Physics
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmsa41b0741l&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #SA41B-0741
Physics
0358 Thermosphere: Energy Deposition, 2407 Auroral Ionosphere (2704), 2471 Plasma Waves And Instabilities
Scientific paper
Polar Mesospheric Summer Echoes (PMSE) have been studied by analysing their spectra obtained with the EISCAT VHF Radar in Northern Scandinavia in an attempt to unravel the possible scattering mechanism(s). Narrow and broad spectra were identified. Assuming that PMSE is caused by background turbulence of the neutral atmosphere it is estimated that the average turbulent dissipation energy of the broad spectra should be about 60 times stronger than that of the narrow spectra. Contrariwise, the observed echo strengths of the broad spectra are in fact 10 times weaker than the narrow spectra. In one case both types of spectra occurred simultaneously in layers separated by a few kilometers. These observations suggest that at least two types of scattering mechanisms may be necessary to account for the characteristics of the echoes. Multilayer PMSE structures were frequently observed. It is suggested that the layering is caused by height variations of the temperature profile, the colder layers favouring PMSE and the warmer ones suppressing it. A quantitative comparison between the time development of the altitude of distinct layers and the Doppler shift of the signals originating from those layers indicates that the Doppler velocity is equal to the bulk velocity of the layers. Thus, PMSE can be used as a tracer of the large scale dynamics of the mesosphere.
La Hoz Cesar
Swarnalingam N.
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