Preliminary Study Of The Melting Layer In The Tropic Using A Polarimetric Doppler X-Band Radar

For the Caribbean Tropic, there is no evidence in the literature of studies concerning the melting layer. Often, scientist had opted to neglect the presence of the melting layer in this region, since it might be too high in the atmosphere to affect radar measurements. But recent observations with the UPRM X-Band radar indicate that the melting layer can be low enough that its effects on radar measurements should be considered. In addition, this higher reflectivity measured by the radar results in excessive estimation of the accumulated water on the ground, a problem that has been observed before in the Puerto Rico's west coast with the use of long-range radars (i.e. NEXRAD). The over estimation creates discrepancies between the readings of the radar and other sensors deployed on the ground, making it more difficult for the scientists to create new precipitation models and properly calibrate the system. It is then of special interest, to study this layer in the tropics and analyze the effects that it might have on the measurements provided by weather radars. The use of a state of the art agile polarimetric radar will serve as the main experimental tool, and the data collected will be used to analyze the effect of the melting layer on rain quantification over the Caribbean Island of Puerto Rico. It is the first time that an X-band Dual Pol Doppler radar is installed in the PuertoRico's west coast and the first time that different radar polarimetric products are analyzed to observe the melting layer in this tropical region. The main products that will be used to identify the melting layer are going to be corrected reflectivity (ZHcorrected), cross-polar correlation (ρHV), and specific differential phase (KDP). This is the first of three polarimetric radars that will form a radar network that will densely monitor the west coast of the Island and at the same time will provide lower atmosphere data to complement the NWS long-range radar located in the east coast of the Island. Some of the characteristics of the melting layer, such as the height and width, are computed through algorithms developed in this work. For the purpose of this study, two different techniques to detect the melting layer were considered; vertical bidirectional sector scan technique and vertically pointing non-scanning technique. A statistical analysis of the percentage of times the melting layer is present in the atmosphere during this study is also completed. Approximately fifty rain events were considered for the duration of the study. The features of the rain events were different from light to strong convective, and mixed. Finally, with the statistical analysis and the characteristics of the melting layer, it is determined the necessity to incorporate algorithms to the analysis to correct for attenuation or errors in the quantification of precipitation caused by the melting layer.