Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsa31c..07l&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #SA31C-07
Physics
[2403] Ionosphere / Active Experiments, [2461] Ionosphere / Plasma Interactions With Dust And Aerosols, [3332] Atmospheric Processes / Mesospheric Dynamics
Scientific paper
Joint measurements of PMSE under the influence of artificial RF heating have been carried out at the EISCAT site in Tromso with the EISCAT VHF radar at 224 MHz (Bragg scale of 0.67 m) and the MST MORRO radar at 54 MHz (Bragg scale of 2.76 m) in July of this year (2010). The EISCAT Heater was cycled for 20/24 sec on and 160/154 sec off respectively resulting in a period of 180 sec in both cases. In contrast to null results in earlier attempts in 2009 and 2008, clear evidence of weakening of PMSE during the interval of heater on and of strengthening during the interval of heater off was observed with both radars. While over some periods the ESCAT radar measured considerable strengthening on turn off, generally the strengthening measured by the MORRO radar was modest. It is possible that a role in lessening the MORRO overshoots is played by a combination of a wider antenna beam and not so negligible horizontal winds, which together will have the effect of partially smoothing out the heater induced variations due to finite integration time. This possibility will be further investigated by analysing the multi-beam MORRO data to obtain horizontal winds. Some theoretical models of the effects of electron heating on PMSE, such as the one produced by the EISCAT Heater, predict an overshoot (strengthening) both on heater turn-on and heater turn-off (Chen and Scales, 2005) for Bragg scale lengths around MORRO's (2.76 m). In contrast, these measurements indicate that on turn on, diffusion effects are dominant causing sometimes deep weakening of the PMSE signals on both radars, while on turn off effects due to charging of the dust particles during heater on are dominant. By comparing the weakening of PMSE during the heater on period measured by both radars, it should be possible to establish the relative roles of the two diffusion modes of a three-species plasma (electrons, ions, charged dust) as the diffusion time is inversely proportional to the square of the scale length (the Bragg length); a possibility that is under investigation.
Havnes Ove
La Hoz Cesar
Rietveld M.
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