夏季我国干旱、半干旱区陆面过程能量平衡及其局地大气环流

利用NCEP资料分析得出,夏季我国干旱,半干旱区在整个欧亚大陆上是陆面感热通量最强的地方,与此对应的陆面潜热通量则最弱.陆面所接收的太阳短波辐射主要以感热和长波辐射的能量形式释放.该区降水量很少,降水量的年际变率也很弱;因此,该区的陆面热量通量都显出很弱的年际变率;然而,这些通量的年代际变率信号则比较显著.我国干旱、半干旱区大气环流的热力过程与其陆面过程特征密切相关.该区对流层大气的辐射冷却很强,达-3 K d-1.由于缺乏水汽和上升运动,大尺度凝结加热率、深对流加热率、浅对流加热率都非常弱.因此,600hPa以上的大气以绝热下沉加热来平衡辐射冷却;600hPa以下,陆面感热引起的垂直扩散加热率非常强,多达8 K d-1,它除了平衡辐射冷却以外还制造对流层低层的对流运动,以绝热上升冷却来平衡多余的垂直扩散加热.总之,我国干旱、半干旱区的陆面过程特征决定了该区大气运动的特殊垂直结构,即对流层低层对流上升运动及其上层的下沉运动.我国干旱、半干旱区陆面能量平衡及其局地大气环流的年代际变率,是全球气候系统年代际变率的必然结果.

Energy Balance of Land Surface Process in the Arid and Semi-Arid Regions of China and Its Relation to the Regional Atmospheric Circulation in Summer

The surface sensible heat flux of the arid and semi-arid regions of China is the strongest in Eurasian continent. The corresponding surface latent heat flux in this area, however, is very weak. In this area, the short wave radiation accepted by the surface is mainly released by sensible heat flux and long wave radiation. The annual precipitation here very deficient, thus its interannual variability is con- siderably weak. consequently, the surface energy fluxes show much weak interannual variability. But the interdecadal variability of the surface sensible heat flux in this area is significant compared to the corresponding interannual variability. In the arid and semi-arid regions of China, the thermal process of the atmospheric circulation is closely related to its land surface process. The troposphere radiative cooling is strong and up to -3 K d-1, whereas the large-scale condensation heating, deep and shallow convection heating is negligibly weak. As a consequence, the radiative cooling above 600 hPa layer is balanced by the adiabatic warming of descending motion. Below 600 hPa layer, quite differently, the vertical diffusion heating caused by surface sensible heat flux prevails and reaches about 8 K d-1. It bal- ances not only the radiative cooling but also the adiabatic cooling accompanying an upward rising mo- tions. In other words, the land surface process in the arid and semi-arid region of China is responsible for the vertical structure of its regional atmospheric motion, i. e., the upper layer descending and lower layer rising motion. The interdecadal variability of surface energy balance and its related regional at- mospheric circulation results from that of the global climate system.