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.
[1] A sequence of nine weather balloons were launched recently over the island of Hawaii during the nights of 12, 13, and 17 December, 2002, providing measurements of ascent rate, horizontal wind speed and direction, temperature, and other quantities. The measurements show short intervals of altitude with a large increase in ascent rate, occurring only near the tropopause, indicating regions of strong upward air velocity at this location. The large ascent rates correlate well to the strength of a jet stream, and with the presence of a local critical level, indicating mountain waves as the primary cause. No corresponding decreases in ascent rate were measured, suggesting strong threedimensional effects.
Area-averaged estimates of C n 2 from high-resolution numerical weather prediction (NWP) model output are produced from local estimates of the spatial structure functions of refractive index with corrections for the inherent smoothing and filtering effects of the underlying NWP model. The key assumptions are the existence of a universal statistical description of small-scale turbulence and a locally universal spatial filter for the NWP model variables. Under these assumptions, spatial structure functions of the NWP model variables can be related to the structure functions of the atmospheric variables and extended to the smaller underresolved scales. The shape of the universal spatial filter is determined by comparisons of model structure functions with the climatological spatial structure function determined from an archive of aircraft data collected in the upper troposphere and lower stratosphere. This method of computing C n 2 has an important advantage over more traditional methods that are based on vertical differences because the structure function-based estimates avoid reference to the turbulence outer length scale. To evaluate the technique, NWP model-derived structure-function estimates of C n 2 are compared with nighttime profiles of C n 2 derived from temperature structure-function sensors attached to a rawinsonde (thermosonde) near Holloman Air Force Base in the United States.
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