近50年来青藏高原地气温差的时空变化规律及其主导影响因素

The temperature increased obviously but the surface sensible heat flux (SHF) presented weak downward trend over Tibetan Plateau (TP) during the recent decades. The difference between ground and air surface temperature (Tg-Ta) is as the key parameter for SHF calculation. However, there were relatively less studies and no unified conclusion on the variation of (Tg-Ta) until now. Base on the meteorological data and satellite data, as well as reanalysis data, this study would firstly analyze the temporal and spatial variation of (Tg-Ta) over TP with statistical analysis technique. Then monsoon and circulation indices would be selected to analyze the relationship with (Tg-Ta), since westerly and monsoon which could influence the precipitation played an important role on climate change over TP. Same correlation analysis would be done for the solar radiation and NDVI index which could determine the surface heat level and reflect vegetation condition of TP respectively. In addition, surface soil hydrothermal process would be simulated and compared in different climatic zone with the soil thermal and moisture observation data of typical stations in westerly, monsoon regions and transitional zone, respectively. The sensitivity analysis was conducted to understand the response of (Tg-Ta) on precipitation, solar radiation and vegetation changes. Ultimately, the spatio-temporal variation of (Tg-Ta) on TP and their changing reason would be expected to clarify. This research could provide the basis for calculating SHF over TP executively. It has important implications for understanding the thermal effect on TP and its surrounding climate impact, and then for climate change prediction.

青藏高原升温明显，但地表感热却表现出减弱趋势。作为感热计算的关键参数，地气温差的研究相对较少且结论不一致。本研究将综合利用台站、遥感和再分析资料，分析青藏高原地气温差的时空分异特征；同时，考虑到西风和季风两大环流系统在青藏高原气候变化中的重要作用，研究将从大气环流通过降水对地气温差的影响为切入点，分区域对能够代表青藏高原大气环流状况的季风和环流指数、决定地表热量的太阳辐射、反映地表植被状况的NDVI指数与地气温差进行关联性分析；并借助青藏高原西风带、季风区及西风-季风过渡带典型点土壤水热观测资料，比较不同气候区地表水热状况差异，通过土壤水热过程模拟及敏感性分析，解析降水、太阳辐射、植被变化对青藏高原地气温差的影响；最终阐明青藏高原地气温差的时空变化规律，揭示青藏高原地气温差的变化机理。为精确描述青藏高原地表感热通量、深入了解高原热力作用及对周边气候的影响、进行青藏高原气候变化预测提供依据。

地气温差是计算地表感热的关键参数，很大程度上决定了地表感热通量的变化，对青藏高原地气温差的研究，尤其是对其时空变化规律的研究，可有效反映青藏高原地表热状况的变化。本项目对青藏高原地气温差进行了时空分布特征研究，并借助典型区土壤水热过程观测，探讨了降水、太阳辐射等对青藏高原不同气候区地气温差的影响。重要结果有：.（1）本项目利用青藏高原及其周边台站观测资料，对比分析了青藏高原地表温度与地气温差时空分布特征的差异，表现为：高原地表温度展现了强烈的纬度和海拔高度地带性，升温普遍且显著；地气温差则分布相对均匀，相对高值则分布在高原中南部且有下降趋势，其他大部分地区也表现出增加的趋势，但幅度普遍小于地表升温。.（2）高原动态季风指数与地气温差的相关分析表明，青藏高原冬季的地表热状况受冬季风控制，冬季风强度大，地气温差大，发现了青藏高原地气温差与大气环流特征的密切关系。.（3）应用冻土水热耦合（SHAW）模型模拟了不同气候区典型土壤温度变化，并利用敏感性分析解析了降水和太阳辐射对地气温差的影响：地气温差对太阳辐射正响应，以西风带、季风区、过渡区的顺序敏感度依次下降；地气温差对降水负响应，降水对西风带、过渡区、季风区的影响逐渐增强。