Publication Date: 2008.
The horizontal averaging of global positioning system radio occultation retrievals produces an amplitude attenuation and phase shift in any plane gravity wave, which may lead to significant discrepancies with respect to the original values. In addition, wavelengths cannot be straightforwardly inferred due to the observational characteristics. If the waves produce small departures from spherical symmetry in the background atmosphere and under the assumption that the refractivity kernel may be represented by a delta function, an analytical expression may be derived in order to find how the retrieved amplitudes become weakened (against the original ones). In Particular, we study the range of waves that may be detected and the consequent reduction in variance calculation, which is found to be around 19%. A larger discrepancy was obtained when comparing an occultation variance with the one computed from a numerical simulation of that case. Wave amplitudes can be better resolved when the fronts are nearly horizontal or when the angle between the occultation line of sight and the horizontal component of the wave vector approaches π/2. Short horizontal scale waves have a high probability of becoming attenuated or of not being detected at all. We then find geometrical relations in terms of the relative orientation between waves and sounding, so, as to appropriately interpret wavelengths extracted from the acquired data. Only inertio-gravity waves, which exhibit nearly horizontal fronts, will show small differences between detected and original vertical wavelengths. Last, we analyze the retrieval effect on wave phase and find a shift between original and detected wave that generally is nonzero and approaches π /4 for the largest horizontal wavelengths. Copyright 2008 by the American Geophysical Union.
Author affiliation: Alexander, P. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.
Author affiliation: de la Torre, A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.
Author affiliation: Llamedo, P. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.
Keywords: Computer simulation; Global positioning system; Gravity waves; Radio waves; Wavefronts; amplitude; computer simulation; GPS; gravity wave; refractive index; spherical harmonics; wavelength; numerical model; variance analysis; wave propagation; Analytical expressions; Delta functions; Geometrical relations; High probability; Line of Sight; Numerical simulation; Radio occultations; Relative orientation; Spherical symmetry; Wave amplitudes; Wave phase; Wave vector; Computer simulation; Global positioning system; Gravity waves; Hydrodynamics; Waves; Gravitational effects.
Repository: Biblioteca Digital (UBA-FCEN). Universidad Nacional de Buenos Aires. Facultad de Ciencias Exactas y Naturales