Diurnal cycle of precipitation over complex Alpine orography: inferences from high‐resolution radar observations

Abstract

AbstractThe study describes the diurnal cycle of precipitation in the Alps and surrounding forelands using high‐resolution volumetric data from a network of three ground‐based radars. First, the study focused on the regional, seasonal and interannual variability in the diurnal behaviour of surface rainfall intensity, frequency and spatial correlations. Secondly, the study examined the diurnal variation in the vertical structure of summertime precipitation. Significant regional and seasonal differences are noticed in the diurnal cycle of precipitation features. The signal is strongest in the Alps, moderate in the plains north of the Alps and weak in the Po River Plain south of the Alps. The phase of the diurnal cycle is around 1630 UTC over the Alps for both spring and summer seasons. During autumn, the signal is weakest with no well‐defined phase. The spatial variogram analysis showed that rainfall patterns are most variable between 1200 and 1400 UTC, approximately 3 h before the occurrence of diurnal maximum in precipitation frequency and intensity. The vertical structure of precipitation is characterized using frequency–altitude diagrams, and its diurnal behaviour is analysed using Hovmöller diagrams. The results show that the diurnal cycle of precipitation varies significantly with height. Copyright © 2012 Royal Meteorological Society