青藏高原东南部复杂地形区不同天气状况下陆气能量交换特征分析

Characteristics of Land–Atmosphere Energy Exchanges over Complex Terrain Area of Southeastern Tibetan Plateau under Different Synoptic Conditions

青藏高原地理环境复杂,已有大气陆面—边界层研究工作多集中于不同下垫面,很少有对复杂地形区的研究。本文利用青藏高原东南部林芝地区2013年5月20日至7月9日四个野外试验站点的观测资料,分析了不同天气条件下,高原复杂地形区不同下垫面的陆—气能量交换特征。结果表明:在各站向下短波辐射基本一致的情况下,地形较陡的北坡阔叶林站感热通量远大于其他3个站点;下垫面植被覆盖最多的南面麦田站潜热通量最大。各站能量通量有明显的日变化特征,晴天时,感热通量和净辐射明显大于阴雨天,而潜热通量随天气状况变化不大。青藏高原复杂地形环境比不同天气条件对于感热通量的影响更显著;不同地形阴雨天时对于潜热通量有明显的影响。当南亚季风槽前的西南暖湿气流影响到林芝地区时,该地区以阴雨天为主,反之则以晴天为主。林芝地区地—气通量的月内变化明显受南亚季风活动的影响。

The geographical environment of the Tibetan Plateau is complex. Previous studies of land surface-boundary layer processes mainly focused on different underlying surfaces without complex topography. The characteristics of land-atmosphere exchanges of energy on different underlying surfaces over complex terrain area of the Tibetan Plateau under different synoptic conditions are analyzed in the present study based on observations collected at four ground sites during May 20th to July 9th 2013 over Linzhi. Results indicate that in the case when the downward shortwave radiation is roughly the same at all the sites, sensible heat flux at the northern slope site, which is covered by broad-leaved forest and characterized by steep terrain, is greater than that at the other three sites; latent heat flux at the southern site, which is covered by wheat and thus with large vegetation fraction, is the largest among the four sites. Energy fluxes show obvious diurnal variation at each individual site. In sunny days, sensible heat flux and net radiation are significantly greater than that in rainy days. However, latent heat flux has little changes under different weather conditions. The influence of complex terrain of the Tibetan Plateau on sensible heat flux is more significant than that of different synoptic conditions. Different topographies have significant impacts on latent heat flux on rainy days. When the warm moist southwesterly flow in front of the South Asia monsoon trough affects Linzhi, the weather will be dominated by cloudy and rainy days. Otherwise sunny days are prevalent in this region. Apparently the variation of monthly land-atmosphere fluxes over Linzhi area is modulated by the South Asia monsoon activities.