A study of the power spectra of dPi's and Pi 2's

The geomagnetic field variation spectra for the period range of 5 min to 4 hours were analyzed at 64 world observatories to discover systematic behavior in the spectral composition that could be associated with the time of day, season, solar cycle, activity level, component direction, and geographical location of the station. There was found no consistent frequency location for peaks in the spectral composition. Rather, the displays of spectral amplitudes A were mostly ‘linear’ in form, often obeying A ∼ Tm, where T is the period. The spectral slope m was usually close to 1.0 but varied at times from 0.5 to 2.0. The amplitudes always showed a maximum at the auroral zone latitudes, a minimum near 20°−40°, and a minor maximum near the equator. The positions shifted equatorward with increasing activity. The relative growth in amplitude with rising activity varied with latitude. Seasonal peaks in activity were found at equinoctial months. A summertime minimum occurred at auroral zone stations; elsewhere a summertime enhancement occurred. General findings emphasizing the North American hemisphere and the year 1965 are presented in a number of tables and graphs.

Section: Spectral Amplitudes Maximize At the Auroral Zonesupporting

confidence: 88%

An analysis of the spectra of geomagnetic variations having periods from 5 min to 4 hours

Campbell¹

1976

“…According to their model, the H component is in phase, whereas the D component is out of phase at a conjugate pair for an odd mode oscillation. The present analytical result indicates that the Pi 2 waves observed in the auroral region are caused by the odd mode standing oscillation of localized field lines.According to results 1-3 above, a main cause of Pi 2 is possible to be the hydromagnetic torsional oscillation of the field lines anchored on the northern and the southern auroral ovals, as inferred by several researchers[Saito, 1969;Saito and Sakurai, 1970;Sakurai, 1970;Stuart and Booth, 1974;Saito et al, 1976a]. Hence, we calculated the periods of the torsional standing oscillation in order to compare them with the observed Pi 2 periods shown inFigure 5.…”

mentioning

confidence: 79%

“…Relationships between the Pi 2 period and the geomagnetic activity have been investigated by many researchers using Kp index or the magnitude of the associated bay. According to their results, the Pi 2 period becomes shorter as the geomagnetic activity increases [Troitskaya, 1967;Rostoker, 1967;Saito and Matsushita, 1968;Fukunishi and Hirasawa, 1970;Saito and Sakurai, 1970;Channon and Orr, 1970;Doobov and Mainstone, 1973;Stuart and Booth, 1974;Sutcliffe, 1975] Because of the close relation between Pi 2 and the magnetospheric substorm [Saito et al, 1976a;Sakurai and Saito, 1976], the successive Pi 2 occurrences are thought to correspond to multiple onsets of a substorm. Generally, the instantaneous auroral breakup position shifts from low to high latitude [Kuwashima, 1978].…”

Section: Power Spectra Of Pi Pulsations Simultaneously Observed Over mentioning

confidence: 99%

Spectral characteristics of magnetic Pi 2 pulsations in the auroral region and lower latitudes

Kuwashima¹,

Saito²

1981

The spectral characteristics of magnetic Pi 2 pulsations are studied in detail using data obtained simultaneously over a wide latitudinal range from the auroral region (L=7.5) through low latitudes (L=1.8). Pi 2 is revealed to be observed almost simultaneously with the onset of a substorm expansion over the wide latitudinal range with the common predominant period. The Pi 2 amplitude shows a primary maximum at the auroral oval and an additional secondary maximum near the plasmapause. The Pi 2 period generally becomes shorter (longer) when the associated auroral breakup starts at lower (higher) latitudes. Pi 2 is also observed simultaneously at a pair of conjugate stations in the auroral region with similar waveforms. These observational results support the torsional oscillation model which suggests that Pi 2 is caused by the hydromagnetic torsional oscillation of the geomagnetic field line anchored on the auroral oval.

“…Yeoman et al [1990] used observations from the SAMNET array to suggest that the subauroral region is a transition zone in which the Pi 2 signal changes from its high-latitude auroral form to a different middle-to lowlatitude form. In the auroral region the spectra of Pi 2 pulsations are noisy, containing many spectral components [Stuart and Booth, 1974]. At lower latitudes they are small amplitude and much less noisy.…”

Section: General Principlesmentioning

confidence: 99%

Global modeling of Pi 2 pulsations

Pekrides¹,

Walker²,

Sutcliffe³

1997

Abstract. A numerical model of Pi 2 disturbances in the magnetosphere is developed. The model of the magnetosphere is the same as one previously used for the study of Pc 5 pulsations. It is semicylindrical with field lines being semicircular arcs and longitude measured parallel to the axis. The model magnetosphere is excited by a source on the boundary which is limited both in time and in longitude. The disturbance is then a superposition of modes corresponding to all the azimuthal wave numbers excited by the source. The computations show that a global oscillation is excited and that there can be a significant signal on the dayside at low latitudes. The role of the plasmasphere in producing a low-latitude response is important. Because of the simplifications of the model the most important aspect of the calculations is the qualitative understanding that they supply. Nevertheless, quite good quantitative agreement with observation is obtained. The calculations support earlier suggestions about the response of the magnetosphere to the initiation of the substorm current wedge.