A new multi-zone concept for forecasting magnetic activity at high geomagnetic latitudes (above 55° N), resulting in more definitive medium-term forecasts (for up to 27 days in advance) for the Canadian region, shows good agreement between forecast and observed levels. A magnetic activity index DRX (being the daily mean of the 24 one-hour ranges in the north component) calculated for each of three zones-polar cap, auroral, and sub-auroral-demonstrates the distinctly different characters of these magnetic zones. Accordingly, values of DRX are forecast for each of these three zones. Recurrent patterns of solar phenomena and their observed interactions with the geomagnetic field form the basis of the forecasting technique. Coronal holes predominate as sources of recurrent magnetic . activity. During an interval in 1984-1985, 88% of solar coronal holes were followed by an increase in geomagnetic activity.
Similarities have been found between the yearly trends of magnetic activity and the occurrences of electrostatic discharge events on a geosynchronous communication satellite from April 1983 to December 1987 in the declining portion of the 11-year solar cycle. The seasonal variations of magnetic activity and electrostatic discharge events show maxima around the equinoxes and minima during solstitial months. Detailed comparisons of the events with magnetograms from Yellowknife, Canada, near the footprint of the satellite, indicate that magnetic storms, substorms, and bays offer magnetic signatures for the discharge events with substorms playing a dominant role. A study of the occurrences of electrostatic discharge with respect to the magnetic perturbations indicates a variable time delay in the occurrence after the initiation of the magnetic disturbance. The local time variation pattern in the occurrence of electrostatic discharge shows preferred occurrences in the afternoon and evening sector. It is possible that a delay mechanism is operating, whereby the surface of the satellite is charged differentially in the midnight to dawn sector during substorm and discharged at some later time. It is also conceivable that the daytime anomalies are caused by buried charge processes. The occurrences of electrostatic discharge events in the traditional midnight to dawn sector and in the local time interval encompassing the Harang discontinuity appear to be immediate responses to the magnetic perturbations.
The hourly values of solar wind parameters and AE indices at times when the interplanetary magnetic field has a strong northward component are used to study the dependence of AE on the value of the interplanetary magnetic field (B) and on the temporal trends of the solar wind velocity (V). In any randomly chosen statistical set of data, the dependence of AE on B is substantially modified by spurious effects related to the structure of the solar wind streams. In particular, the leveling off of AE at high values of B is spurious; d(AE)/dB is positive for all values of B. AE values corresponding to negative dV/dt are lower than AE values corresponding to positive dV/dt. This effect is caused by physical processes involving the solar wind‐magnetosphere coupling. It is suggested that slow variations of the magnetospheric structure, which are due to slow changes of the solar wind pressure upon the magnetospheric boundary, are a likely cause of the amplification and damping of the MHD perturbations existing in the magnetosphere; they are also a likely cause of the observed dependence of AE on dV/dt.
The solar-terrestrial event of 22-25 March 1991, was one of the largest this solar cycle, producing a very strong particle flux, a second inner radiation belt, and a large geomagnetic disturbance. This caused solar panel degradation and other satellite malfunctions as well as communication and power system problems. This report examines the resulting magnetic disturbance observed across Canada on 24-25 March, presenting stack plots of the temporal variations and using equivalent current plots to map the spatial characteristics of the disturbance. A notable feature of the results is that the largest magnetic field variations occurred in the polar cap and not, as is more common, in the auroral zone. These polar cap magnetic variations are attributed to Hall currents in the ionosphere resulting from the enhanced convection of field lines across the polar cap. The extreme magnitude of the polar cap disturbance indicates the severity of the solar wind plasma cloud interaction with the earth's magnetosphere.
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