Statistics of convection initiation by use of Meteosat rapid scan data during the Convective and Orographically-induced Precipitation Study (COPS)

Abstract

Rapid Scan (RS) service from the Spinning Enhanced Visible and Infrared Imager (SEVIRI) on Meteosat8 (also called Meteosat Second Generation 1, MSG1) during the Convective and Orographically-induced Precipitation Study (COPS) provided five-minute scans of the latitude belt from approximately 15 to 69 ◦N from 1 June to 31 August 2007. With these high-temporal resolution data, we investigate convection initiation (CI) in the COPS domain, an area covering the low-mountain regions of the Vosges and Black Forest with the Rhine Valley in between in eastern France/south-western Germany. In total, 94 CI events are identified during all COPS Intensive Observation Periods (IOPs) for which Meteosat-8 data are available, i.e., on 30 days within 16 IOPs. The algorithm to find CI sites is illustrated by the isolated CI event of 15 July 2007 (COPS IOP 8b) for which the RS brightness temperature data at 10.8 μm reveal a minimum temperature change rate at the cloud top of –4.0 K/min. We find that the CI sites are distributed over the whole COPS region; however, the CI density is about 3 times higher in the mountainous regions of the Vosges and the Black Forest (∼30 storms/(10000 km) on the 30 days investigated in this study) than in the Rhine Valley. The CI distribution shows a diurnal cycle with a pronounced CI maximum between 1300 and 1400 UTC, i.e., 2 hours after the local noon of 1130 UTC. In this 1-hour period alone, 18 % of all CI events take place (25 % if we neglect those CI events which are related to a synoptic surface front). In contrast to this, we find only 4 % of all CI events at night between 2100 and 0400 UTC.