occurrence of the lobe plasma at lunar distance

Authors:
  • DHD. A. Hardy
    D. A. Hardy
  • HHH. K. Hills
    H. K. Hills
  • JFJ. W. Freeman
    J. W. Freeman
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Abstract
Recent analysis has confirmed and expanded the characterization of the lobe plasma, the extension of the ‘boundary layer’ and ‘plasma mantle’ to lunar distances. Careful statistical analysis has verified that the observation of the ‘lobe plasma’ is strongly correlated with the y component of the Interplanetary Magnetic Field (IMF). When the moon is in the dawnside of the northern lobe or duskside of the southern lobe, the probability for observation of the lobe plasma is greatly increased when, in the hour preceding, the IMF has had a positive y component. Conversely, when the moon is in the duskside of the northern lobe or dawnside of the southern lobe, the probability for observation is much increased when the IMF has a negative y component. Analysis of lobe plasma data in conjunction with high time resolution IMF data has shown the probability of observation also is greater with a southward pointing IMF. The observed correlations with the y and z components the IMF reflect the fact that the asymmetry and changes in magnitude of the polar cap electric field induced by the IMF extends to lunar distances and determines the depth into the tail to which the ions can drift. Generally, the lobe plasma is observed sporadically for a full day after the moon has entered the tail and a full day before the last magnetopause crossing as it exits the tail. An average extent of ∼8–10 RE inward from the magnetopause is inferred; however, the lobe plasma has been seen all across the tail.

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