Geostatistical Analysis of Orographic Rainbands

Abstract

Based on weather radar detection, orographic rainbands parallel to wind direction may persist for several hours over a Mediterranean mountainous region prone to stable wind and humidity conditions. A statistical analysis shows that orographic rainbands are more active and more stable over the mountains than over the lower hills. By the mean of the range?time indicator technique, the northward advection velocity of the rain cells is deduced (60 km h?1) and is slightly lower than the wind velocity (85 km h?1) measured at the high-altitude weather station (Mont Aigoual, 1565 m above mean sea level). The detailed analysis highlights that the positioning of individual orographic cells in relation to the relief is not random: they are triggered by relief shoulders on their southeast flank. Their regular spacing (typically 15 km) is responsible for the general organization of the rainbands. Rain accumulations vary from 20 to over 100 mm day?1 from the outside to the center of the rainbands.