Lightning Prediction by Wavelet Analysis of Atmospheric Pressure, Wind Speed and Electrostatic Field Signals

为了研究冬季雷雨云的结构，我们采集了整个冬季的静电场和气象变量(气压和风速)的数据。利用最近推出的分析地震和声信号的数学方法-小波变换方法对这些数据进行了研究。用移动平均法从未处理的时间序列中提取气压和风速的微观变化，然后用小波方法进行分析。对于每个变量，小波变换系数(模)以灰度作为其等级来显示。这些数字提供了时间序列信号的清晰可解释的直观表示。也就是说，很容易理解在有关时间存在的重要尺度。还计算了气压和风速变化之间的模间相关系数，以阐明这两个变量是如何相互关联的。以与小波变换相同的方式，采用尺度参数和时间相移作为二维坐标。这张图显示了两个要素之间是否存在很强的相关性，如果是的话，它的时间和/或位置。当雷云经过观测站附近时，可以在气压变化中检测到特征振荡。用小波变换的方法证明了气压与风速之间有很强的相关性。另一方面，当气候平静时，没有相关性。气压变化与地面静电场之间的关系也得到了澄清。

To investigate a winter thundercloud structure, we have bee acquiring data of the electrostatic field and the meteorological variables (atmospheric pressure and wind speed) over a full winter season.These obtained data have been investigating by a wavelet transform method that is a mathematical technique introduced recently for analyzing seismic and acoustic signals.Microscopic variations in time series of the pressure and the wind speed are extracted from not-processed ones using a moving average method, then analyzed by a wavelet method. For each variable, wavelet transform coefficients (modules) are displayd using gray scales as its grade. These figures provide a clearly interpretable visual representation of time series signals. Namely, it is easily understood what the significant scales exist at the concerned time.Mutual correlation coefficients of modules between the pressure and the wind speed variation are also calculated to clarify how these two variables are relted each other. A scale parameter and a phase shift in time are adopted as two dimensional coordinates in the same manner as the wavelet transform. This figure shows whether there is a strong correlation between two elements or not, and if it was, its time and/or position.When thunderclouds pass nearby the observation station, characteristic oscilations are detected in a pressure variation. A strong correlation between the pressure and the wind speed has been proved by a method of a wavelet transform analysis. On the other hand, when a climate is quiet, there is no correlation.A correlation between the presuure variation and the electrostatic fiield at the ground has been also clarified.