Circulation Systems Over China :: essays research papers

Circulation Systems Over chinaw beIntroduction The Earths atmosphere is in continuous motion movement which isattempting to balance the constant variances in coerce and temperaturebetween diverse parts of the globe. It is this motion which carries water fromthe ocean to the continents to provide precipitation and moves heat energy fromthe tropical regions toward the poles, warming the high latitudes. It is thiscirculation which plays a basic part in maintaining a steady state in theatmosphere and generating the climatic zones which characterise different partsof the earth. China, from its latitudinal location, mostly belongs to the mid-latitudes, with a small part to the humiliated latitudes. It is located at south ofSiberia and the north of the tropical Pacific. At this distinctive location, thecountry is affected by the alternate seasonal expansion and contraction of the gelid continental highs and tropical maritime air masses, on with theseasonal shifts of the everywherehe ad sun. These changes in the military press systems overAsia generate the unique Asian monsoon circulation which prevails over Chinathroughout the year.Surface Pressure Field and Winds For any fluid to initiate movements, pressuregradient must exists. Therefore, for a close understanding of the circulationsystem that operates over China, we should start from discussing the seasonalpressure distribution at sea-level over the Asia-Pacific region, which is thedriving force for the air movements in China. Most clearly to be seen, thelargest difference in the atmospheric pressure occurs between winter and summer,whereby January and July can be considered as representative months. In January,a typical cold anticyclone with central pressure above 1,040 hectopascals (hPa)developed over mid-Siberia and Mongolia (Mongolian High) while a stronglyestablished cyclone over the north-western Pacific Ocean (Aleutian Low). Sinceboth pressure systems practically lie in the same latitude of 50 to 55N , asteep pressure gradient occurs which produces strong and persistent north-westerlies over Northeast China. A third pressure system which affects China,although limited only to south-eastern China, is the equatorial Low overAustralia and New Guinea. The vast territory of East China lies in the middle ofthe path along which the Mongolian cold air tries to rush southward into theEquatorial Low. Northerly and north-easterly flows prevail over the eastern halfof China. As a typical feature, the Mongolian High is only a rather shallowpressure system. It disappears at the 500-hPa level. West China which has ahigher elevation, therefore feels little of its influence Yunnan highlands areeven predominated by south-westerlies during most of the winter. The pressurepattern at sea-level during summer differs completely from winter conditions.