Global distribution of vertical wavenumber spectra in the lower stratosphere observed using high-vertical-resolution temperature profiles from COSMIC GPS radio occultation

摘要

We retrieved temperature () profiles with a high vertical resolution usingthe full spectrum inversion (FSI) method from the Constellation ObservingSystem for Meteorology, Ionosphere and Climate (COSMIC) GPS radiooccultation (GPS-RO) data from January 2007 to December 2009. We studied thecharacteristics of temperature perturbations in the stratosphere at 20–27 km altitude. This height range does not include a sharp jump in thebackground Brunt–Väisälä frequency squared () near the tropopause, andit was reasonably stable regardless of season and latitude. We analyzed thevertical wavenumber spectra of gravity waves (GWs) with verticalwavelengths ranging from 0.5 to 3.5 km, and we integrated the (total)potential energy . Another integration of the spectra from 0.5to 1.75 km was defined as for short vertical wavelength GWs,which was not studied with the conventional geometrical optics (GO)retrievals. We also estimated the logarithmic spectral slope () for thesaturated portion of spectra with a linear regression fitting from 0.5 to1.75 km.Latitude and time variations in the spectral parameters were investigated intwo longitudinal regions: (a) 90–150° E, where the topography was more complicated, and (b) 170–230° E, which is dominated by oceans. We compared , , and , with the meanzonal winds () and outgoing longwave radiation (OLR). We also show a ratioof to and discuss the generation source of. and clearly showed an annual cycle, with theirmaximum values in winter at 30–50° N in region (a),and 50–70° N in region (b), which was related to thetopography. At 30–50° N in region (b), and exhibited some irregular variations in addition to anannual cycle. In the Southern Hemisphere, we also found an annual oscillationin and , but it showed a time lag of about 2 months relativeto . Characteristics of and in the tropical region seem to berelated to convective activity. The ratio of to the theoreticalmodel value, assuming saturated GWs, became larger in the equatorial regionand over mountainous regions.