Vertical Wave Number Spectrum of Temperature Fluctuations in the Stratosphere using GPS Occultation Data

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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 was sometimes smaller than that predicted by the model. At 30-40 km both the spectral slope and density agreed well with the model for wavelengths shorter than about 1.5 km, though the slope was more 2 gradual for small m. We have calculated the variance (T'/T) integrating the spectra in two vertical wavelength ranges: 10-2.5 km and 2-0.4 km, and estimated potential energy per unit mass (Ep). Seasonal and latitudinal variations of Ep were evident at 20-30 km, in particular, Ep was highly enhanced near the equator for both long and short wavelength ranges. At 30-40 km the enhancement of Ep at low latitudes became less evident than at 20-30 km.
2002-09-25

Vertical Wave Number Spectrum of Temperature Fluctuations in the Stratosphere using GPS Occultation Data

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