Studies On The Changing Characteristics Of South Asia High And The Relation With Relevant Impact Factors

South Asian High (SAH) is the strongest and the most stable atmospheric active centers on the height of100hPa except the Polar low. It affects part of Asian and African which cover the areas starting from the west coast of African at its west end and the west Pacific at its east end, and also affects the tropical and subtropical areas. Particularly, SAH plays an important role in weather and climate during the summer half year in China. As a result, a further study on SAH can improve our understanding about the evolution of atmospheric circulation anomalies, and the prediction skill of regional extreme weather/climate.By using the NCEP/NCAR reanalysis data and station observation data,this study gives a systematic research on the characteristics of variations in the location of ridge line, center, area, intensity and the index of eastward ridge point of SAH in different time scales during1961-2010, and investigates the thermal and dynamic features of SAH in different months and the relationships with Western Pacific Subtropical High (WPSH), and explores the impacts of the temperature of Tibetan plateau, Sea-surface temperature,Australian high, Mascrene high, and Somali jet on SAH. Results show that:(A) The characteristics of SAH:During1961-2010, In particular, in the1980s, the ridge line of the South Asia High in the winter half year position southerly area increases, the intensity increases, the eastward shift of the center position southward obvious.Relatively speaking the characteristic exponent of the summer half year, the trend was not significant.The Position prediction of SAH's Ridge:the1-20th pentad is mainly North-South movements, the18th pentad of the most southern (10.5°N); After the20th pentad of different ranges of the North, jump in the North for the first time, on the24th pentad Ridge, across15°N; the28th pentad North jumped for the second time, over20°N, North from the30th pentad after lifting rates decrease; the37th pentad North jumps again, crossed the30°N, North jump to the most northern location on the42th pentad (33.63°N), then began to withdraw South..Doughnut-shaped mobile track about the centre of SAH from January to December, Moving to the Philippines in the Pacific along the West from January to April, continuing along the West and accompanied to the North in the direction of movement,East-West oscillation over the Qinghai-Tibet plateau and Iran plateau from July to August,SAH began to retreat South from August-September, continuing along the South and accompanied to the East in the direction of movement from September toJanuary in the coming year, the end returned to the Pacific. (B) Investigates the thermal and dynamic features of SAH in different months:With the removing of SAH's center, the direction of dip, difference of level, and mean status of the ridge line of temperature shows that it trend to north distinctly and far from south, even return to vertical. Hidden heat is much clearly action which effecting on moving of South Asia high center in winter year, compared with the action of sensible heat. However, it has a opposite phenomenon in summer year.Vorticify, divergence, vertical velocity fields on100hPa, also can show the SAH's center moving track of doughnut-shaped With mobile low-level vorticity zone that corresponds to the gradual elevation From January to June, From July to September of relative stability, from October to December drift down.The monthly variations in divergence.vorticity and vertical motion field reflect the movement path of SAH, and that in divergence and ertical motion filed also present the upture of the divergence Field which shifts from offing to the south of Philippine Islands in May. The northern divergence Center after rupture combines with the divergence center over the south of Tibetan plateau in une,which cooperates with the strong low layer ascending motion, resulting in the intensity of SAH.(C) Influence factors on SAH:If the mean temperatureand When high temperatures in the Plateau South-East on January,Central and South-East of February.ln the South and East on April,in the South on May, SAH in the Highlands and to establish a time-early in the year,and in November is much higher over Southeast Qinghai-Tibet plateau. The ridge line of SAH occurred earlier in Qinghai-Tibet plateau.Moreover, it would be come much later while the mean temperature in that time.Canton Island sea temperature, Mascarene high and Australian high and TNI index of the four climatic factors and the South Asia High characteristic index lag correlation between the first three climatic factors and the South Asian high-pressure hysteresis area index of3-5months.delay of four months (Mascarene high lag9) intensity index exists a significant positive correlation, and lag the position of the ridge in January-March, the central latitude exists a significant negative correlation; the TNI index and the South Asia High area index lagged one month, hysteresis strength index of16months was significantly negatively correlated with lag15months ridge line position, the center latitude significantly positively correlated.In June, the weaker Somali jet. South Asian High and central longitude of the more easterly;In July the Somali Jet intensity increases, the South Asia High East ridge point, the more easterly;Somali Jet intensity increases in August, more large high-pressure area in South Asia.(D) The relationship between SAH and WPSH:Summer of nearly50years, the SAH and Western Pacific subtropical high (WPSH) Ridge position, size, and intensity of average annual change of trend line; the East and West ridges of SAH and WPSH daily changes in some locations, the lag associated with phase change from a year earlier, some years for reversed phase change.During1961-2010, the relationship of the west ridge points of WPSH and eastward ridge point of SAH is that they are the nearest with each other during the36-37th pentad. In June, if the distance between the west ridge points of WPSH and eastward ridge point of SAH is small, occurred in the north side of the the west ridge points of WPSH on the north side from East to West in strong precipitation process releases large amounts of latent heat, makes SAH move to the East. Precipitation in which the North,Southwest and Northeast of China.and the upper-middle reaches of Yangtze River has been influenced by the interaction of SAH and WPSH. In June SAH and WPSH when the margin between the two ridges farther, and two ridges continue does not appear similar to longitude, to the detriment of summer precipitation in China; In July, when both North ridge lift, drought occurs in areas controlled by the WPSH; when WPSH in advance East to retreat and SAH still stable in Iran Plateaus and Qinghai-Tibet plateau.will result in low precipitation over the same period in China.