2002 Volume 80 Issue 4B Pages 925-938
We have analyzed small-scale fluctuations of temperature in the stratosphere using radio occultation data from the GPS/MET (GPS/Meteorology) experiment. From this, we have determined a vertical wave number spectrum of the normalized temperature fluctuations (T"/T) at 20-30 km and 30-40 km during three periods in June/July 1995, October 1995 and February 1997. The spectra at 20-30 km in the equatorial region in February 1997 agreed very well with radiosonde results in Indonesia as well as with a model spectrum assuming a linear saturation of gravity waves. We have found that the GPS radio occultation technique could measure meso-scale temperature perturbations in the lower stratosphere with a vertical wavelength down to 400 m. We have investigated the dependence of the mean wave number spectra on latitude, height and season. At 20-30 km the power law index for short wavelengths (<2 km)was about -3, consistent with a saturated gravity wave model. However, the spectral density wassometimes smaller than that predicted by the model. At 30-40 km both the spectral slope and densityagreed well with the model for wavelengths shorter than about 1.5 km, though the slope was moregradual for small m. We have calculated the variance (T"/T)² integrating the spectra in two verticalwavelength ranges: 10-2.5 km and 2-0.4 km, and estimated potential energy per unit mass (Ep). Seasonaland latitudinal variations of Ep were evident at 20-30 km, in particular, Ep was highly enhancednear the equator for both long and short wavelength ranges. At 30-40 km the enhancement of Ep at lowlatitudes became less evident than at 20-30 km.