An interhemispheric model of artificial ionospheric ducts

Radio Science (Impact Factor: 1). 01/2006; 41. DOI: 10.1029/2005RS003371

ABSTRACT 1] A duct in Earth's ionosphere is characterized by density gradients perpendicular to the magnetic field, which enhance refractive indices and act as waveguides to whistler-range waves. Interhemispheric ducts along magnetic field lines have implications for the transmission of ELF radio waves across the globe. Strong HF ionospheric heating has been shown to create a depletion of electrons at the heated region and could lead to a pressure perturbation that propagates along the entire magnetic field line, potentially forming an artificial duct. Here we present results from an ionospheric numerical model used to study the effects of localized HF heating on an interhemispheric magnetic flux tube. The existing Sami2 is Another Model of the Ionosphere (SAMI2) ionospheric model has been modified to include a flexible source of strong HF heating that can be varied to mimic the fluctuations in HF heating efficiencies and ionospheric conditions. Our parametric study includes varying the heating source intensity and location along the magnetic field line, revealing both linear and nonlinear relationships connecting these source parameters to maximum pressure, temperature, and density perturbations; propagation velocity of density perturbations; and characteristic heating and cooling times of the irradiated region. After a transient state, the duct structure achieves a quasi-steady state, showing electron depletion at the heated region and density enhancements in the regions just below and above the heated region. The density perturbations propagate deep inside the plasmasphere to the conjugate F 2 peak, with density enhancements along the traveling pulse boundary. The possibility of generating interhemispheric ducts is discussed.

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    ABSTRACT: On 16 October 2009, the Detection of Electromagnetic Emissions Transmitted from Earthquake Regions (DEMETER) satellite observed VLF whistler wave activity coincident with an ionospheric heating experiment conducted at HAARP. At the same time, density measurements by DEMETER indicate the presence of multiple field-aligned enhancements. Using an electron MHD model, we show that the distribution of VLF power observed by DEMETER is consistent with the propagation of whistlers from the heating region inside the observed density enhancements. We also discuss other interesting features of this event, including coupling of the lower hybrid and whistler modes, whistler trapping in artificial density ducts, and the interference of whistlers waves from two adjacent ducts.
    Journal of Geophysical Research 10/2013; 118(1–8). · 3.17 Impact Factor
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    ABSTRACT: We present results from numerical studies of whistler mode wave propagation in the Earth's ionosphere when artificially created plasma ducts are present. Using realistic density profiles from the SAMI2 ionospheric code, we solve the two-dimensional electron magnetohydrodynamics equations to study the trans-ionospheric propagation of artificially generated whistler waves at HAARP latitudes (L = 4.9). Both ducted and non-ducted propagation is considered, but only ducted whistlers are able to propagate without a significant reduction in wave amplitude. The conditions necessary for the trapping of waves in both high- and low-density ducts are discussed with particular attention paid to the practical accessibility of these parameter regimes.
    Journal of Geophysical Research 08/2012; 117(A8):8302-. · 3.17 Impact Factor
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    ABSTRACT: We report on satellite observations of plasma density enhancements (ducts) in the topside ionosphere during four HAARP/BRIOCHE campaigns during 2009–2010. Artificial ducts, caused by high-power HF radio wave injections from the HAARP transmitter toward the magnetic zenith, are detected by the DEMETER and DMSP satellites on a regular basis when there is a perceptible ionospheric F2 peak density. Overall, the plasma density enhancements detected between 0930 and 1230 LT varied from 3–13%, while those during 1730–2215 LT were typically 15–40%. We also used a modified SAMI2 model to study the artificial ducts' mechanism driven by HF electron heating in the bottomside F2 region. The heating builds up the plasma pressure, thus pushing plasma along the magnetic field. The simulation results performed for the input parameters similar to the conditions of the heating experiments are in fair agreement with the pertinent observations. The ducts seem to be produced most efficiently for heating frequencies quite close to the critical frequency foF2 .
    Journal of Geophysical Research 10/2012; 117(A10307). · 3.17 Impact Factor

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