Field-Aligned Lorentz Forces with Application to Thermal-Ion Upflows into the Magnetosphere

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This is a three-year research program to investigate the nature of a newly discovered ionospheric source for ion energization and transport. The topic of ion energization is one of paramount importance in magnetospheric physics because ions carry the bulk of the particle energy and thereby play a central role in the molding of that environment. The proposed program directly addresses one of the most puzzling problems of ion energization - that is, how are heavy (O+) ions accelerated at low altitudes in the ionosphere and transported upward in large numbers to the magnetosphere? This question is crucial because (1) the abundance of O+ ions found throughout the magnetosphere requires some means by which large fluxes of thermal ions are transported upward from the ionosphere, and (2) thermal-ions upflows (TIU) and transversely accelerated ions (TAI) have been observed at altitudes as low as 400 km in the ionosphere. Other observations have demonstrated the existence of at least one class of TIU events that is characterized by the absence of ion frictional heating and the presence of elevated electron temperature, features that cannot be easily explained by known mechansisms. These findings indicate that the process responsible for the transport of large fluxes of terrestrial ions to the magnetosphere has not yet been identified. We have recently described a new, ion energization souce Tsunoda and Kagan, 1995 that appears to be the missing mechanism. The new source consists of Lrentz-type forces that arise because of the presence of a perturbation magnetic field, for example, that associated with a large-scale field-aligned current system. This perturbation magnetic field acts together with a latituinal pressure gradient or current (directed orthogonal to one another and transverse to B) to produce a Lorentz-type force in a direction parallel or antiparallel to B. As described by Tsunoda and Kagan 1995 , and in this proposal, this mechanism is capable of accounting for the class of TIU events that occur without ion heating. More exciting however, is the likelihood that these field-aligned Lorentz forces can account for a number of related but still puzzling observations including (1) TIUs produced by ion heating, (2) the transport of molecular ions into the magnetosphere, (3) the triggering of the ion-cyclotron and ion- acoustic instabilities, (4) the transverse acceleration of ions by electrostatic ion-cyclotron waves, (5) the development of ion- acoustic turbulence and anomalous resistivity, and (6) elevated electron temperatures in upward field-aligned current regions. Given the potential of field-aligned Lorentz forces for explaining a variety of ion-acceleration-related phenomena, an investigation of a larger database of incoherent scatter radar data will be undertaken of determine if the observations support the predictions of this novel theory.