificantly affects the winter climate in Northeast China. Lower temperature andhigh snow corresponds with winter in Northeast China climate anomaly, which couldfurther influenced precipitation in Northeast China. Thus, autumn SSTA in highlatitude not only influenced winter in Northeast China climate, but also affectssummer in Northeast China climate change in the following year. The conclusionsabove are bound to deepen our knowledge about the mechanism of the high latitudeair-sea interaction, as well as provide valuable reference for climate prediction.