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Whistler-triggered lower hybrid resonance noise in irregularites [sic] of the ionosphere Michkofsky, Ronald Nick

Abstract

The mechanism suggested for whistler triggered LHR noise is that of a whistler propagating from a region of the ionosphere where the unperturbed number densities are uniform into one where there is a small spatial irregularity in number density. To investigate at what frequencies the resulting induced electric field may be significant compared to the inducing field (a whistler), steady state solutions were obtained for the electric and magnetic fields that may exist in a fully ionized plasma that has a small spatial irregularity in number density. The plasma is taken to be in a constant and uniform background magnetic field and to have parameters consistent with the upper ionosphere. The irregularity is taken to be a spatially varying cosine function with wave number K. Assuming the governing equations to be Maxwell's equations and the zeroth and the first moment equations of the collisionless Boltzmann equation, we obtained solutions with a perturbation scheme. The equations were linearized and terms were only kept to second order. The first order terms formed a set of equations governing a plasma with unperturbed number densities that were constant in time and space. For first order variables that are plane waves with wave number k and frequency co, the postulated irregularity gives rise to a second order electric field with a frequency dependence of CJ. An investigation was made to determine at which frequencies the second order electric field was significant compared to first order fields. For k parallel to K and perpendicular to B^, it was found that the second order field had a peak value at the LHR (lower hybrid resonance) frequency. For K of the order of 10⁻³ cm⁻¹ , an additional peak occurred for a frequency less than the LHR frequency, when K = 2k. With K -4 -2 -1 increasing from 10 ⁻³ to 10 cm⁻¹ , this frequency increased from 36% to within .3% of the LHR frequency. Neglecting the second order magnetic field, solutions were obtained for k in the x-z plane, B[sup (0)] in the positive z-direction, and K in the positive x-direction. For 9, the angle formed by lc and B[sup (0]), not equal to 90°, the second order electric field had a peak that was greater than the LHR frequency. For 6 = 71.57°, the frequency of the peak changes from 1.005 to 31 times the LHR frequency as K varies from 10⁻² to 10⁻⁴ cm⁻¹ . For K = 10⁻³ cm⁻¹ , the frequency of the peak changes from 1 to approximately 3.5 times the LHR frequency as 8 varies from 90° to 0°.

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