RADAR Use of Dual-Polarization Wave Meteorological Radar Data to Determine Precipitation Intensity

The paper presents the results of a preliminary study of cloudiness area with hail precipitation based on data from a dual-polarization electromagnetic wave radar operating in Rzeszów-Jasionka (Poland) which is one of ten meteorological radars belonging to the POLRAD managed by the Institute of Meteorology and Water Management – National Research Institute. Remote sensing of the occurrence of hazardous weather phenomena is related to scanning of the atmosphere by radars with single and dual electromagnetic wave polarization. Radars with dual wave polarization located in Poland allow more effective analysis of the synoptic situation due to the classification and identification of phenomena, their shape and size, as well as the availability of a larger number of radar products and a wider gradation of their values. Radar products resulting from the processing of radar data allow frequent monitoring of the selected area, and the time interval of measurement results every 5 minutes makes it possible to detect possible errors associated with this measurement method. Atmospheric dual-polarization wave scanning provides a significant radar data that accurately describes detected meteorological objects, including the sizes of cloud and precipitation particles. In the POLRAD network, the standard procedure for generating the DPSRI radar image (precipitation intensity based on data from dual-polarized electromagnetic wave radar) each time uses the Marshall-Palmer relation and radar reflectivity values from a height of 1 km above the ground surface. This means that the actual structure of the precipitation cloud and the type of precipitation occurring are only partially taken into account in the calculations. The conducted research enabled us a qualitative and quantitative description of cloudy zones with precipitation of variable intensity and variable spatial and temporal distribution. Obtaining data on the structure of the cloud cover zone requires the creation of new and non-standard imagery showing horizontal and vertical distributions of radar reflectivity determined on the basis of measurements in the classic radar channel. Radar data were processed using RAINBOW DART and RAPOK software. Completely new rainfall datasets were generated for the selected region with consistency of location and observation date, in which precipitation intensity, phase state, and environmental factors were taken into account. Developed vertical cross-sections of the atmosphere along the set route provided information on the structure and activity of the studied storm cell and the precipitation core present. Precipitation intensity was determined from the Marshall‒Palmer, Joss and Muchnik correlations, which used radar reflectivity at heights of 1 km, 1.5 km, and 2 km above the ground surface, taking into account the freezing level. The choice of correlations used took into account the conclusions of the analysis of the synoptic situation, environmental conditions and the type of precipitation occurring in the study area. The paper presents a comprehensive analysis of the hail situation based on synoptic data and images of hail intensity and hail probability. It was shown that, available in the meteorological data exchange network, the standard images of precipitation intensity generated in each case based on the Marshall‒ Palmer correlation for radar reflectivity at a height of 1 km above the ground surface may contain errors, which require changes in calculation algorithms to be minimised. At this stage of the research, other dependencies were used in the calculations, which took into account the type of precipitation. On the other hand, data on the structure of the studied storm cell allowed us calculations based on the values of radar reflectivity determined at different levels in the rain core. The analysis of the obtained radar precipitation data was carried out on the basis of both synoptic and climatic data for the studied region. Analyses of synoptic situations carried out have shown that radar data support the detection of zones of hazardous weather phenomena. The high frequency of obtaining radar products makes it possible to track the development of occurring phenomena. It is possible to determine the type and intensity of precipitation and the vertical expansion of convective clouds. Modern radars with dual polarization of electromagnetic waves provide previously unavailable data on cloud structure. The results of the study lead to the conclusion that the development of measurement technology also forces changes in the previously used calculation procedures. It would be reasonable to identify empirical correlations and the selection of data from an appropriate height above ground level recommended for determining precipitation intensity - depending on the type of precipitation, convective cloud structure and environmental conditions. In the next stage of research, the results of field measurements carried out in regions with an extensive network of direct precipitation measurements will be used. The results of these studies will allow us to recommend empirical relationships for determining precipitation intensity depending on the type of precipitation, the structure of the precipitation cloud and environmental conditions.