Implementation of a methodology to calibrate ground radars using TRMM-PR over Argentina

Since the TRMM (Tropical Rainfall Measuring Mission) satellite was launched has provided valuable information allowing to study the global distribution of the convection, mainly in tropical areas. In order to use the existing network of radars available in the world, many authors contrast the values of ground-based weather radar reflectivity with values obtained by the algorithms associated with Precipitation Radar information (PR). Measurement error in the field of radar reflectivity of PR is about ± 0.8 dB, while it has an observation threshold of 17 dBZ, the data are highly reliable due to the strong consistency. These arguments make this source of information a valuable tool when calibrating the reflectivity values observed by ground-based radars and its subsequent use in order to obtain a possible estimate of the values of precipitation near the surface for more accurate moderate to strong events.

The main objective of this study is to analyze the behavior of the ground radar reflectivities of the radar network in Argentina from the analysis of BIAS and Cumulative Distribution Functions (CDFs) to identify systematic errors and obtain a calibration curves to adjust the same from PR observations. The argentinian weather radar network is composed by four radar located in Ezeiza, Pergamino, Paraná and Anguil.

In this research, a methodology is developed that matches coincident PR and ground-based volume scanning weather radar observations in a common earth parallel three-dimensional cartesian grid. The data matching is performed in a way that minimizes uncertainties associated with the type of weather seen by the radars, grid resolution, attenuation and differences in radar sensitivities, sampling volumes, viewing angles, and radar frequencies.

The results show that the Ezeiza radar underestimates the reflectivity, especially those above 30 dBZ. In the case of Paraná radar, it shows that it overestimates the high reflectivity in the order of 8 to 10 dBZ, while something like that happens to Anguil radar. In the case of Pergamino, underestimated as Ezeiza but to a much lesser extent.