Nonlinear Resonant Wave-Wave Interaction (Triad): Case Studies Based on Rocket and Satellite Data
Sabine Wuest(1) and Michael Bittner(1)
(1) German Aerospace Center (DLR-DFD), Muenchner Strasse 20, 82234 Wessling, Germany
Because of its low density, the upper atmosphere mainly addressed by satellites is important for the early detection of climate signals. There, gravity waves have significant influence on circulation and thermal structure by transporting energy and momentum. Knowledge about their sources, energy dissipation rates or the amount of energy which is transferred via nonlinear wave-wave interaction is essential.
Using ozone data derived from GOME, regions of high variability (so called hotspots) were identified and are supposed to generate gravity waves. In this context, knowledge about occurrence of nonlinear resonant 3-wave interaction (triad) is important. In a case study a software instrument for the detection of a triad is presented. Due to the higher spatial resolution it is developed by using rocket data which were derived during the DYANA campaign. Furthermore energy dissipation rates are calculated. The improved methods of the case study are applied to GOMOS data of a hotspot.
During the DYANA campaign four foil chaff and three falling sphere rockets were flown at Biscarosse (44°N,1°E), Southern France on 20th February 1990 during a period of only four hours. Vertical, meridional and zonal wind profiles from about 83 km to 98 km height as well as corresponding vertical temperature profiles were measured. By using cubic splines the wind data are detrended and gravity wave signals are obtained as residuals. In order to specify an appropriate number of spline sampling points the intrinsic disadvantage of the chaff method, namely non-sensitivity for small wavelengths in the upper region of the measurement is used.
For a proof of a triad two criteria (k1 +/- k2 = k3, w1 +/- w2 = w3) have to be fulfilled. Maximum entropy method (MEM) in combination with former wavelet analysis shows nearly the same five wavelengths in all four flights in a height interval of 4 to 6 km. These can be combined to possible nonlinear wave-wave interactions. The problem of determining the right order of MEM is solved by an experimental criterion. Bispectral and hodograph analysis proves the results in parts. Indication for nonlinear resonant 3-wave interaction is found.
Furthermore, energy dissipation rates are derived by using falling sphere experiments.
In a first case study parts of the improved methods are applied to GOMOS ozone measurements also revealing nonlinear processes.
Keywords: ESA European
Space Agency - Agence spatiale europeenne,
observation de la terre, earth observation,
satellite remote sensing,
teledetection, geophysique, altimetrie, radar,
chimique atmospherique, geophysics, altimetry, radar,