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Type Pc 1 micropulsation activity at high latitudes: Statistical analyses were made on structured Pc 1 micropulsation data recorded at College (Alaska), Thule (Greenland), and Sodankyla and Nurmijarvi (Finland) from November 1967 through January 1970. Hourly occurrences of Pc 1 were scaled for mid-frequencies, amplitudes, and “sameness” of event as seen at two or more sites. The data give evidence for the existence of a global effect in Pc 1 activity. The effect is thought to be related to drifting trapped solar wind protons, i.e. to some form of proton ring current. The existence of a midday maximum in Pc 1 production at source latitudes is verified. The Pc 1 diurnal variations observed at other latitudes, including Thule (89°), are mainly shaped by characteristics of propagation in the ionosphere horizontal duct. An event occurring on 23 Feb 1967 propagated from the vicinity of Finland, completely over the polar cap, to Alaska, at a time when the disturbance level over the polar cap was minimal. The evidence suggests that E-region electrojets and other ionospheric irregularities are effective in scattering Pc 1 waves which are propagating polewards in the duct. The scattering mechanism explains some of the occurrence characteristics, e.g. the lack of the 2-4 Hz events within the polar cap though these events are fairly common at subauroral and middle latitudes. Main regularities of micropulsations at the geomagnetic poles: Observations of micropulsations in the range from small fractions of an Hz up to several Hz were conducted at the geomagnetic poles, Thule and Vostok, from 1964 to date. Main morphological regularities of different types of pulsations in these regions were investigated. Most typical for the geomagnetic poles in the family of continuous pulsations are types Pc 2 and Pc 3. A distinct seasonal variation was established for the intensity of Pc 3. It is suggested that Pc 2 pulsations penetrate to the polar cap from the far regions of the magnetospheric tail. The deformation in the shape of the Pi 2 pulsations in the region of the geomagnetic pole is stressed. The character of their propagation from the auroral zone where their amplitude is maximum is different towards the pole and towards middle latitudes. The connection of irregular short period magnetic disturbances of the PD* type with disturbances in the interplanetary field was investigated. It was revealed that the delay in PD occurrence is different for day and night hours. Investigation of pulsation behavior at the geomagnetic poles during the growth phase of substorms led to the discovery of precursors having periods equal to several minutes. Bursts of irregular oscillations with periods of 2 to 7 minutes either appear or are intensified approximately one hour before the substorm. It is suggested that these bursts of pulsations correspond to similar oscillations at the boundary of the magnetosphere discovered by direct measurements. Preliminary results of comparison of pulsation behavior at the geomagnetic poles and of aurora development are outlined. Micropulsations associated with polar magnetic substorms: This paper presents a comprehensive study of the irregular type of electromagnetic micropulsations which occur in association with the polar substorm. An extensive review of the literature serves to define the problem and to guide the ensuing scaling, analysis and discussion of results. The study utilizes data recorded on strip chart and magnetic tape over a period of several years from several stations in Alaska and Finland and from Thule, the Danish station near the North geomagnetic pole. The analysis includes extensive statistical studies of the incidence of Pi 1 and 2 at College in relation to magnetic bays and riometer data. Incidence is measured in terms of both spectral and amplitude characteristics. Individual events are studied in detail to determine the temporal and spatial distributions of the micropulsations in relation to the magnetic substorm and electron precipitation. Charts presenting the development of the polar micropulsation substorm are prepared from the above analysis. The results of the analysis are discussed in relation to the properties of the solar wind, velocity, particle densities, and magnetic field, and to the magnetospheric substorm.

Publication Date

5-17-1972

Keywords

Geomagnetic micropulsations

Handle

http://hdl.handle.net/11122/15633

Polar micropulsations

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