台风“海马”对洞庭湖流域降水同位素的影响研究

基于2011年第4号台风“海马”登陆前后洞庭湖流域内长沙降水同位素资料,分析了降水同位素的变化特征以及水汽输送对降水同位素的影响。结果表明：台风“海马”在洞庭湖流域内长沙所形成降水的大气水线的斜率和截距均小于长沙夏季大气水线,这与根据同位素分馏理论做出的推测相吻合。台风天气系统影响下的流域降水δ ¹⁸O值为研究时段内的最低值,即降水同位素被显著贫化,而降水过量氘（deuterium excess,记为d）波动明显要小于其他时段,后者反映了形成台风降水的水汽来源较为单一。研究时段内长沙降水d指示台风降水前、台风降水中两个阶段水汽来源于西太平洋,水汽输送轨迹也印证了降水d所指示的水汽来源情况,如流域台风降水的水汽主要来自前期台风输送至南海北部的西太平洋水汽。台风降水后这一阶段降水中d指示海洋水汽来源的效果降低,其原因在于海洋水汽输送减少、陆地蒸发旺盛以及下落雨滴蒸发强烈所致。

Precipitation Isotopes Formed by Typhoon “Haima” in the Dongting Lake Basin

The variation characteristics of precipitation isotopes and the influence of moisture source on them are analyzed by using precipitation isotope data collected around the No. 4 typhoon, named ‘Haima’, in 2011 at Changsha, which located in the Dongting Lake Basin. The results show that both the slope and the intercept of meteoric water line produced by the typhoon precipitation are smaller than that of summer’s at Changsha, which is consistent with water isotope fractionation theory. Significant deplete in heavy isotopes leads to lowest value of precipitation δ ¹⁸O under the typhoon weather system during the study period, while the deuterium excess(d) is less fluctuation than in the rest time, the latter reflects that the moisture source of the typhoon is relatively single. Precipitation d-excess indicates that moisture is transported from the western Pacific Ocean both before and during the typhoon precipitation, while unclear moisture source after the typhoon precipitation. Also the moisture transport trajectory for precipitation in the basin confirms the moisture sources indicated by precipitation d, for example, the water vapor of typhoon precipitation in the basin mainly comes from the northern South China Sea, and huge water vapor over northern South China Sea had been carried by the typhoon from the western Pacific.