Physics
Scientific paper
Jan 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006adspr..38.2408r&link_type=abstract
Advances in Space Research, Volume 38, Issue 11, p. 2408-2412.
Physics
2
Scientific paper
Motivated by recent progress in the understanding of PMSE we have reconsidered the relation between observed echo power and spectral widths. We have analyzed data obtained with the EISCAT VHF radar operating at a vertical resolution of 300 m and a time resolution of 2 s. Considering the spatial and temporal morphology of echo power, spectral width, and vertical velocity, we have identified a dominant anti-correlation between power and spectral width. This anti-correlation has formerly been interpreted as evidence against a turbulent creation mechanism for PMSE. Taking into account state of the art direct numerical simulations and their application to the interpretation of radar backscatter from the mesopause region, we find, however, that from theory we indeed expect to find the observed anti-correlation. The main reason for this is a clear spatial separation between the maxima of turbulent kinetic energy dissipation (i.e., velocity fluctuations determining the spectral width) and the thermal dissipation (i.e., the production of fluctuations in a tracer like the electron number density) associated with turbulence being due to both Kelvin Helmholtz instabilities and gravity wave breakdown (Fritts, D.C., Bizon, C., Werne, J., Meyer, C. Layering accompanying turbulence generation due to shear instability and gravity-wave breaking. J. Geophys. Res. 108(D8), 8452, doi:10.1029/2001JD002406, 2003). This means that the observed anti-correlation between radar echo power and spectral width does not rule out a turbulence-related creation mechanisms for PMSE. In fact, the observations are in full agreement with the best available direct numerical calculations of the related physical processes.
Hoppe Ulf-Peter
Rapp Markus
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