Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsa42a..04b&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SA42A-04
Physics
[2403] Ionosphere / Active Experiments
Scientific paper
Efficient generation of ELF/VLF waves through the modulation of ionospheric currents requires reliable measurements of the modulated current for different heater parameters. Incoherent scatter radar (ISR) measurements of modified plasma densities/temperatures would be ideal in quantifying the heating and cooling cycles in response to modulated heating by high-power HF waves. Considering the ms time scales of ELF/VLF generation processes, it is necessary to resolve the heating and cooling cycles at sub-ms time scales. Such measurements using ISRs have largely been avoided due to the common knowledge that the instrument requires minutes of integration. We present herein the results of an epoch averaging experiment using EISCAT that provides 0.2 ms resolution ISR power measurements as a function of phase into the HF heater ON and OFF cycle. In ELF/VLF generation, it is the electron temperature (Te) modulation that results in the modulation of electron collision frequency/mobility and therefore the electrojet modulation. Assuming a reliable electron collision frequency for transport as a function of Te, it is necessary to measure Te and electron density (Ne) simultaneously to predict the ionospheric current modulation. This is possible if (1) two incoherent scatter radars operating at sufficiently different frequencies are used and if (2) the Debye length and Bragg wavelengths are comparable. For the experiment results presented here, the ionospheric volume modified by the EISCAT heater were probed by both EISCAT UHF and VHF incoherent scatter radars operating at 0.16 m and 0.67 m Bragg wavelengths. Considering Ne=1e9 e/m3 in the D region ionosphere, for electron temperature Te=300 K, the Debye length is 0.38 m, where as for Te=1000 K the Debye length is 0.69 m; these parameters are reasonably appropriate to extract Te/Ne from simultaneous UHF/VHF data. We successfully detected ISR power modulation both in the E and F region heated ionosphere. Our findings are as follows: (1) D region ISR spectral broadenings are identified as evidence of plasma heating from 100 km down to 75 km altitude; (2) During the 1.4 ms ON and 1.4 ms OFF heating cycle at 4 MHz X mode, we successfully detected D region modulations of ISR power, with the modulations never recovering to the non-heated state. This implies a time-scale for heating/cooling greater than several ms or longer; (3)In the F region, the time scale of the development of plasma turbulence is measured to be near 0.3 ms; and the decay is around 0.2 ms. In addition, we will present the results of our ongoing attempts to infer Te and Ne profiles by combining UHF and VHF radar measurements.
Bahcivan Hasan
Nicolls Michael J.
No associations
LandOfFree
EISCAT incoherent scatter radar measurements of artificial ionospheric modification at sub-ms time scales does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with EISCAT incoherent scatter radar measurements of artificial ionospheric modification at sub-ms time scales, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and EISCAT incoherent scatter radar measurements of artificial ionospheric modification at sub-ms time scales will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-875117