青藏高原土壤湿度的变化特征及其对中国东部降水影响的研究进展

The variation characteristics of soil moisture in Tibet Plateau and its influences on the precipitation in eastern China:Recent progress

青藏高原土壤湿度受积雪与冻土的共同影响,能够记忆长时间的陆面干湿过程,是气候变化的重要因子,对随后的中国东部降水有预测意义。由于高原观测站点稀少,土壤湿度观测资料匮乏,致使现有相关研究大多是基于再分析资料、模式资料和卫星遥感资料(统称替代资料)进行的,且所得结论既有差异,也存在不确定性。因此本文首先综述了各种土壤湿度替代资料的适用性对比研究,进而讨论了青藏高原地区土壤湿度的变化特征及其对我国东部气候的影响。现有研究表明:1)资料对比研究指出,现有的各种替代资料对高原土壤湿度存在明显的高估或低估现象,且评估结论受评估指标和插值方法不同的影响。相对而言,SSM/I和风云3B的土壤湿度产品与实际观测资料相关性较好。2)高原土壤湿度具有多时间尺度变化特征和空间非均匀性,在年变化上具有显著的融冻特征,年代际变化趋势和年际特征呈现显著的区域性差异。SSM/I资料表明春季高原主体土壤湿度的年代际变化趋势呈现为增加的特征,与高原的增暖相一致;年际变率存在东、西两个高值区,与其相关的潜热、感热通量能共同激发遥相关波列影响我国长江流域降水;同时高原土壤湿度在垂直方向上具有一致性,在空间分布上具有南部边缘最大、由东南向西北递减的特征。3)前人对高原土壤湿度影响中国东部降水的结论各有不同,其可能原因之一是采用的替代资料及其适用性不同,其二是模式试验中忽略土壤湿度的空间差异性而带来的误差等。相关问题需要进一步深入研究。

The soil moisture over the Tibetan Plateau(TP),collectively affected by the snow cover and permafrost,has a long memory of wet and dry of land surface processes.Therefore,the soil moisture over TP,as an important factor of climate change,could be used to forecast the precipitation pattern in East China.However,because of rare observation stations over TP,the soil moisture observation in long time series is very deficient over TP.It leads to most of recent studies were based on reanalysis data,modeling data and satellite remote sensing data(named substitute data).Moreover,their findings were uncertain and different from the others.Therefore,in this study,studies about the applicability of various kinds of substitute data are summarized firstly,then characteristic of the soil moisture over TP as well as its climate effect are discussed.1)Comparison shows that current substitute data of soil moisture has significant over-or under-valuation over TP.Different conclusion could be drew according to various evaluation indicators and interpolation methods.Comparatively speaking,soil moisture products of SSM/I and FY 3B are in good correlation with observations.2)Soil moisture over TP has significant variations in multi-time timescale and remarkable spatial inhomogeneity in decadal trend pattern and interannual characteristic.There is significant ascending trend in spring soil moisture over TP based on SSM/I,in agreement with remarkable warming over TP.Two large interannual variation centers exit in east and west TP,whose related latent heat flux and sensible heating flux could motivate teleconnection wave train to affect precipitation anomaly in Yangtze River.3)Previous studies is different with each other about the effect of soil moisture over TP on precipitation over East China.One of the possible reason is that their substitute data is various with different applicability.Another reason may be the spatial inhomogeneity ignored in modeling design.Related issues need further research.