Case Study and Climatological Analysis of Upper-Tropospheric Jet Stream and Stratosphere-Troposphere Exchanges Using VHF Profilers and Radionuclide Measurements in France

摘要

The authors present a climatological analysis of tropospheric horizontal wind profiles and jet stream events using long series of wind profiles from two VHF profilers located in France: Lannemezan (2001-14) and Opme (1999-2014). A case study of jet stream and stratospheric intrusion of air into the troposphere that occurred in January 2013 is first described and demonstrates the capability of the VHF profilers to detect jet stream events. The climatology study over the two sites reveals the strongest values of seasonal wind during winter (21.4 m s(-1) at 8.7-km height at Opme; 25.1 m s(-1) at 9.6-km height at Lannemezan). A methodology based on the automatic detection of maximum winds on a decadal series of hourly wind profiles allows the detection of jet stream events and establishes its climatology for each site. A frequency analysis of jet stream events of westerly winds over 50 m s(-1) presents a clear seasonality at the two sites, with a maximum in winter (3.5%-9.7% of hourly profiles) and a minimum in summer (near 1%). Cosmogenic radionuclides sampled at Opme also exhibit a clear seasonal variation with maximum in spring and minimum in the cold seasons; the Be-7/Na-22 activity ratio confirms stratosphere-to-troposphere exchanges for the studied cases. The mean interannual variability of the frequency of jet stream events is 1.5% in Opme and 2.9% in Lannemezan. Positive decadal trends are observed for the two sites: +1.6 +/- 1.2% decade(-1) for Opme and +2.4 +/- 2.2% decade(-1) for Lannemezan.