基于粒子成像测速技术的降雪微物理特性研究

Research on microphysical property of snowfall based on particle imaging velocimetry technology

为了获取自然环境条件下的降雪的微物理特性,本文利用自主研制的降水微物理特征测量仪,研究基于雪花速度的完整俘获概率和空间谱反演算法,并通过外场观测试验研究了雪花的形状、尺度、速度、轴比、空间取向及其谱分布等微观物理特性.结果表明,雪花形状呈现针状、片状、粘连状、扁球状等多种形状,雪花速度随直径的增大而略有增大,轴比随直径的增大略有增大,空间取向易受环境风的影响,倾斜角的平均值在0.9°左右,标准偏差为13.2°;基于实测数据拟合了雪花速度和轴比随直径的变化关系,与国外已有模型相比,本文进一步得出了具有本地化特征的降雪微物理特性.所得到的结论对于云降水物理学研究、天气雷达地面定标、降水导致微波衰减评估等方面的应用有着重要意义.

In order to obtain the microphysical features of snowflakes under the natural conditions by using the self-developed sensor, precipitation microphysical characteristics, capture probability, and space distribution retrieve algorithm based on the velocity of snowflakes are discussed; and the shape, size, velocity, axial ratio, orientation and the space distribution of snowflakes are investigated by the field observation. Results show that the snowlakes may take needles, flakes, and oblate ellipsoids shapes; the falling velocity of snowflakes will increase slightly with inereasing diameter, their axial ratio may increase linearly with the diameter, and their orientations are easily influenced by the wind; the canting angle may be 0.9°and tends to be nearly symmetric with a standard deviation around 13.2°. Empirical equations of velocity and diameter, and of axial ratio and diameter are fitted by nonlinear fitting and linear fitting of observed data respectively.Compared with previous model proposed by authors abroad, this paper further provides the microphysical characteristics of snowflakes with localization features. The above conclusions can be of significance for the research on cloud precipitation physics, ground validation of weather radar, assessment of precipitation-induced microwave attenuation,etc.