|Proposed Statement of Research
John P. Keady
University of Texas at Dallas
Small scale structure in the electric and magnetic fields is a pervasive feature of the high latitude ionosphere. Heppner et al.,  describe the structure in the electric field at scale sizes from hundreds of kilometers to hundreds of meters and show dependencies on season and magnetic activity. The relationships between the electric and magnetic field are determined in large part by the presence of static field-aligned current systems and the presence of electromagnetic waves. The expected relationships between structure in the electric and magnetic field have been investigated by Knudsen et al. where the both the ratio of the magnitudes in the structure and their temporal correlation can be examined to determine a preference for the existence of static field-aligned currents or Alfven waves. In the simplest case the relationships between the electric and magnetic fields can be straightforwardly deduced.
In practice, waves and currents may exist simultaneously and waves may undergo multiple reflections between the magnetosphere and the ionosphere that reduce the clarity with which the ratios can be determined.
Examinations of the variations in the behavior of the structures in the electric and magnetic field have been examined by Forget et al,  and by Iishi et al.,  Forget et al.  note that in the case of static field aligned currents a scale size dependence in the ratio of the electric and magnetic fields may be expected due to a scale size dependence in the mapping properties of electric fields that affects the flux tube integrated Pedersen conductivity. Iishi et al., [1992 ] point out that a similar change in the ratio of electric to magnetic field structure magnitudes will result if a transition from static currents to Alfven waves occurs for decreasing spatial scale size.
In all the studies performed so far the data sets examined have been quite small and no systematic behavior over the high latitude region has been confirmed. However, data available from the Dynamics Explorer satellite provides samples of the electric field and the magnetic field at 16 Hz throughout the northern and southern polar regions. This data, allowing resolution of structures with spatial scales down to 1 km, can be used to provide a description of the relationships between electric and magnetic field structures throughout the high latitude region as a function of magnetic activity, season and interplanetary magnetic field orientation. We propose to conduct such a study.
The data we will use is obtained from the ion drift meter [Heelis et al., 1981] and the Magnetometer [Farthing et al., 1981] on the DE-2 spacecraft.- Figure 1 shows an example of the data taken at the highest resolution from a polar pass of the spacecraft. we will examine this data over 8 and 16 second intervals corresponding to sampling distances of 60 km and 120 km respectively. In addition to the usual spectral analysis, that will be performed to describe the scale size dependent properties of the structure, we also propose to systematically examine a coherence spectrum that will be used to determine the spatial scales within these sampling distances over which the structure in the electric and magnetic fields are sensibly correlated. We will note these scale sizes and the magnitude of the ratio of the electric to magnetic field. We will also record the local ion concentration, for evaluation of the local Alfven speed and the location that will allow us to later retrieve the recorded average energy flux and average energy of the precipitating electrons This data can be used to determine the flux-tube integrated Pedersen conductivity.
In the final analysis we expect to build a data base describing the individual spectral characteristics of AE and AB and the relationships between them that will relate to the existence of static field aligned currents and waves. This work will be conducted in consultation with Dr. J. Slavin at Goddard Space Flight Center and with Dr. R. Heelis at the University of Texas at Dallas, where I am a graduate student. The data bases we require exist at the university and can be augmented with the DE data base available from the National Space Science Data Center.
Farthing, W. H., M. Sugiura and B. G. Ledley, Magnetic field observations on DE-A and DE B, Space Sci. Instrum., S, 551, 1981.
Forget, B., J.-C. Cerisier, A. Berthelier and J.-J. Berthelier, Ionospheric closure of smallscale Birkeland currents., J. Geophys. Res., 96, 1843-1847, 1991.
Heelis, R. A., W. B. Hanson, C.R.Lippincott, D. R. Zuccaro, L. L. Harmon, B. J. Holt, J. E. Doherty and R. A. Power, The ion drift meter for Dynamics Explorer-B, Space Sci. Instrum., 5, 511, 1981.
Heppner, J. P., M. C. Liebrecht, N. C. Maynard and R. F. Pfaff, High latitude distributions of plasma waves and spatial irregularities from DE 2 alternating current electric field observations., J. Geophys. Res., 98, 1629-1652, 1993.
Ishii, M., M. Sugiura, T. Iyemori and J. A. Slavin, Correlation between magnetic and electric field perturbations in field aligned current regions deduced from DE 2 observations., J. Geophys. Res., 97, 13,877-13,887, 1992.
Knudsen, D. J., M. C. Kelley, G. D. Earle, J. F. Vickrey and M. Boehm, Distinguishing Alfven Waves from quasi-static field structures associated with the discrete aurora: Sounding rocket and H1LAT satellite measurements, Geophys. Res. Lett., 17, 921-924, 1990.
Wednesday, 26-Mar-2003 22:09:22 CST
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