蒸发皿蒸发量的物理意义、近40年变化趋势的分析和数值试验研究

依据边界层梯度输送理论和能量守恒原理分析了蒸发皿蒸发量的物理意义，蒸发皿蒸发量是多环境因子共同非线性相互作用的结果，并利用我国有长期太阳辐射观测的62个常规气象站观测资料，通过蒸发皿蒸发量与环境气象因子的相关分析对其进行了验证. 分析了近40年蒸发皿蒸发量和环境气象因子的变化趋势，分析结果也表明只利用单个环境因子的变化来解释蒸发皿蒸发量的气候变化会产生偏颇，譬如将蒸发皿蒸发量的逐年减少归因于地表接收的太阳辐射减少的解释在中国东部比在中国西部较合理. 分析1983～2001年间国际卫星云气候计划观测的资料得出，我国大部分地区的总云量保持微小的减少趋势而总云水路径处于明显的增加趋势，这表明云变得更不透明了,它的物理属性发生了明显的变化;预示着大气可降水量有逐年增加的趋势, 地气系统变得更湿润. 结合水循环过程，利用大气环流模式用数值方法证明地气系统的水汽变化能引起陆地近地层大气相对湿度、地表接收的太阳总辐射和地表潜在蒸发量的明显变化.

An analytic and numerical study on the physical meaning of pan evaporation and its trend in recent 40 years

The physical meaning of pan evaporation is analyzed based on the gradient transport theory in boundary layer meteorology and energy conservation principle,and verified by the correlation analyses between pan evaporation and environmental factors with the data from 62 Chinese routine weather stations at which the data of long-term solar radiation is available.The trends of pan evaporation and environmental factors in the last 40 years are analyzed.The result indicates that the long-term trend of pan evaporation cannot be explained by the change of a environmental factor,such as,it is more reasonable to attribute the decrease of pan evaporation to the global radiation reduction in eastern China than in western China.The data observed during the International Satellite Cloud Climatology Project(ISCCP) from 1983 to 2001 demonstrates the slight decrease of total cloud amount and the obvious increase of total cloud water path in most of China,which means the cloud property has changed,and the cloud becomes more opaque.These cloud changes show the precipitable water in atmosphere has an increasing trend,and the earth-atmosphere system becomes moister year by year.Based on the hydrological cycle,it is proved that the variation of water vapor in the earth-atmosphere can make the relative humidity,the global radiation and the potential evaporation in the boundary layer change evidently,as shown by numerical experiments with an atmospheric general circulation model.