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首页> 外文期刊>Earth, planets and space: EPS >Azimuthally small-scale Alfvén waves in magnetosphere excited by the source of finite duration
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Azimuthally small-scale Alfvén waves in magnetosphere excited by the source of finite duration

机译：由有限持续时间源激发的磁层中的方位角小规模Alfvén波

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In this paper the spatial structure of azimuthally small-scale Alfvén waves in magnetosphere excited by the impulse source is studied. The source is suddenly switched on at a definite moment and works as e - i ω0 t during the finite time interval. The influence of factors which lead to the difference of toroidal and poloidal eigenfrequencies (like curvature of field lines and finite plasma pressure) is taken into account. Due to these factors, a radial component of the group velocity of Alfvén wave appears. An important value is the time moment, t 0, when a wave front moving with radial component of wave group velocity from the poloidal surface (a magnetic surface where the source frequency ω0 coincides with the poloidal frequency) passes the given magnetic shell with the radial coordinate x . The temporal evolution at all the points, where the front has not come yet, is determined by the phase mixing of the initial disturbance. At the points through which the wave front has already passed, the wave field structure almost coincides with the structure of monochromatic wave. The region where the front propagates is bounded by the interval between the poloidal surface and the toroidal one (that is, the Alfvén resonance surface). For this reason, outside this region the evolution is always determined by the phase mixing, which leads to much smaller amplitudes than between poloidal and toroidal surfaces. After the source turned off, a back wave front is formed, which comes through the given point in direction from the poloidal surface to the toroidal one. After the back front has come, the monochromatic wave structure disappears and there is only a weak disturbance, which steadily disappears because of the phase mixing and the final conductivity of ionosphere.
机译：本文研究了脉冲源在磁层中方位小尺度阿尔夫芬波的空间结构。信号源在确定的时间突然打开，并在有限的时间间隔内用作e -iω 0 t 。考虑了导致环和倍数本征频率差异（例如场线曲率和有限等离子压力）不同的因素的影响。由于这些因素，出现了Alfvén波群速度的径向分量。一个重要的值是时间t t 0 ，当波前以波群速度的径向分量从极表面（磁表面，源频率ω 0 与极坐标频率重合）以给定的磁性壳通过径向坐标x。尚未到达前沿的所有点的时间演变取决于初始扰动的相位混合。在波前已经通过的点处，波场结构几乎与单色波的结构重合。正面传播的区域受极表面和环形表面（即Alfvén共振表面）之间的间隔限制。因此，在该区域之外，演化总是由相混合来确定，相混合导致的振幅远小于极性和环形表面之间的振幅。在源关闭后，形成了一个回波波前，该波前经过给定点，从多面体表面到环形表面。在后方到达后，单色波结构消失，只有微弱的干扰，由于相位混合和电离层的最终电导率，该干扰稳定地消失了。

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