No abstract

Amm and Viljanen (1999) in order to calculate maps of ionospheric equivalent currents over the whole North American auroral region. This study is the first to apply the SECS technique to a large nonrectangular area with widely separated ground magnetometers (∼350 km). For this study we will first demonstrate the validity of the technique using synthetic data and then examine equivalent ionospheric currents associated with a Harang discontinuity for a case study on 10 December 2007. The results show in detail the dynamic evolution of the currents over the entire North American ground magnetometer network. Equivalent ionospheric current (EIC) maps inferred at the minimum resolution of the database, in this case 10 s, can thus be analyzed further in conjunction with near-simultaneous images of the THEMIS all-sky imager mosaics and Super Dual Auroral Radar Network radar data. The EIC maps represent a value-added product from the raw magnetometer database and can be used for contextual interpretation as well as help with our understanding of magnetosphere-ionosphere coupling mechanisms using the ground arrays and the THEMIS spacecraft data.

Abstract. Changes in ionospheric flow patterns provide direct observations of how the magnetosphere-ionosphere system is coupled to the IMF. The nature and location of reconnection on the magnetopause is communicated to the ionosphere, which responds by reconfiguring global convection patterns. We investigate the dynamics of the changing global ionospheric convection patterns using a large twodimensional array of ground magnetometers. We have found that for sharp north to south transitions of the IMF, dayside ionospheric convection patterns globally reconfigure themselves in timescales as short as 8 minutes.We find that all local times initially respond within 1-2 minutes of the first detectable response in the ionosphere.

Observations from AMPTE/CCE in the Earth's magnetosheath on October 5, 1984 are presented to illustrate 0.1–4.0 Hz magnetic field pulsations in the subsolar plasma depletion layer (PDL) for northward sheath field during a magnetospheric compression. The PDL is unambiguously identified by comparing CCE data with data from IRM in the upstream solar wind. Pulsations in the PDL are dominated by transverse waves with F/FH+ ≤ 1.0 and a slot in spectral power at F/FH+ = 0.5. The upper branch is left hand polarized while the lower branch is linearly polarized. In the sheath the proton temperature anisotropy, A = T⟂/T∥ − 1, is ≈ 0.6 but it is ≈ 1.7 in the PDL during wave occurrence. The properties and correlation of waves with increased anisotropy indicate that they are electromagnetic ion cyclotron waves.

We have used simultaneous observations from the AMPTE CCE satellite, in an elliptical orbit with apogee at 8.8 R E, and GOES 5 and GOES 6, in a geostationary orbit at 6.6 RE, to investigate the radial and longitudinal extent of magnetic pulsation events with predominantly radial polarization. Twenty-one events were selected by visual inspection of color-coded Fourier spectrograms produced from data from all three satellites during a several month interval in fall 1984 when the apogee of AMPTE CCE was on the dayside; sixteen events were observed at all three satellites. Local time of the observed events ranged from 0900 to 1900 MLT, but the apparent longitudinal extent of the oscillation region varied considerably from event to event, ranging from the minimum resolution of 1.5 hours MLT (the local time separation of GOES 5 and GOES 6) to 8 hours MLT. Plasma wave data from AMPTE CCE indicated the waves occurred in regions of density characteristic of the outer plasmasphere (-10 cm '3) and quite far outside the L shell region where densities reached 400 cm '3. These events occurred during magnetically quiet times usually after magnetic storms; interplanetary magnetic field data, when available, indicated an either roughly radial or northward orientation during the events. Wave onset often (but not always) occurred within one hour after sharp drops in the AE index to values of 100 or below. There was no apparent correlation of wave onset or amplitude with plasma beta, which ranged from 0.23 to 1.09 during the nine events presented here. Our frequent observation of the simultaneous onset of waves at different local times with considerably different frequencies reinforces the belief that the onset of these pulsations is determined by an instability that covers some longitudinal extent but that the frequencies are determined by local Alfven resonance conditions, not by the bandwidth of an external source. The data suggest that local plasma density increases associated with plasmaspheric refilling are the immediate cause of local instabilities leading to wave onset; the increase in density may alter the field line resonance conditions to allow the free energy of -100-keV trapped ions to drive waves via the drift-Alfven-ballooning-mirror mode instability.