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

Jean-Luc Baray,Sandra Banson,Yannick Bezombes,Aurélie Colomb,Claude Hervier,Dany Hadad,Marie Lothon,Christophe Duroure,Yves Pointin,Jean-Pierre Cammas,Frédéric Tridon,Olivier Masson,Joël Van Baelen,Bernard Campistron

doi:10.1175/jamc-d-16-0353.1

Abstract

AbstractThe 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−1at 8.7-km height at Opme; 25.1 m s−1at 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−1presents 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; the7Be/22Na 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−1for Opme and +2.4 ± 2.2% decade−1for Lannemezan.

Highlights

Jet streams are strong zonal winds in the upper troposphere, identified in the first half of the twentieth century by observing the motions of clouds (Schaefer 1953)
We used a long series wind measurement from two very high frequency (VHF) profilers in France to establish the climatological behavior of upper-tropospheric winds and of the frequency of jet stream events
A case study of jet stream and stratosphere– troposphere exchange occurring in January 2013 was characterized using VHF wind profiler data, water vapor lidar measurements, ERA-Interim, trajectories, and reverse domain-filling calculations

Summary

Introduction

Jet streams are strong zonal winds in the upper troposphere, identified in the first half of the twentieth century by observing the motions of clouds (Schaefer 1953). A number of observational studies have demonstrated the feasibility of using cosmogenic radionuclide measurements to estimate the presence of stratospheric air at ground level (Leppänen et al 2012; Steinmann et al 2013) Because some such measurements are routinely sampled at Opme and Lannemezan, their concentrations will be studied to develop a jet stream climatology. LACYTRAJ and LACYTRAJ-RDF have previously been used to study stratosphere–troposphere exchange in the southern subtropics (Clain et al 2010), monsoon depressions (Baray et al 2010), long-range interhemispheric transport of carbon monoxide (Duflot et al 2010), or interactions between the mixing layer and the free troposphere (Freney et al 2016)

Example of jet stream and stratosphere– troposphere exchange

Findings

Conclusions