Midday Pc 1-2 pulsations observed at a subcleft location

Heacock, R. R.

doi:10.1029/ja079i028p04239

Cited by 30 publications

(6 citation statements)

References 28 publications

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“…In conclusion, we believe that most of our observed wave events suggest that ion cyclotron waves are being generated in the outer magnetosphere, consistent with ground observations by Heacock [ 1974] and Feigin et al [ 1978]. In addition, the few intervals of right-hand-polarized waves seen in Figure 6 suggest that a second source of Pc 1-2 waves other than ion cyclotron resonance must exist.…”

Section: The Three Intervals Onsupporting

confidence: 92%

Observations of Pc 1–2 waves in the outer magnetosphere

Kaye¹,

Kivelson²

1979

J. Geophys. Res.

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High time resolution measurements made inside the magnetopause from L = 7 to L = 14 by the University of California at Los Angeles fluxgate magnetometer aboard the Ogo 5 satellite demonstrate that Pc 1-2 magnetic field oscillations are occasionally present in portions of the outer magnetosphere. Eleven events have been studied so far, and all of them occurred in the afternoon sector at geomagnetic latitudes from 0 ø to +30 ø. Both the solar wind dynamic pressure and the magnetospheric cold plasma density were enhanced during events for which the respective data were available. The IMF had a southward component approximately 2 hours before the events; however, there was no significant correlation between the time of the events and either storm recovery phase or substorm onset. The magnetic field perturbations in each event were primarily transverse to the ambient field with amplitudes ranging from 2 to 8 3•; however, small compressional oscillations, evidenced by l-to 2-3• fluctuations in the total field magnitude, were sometimes present. Most of the transverse perturbations exhibited lefthanded polarization. Brief excursions into the magnetosheath during two of the events revealed a highly disturbed magnetic field with significant power in frequencies of _>0.1 Hz. Although the magnetosheath was a source of free energy for waves at Pc 1-2 frequencies, the data within the magnetosphere suggest that the observed pulsations were ion cyclotron waves generated at the geomagnetic equator at large radial distances.

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Section: The Three Intervals Onsupporting

confidence: 92%

Observations of Pc 1–2 waves in the outer magnetosphere

Kaye¹,

Kivelson²

1979

J. Geophys. Res.

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“…A 4-s band does not appear very often in our data; neither does it appear any more consistently than other short-lived frequency bands. These results are to be expected, however, because the activity in the 4-s band is predominantly a high-latitude phenomenon and it has pronounced seasonal variation with a maximum in summer [Heacock, 1966[Heacock, , 1974. Our mid-latitude observations were made at the end of winter, when the hourly occurrence rates of 4-s activity measured by Heacock [1966] were a factor of 10 less than those in summer.…”

Section: Figure 1 Shows a Complete 24-hour Series Of Hourly Averagementioning

confidence: 50%

Superconducting magnetometer measurements of geomagnetic activity in the 0.1- to 14-Hz frequency range

Fraser–Smith¹,

Buxton²

1975

J. Geophys. Res

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A high-sensitivity superconducting magnetometer has been used to measure geomagnetic activity at Stanford, California, in the 0.1-to 14-Hz frequency range. The measurements, which covered the 2-month interval January 26 to March 26, 1974, consistently show a minimum of activity in the interval 3-7 Hz, where conventional measurement systems are likely to be limited by their internal noise. At frequencies, below the minimum, in the range 0.1-3 Hz, there is typically a monotonic decrease of background activity with frequencyf. The variation is approximately of the form f-' 25 for the Pc 1 frequency range (0.2-5 Hz). At frequencies above the minimum, in the range 7-14 Hz, the activity is dominated by the first Schumann resonance. The peak amplitude of this activity is usually low in comparison with the amplitude of the background activity at 1 Hz. No splitting of the first Schumann resonance peak into a triplet could be detected, but a doublet structure was observed on 7 days in the 2-month measurement interval. This paper reports high-sensitivity measurements of geomagnetic activity in the frequency range 0.1-14 Hz made with a superconducting magnetometer system [Buxton andFraser-Smith, 1974] at a mid-latitude location (Stanford, California; geomagnetic latitude 43.5øN). The data are new in two respects. First, unlike past measurements, which emphasize the properties of particular large-amplitude events, our measurements are concerned primarily with the properties of the underlying component of geomagnetic activity in the Pc I pulsation frequency range (0.2-5 Hz) which forms a comparatively stable background to the better studied largeamplitude events. We believe that the data presented here are the first fully calibrated measurements of this background activity. Second, our measurements consistently show a minimum of activity in the interval 3-7 Hz (i.e., at the junction of the ultralow frequency band (ULF: frequencies less than •5 Hz) with the extremely low frequency band (ELF: frequencies in the range •5 Hz to 3kHz)), where conventional ULF/ELF measurement systems are likely to be limited by their internal noise. The internal noise level of the Stanford superconducting magnetometer is significantly lower than the noise level in these conventional systems, and it has been shown to be lower than the level of natural background activity in the frequency range 3-7 Hz [Buxton and Fraser-Smith, 1974]. Thus our data are probably the first largely noise-free measurements of geomagnetic activity at frequencies near 5 Hz. In addition to these two features of our data the superconducting magnetometer measurements fill a gap between background measurements made by other investigators at frequencies below 1 Hz and above 7 Hz (both frequencies are approximate; superconducting magnetometer measurements at lower frequencies have recently been reported by Zimmerman and Campbell [1975]). It is possible as a result to relate the natural background in the frequency range 0.1-14 Hz to the background outside the frequency range, i.e.,...

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“…Pulsations in this period range have also been classified into two main categories according to whether they exhibit structures with frequency rising with time (structured) or not (unstructured) [Heacock and Akasofu, 1973]. Investigations have shown that structured Pc1 pulsations are typical at low and middle latitudes [Webster and Fraser, 1985], while unstructured Pc I pulsations occur mostly at high latitudes [Heacock, 1974;Arnoldy et al, 1988]. Considering the close similarity that often prevails between Pc 1 and Pc 2 pulsations, it is questionable whether the separation into these two classes with a transition at a period of 5 s has any physical significance.…”

Section: Introductionmentioning

confidence: 99%

Pc 1–2 and Pc 4–5 pulsations observed at a network of high‐latitude stations

Plyasova-Bakounina¹,

Kangas²,

Мурсула³

et al. 1996

J. Geophys. Res.

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Analysis of magnetospheric Pc 1 and Pc 2 (in brief Pc 1–2) pulsations at a network of six northern hemisphere stations at latitudes 65°–76° CGM shows that their average frequency decreases with increasing latitude of the station. Their maximum occurrence is at L=6–9 and 1200–1600 LT. The ionospheric ducting is weak for f < 0.3 Hz. Occasionally the Pc 1 intensity at a station is modulated by a simultaneously arriving quasi‐periodic Pc 4–5 signal. A mechanism for generating micropulsations which is common to both high‐frequency and low‐frequency waves is presented and discussed, the proposed mechansim being that a broadband signal from the solar wind is amplified in the magnetosphere in the frequency bands of the field line resonance (Pc 4–5) and in the He+ cyclotron frequency (Pc 1–2) range.

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Midday Pc 1-2 pulsations observed at a subcleft location

Cited by 30 publications

References 28 publications

Observations of Pc 1–2 waves in the outer magnetosphere

Observations of Pc 1–2 waves in the outer magnetosphere

Superconducting magnetometer measurements of geomagnetic activity in the 0.1- to 14-Hz frequency range

Pc 1–2 and Pc 4–5 pulsations observed at a network of high‐latitude stations

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