Climatology of Anomalous Propagation Radar Echoes in a Coastal Area

Abstract

Anomalous propagation (AP) of ground-based radar beam results in the detection of ground echoes beyond the horizon. One year of data gathered with an S-band meteorological radar located on the coast in southwest France is used to analyze the spatial distribution of AP ground echoes (APE). The APE distributions of duration and reflectivity in the radar-observed area are found to be strongly related to the main feature of the regional orography and topography up to the farthest distance (250 km) observed by the radar, notably the nature of the surface, the topographic orientation with respect to the radar beam direction, and the altitude. The distribution of APE in the studied area is found to be strongly anisotropic around the radar, with wide differences between land and sea. Rain accumulation equivalent to the APE is, in certain places, of the same order or higher than the real rain depth. The distribution of the ground surfaces, as calculated from a ground numerical model, compares qualitatively well with the APE radar reflectivity distribution.