Characterization of Complex Water Vapour Field Structures and their Genesis Based on the Combined use of Raman Lidar Measurements and MESO-NH Model Simulations

Abstract

As part of the Cevennes-Vivarais site, the University of Basilicata Raman lidar system (BASIL) was deployed in Candillargues throughout the duration of HyMeX-SOP 1 (September-November 2012), providing high-resolution and accurate measurements, both in daytime and night-time, of atmospheric temperature, water vapour mixing ratio and particle backscattering and extinction coefficient at three wavelengths. Measurements carried out by BASIL on 28 September 2012 reveal a quite complex vertical structure of the water vapor field. Reported Raman lidar measurements were run in the time interval between two consecutive heavy precipitation events, from 15:30 UTC on 28 September to 03:30 UTC on 29 September 2012. Throughout most of this observation period, lidar measurements reveal the presence of four distinct humidity layers. The present research effort aims at assessing the origin of the different humidity filaments observed by BASIL on this day. The analysis relies on the comparisons between Raman lidar MESO-NH model simulations. Back-trajectory analyses from the model reveal that air masses ending in Candillargues at different altitudes levels are coming from different geographical regions. Specifically, the analysis reveals that air masses within the surface humidity layer were originated over the Atlantic Ocean, while air masses within the elevated filamentary humidity layer, also coming from the Atlantic Ocean, overpassed the sea stretch North of Spain and Southern France at an altitude of ~1 km. In addition, air masses within the lower of the two upper layers are found to overpass Southern Spain and Marocco, descending from an elevation of 2-3.5 km, while air masses within the uppermost layer are found to overpass Algeria, descending from an elevation of 3.5-5 km.