Geomagnetic pulsations

Saito, Takao

doi:10.1007/bf00203620

Cited by 436 publications

(232 citation statements)

References 122 publications

(285 reference statements)

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“…Furthermore, the low-latitude Pi2 is sensitive to small substorms, even extremely small ones that are hardly detectable with the AE index [e.g., Sakurai and Saito, 1976], and they prevail over other subtypes of irregular pulsation at low latitudes [Saito, 1969]. Although there seemed to be a good one-to-one correspondence between Pi2 pulsations and substorms as first concluded by Saito et al [1976], in fact, there often appeared to have more than one detectable Pi2 pulsations associated with every substorm [e.g., Rostoker, 1968].…”

mentioning

confidence: 99%

Evaluation of low‐latitude Pi2 pulsations as indicators of substorm onset using Polar ultraviolet imagery

Liou¹,

Meng²,

Newell³

et al. 2000

J. Geophys. Res.

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Abstract. Impulsive Pi2 pulsations have long been recognized as one of the key signatures of magnetic activity during substorm periods due to their wide observable range both in latitudes and longitudes. It is well documented that there is usually more than one Pi2 wave burst associated with a substorm and only one of them corresponds to the onset of the substorm. This observational fact poses obstacles to determining substorm onsets with Pi2 signals. Although the Pi2 have become one of the most popular indicators for substorm onsets, the reliability of using the Pi2 in this fashion has not been seriously investigated. In this paper we address this question with a statistical approach by using ,- This result suggests that Pi2 may not be as a good indicator of the substorm onset as it was thought to be. Interestingly, it is always possible to associate Pi2 pulsations with some forms of auroral intensification. When compared to auroral breakups, Pi2 onsets are subject to a small delay of I -3 min, with a peak around 1 min. Delays of Pi2 onsets are revealed to be a function of location relative to auroral breakup. This dependence is found to be consistent with the time of flight for a fast-mode wave, in a plasmapause cavity mode model, propagating in the magnetosphere.•

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mentioning

confidence: 99%

Evaluation of low‐latitude Pi2 pulsations as indicators of substorm onset using Polar ultraviolet imagery

Liou¹,

Meng²,

Newell³

et al. 2000

J. Geophys. Res.

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“…Continuous pulsations are quasiperiodic oscillations whose occurrences vary during the day. For example, Pc1 pulsations are predominant during dayhours (in local time) at high latitudes and during nighthours at low latitudes (Saito 1969;Bortnik et al 2007). Moreover, even during periods of occurence, they often appear as pearls on magnetograms with alternating periods of high and low signal-to-noise ratios (Jun et al 2014).…”

Section: Pulsationsmentioning

confidence: 99%

“…Among transient events at periods lower than 200 s, there are Pc5 geomagnetic pulsations that have periods up to 500-600 s (Saito 1969). Geomagnetic storms are also low-frequency sources of induction.…”

Section: Other Transient Applicationsmentioning

confidence: 99%

“…High-frequency (HF) signals (with frequencies over 1 Hz) are mainly due to lightning activity, and the associated EM waves conveyed in the waveguide made of the ionosphere and the conductive earth. The other main class of EM waves is due to the interaction of the solar wind with the Earth's magnetic field, and this produces magnetohydrodynamic waves that are transmitted in the atmosphere through the ionosphere from the magnetosphere (Saito 1969;McPherson 2005).…”

Section: Introductionmentioning

confidence: 99%

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New application of wavelets in magnetotelluric data processing: reducing impedance bias

2016

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Magnetotelluric (MT) data consist of the sum of several types of natural sources including transient and quasiperiodic signals and noise sources (instrumental, anthropogenic) whose nature has to be taken into account in MT data processing. Most processing techniques are based on a Fourier transform of MT time series, and robust statistics at a fixed frequency are used to compute the MT response functions, but only a few take into account the nature of the sources. Moreover, to reduce the influence of noise in the inversion of the response functions, one often sets up another MT station called a remote station. However, even careful setup of this remote station cannot prevent its failure in some cases. Here, we propose the use of the continuous wavelet transform on magnetotelluric time series to reduce the influence of noise even for single site processing. We use two different types of wavelets, Cauchy and Morlet, according to the shape of observed geomagnetic events. We show that by using wavelet coefficients at clearly identified geomagnetic events, we are able to recover the unbiased response function obtained through robust remote processing algorithms. This makes it possible to process even single station sites and increase the confidence in data interpretation.

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“…They are commonly observed from high latitude in the auroral zone to the magnetic equator on the nightside at the onset of magnetospheric substorms [Saito, 1969], but different models for different latitudes have been proposed [Olson, 1999]. Since Pi2 pulsation occurs at a substorm onset, it is believed that its energy is released as the magnetic field of the near-Earth magnetotail suddenly changes from a tail-like configuration to a dipole-like configuration.…”

Section: Introductionmentioning

confidence: 99%

Pi2 pulsations in a small and strongly asymmetric plasmasphere

Kim¹

2005

J. Geophys. Res.

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[1] We study a Pi2 pulsation that occurred at $1520 UT on 29 August 2000. This Pi2 event was observed at ground stations from high (geomagnetic latitude $65°) to low latitudes ($17°) near midnight with an identical waveform and oscillated with a frequency of $11 mHz. During the event, a global image of the plasmasphere was obtained from the IMAGE satellite, and the location of the plasmapause was clearly identified. The plasmasphere was small and strongly asymmetric in longitude. The plasmapause was located at L $ 2.4, 3.8, and 3.3 near the duskside, midnight, and the dawnside, respectively. Using a magnetospheric mass density model constructed from the IMAGE satellite data and ground-based data, we examine whether the Pi2 pulsation observed inside the plasmasphere can be explained by a plasmaspheric cavity mode. We find that the frequency of 11 mHz is too low for a cavity mode in the plasmasphere. Thus the plasmaspheric cavity mode is not an appropriate model for our Pi2 event observed at midlatitudes and low latitudes. We discuss what determines its period and waveform inside such a small and asymmetric plasmasphere.Citation:

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Geomagnetic pulsations

Cited by 436 publications

References 122 publications

Evaluation of low‐latitude Pi2 pulsations as indicators of substorm onset using Polar ultraviolet imagery

Evaluation of low‐latitude Pi2 pulsations as indicators of substorm onset using Polar ultraviolet imagery

New application of wavelets in magnetotelluric data processing: reducing impedance bias

Pi2 pulsations in a small and strongly asymmetric plasmasphere

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