| dc.description.abstract | In recent years, many of the natural disasters that Taiwan has experienced have been closely related to the heavy rain brought by severe precipitation. However, there are still many uncertain variables and errors in the ”quantitative rainfall” forecast. Therefore, if telemetry can be used for dense and continuous observation of heavy precipitation systems, to understand its vertical structure and cloud physics process, it can provide a more realistic reference for parameter setting in meteorological numerical model and improve the accuracy of precipitation forecasting. The present study employed the data collected between 20 and 23 August 2013 by Chung-Li VHF radar and CCIT microwave radiometer, when the typhoon Trami passed through Taiwan, and use multi-frequency range imaging (RIM) technology for precipitation echo analysis. RIM processes the echo signals with a group of closely spaced transmitting frequencies through appropriate inversion methods to obtain high-resolution distribution of echo power in the range direction, and can obtain the high-range resolution Doppler spectra using Fourier transform. Point-by-point correction of range delay combined with compensation of range-weighting function effect has been performed during the retrieval of temporal signals to improve the continuity of power spectra at gate boundaries, making the small-scale structures in the power spectra more natural and reasonable. Using the Capon methods, the radar echoes were synthesized to retrieve the temporal signals at a smaller range step than the original range resolution, and such retrieved temporal signals were then processed in the Doppler frequency domain to identify the atmosphere and precipitation echoes. An analysis called conditional averaging was further executed for echo power, Doppler velocity, and spectral width to verify the potential capabilities of the retrieval processing in resolving small-scale precipitation and atmosphere structures. The performance is better especially in the case of stratiform precipitation, and the Doppler velocity of melting layer change with height is more reasonable. This study also proposes the Contour-Based and Peak-Finding method for automatic localization and spectral parameter analysis of atmospheric and precipitation echo centers, and we found the results of the two methods were in good agreement. However, it also shows that different numbers of data points in FFT could produce slightly different spectra widths, especially in rainy condition: the smaller the FFT number was, the broader the spectral width could be. In this study, it is the first time to use the ground-based double-polarized microwave radiometer and the Chung-Li VHF radar for combined precipitation observation, and the rain rate and the polarization difference shows a good positive correlation in the case of convective precipitation. Also, the polarization difference data can be used to judge whether the environment is convective precipitation at that time. In addition, the analysis results also found that the strong updraft associated with convective precipitation may cause supercooled water droplets collide with ice crystals and adhere to it, which could lead to radar echo power and spectrum width reduction. The results show that joint observation has great potential for understanding the cloud-physical mechanism of the formation of severe precipitation systems. | en_US |