Application of the bandpass filter for forecasting squall line in North China
The bandpass filter has been utilized to analysis two cases of squall line event in North China. The realistic wind field has been successfully seperated into a slowly variable, more stable macroscale environment field and an obviously movable meso-scale disturbances field. In general, there are several meso-a scale(250-2500km) disturbances emerged into the disturbances field, some of them is deep and moving steadily. The squall line systems occurred in a region of strong air flow associated with one of these disturbances, which is larger and formed earlier and persisted quite longer than the life cycle of the squall lines.