长江三角洲常熟地区近地层湍流特征的研究

TURBULENT FEATURES NEAR THE SURFACE OVER THE YANGTZE DELTA

摘要:

利用1999年5～9月长江三角洲常熟地区的湍流脉动观测资料,分析了该地区感热、潜热和动量通量的日变化以及湍流强度和湍流谱特征,结果表明:该地区各能量的日变化与常见情况相同,白天潜热通量的输送占主导地位,感热通量比潜热小得多,且湍流的日变化与天气的关系非常密切,晴天比阴天要大得多。湍流强度和湍流谱的分析结果表明,在近中性条件下,常熟地区各方向湍流强度接近典型平坦下垫面的值。非中性条件下,垂直方向规一化标准差与稳定度的关系都较好地满足1/3次幂定律,水平方向没有垂直方向上的规律好,特别是稳定条件下,数据点分散性大;各风速分量谱在高频段满足理论上的-2/3次幂定律,纵向和垂直方向速度谱的峰值频率与典型平坦下垫面上的结果一致。总体输送系数C_D、C_H与稳定度的关系密切,随稳定度增加有减小的趋势。

关键词:常熟地区;近地层;湍流强度;湍流通量;湍流谱

Abstract:

In the context of turbulent observations in Changshu over the Yangtze delta from May to September in 1999, research is done for daily changes of sensible, latent heat and momentum flux, turbulence intensity and spectral pattern. Results suggest that various flux daily patterns are the same as ordinary ones: latent heat flux is dominant during daytime with much smaller sensible heat flux than latent one, and moreover, daily turbulence variation has close relationship with a weather condition in such a way that it is much stronger in sunny than cloudy sky. Evidence from analyzing turbulence intensity and spectral pattern indicate that turbulence intensity in three directions approaches to that over a typical flat underlying surface in Changshu at near neutral stratification ; for other cases, the relationship between normalized standard deviation and stability is in conformity with power 1/3 in vertical direction but not so good in horizontal direction, particularly in stable stratification data dots disperse greatly; spectral patterns correspond to power -2/3 in high frequency for wind speed of three directions; peak frequency of speed spectral pattern is in correspondence with that of typical flat underlay surface in horizontal and vertical direction.Total transportation coefficients C D and C H have tight relationship with stability:C_D, C_H will decrease with increasement of stability.

Key words:Changshu region;surface layer;turbulent intensity;turbulent flux;turbulent spectrum