OHP02 gravity wave campaign in relation to optical turbulence

Abstract

Herein we present a campaign dedicated to the detection and the characterization of Gravity Waves (GW) in the Earth's atmosphere in relation to the generation of Optical Turbulence (OT). The observations took place in France from 17 to 24 July 2002 at the Haute Provence Observatory (OHP) and simultaneously at the Sirene Observatory, some 20 km apart. From both sites, several balloons were launched that measured the classical PTU-Wind profiles and additionally the structure constant of the temperature field C 2 T vertical profiles. A Generalized Scidar (GS) technique was implemented at the 1.93 m-diameter OHP telescope, providing C 2 N (h) profiles every minute. From our observations, a significant amount of GW activity was observed at both sites, but without clear evidence of correlation between the two sites. It seems from our observations that a wide spectrum of GW is present at a given altitude and that this could result in a lack of correlation between observations made from two sites 20 km apart. Most GW are non-stationary with long horizontal wavelengths (λ ∼ 100-200 km), kilometric vertical wavelengths (λ ∼ 0.5-2 km) and long intrinsic period (T ∼ 2-15 h). They belong in the category of "hydrostatic rotating or non-rotating waves". Layers of optical turbulence detected by balloons and the Scidar technique correlate well with regions of GW activity.

The effect of shear on the generation of gravity waves

“…These results will be useful both experimentally and theoretically. Currently the experimental practice is to ignore the shear in the base flow (Shutts et al, 1988;Vernin et al, 2007) and attempt to deduce the quantitative attributes of the gravity waves using the shearless Long's equation. As a result several models for the generation of gravity waves overestimate their production.…”

“…Long's equation also provides the theoretical framework for the analysis of experimental data (Shutts, 1988(Shutts, , 1994Vernin, 2007) under the assumption of shearless base flow. (An assumption which, in general, is not supported by the data; Humi, 2004b).…”

Analytic solutions for Long's equation and its generalization

“…However, these approximations and the solutions that are derived from Eq. (46) are used routinely in the analysis of experimental atmospheric data (Shutts et al, 1988;Baines, 1995;Jumper et al, 2004;Vernin et al, 2007).…”

“…Solutions of Long's equation were also used as a framework for the examination and study of experimental data on gravity waves (Shutts et al, 1988(Shutts et al, , 1994Fritts and Alexander, 2003;Jumper et al, 2004;Vernin et al, 2007;Richter et al, 2010;Geller et al, 2013). In all of these studies it was assumed that the base flow is shearless.…”

Using stellar scintillation for studies of turbulence in the Earth’s atmosphere

“…Scidar data have also been used in GW studies for characterization of associated turbulence [87][88][89].…”