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

Abstract

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.

Magnetic field power spectra and magnetic radial diffusion coefficients using CRRES magnetometer data

“…Mozer [] and Holzworth and Mozer [] used data from balloon campaigns to determine the K p dependence of the electric field PSDs. Magnetic field power spectra have been analyzed and have been computed at L = 4 [ Lanzerotti and Robbins , ; Lanzerotti and Morgan , ] and at L = 6.6 [ Lanzerotti et al , ; Arthur et al , ; Huang et al , ; Tu et al , ]. Brautigam and Albert [] showed that in order to model magnetic storm time behavior of relativistic electrons, an activity‐dependent D L L is necessary.…”

CRRES electric field power spectra and radial diffusion coefficients

“… Mozer [1971] had earlier found that the power spectra related to D LL E show a Kp dependence but no L or local time dependence. Magnetic field power spectral densities and the corresponding D LL M have been determined at L = 4 [ Lanzerotti and Robbins , 1973; Lanzerotti and Morgan , 1973] and at geosynchronous orbit [ Arthur et al , 1978; Lanzerotti et al , 1978].…”

Geomagnetic field fluctuations at synchronous orbit 1. Power spectra

“…Over the years, power spectra have been determined in several distinct regions of space near earth (interplanetary medium, magnetosheath, outer magnetosphere, and the ground). In some cases, the spectra were calculated in order to study the spectrum itself (or enhancements which represent wave events) [e.g., Davidson, 1964;Lanzerotti and Robbins, 1973;Humble and Hedgecock, 1974]; in others, for use in other types of analysis, such as the calculation of radial diffusion coefficients [Lanzerotti and Morgan, 1973] or the study of cosmic ray modulation [e.g., Siscoe et at., 1968;Sari, 1975;Sari and Valley, 1976]. Compiling the spectra from these various regions, including the results from synchronous orbit as presented in this paper, we obtain a general picture of background power level variations from region to region.…”