Abstract
We conducted a statistical analysis of the physical characteristics of the micropulsation activity (Pc3 and Pc4 range) detected, during the austral summer 1994â95, at Terra Nova Bay (Antarctica, corrected latitude 80.0°S), a station which is few degrees poleward of those where most of the Antarctic measurements in these frequency ranges have been performed. The emerging overview suggests that the correspondence between the pulsation power and the external parameters (solar wind speed, interplanetary magnetic field magnitude and orientation) is significantly stronger than at somewhat lower latitudes. The day-to-day power variability was found to be strictly related to the general level of the geomagnetic activity, and the power level sharply maximizes at local magnetic noon. In the Pc4 range peaks of correlation with the SW speed are found in the dawn and dusk sides of the Earth's magnetosphere and the daily variation of the polarization pattern is closely consistent with that found at auroral latitudes and at lower frequencies. In the Pc3 range the correlation coefficient between the pulsation power and the SW speed has maximum values in the local morning, and the frequency of selected events reveals a strong IMF control during closed magnetospheric conditions. The local time dependence of the correlation coefficient between the pulsation power and the cone angle reveals an additional control by the IMF orientation, which becomes more explicit around local noon.Key words: Magnetospheric physics (magnetopause, cusp, and boundary layers)
Highlights
As underlined by several authors, geomagnetic pulsation research at high latitudes is important in that local ®eldThe occurrence properties of Pc3 and Pc4 pulsations in the polar caps could be considered similar to those observed at lower latitudes in that theseuctuations appear to represent predominantly a daylight phenomenon which becomes more frequent in the local summer (Fraser-Smith, 1982). Wolfe et al (1987), who examined the power level of pulsations (H component, June± September, 1982) in the Pc3 and Pc4 band at South Pole, found in both frequency bands that largest power enhancements were one to two hours before the local magnetic noon
The pulsation energy has been found to be dramatically inuenced by the solar wind (SW) speed (Fig. 2): we found, correlation coecients such as 0.88 and 0.84 (Pc3 and Pc4 band) between logarithm of the total power of components (log PT) and SW speed
Any comparison of experimental observations performed at dierent stations and at dierent times can be inuenced by several factors such as the solar cycle, the seasonal variations, the selection criteria, the data processing, etc., the emerging overview of the present investigation suggests that several aspects of the pulsations activity at TNB may be signi®cantly dierent than at lower latitudes
Summary
As underlined by several authors, geomagnetic pulsation research at high latitudes is important in that local ®eld. We examined the MLT dependence of the pulsation power and its relation with the external SW and IMF parameters to provide additional insights into the exogenic sources of polar capuctuations; in addition, we carefully examined the polarization pattern which is important for a better understanding of the propagation aspects When compared with those obtained at other high-latitude stations, our results show that the nighttime power enhancement of the pulsation power appears con®ned to narrow latitudinal bands; on the other hand, the relationships with the SW and IMF parameters (as well as the observed polarization pattern) appear more explicit than at lower latitudes and reveal some features which are useful to distinguish between dierent generation processes. Years the reader is referred to the review paper by Villante et al (1999b)
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