Automated detection of Pi 2 pulsations using wavelet analysis: 1. Method and an application for substorm monitoring

Nosé, M.; Iwamoto, Toshihiko; Takeda, Masahiko; Kamei, T.; Milling, D. K.; Orr, D.; Singer, H. J.; Worthington, E. William; Sumitomo, Norihiko

doi:10.1186/bf03352169

Cited by 63 publications

(67 citation statements)

References 19 publications

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“…The rate of successful detection of Pi2 pulsations by the automated detection software is higher than 80% on the nightside, but less than 30% on the dayside (Nosé et al, 1998). In detection of the Pi2s by the software, we did not limit the local time to the nightside.…”

Section: Data Set and Event Selectionmentioning

confidence: 99%

“…The coordinates of these stations are given in The events analyzed in this study were defined from the Kakioka data. Applying an automated detection software developed by Nosé et al (1998) to the Kakioka data, we picked up the onsets of Pi2s at first. Then, one-hour data starting 20 minutes before the onsets for all of the 5 stations were truncated out and saved into a separate file.…”

Section: Data Set and Event Selectionmentioning

confidence: 99%

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Local time dependence of the frequency of Pi2 waves simultaneously observed at 5 low-latitude stations

Han

Iwamoto

Gao³

et al. 2014

Earth Planet Sp

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One-second resolution geomagnetic data from 5 stations located at low-latitudes (i.e., L = 1.2 ∼ 1.6) were used to examine the local time dependence of the dominant frequency of Pi2 pulsations. We analyzed 183 Pi2 events simultaneously recorded at the 5 stations and discussed their possible generation mechanisms. The averaged dominant frequency of the H (horizontal) component is higher on the dawn side than that on the dusk side and shows a peak value in the post-midnight at around 03 LT, which confirms the LT dependence previously suggested from single station data (i.e., non-simultaneous observation). However, some of the events have no LT dependence. For the events which show the LT dependence at low-latitudes, we infer that the cavity resonance mode is a plausible generation mechanism, but we do not rule out the possibility of the plasmaspheric surface wave mode which has also been suggested. For the events having a common frequency between the eastern and western stations, we suggest the cavity resonance mode to be the mechanism. The averaged dominant frequency of the D component does not show any clear LT dependence, and only about 20% of Pi2s have identical frequency for both the H and D components, therefore we suggest that the H and D oscillations of Pi2s are generated from different mechanisms. We also found that the frequency of different parts of a Pi2 pulsation, i.e., the dominant frequency for leading part and trailing part of the pulsation, is different, and the frequency of the trailing part is lower than that of the leading part.

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Section: Data Set and Event Selectionmentioning

confidence: 99%

Section: Data Set and Event Selectionmentioning

confidence: 99%

Local time dependence of the frequency of Pi2 waves simultaneously observed at 5 low-latitude stations

Han

Iwamoto

Gao³

et al. 2014

Earth Planet Sp

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“…In this paper, a discrete wavelet transform (DWT) based upon the Pi2 algorithm outlined by Nose et al (1998) was used to investigate the entire ULF wave spectrum during substorm expansion phase onset. The Meyer wavelet was used for the analysis as it closely resembles the impulsive nature of nightside ULF waves and has excellent timing resolution, and hence is ideal for defining any "onset".…”

Section: Introductionmentioning

confidence: 99%

Using ultra-low frequency waves and their characteristics to diagnose key physics of substorm onset

et al. 2017

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Substorm onset is marked in the ionosphere by the sudden brightening of an existing auroral arc or the creation of a new auroral arc. Also present is the formation of auroral beads, proposed to play a key role in the detonation of the substorm, as well as the development of the large-scale substorm current wedge (SCW), invoked to carry the current diversion. Both these phenomena, auroral beads and the SCW, have been intimately related to ultra-low frequency (ULF) waves of specific frequencies as observed by ground-based magnetometers. We present a case study of the absolute and relative timing of Pi1 and Pi2 ULF wave bands with regard to a small substorm expansion phase onset. We find that there is both a location and frequency dependence for the onset of ULF waves. A clear epicentre is observed in specific wave frequencies concurrent with the brightening of the substorm onset arc and the presence of "auroral beads". At higher and lower wave frequencies, different epicentre patterns are revealed, which we conclude demonstrate different characteristics of the onset process; at higher frequencies, this epicentre may demonstrate phase mixing, and at intermediate and lower frequencies these epicentres are characteristic of auroral beads and cold plasma approximation of the "Tamao travel time" from near-earth neutral line reconnection and formation of the SCW.

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“…A series of studies highlighted the significance of applying wavelet analysis, especially its suitability for multi-point, small-scale disturbances, in the investigation of ULF wave events (e.g., Nosé et al, 1998;Balasis et al, 2012;Xu et al, 2013). Using the wavelet method, with the Morlet mother function, we produce the power spectrum of the magnetic field series for 50 logarithmically spaced frequencies from 20 to 100 MHz (Balasis et al, 2013), and remove the aforementioned margins.…”

Section: Data Processing and Analysis Techniquementioning

confidence: 99%

An initial ULF wave index derived from 2 years of Swarm observations

et al. 2018

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Abstract. The ongoing Swarm satellite mission provides an opportunity for better knowledge of the near-Earth electromagnetic environment. Herein, we use a new methodological approach for the detection and classification of ultra lowfrequency (ULF) wave events observed by Swarm based on an existing time-frequency analysis (TFA) tool and utilizing a state-of-the-art high-resolution magnetic field model and Swarm Level 2 products (i.e., field-aligned currents -FACs -and the Ionospheric Bubble Index -IBI). We present maps of the dependence of ULF wave power with magnetic latitude and magnetic local time (MLT) as well as geographic latitude and longitude from the three satellites at their different locations in low-Earth orbit (LEO) for a period spanning 2 years after the constellation's final configuration. We show that the inclusion of the Swarm single-spacecraft FAC product in our analysis eliminates all the wave activity at high altitudes, which is physically unrealistic. Moreover, we derive a Swarm orbit-by-orbit Pc3 wave (20-100 MHz) index for the topside ionosphere and compare its values with the corresponding variations of solar wind variables and geomagnetic activity indices. This is the first attempt, to our knowledge, to derive a ULF wave index from LEO satellite data. The technique can be potentially used to define a new Level 2 product from the mission, the Swarm ULF wave index, which would be suitable for space weather applications.

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Automated detection of Pi 2 pulsations using wavelet analysis: 1. Method and an application for substorm monitoring

Cited by 63 publications

References 19 publications

Local time dependence of the frequency of Pi2 waves simultaneously observed at 5 low-latitude stations

Local time dependence of the frequency of Pi2 waves simultaneously observed at 5 low-latitude stations

Using ultra-low frequency waves and their characteristics to diagnose key physics of substorm onset

An initial ULF wave index derived from 2 years of Swarm observations

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