HR: 17:15h
AN: SA24A-06    [Abstracts]
TI: Polar Mesospheric Summer Echoes at a Bragg Wavelength of 16 cm
AU: * La Hoz, C
EM: Cesar.La.Hoz@phys.uit.no
AF: University of Troms\o, Department of Physics, Troms\o, N-9037 Norway
AU: Havnes, O
EM: Ove.Havnes@phys.uit.no
AF: University of Troms\o, Department of Physics, Troms\o, N-9037 Norway
AU: N\ae sheim, L
EM: Lars.Naesheim@phys.uit.no
AF: University of Troms\o, Department of Physics, Troms\o, N-9037 Norway
AU: Hysell, D
EM: dlh@cornell.edu
AF: Cornell University, Dept. of Earth and Atmospheric Sciences, Ithaca, NY 15853 United States
AB: We present measurements of Polar Mesospheric Summer Echoes, PMSE, at the very short Bragg wavelength of 16 cm which is known to occur infrequent. The measurements were carried out with the EISCAT 930 MHz UHF radar. Part of the data was taken under the influence of RF heating. A comprehensive comparison of the measurements with the theory of turbulence including enhancement of the Schmidt number is carried out, but other theories are also considered. Estimates of the energy dissipation rates inferred from the signal spectral widths are used to calculate Batchelor scale lengths as a function of the Schmidt number. Hill's multipolar diffusion model is used to calculate the diffusion rates (which depend on the charge number of ice particles of nanometer size radius) leading to estimates of the Schmidt numbers. It is argued that the use of the slow diffusion coefficient in the calculations should give conservative estimates, i.e., lower bounds, of the necessary ice charge numbers to explain the measurements, the condition for scattering being that the Bragg scale of the radar should be greater than the Batchelor scale. Based on information from other experiments published in the literature, e.g., the charge number of mesospheric ice particles, the main conclusion of this investigation is that none of the most prominent theories can explain satisfactorily the measurements unless charge numbers in excess of 10 electrons for the measured wide spectra and at least in excess of 100s of electrons for the measured narrow spectra. RF heating of the mesosphere appears to have a similar influence on PMSE at a Bragg wavelength of 16 cm as it has at greater wavelengths, namely a weakening of PMSE during the heater on periods and a recovery during the heater off periods. This behaviour is as expected given the rapidity and large amount of electron heating that RF heating produces with the consequent rapid and large enhancement of the electron diffusion rate during heater on periods regardless of the electron diffusion model or reference to any particular model of PMSE.
DE: 9800 GENERAL OR MISCELLANEOUS
DE: 6952 Radar atmospheric physics
DE: 3332 Mesospheric dynamics
DE: 3379 Turbulence
DE: 0305 Aerosols and particles (0345, 4801)
SC: SPA-Aeronomy [SA]
MN: 2004 AGU Fall Meeting