Gravity-wave effects on tracer gases and stratospheric aerosol concentrations during the 2013 ChArMEx campaign

Coupled balloon-borne observations of Light Optical Aerosol Counter (LOAC), M10 meteorological global positioning system (GPS) sondes, ozonesondes, and GPS radio occultation data, are examined to identify gravity-wave (GW)-induced fluctuations on tracer gases and on the vertical distribution of stratospheric aerosol concentrations during the 2013 ChArMEx (Chemistry-Aerosol Mediterranean Experiment) campaign. Observations reveal signatures of GWs with short vertical wavelengths less than 4 km in dynamical parameters and tracer constituents, which are also correlated with the presence of thin layers of strong local enhancements of aerosol concentrations in the upper troposphere and the lower stratosphere. In particular, this is evident from a case study above Ile du Levant (43.02 degrees N, 6.46 degrees E) on 26-29 July 2013. Observations show a strong activity of dominant mesoscale inertia GWs with horizontal and vertical wavelengths of 370-510 km and 2-3 km respectively, and periods of 10-13 h propagating southward at altitudes of 13-20 km during 27-28 July. The European Centre for Medium-Range Weather Forecasts (ECMWF) analyses also show evidence of mesoscale inertia GWs with similar horizontal characteristics above the eastern part of France. Raytracing experiments indicate the jet-front system as the main source of observed GWs. Using a simplified linear GW theory, synthetic vertical profiles of dynamical parameters with large stratospheric vertical wind maximum oscillations of +/- 40 mms(-1) are produced for the dominant mesoscale GW observed at heights of 13- 20 km. Parcel advection method reveals signatures of GWs in the ozone mixing ratio and the tropospheric- specific humidity. Simulated vertical wind perturbations of the dominant GWs and small- scale perturbations of aerosol concentration ( aerosol size of 0.2- 0.7 mu m) are revealed to be in phase in the lower stratosphere. Present results support the importance of vertical wind perturbations in the GW- aerosol relationship. Observed mesoscale GWs induce a strong modulation of the amplitude of tracer gases and the stratospheric aerosol background.