Effects of finite current channel width on the current convective instability

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The effects of the finite current channel width on the current convective instability are studied both analytically and numerically. First, using a sharp boundary field‐aligned current distribution which has a finite width along the plasma density gradient, the dispersion relation is obtained analytically. It is found that for the long wavelength modes (kyd ≪ 1) where the nonlocal effects are most prominent, the growth rate γ is proportional to in the collisional limit (νin ≫ |ω|), where d is the half width of the current channel, L is the plasma density gradient scale length, is the field‐aligned current velocity, νin is the ion‐neutral collision frequency, and ω is the perturbation frequency. For the long wavelength modes in the inertial limit (νin ≪ |ω|) the growth rate γ scales as , where α = 1/2 (2/3) for kz²/ky² Ωe/νei much less than (greater than) |ω|/Ωi, kz(ky) is the wave number parallel (perpendicular) to the magnetic field, Ωe(Ωi) is the electron (ion) gyrofrequency, and νei is the electron‐ion collision frequency. Numerical results are also presented for a diffuse boundary current velocity distribution. Applications to the high‐latitude ionosphere are discussed.