The Relationship Between Abnormal Thermal Characteristics Of West Pacific And The Climate On Autumn And Winter Over Southern China And Its Possible Physical Mechanism

Recently autumn drought and extreme low temperature in winter occurred frequently in China, so it is still hard to predict the autumn rainfall and winter temperature over southern China. Especially, the correlation between the predictive factors and the climate in in autumn and winter has changed on the background of global warming, some factors become less significant which makes the short-term climate prediction more difficult.Based on Indian-Pacific Ocean heat Flux data provided by Institute of Oceanology in Chinese academy of Sciences, historical SST data supported by Japan Meteorological Agency, NCEP/NCAR reanalysis data, SST data supported by Hadley Center and China 160 stations rainfall and temperature data, the study is conducted with focus on the climate change of Latent heat flux in Asian Indian Ocean Pacific Ocean, and exploring the relationship between the latent heat flux in Pacific Northwest and autumn precipitation and winter temperature. The results show that there are latent heat flux signals in spring in the Northwest Pacific, accordingly the possible physical mechanism involved is discussed. The main conclusions are as follows:1) The latent heat flux in Asian Indian Ocean Pacific Ocean has obvious seasonal and geographical distribution, there are three big value in average years of state: South Indian ocean, kuroshio sea and sea warm pool. The latent heat flux changes in the three sea area are:kuroshio region latent heat flux from summer to winter, from weak gradually increased, reaching a maximum, the air-sea heat flux in South Indian ocean is opposite to the kuroshio region, and the western Pacific warm pool was slightly changed mainly.2) There is a strong positive correlation between autumn precipitation and winter temperature over Southern China and early latent heat flux over Pacific west, the precursory signals to autumn rainfall is the previous April latent heat flux in key area I (15°-30°,150°-170°E), and the signals to winter temperature is the previous May latent heat flux in key area Ⅱ (0°-20°N,100°-130°E).3) The April latent heat flux anomaly in key area I has indicative function to the atmospheric circulation and precipitation anomaly in fall in East Asia. The abnormal distribution of 500hPa geopotential height,850hPa wind,850hPa vapor flux and its divergence and outgoing longwave radiation fields and other elements fields when the latent heat flux is in the high value are in contrast with in the low value.When the previous April latent heat flux in the key area I is higher, autumn rainfall in the south by the beneficial impact of the atmospheric circulation system,which shows favorable water vapor and vertical raise conditions that make rainfall more than usual,and vice versa. The May latent heat flux anomaly in key area Ⅱ has indicative function to the atmospheric circulation and temperature anomaly in winter in East Asia. When the current is on the high side, it’s conducive to wanner in Southern China for each element of circulation distribution situation in winter in East Asia, and vice versa.4) When the April latent heat flux is higher than usual in key area I, It is found that the high latent heat flux in key area is due to the cyclonic wind shear in the Northwest Pacific. Northeasterly anomalies north of the anomalous cyclone enhance the wind speed, which would cause a cooling in heat content. The associated westerly anomalies south of the anomalous cyclone lead to the occurrence of anomalous warm heat content near the date line. After that, the anomalous warm heat content is transported eastward through the warming Kelvin Wave effect. Correspondingly, the anomalous cold heat content migrates westward accompanied by the cooling Rossby wave. When the Rossby wave reaches the western tropical Pacific, it motivates the anomalous Philippine Sea anticyclone.It is conductive to more water vapor being transported towards South China and thus more rainfall appears over southern China during autumn. This research provides a potential signal for predicting the autumn precipitation over South China two seasons in advance, and vice versa.5)When the May latent heat flux is higher than usual in key area Ⅱ, the key area is just in the region of the northeast wind of anomalous cyclonic which is south to the Kuroshio warm area, and it strengthens the ocean evaporation, result to local stronger latent heat flux. At the same time, there is weak warm anomaly in the southern Indian Ocean south to Australia. Because of the wind flow weakening, the abnormal warm continuously strengthen, and combined with the atmospheric response to it, there is cyclonic shear crossing equatorial flow at the north of the warm anomaly. This flow weaken the background wind, and makes warm anomaly occurred in bay of Bengal to the South China Sea area, after that, warm abnormal strength, expanded rapidly, and maintain stability in winter, then the anomalous cyclonic circulation is excited in the north of the warm anomaly, the South China is in the control of southwest heating flow, so It is in favor of to the winter temperature rise, and vice versa.