湍流低频贡献对半干旱区地表能量平衡的影响

The Contribution of Turbulent Low Frequency to Surface Energy Balance in Semi-arid Area

利用中国气象局兰州干旱气象研究所定西干旱气象与生态环境试验基地的陆面过程观测资料,通过Finnigan等提出的获取湍流低频贡献的总块平均方法研究了低频部分对地表能量不平衡的影响。结果发现:(1)感热和潜热的低频部分较小,对感热的贡献在-1%～11%之间,对潜热的贡献在-7.3%～0.3%之间,对感热与潜热和的贡献在-1.4%～0.7%之间;(2)低频部分对感热和潜热的贡献随平均周期呈现先增后减的变化趋势;(3)不计低频部分时,地表能量的闭合度在晴天、阴天和阴晴混合天分别为0.93、0.76和0.87;(4)计入低频部分时,闭合度在晴天、阴天和混合天分别提高到0.98、0.86和0.93,提高了5%～10%;(5)阴天低频部分对闭合度的贡献随平均周期的加长而加大,晴天则增至1.5 h后开始递减,混合天增至1.5 h后保持定值。所以,低频贡献可以显著提高地表能量闭合度。但是考虑低频贡献后,仍存在2%～14%的欠闭合度,地表能量平衡问题还有未知的原因存在。

The contribution of turbulent low frequency to closure degree of surface energy balance was investigated by using the block ensemble averaging technique（a method to fetch the low-frequency formation proposed by Finnigan et al in 2003） and observation data of land surface process collected in the Dingxi Arid Meteorological and Environment Experimental Base of Lanzhou Institute of Arid Meteorology,China Meteorological Administration.The results are as follows：（1） The low-frequency part accounts for-1%-11% of sensible heat,-7.3%-0.3% of latent heat and-1.4%-0.7% of the sum of sensible heat and latent heat,respectively,relatively small;（2） The contributions of the low frequency part to sensible heat and latent heat increase first and then decrease with averaging period＇s increase;（3） If we don＇t take the low-frequency contribution into consideration,the closure degrees of surface energy are 0.93 in sunny day,0.76 in cloudy day and 0.87 in sunny and cloudy mixed day,respectively;（4） If we take the low-frequency contribution into consideration,the closure degrees of surface energy increase to 0.98 in the sunny day,0.86 in the cloudy day and 0.93 in the mixed day,respectively,which has an improvement of 5%-10%;（5） The contributions of the low frequency part to the closure degree increase monotonically with the averaging period＇s increase in the cloudy day,but in sunny day（mixed day）,it increases first within 1.5 hours of the averaging period and then decreases（keeps constant value）.So,the low-frequency contribution can improve the surface energy closure degree significantly.But there still remains 2%-14% unclosure degree even when the low-frequency contributions are included.The problem of the surface energy balance still needs further researches.