Geomagnetic Micropulsations

Ellis, GRA

doi:10.1071/ph600625

Cited by 32 publications

(12 citation statements)

References 4 publications

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“…However, we believe that this oscillation is possible when these periods of oscillations become equal at finite interval of latitudes. This supposition is in agreement with the observations of Ellis (1960), Kokubun and Nagata (1965), Obertz and Raspopov (1968), who have shown that geomagnetic pulsations observed simultaneously at different latitudes have the equal period and a similar spectrum. The component changes its sign when crossing the longitude of the source of oscillations.…”

supporting

confidence: 81%

Periods of the Magnetospheric Oscillations and the Plasma Density

Namgaladze

Brunelli

1970

J. geomagn. geoelec

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Using the model magnetosphere of the Mead's type, periods of self oscillation of the magntosphere are calculated for the cases of weak or strong dependence of its amplitude on longitude. It is shown that the transverse wave can exist when the periods of these two modes are equal. This condition is satisfied at latitudes near the auroral zone. The oscillations with a longitudinal dependence in form of Gauss-function are also considered, and the values of Ne/T2 are calculated. The plasma density Ne in the magnetosphere is estimated using the period T of observed geomagnetic pulsations ; the result is in agreement with the data of other methods.The idea that the geomagnetic pulsations are due to hydromagnetic oscillations of the magnetosphere gave the possibility that their periods are connected with the plasma density distribution of magnetosphere. In several works (Obayashi 1958, 01' 1963, Gul'elmi 1967 this possibility was utilized, the period of pulsations being taken equal to the echoing period of Alfven wave along the geomagnetic field line. Radoski (1966), Radoski and Carouillano (1966) pointed out that the WKB-approximation is applicable only in the (1968) found the period of self-oscillations, making the numerical integration of equation concordant with the boundary conditions. Dungey (1963) has formulated the equation of magnetospheric oscillationsIn the coordinatite system (q1, q2, q3) with unit-vectors shown in Fig 1, it can be written as (2)and it is assumed that E1=0 in consequence of

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supporting

confidence: 81%

Periods of the Magnetospheric Oscillations and the Plasma Density

Namgaladze

Brunelli

1970

J. geomagn. geoelec

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“…That is, the pulsations at lower latitude stations were abundant in the vicinity of 180 sec while at higher latitudes the pulsations with period nearly 270 sec occurred more frequently. In some earlier investigations no change in the period of Pc5 with increasing latitude was detected (ELLIS, 1960;KOKUBUN and NAGATA, 1965;OBERTZ and RASPOPOv, 1968) but some other authors reported an increase of the period with increasing latitude (OBAYASHI and JAcoBS, 1958;OGUTI,1963;OL',1963;HIRASAWA,1970;GUPTA, 1974a). For pulsations in the period range 180-300 sec the period-latitude profile, obtained from the whole body of data at individual stations, is shown in Fig.…”

Section: Periodmentioning

confidence: 99%

Some features of Pc5 pulsations in the period range 180-300 sec.

Gupta¹

1976

J. geomagn. geoelec

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Geomagnetic pulsations with periods between 180 and 300 sec recorded at 7 Canadian magnetic observatories during 1967 were examined to determine the relationships of occurrence, amplitude and period to latitude, time and the level of magnetic activity. Their characteristics are compared with those of long-period Pc5's (periods 300 to 600 sec). Results are examined in the light of existing theoretical models. However, it has been found that these models do not explain satisfactorily the observed evening occurrence peak in the polar cap.

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“…The statistical behavior of ground Pc4 pulsations is well documented, including an amplitude maximum on the dayside and lack of events on the nightside [ Saito , 1964; Fukunishi and Lanzerotti , 1974; Chi et al , 1994, 1996]. The Pc4 amplitude peaks at magnetic latitudes below ∼60° [ Samson and Rostoker , 1972], and at low latitudes the amplitude is typically 0.5 nT [ Ellis , 1960]. Possible sources of the pulsations are ULF waves generated by ion‐beam instability in the solar wind upstream of the bow shock [ Troitskaya et al , 1971] and the Kelvin‐Helmholtz instability on the magnetopause [ Greenstadt et al , 1979].…”

Section: Introductionmentioning

confidence: 99%

Source of Pc4 pulsations observed on the nightside

et al. 2005

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We have studied magnetic pulsations in the 5‐ to 20‐mHz (Pc4) band observed on 7 January 1997 from ∼1400 UT to ∼1600 UT at ground stations located on the nightside. At low latitudes (L < 2) the spectral content of the pulsations did not differ much from the Pi2 pulsations that were observed adjacent to the above interval. However, during the Pc4 event the auroral luminosity measured by the Ultra Violet Imager instrument on the Polar spacecraft was steadily declining toward a very low level. Also, the Geotail spacecraft, located in the plasmasheet at a geocentric distance of ∼30 RE did not detect strong plasma flows. Looking for clues of possible dayside sources for the pulsations, we find that the interplanetary magnetic field measured by the IMP‐8 spacecraft made a small (<30°) angle with the Sun‐Earth axis. This condition is favorable for generation of ultra‐low‐frequency (ULF) waves in the region upstream of the bow shock, and it is known that the upstream waves are a major source of Pc4 pulsations observed on the dayside. Pointing to a common upstream energy source, strong low‐latitude Pc4 pulsations were observed on the dayside during the period of the nightside Pc4 pulsations. However, the spectrum of the upstream magnetic field oscillations at IMP‐8 was characterized by broadband power below 20 mHz instead of a strong peak at the frequency of the observed ground Pc4 pulsations. Plasmaspheric cavity mode resonance may have played a role in filtering the Pc4 pulsations from the broadband input to the magnetosphere.

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Geomagnetic Micropulsations

Cited by 32 publications

References 4 publications

Periods of the Magnetospheric Oscillations and the Plasma Density

Periods of the Magnetospheric Oscillations and the Plasma Density

Some features of Pc5 pulsations in the period range 180-300 sec.

Source of Pc4 pulsations observed on the nightside

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