Observations of high-frequency temporal gravity wave spectra in the middle upper stratosphere

Abstract

There is a paucity of high-frequency temporal gravity wave spectra in the middle upper stratosphere (30-40 km) as most instruments that are capable of accessing this region do not have the capability to make measurements for any extended period of time. The spectral analysis of density fluctuations obtained with the Purple Crow Rayleigh scatter lidar has shown that middle upper stratospheric temporal spectra follow the expected -1.5 to -2.0 power law relationship for frequencies less than 1 × 10-3 s-1. At frequencies greater than 1 × 10-3 s-1, the shape of the temporal spectrum is much more variable, with strong quasi-monochromatic features appearing intermittently on certain nights. These higher-frequency features have been attributed to nonlinear wave interactions and suggest that estimates of gravity wave activity in the middle upper stratosphere may be larger and much more variable than previously assumed. This variability also suggests that middle upper stratospheric energy dissipation and eddy diffusion values may be much larger and more variable than previously assumed. Current parameterizations of subgrid dynamical processes in general circulation models that resolve this region may need to be reexamined in this light. Copyright 2001 by the American Geophysical Union.