Abstract
Abstract. We retrieved temperature (T) profiles with a high vertical resolution using the full spectrum inversion (FSI) method from the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) GPS radio occultation (GPS-RO) data from January 2007 to December 2009. We studied the characteristics of temperature perturbations in the stratosphere at 20–27 km altitude. This height range does not include a sharp jump in the background Brunt–Väisälä frequency squared (N2) near the tropopause, and it was reasonably stable regardless of season and latitude. We analyzed the vertical wavenumber spectra of gravity waves (GWs) with vertical wavelengths ranging from 0.5 to 3.5 km, and we integrated the (total) potential energy EpT. Another integration of the spectra from 0.5 to 1.75 km was defined as EpS for short vertical wavelength GWs, which was not studied with the conventional geometrical optics (GO) retrievals. We also estimated the logarithmic spectral slope (p) for the saturated portion of spectra with a linear regression fitting from 0.5 to 1.75 km.Latitude and time variations in the spectral parameters were investigated in two longitudinal regions: (a) 90–150° E, where the topography was more complicated, and (b) 170–230° E, which is dominated by oceans. We compared EpT, EpS, and p, with the mean zonal winds (U) and outgoing longwave radiation (OLR). We also show a ratio of EpS to EpT and discuss the generation source of EpS. EpT and p clearly showed an annual cycle, with their maximum values in winter at 30–50° N in region (a), and 50–70° N in region (b), which was related to the topography. At 30–50° N in region (b), EpT and p exhibited some irregular variations in addition to an annual cycle. In the Southern Hemisphere, we also found an annual oscillation in EpT and p, but it showed a time lag of about 2 months relative to U. Characteristics of EpTand p in the tropical region seem to be related to convective activity. The ratio of EpT to the theoretical model value, assuming saturated GWs, became larger in the equatorial region and over mountainous regions.
Highlights
Atmospheric gravity waves (GWs) play an important role in driving the general circulation of the middle atmosphere, transporting momentum flux, and kinetic energy from the lower atmosphere to the stratosphere and mesosphere (e.g. Fritts and Alexander, 2003; Alexander et al, 2010)
The present study is an extension of Tsuda et al (2011), and we aimed at studying the global distribution of vertical wavenumber spectra by applying full spectrum inversion (FSI) retrieval in the lower stratosphere using COSMIC GPS radio occultation (GPS-RO) data
It is expected that the increase in N 2 could be related to an enhancement of GW energy in winter in the polar region, because the model spectrum indicates a proportionality of the spectral density with N 2 as in Eq (1)
Summary
Atmospheric gravity waves (GWs) play an important role in driving the general circulation of the middle atmosphere, transporting momentum flux, and kinetic energy from the lower atmosphere to the stratosphere and mesosphere (e.g. Fritts and Alexander, 2003; Alexander et al, 2010). Latitude variations in the vertical wavenumber spectra of GW have been studied using GPS-RO temperature profiles with the GPS/Met and CHAMP satellites (Tsuda and Hocke, 2002; Ratnam et al, 2004) Note that these profiles were retrieved using the geometrical optics (GO) method, whose vertical resolution is limited to approximately 1.4 km by a Fresnel zone. This research describes global distributions of vertical wavenumber spectra of temperature profiles derived using the full spectrum inversion (FSI) retrieval method (Jensen et al, 2003). The present study is an extension of Tsuda et al (2011), and we aimed at studying the global distribution of vertical wavenumber spectra by applying FSI retrieval in the lower stratosphere using COSMIC GPS-RO data. We investigated the ratio of the observed GW potential energy and the model prediction by the saturated gravity wave theory (Smith et al, 1987)
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