Abstract
Based on conventional meteorological observation data, NCEP 1° × 1° reanalysis data, reanalysis data with resolution 0.75° × 0.75° from ECMWF and Doppler weather radar, we analyzed the weather conditions and physical characteristics of Super Typhoon Rammasun (1409), which caused special strong wind and severe rainstorm in Guangxi. The results show that: 1) Typhoon Rammasun offshore sudden strengthening in one of the main reasons was that loop pressure ridge superimposed into the westward extension of subtropical high, to making enable rapid strengthening of the subtropical high, so the subtropical high advanced faster than the Rammasun move, Rammasun center of the subtropical high distance reduced and the gradient increased; 2) Rammasun northward to south china coast with plenty of vapor following ITCZ, before landing, southwest monsoon and cross-equatorial flow were involved, Rammasun got latent heat of monsoon jet, enabling it to strengthen in offshore; 3) Rammasun from the Qiongzhou Strait into the northern Gulf, therefore the Strait of short passages and both sides belong to the low zone, friction consumption smaller, that was the main reason what was able to maintain the strength of the super typhoon, when Rammasun into the Beibu Gulf; 4) Diagnostic analysis shows that Rammasun before entering the northern Gulf and into the Beibu Gulf later, vorticity weakened, divergence and vapor flux divergence changed were smaller, meanwhile, vertical ascent speed and latent heat transport both increased, which was important reason of severe rainstorm caused by Rammasun.
Highlights
The typhoon “Rammasun” is one of the major disaster weather events that seriously affected South China
Compared with the intensity of the Gulf of Tonkin significantly weakened into difference of strong typhoon in previous years through Hainan Island or Leizhou Peninsula, with the “Rammasun” landing the North Bay, the wind speed is very small, still maintain a super typhoon intensity
The analysis of the “Rammasun” shows that its movement is in the background of low circulation, and the intensification of the subtropical high, the southwest monsoon and the cross-equatorial air entrainment are the important reasons for the sudden intensification of the offshore intensity
Summary
The typhoon “Rammasun” (super typhoon level) is one of the major disaster weather events that seriously affected South China. Due to the intensity of the “Rammasun” and the extreme nature of the disaster, it is necessary to analyze the reason why the intensity of the anomaly increases suddenly in the coastal waters and reaches the super-intensity level after entering the northern Gulf, so as to provide reference for future similar process forecast. It is pointed out that the major weather systems affecting tropical cyclone intensity variation are the subtropical high, the tropical convergence zone, the southwest monsoon trough, the westerly trough and the typhoon. The analysis of the “Rammasun” shows that its movement is in the background of low circulation, and the intensification of the subtropical high, the southwest monsoon and the cross-equatorial air entrainment are the important reasons for the sudden intensification of the offshore intensity. There are weather forecasters, according to the various information obtained, the analysis of the trend of typhoons and the landing location and time, timely release of typhoon forecasts and typhoons or emergency warning, through television, radio and other media for the public service, fishing vessels in time to shelter, at the same time for all levels of government to provide decision-making basis, the release of typhoon forecast or alarm is an important measure to reduce typhoon disaster
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