An analysis of micropulsation spectra (Pc) obtained from the U.E. observatories

Stuart, W.F.; Sherwood, Vicki E.; Macintosh, Sheena M.

doi:10.1016/0021-9169(71)90087-0

Cited by 19 publications

(4 citation statements)

References 10 publications

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“…There have been numerous spectra emphasizing the field pulsation frequencies just above those studied here [Davidson, 1964;Swift and Hessler, 1964;Stuart et al, 1971;Lanzerotti and Robbins, 1973;Morgan and Lanzerotti, 1973;Stuart and Booth, 1974;Fukunishi and Lanzerotti, 1974;Surkan and Lanzerotti, 1974]. Most of these spectra overlap, to a small degree, some of the 5-min to 4-hour period range of this paper and are in agreement with the spectral magnitudes presented.…”

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

J. Geophys. Res.

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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.

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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

J. Geophys. Res.

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“…terms of noticeable enhancements (perhaps resonances due to plasma waves) observed in time-averaged spectra [e.g., Davidson, 1964;Stuart et al, 1971]. A few studies have discussed the measured power spectra (and the occurring resonances) in terms of operative magnetospheric processes [e.g., Hirasawa and Nagata, 1966;Rostoker, 1967;Fukunishi and Hirasawa, 1970].…”

mentioning

confidence: 99%

ULF geomagnetic power nearL= 4: 1. Quiet day power spectra at conjugate points during December Solstice

Lanzerotti¹,

Robbins²

1973

J. Geophys. Res.

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Hourly determinations of the power spectra of the ULF geomagnetic disturbances in the period band of ∼30–512 sec have been made from data obtained at conjugate points near L = 4 on 3 consecutive days during the December solstice when Σ Kp = 2−, 0, and 1 (January 7, 8, and 9, 1971, respectively). The data from January 8 (Σ Kp = 0) are presented in detail in order to study ULF geomagnetic conditions during a time interval defined as ‘quiet’ by current measures of geomagnetic activity (i.e., the K index). The slope s of the frequency dependence of the power density log β ∝ −s log f is found to vary from ∼−1.0 to ∼−2.5 during the day for both the H and D components. The magnetic power at the conjugate points shows a diurnal dependence with higher intensities during local day at both conjugate stations. The power densities β are most conjugate during local day; during local night, when the southern station (Siple, Antarctica) is in continual daylight, the power density is largest at Siple. This relationship holds on the average for all 3 quiet days. A portion of the diurnal dependence of the conjugacy of the power may be associated with the Sq current system through field‐aligned currents, even though the Sq fields at the conjugate stations are observed to be strongly nonconjugate.

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“…This model also explains very well the associated latitudinal variation of the wave polarization (Samson, Jackobs & Rostoker 1971;Lanzerotti et al 1974a, b). However, the above enumerated work does not explain why the resonant response of the magnetosphere is often observed to have a discrete spectrum of frequencies (Kokubum & Nagata 1965;Stuart, Sherwood & Macintosh 1971;Takahashi & McPherron 1982). Moreover, the solution of the field-line resonance mode predicts spatially dependent eigenfrequencies and thus contains mathematical inconsistencies in the analysis (Radoski & McClay 1967).…”

Section: Introductionmentioning

confidence: 99%

Spectral characteristics of hydromagnetic waves in the magnetosphere

Kuo¹,

Lee

Wolfe

1987

J. Plasma Phys.

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This work is intended to explain why the resonant response of the magnetosphere prefers to have discrete frequencies. Using a cylindrical model for the outer magnetosphere with a plasma density profile proportional to 1/r, we show that the eigenequation characterizing the eigenmodes of the hydromagnetic waves in this model has two turning points along the radial axis. The locations of the turning points depend upon the values of the eigenperiod and the associated east-west wavenumber of the eigenmode. The energy spectrum of the excited cavity modes is seen to have sharp peaks at discrete frequencies when the surface perturbations have a uniform spectrum in the frequency range of interest. We, therefore, have also shown that only the discrete set of the magnetospheric cavity eigenmodes can efficiently couple the perturbations excited on the boundary of the magnetosphere to the field-line resonant mode excited inside the inner turning point of the cavity eigenmode. The most likely values of east-west wavenumbers and wave period range are determined.

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An analysis of micropulsation spectra (Pc) obtained from the U.E. observatories

Cited by 19 publications

References 10 publications

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

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

ULF geomagnetic power nearL= 4: 1. Quiet day power spectra at conjugate points during December Solstice

Spectral characteristics of hydromagnetic waves in the magnetosphere

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