Amplitude variation of Pc 5 pulsations at high latitudes

Gupta, Jagdish C.

doi:10.1029/rs009i008p00757

Cited by 13 publications

(3 citation statements)

References 9 publications

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“…Direct ground‐based measurements of FLR frequencies support the time‐of‐flight calculations presented here, where decreased frequencies are observed during disturbed conditions (Du et al, ; Gupta, ; Warner & Orr, ). Some previous observations have been used to infer changes in the mass density distribution.…”

Section: Discussionsupporting

confidence: 82%

Variations of Field Line Eigenfrequencies With Ring Current Intensity

2018

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We present results from the closed magnetosphere (5.9 ≤ L < 9.5 over all magnetic local times) to demonstrate and assess the variations in field line eigenfrequency with geomagnetic activity. Using the time-of-flight technique with realistic magnetic field and mass density models, the spatial distributions of field line eigenfrequencies are determined for a range of different geomagnetic activity levels, as defined by the Dst index. The results indicate that during geomagnetically active conditions, the eigenfrequency of a given field line is generally decreased compared to quiet times, in addition to variations in local asymmetries. By comparing the dependence to changes in the magnetic field and mass density distribution, it is established that the inflation and weakening of the geomagnetic field outweighs decreased plasma mass density and is the sole contributor to decreased eigenfrequencies with increased geomagnetic activity. We highlight the importance of considering the magnetic field, mass density, and average ion mass contributions when using observed eigenfrequencies to probe magnetospheric conditions. Furthermore, the estimates significantly improve upon existing time-of-flight results, through a consideration of mass density changes with geomagnetic activity. We also provide estimates of eigenfrequencies for a comparatively extended spatial region than available from prior direct observations of field line resonances. The results have clear implications for furthering our understanding of how wave energy propagates throughout the magnetosphere during geomagnetic storms. Plain Language SummaryThe Earth's magnetic field experiences resonant oscillations of individual magnetic field lines at discrete frequencies, known as eigenfrequencies, which play an important role in transporting energy throughout the Earth's space environment. The frequencies of these oscillations can be highly variable, and a key factor in this variability is the strength of the geomagnetic ring current. In this study, we employ realistic models describing the magnetic field configuration and the spatial distribution of the plasma mass density, which also account for variations with ring current intensity. This allows us to estimate how the eigenfrequencies vary for different levels of ring current strength. We explore changes in the magnitude as well as the spatial distribution. A key result is an observed decrease in the magnitude of the eigenfrequency with increased ring current strength. This result has important implications for understanding how energy can access regions closer to the Earth and consequently act to significantly energize the plasma.

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Section: Discussionsupporting

confidence: 82%

Variations of Field Line Eigenfrequencies With Ring Current Intensity

2018

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“…the intensity peak of Pc 5 activity on the ground occurs at latitudes of 670-75 ø in the morning sector from 0400 to 0900 LT. The amplitude of Pc 5 maximizes on the dawnside at high-latitude stations of L >• 6 [e.g.,Saito, 1964; Kokubun and Nagata, 1965;Gupta, 1974]. Thus the distribution shown inFigure 2is consistent with the statistical results of ground observations.Figure 3 compares Ogo 5 data with ground data for the L value dependence of Pc 5 period.…”

supporting

confidence: 87%

“…rence and the amphtude. These diurnal variations show a single peak in the morning at auroral latitudes, while they have two peaks in the morning and the evening at subaurorial latitudes [Saito, 1964' Hirasawa, 1970Gupta, 1974]. Hirasawa [1970] noted that Pc 5 are observed most frequently at high latitudes of 70 o to •75 ø in the morning hours in relatively quiet conditions (Kp < 2).…”

Section: Lanzerotti and Fukunishi [1974] Have Recently Reviewed The Pmentioning

confidence: 99%

Ogo 5 observations of Pc 5 waves: Ground-magnetosphere correlations

Kokubun¹,

McPherron²,

Russell³

1976

J. Geophys. Res.

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Twenty-two months of Ogo 5 flux gate magnetometer data in the years 1968-1969 have been scanned for the occurrence of Pc 5 waves. Such waves were observed on 18 orbits inside the magnetosphere in the region of L --6-13 and at a magnetic latitude of 10 ø to 430 ø. Close correlations between magnetospheric waves and Pc 5 pulsations on the ground were found on 13 orbits. The 15 orbits on which waves were observed in the morning sector of the magnetosphere were between 0300 and 1100 LT. Most Pc 5 waves in the morning were left-hand elliptically polarized with respect to the ambient field. The major axis of the polarization ellipse was directed nearly perpendicular to the ambient field and close to the azimuthal direction. The examination of ground Pc 5 pulsations at a conjugate pair of stations, Great Whale River (GWR) and Byrd (BY), indicates that the Pc 5 wave, in terms of the simple string analogy of field line resonance, is an odd mode. The radial location, local time of occurrence, and polarization of the waves observed in the magnetosphere are in agreement with expectations based on ground observations. The fact that the waves were observed well inside the magnetosphere suggests that if the waves are generated by the Kelvin-Helmholtz instability at the magnetopause, then field line resonances must play a role in establishing the observed wave amplitudes.

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A study of magnetic pulsations in the Indian equatorial region

Jain

Srinivasacharya

1975

Journal of Atmospheric and Terrestrial Physics

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Amplitude variation of Pc 5 pulsations at high latitudes

Cited by 13 publications

References 9 publications

Variations of Field Line Eigenfrequencies With Ring Current Intensity

Variations of Field Line Eigenfrequencies With Ring Current Intensity

Ogo 5 observations of Pc 5 waves: Ground-magnetosphere correlations

A study of magnetic pulsations in the Indian equatorial region

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