The Characteristics of Longitudinal Movement of the Subtropical High in the Western Pacific in the Pre-rainy Season in South China

Using the NCEP/NCAR reanalysis data, the China rainfall data of the China Meteorological Administration, and the sea surface temperature (SST) data of NOAA from 1951-2000, the features of the anomalous longitudinal position of the subtropical high in the western Pacific (SHWP) in the pre-rainy season in South China and associated circulation and precipitation are studied. Furthermore, the relationship between SHWP and SST and the eastern Asian winter monsoon is also investigated. Associated with the anomalous longitudinal position of SHWP in the pre-rainy season in South China, the flow patterns in both the middle and lower latitudes are different. The circulation anomalies greatly influence the precipitation in the pre-rainy season in South China. When the SHWP is in a west position (WP), the South China quasi-stationary front is stronger with more abundant precipitation there. However, when the SHWP is in an east position (EP), a weaker front appears with a shortage of precipitation there. There exists a good relationship between the longitudinal position of SHWP and SST in the tropical region. A negative correlation can be found both in the central and eastern tropical Pacific and the Indian Ocean. This means that the higher (lower) SST there corresponds to a west (east) position of SHWP. This close relationship can be found even in the preceding autumn and winter. A positive correlation appears in the western and northern Pacific and large correlation coefficient values also occur in the preceding autumn and winter. A stronger eastern Asian winter monsoon will give rise to cooler SSTs in the Kuroshio and the South China Sea regions and it corresponds to negative SST anomaly (SSTA) in the central and eastern Pacific and positive SSTA in the western Pacific in winter and the following spring. The whole tropical SSTA pattern, that is, positive (negative) SSTA in the central and eastern Pacific and negative (positive) SSTA in the western Pacific, is favorable to the WP (EP) of SHWP.

Diagnosis of the Medium-Range Variation of the Subtropical High over the Western Pacific during a Meiyu Process by Three-Dimensional E-P Flux

In this paper, using the daily grid data (2.5 × 2.5) of the ECMWF / WMO, we have computed respectively the three-dimensional wave activity flux in the stages of pre-onset, prevailing and post ending of Meiyu from 1 to 31 July 1982. The potential vorticity field is taken as the physical quantity relating the wave activity flux to the variation of the subtropical high over the Western Pacific. It is found that the three-dimensional wave activity flux is a powerful means for diagnosis of the variation of the subtropical high over the Western Pacific: The region of the subtropical high is just the confluence area of wave energy, whose changes in intensity and range decide the variation of the subtropical high. The confluence of wave energy comes from the monsoon flow in low latitudes, the Meiyu rain belts in middle latitudes and the heating fields on the eastern side of the Qinghai-Xizang Plateau. The relation between these sources and the subtropical high displays the self-adjusting mechanism among members of East-Asia summer monsoon.

Analysis of Formation Mechanism of Two Successive Heavy Rainfall Processes on the Edge of the Subtropical High

Based on sounding and ground observation data,GPS/MET and FY-2 E satellite data,NCEP/NCAR reanalysis data（ 1°× 1°）,the formation mechanisms of two successive heavy rainfall processes on the edge of the subtropical high were analyzed. The results showed that the two heavy rainfall processes were caused by weak westerly troughs on the edge of the subtropical high at 500 h Pa,and there was strong southwest jet stream at 850-700 h Pa. As the low-level southwest jet stream intensified and moved northwards,heavy rainfall began. When the jet stream weakened,heavy rainfall ended. The heavy rainfall areas had good consistency with the high-value areas of CAPE,the high-value tongue of low-level water vapor flux,water vapor convergence center and warm advection center. Water vapor monitoring by GPS/MET had certain denotative meaning to the short-term prediction of heavy rainfall. The minimum TBB of convective cloud clusters was between-62 and-78 ℃,and the corresponding hourly maximum precipitation was 40-90 mm. In the heavy rainfall process,mesoscale vortexes occurred at 850 h Pa and below,but the scale was small,with weak low pressure but significant cyclonic circulation. The most intense rainfall was generated at the center of warm advection in the southeast of the vortex center at 925 h Pa. In the first heavy rainfall process,the mesoscale vortexes moved less,while strong rainfall was induced by strong upward movement in the southeast of the vortexes. In the second heavy rainfall process,low-level cold air invaded from the northwest into the vortexes to form cyclones and moved northeastwards. Heavy rainfall happened in the warm zone in front of cold front,and convective instability energy was high. Rainfall intensity was high,and rainfall range was large.

Analysis of the Role Played by Circulation in the Persistent Precipitation over South China in June 2010

South China （SC） experienced persistent heavy rain in June 2010. The climatic anomalies and related mechanism are analyzed in this study. Results show that the large-scale circulation pattern favorable for precipitation was maintained. In the upper level, the South Asian High and westerly jet stream provided a divergent circulation over SC. In the middle and low levels, an anomalous strong subtropical high （STH） extended to the South China Sea. The southwesterly monsoon flow along the northwest flank of the STH transported abundant water vapor from the western North Pacific, the Bay of Bengal, and the South China Sea to SC. The precipitation can be classified into two types： the West Siberia low （WSL）-induced low-level cyclone mode, and the STH-induced low-level jet mode. STH and WSL indices are defined to estimate the influence of these two systems, respectively. Analysis shows that both are critical for precipitation, but their respective contributions differ from year to year. In 2010, both were important factors for the heavy rainfall in June.