[1] Recent satellite and conjugate observations of Pc 1 electromagnetic ion cyclotron (EMIC) waves have cast doubt on the validity of the long-standing bouncing wave packet (BWP) model that describes their propagation in the magnetosphere. A study was undertaken using the Combined Release and Radiation Effects Satellite (CRRES) E and B field data to further the understanding of the propagation characteristics of Pc 1 EMIC waves in the middle magnetosphere. CRRES covered the region L = 3.5-8.0, magnetic latitude up to ±30°, and magnetic local time 1400-0800. From 6464 hours of observation a total of 248 EMIC wave events were identified. For the first time the Poynting vector for Pc 1 EMIC waves is presented in the dynamic spectral domain permitting the study of energy propagation of simultaneous waves located in different frequency bands. The maximum wave energy flux for the events was 25 mW/m 2 , averaging range 1.3 mW/m 2 , with the direction of wave energy propagation independent of wave frequency but dependent on magnetic latitude. EMIC wave energy propagation was bidirectional both away and toward the equator, for events observed below 11°jMLatj. Unidirectional wave energy propagation away from the equator was observed for all events located above 11°j MLatj. This supports the concept of unidirectional EMIC wave energy propagation away from a broad source region centered on the geomagnetic equator. No measurable energy was observed propagating equatorward beyond the source region, in contradiction to the BWP paradigm.Citation: Loto'aniu, T. M., B.

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The Active Magnetosphere and Planetary Electrodynamics Response Experiment uses magneticfield data from the Iridium constellation to derive the global Birkeland current distribution every 10 min. We examine cases in which the interplanetary magnetic field (IMF) rotated from northward to southward resulting in onsets of the Birkeland currents. Dayside Region 1/2 currents, totaling~25% of the final current, appear within 20 min of the IMF southward turning and remain steady. Onset of nightside currents occurs 40 to 70 min after the dayside currents appear. Thereafter, the currents intensify at dawn, dusk, and on the dayside, yielding a fully formed Region 1/2 system~30 min after the nightside onset. The results imply that the dayside Birkeland currents are driven by magnetopause reconnection, and the remainder of the system forms as magnetospheric return flows start and progress sunward, ultimately closing the Dungey convection cycle.

Abstract. We present a statistical analysis of Birkeland currents derived from Iridium magnetometer data acquired in the Northern Hemisphere to determine the dependence of large-scale currents on the interplanetary magnetic field (IMF) direction. Because the Iridium data span nearly seven years, we can restrict analysis to only those intervals with stable currents. We used image comparison to quantify the consistency between successive one-hour current distributions and selected 1550 two-hour intervals, 5% of the data, for analysis. Results include: no statistically significant average currents are present poleward of 80 • during southward IMF; Region-2 currents are weak and confined to latitudes >65 • during northward IMF; there is marked contrast between currents for northward and southward IMF but the evolution of the patterns is continuous with IMF rotation. The directions of flows inferred from the most poleward currents are more consistent with theoretical expectations of transport away from magnetopause reconnection than previous results. We attribute the differences to the restriction in this analysis to intervals having relatively stable distributions of current so that the data set corresponds more nearly to pure states of the system.

The spectral difference in ULF wave amplitude between closely spaced meridional ground stations may be used to measure the eigenfrequency of magnetospheric field lines [Baransky et al., 1985]. A more reliable technique based on the crossphase spectrum has been used to identify eigenfrequencies and study the temporal evolution of local field line resonances. Pc3 (22–100 mHz) pulsations recorded with two pairs of low latitude ground stations have been specifically examined. Resonances and harmonics whose frequencies are in excellent agreement with model calculations of standing toroidal field line resonances, when ionospheric mass loading at low latitudes is taken into account, were identified virtually every day. This points to a diagnostic technique for monitoring temporal variations in ionospheric and magnetospheric plasma parameters.