摘要
本文根据摩擦平衡方程,导出了湍流交换系数K(z)的表达式,然后借助于K(z)的有限差分式,直接应用双经纬仪实测风资料,计算了该地Ekman层中湍流交换系数K(z)。计算和分析的结果如下:(1)Ekman层中的湍流交换系数具有显著的日变化特征,日变曲线的基本形式呈双峰双谷型,就整个Ekman层的平均而言,K的平均扰动值约为K的四倍。(2)K的日变规律同气温、位温变化的平均趋势基本一致。(3)K的日变程同风速的涨落有关,例如,黄昏显著的风速涨落,对应于K廊线的特定日变程。其中特别有趣的是:夜间平均风速的变化同平均K的变化趋势完全一致,但二者在白天的变化趋势恰恰相反。这种根据实溅风资料得到的微妙关系,客观地揭示出Ekman层中风速日变化的物理本质,那就是湍流混合强度的日变化。本文还给出了若干个典型的实例。
Based on the friction equilibrium equation, the turbulent exchange coefficient K(z) is derived. Then, its finite difference form is used to compute local K(z) in the Ekman layer, supported by wind data from a double-theodolite. The following is the findings:
(1) The K(z) is marked with daily variations of double peaks and troughs. Its average fluctuation can be four times as large as itself for the mean of the whole Ekman layer.
(2) K undergoes diurnal variations consistent with mean tendency in temperature and potential temperature.
(3) K corresponds to fluctuation in wind velocity. A point to note is that the mean K and the velocity vary in the same way at night, but exactly the opposite in daytime.
An objective picture is thereby given for the daily variation intensity in mixed turbulent exchange.
出处
《热带气象》
CSCD
1989年第2期152-159,共8页
