The Ionospheric Source of the Plasma Sheet During Storm Main Phase

<p>The ionospheric and solar wind contributions to the magnetosphere can be distinguished by their composition.  While both sources contain significant H+, the heavy ion species from the ionospheric source are generally singly ionized, while the solar wind consists of highly ionized ions. Both the solar wind and the ionosphere contribute to the plasma sheet.  It has been shown that with both enhanced geomagnetic activity and enhanced solar EUV, the ionospheric contribution, and particularly the ionospheric heavy ions contribution increases.  However, the details of this transition from a solar wind dominated to more ionospheric dominated plasma sheet are not well understood.  An initial study using AMPTE/CHEM data, a data set that includes the full charge state distributions of the major species, shows that the transition can occur quite sharply during storms, with the ionospheric contribution becoming dominant during the storm main phase.  However, during the AMPTE time-period, there were no continuous measurements of the upstream solar wind, and so both the simultaneous solar wind composition and the driving solar wind and IMF parameters were not known.  The HPCA instrument on MMS and both the LEPi and MEPi instruments on Arase are able to measure He++.   With these data sets, the He++/H+ ratio can be compared to the simultaneous He++/H+ ratios in the solar wind to more definitively identify the solar wind contribution to the plasma sheet.  This allows the ionospheric contribution to the H+ population to be determined, so that the full ionospheric population is known. We find that when the IMF turns southward during the storm main phase, the dominant source of the hot plasma sheet becomes ionospheric.  This composition change explains why the storm time ring current also has a high ionospheric contribution.</p>

Sea Bottom EM Field of M2 Tidal to Probe Upper Mantle Conductivity

Recent laboratory experiments demonstrate that electrical conductivity of upper mantle (UM) minerals is greatly increased by small amounts of water or by partial melt. Determination of deep conductivity using electromagnetic (EM) methods can thus provide constraints on the presence of volatiles and melting processes in UM. Probing conductivity at UM depths requires EM data with periods of a few to one cycle per day. This is a challenging period range for EM studies due to the spatially complex ionospheric source that dominates at these periods. The idea of exploiting tidal signals for EM studies of the Earth is not new, but so far it was used only for interpretation of inland and transoceanic electric field data due to M2. Emphasis in this work is made on a discussion of sea bottom magnetic field of the same origin.