Magnetic pulsation Pi2 as a sensitive indicator of magnetospheric substorm

Saito, Takao; Yumoto, K.; Koyama, Yukinobu

doi:10.1016/0032-0633(76)90120-3

Cited by 100 publications

(59 citation statements)

References 16 publications

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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]. Current consensus, as given by Rostoker et al [1980], is that in a series of Pi2 wave trains only one coincides (within +1 min) with the onset of the substorm and the rest correspond to auroral intensifications.…”

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confidence: 84%

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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confidence: 84%

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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“…irregularly shaped 7-25 mHz waves referred to as Pi2s are clearly linked to substorm activity (e.g. Saito et al, 1976).…”

Section: Discussionmentioning

confidence: 99%

Empirically modelled Pc3 activity based on solar wind parameters

et al. 2010

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Abstract. It is known that under certain solar wind (SW)/interplanetary magnetic field (IMF) conditions (e.g. high SW speed, low cone angle) the occurrence of groundlevel Pc3-4 pulsations is more likely. In this paper we demonstrate that in the event of anomalously low SW particle density, Pc3 activity is extremely low regardless of otherwise favourable SW speed and cone angle. We re-investigate the SW control of Pc3 pulsation activity through a statistical analysis and two empirical models with emphasis on the influence of SW density on Pc3 activity. We utilise SW and IMF measurements from the OMNI project and groundbased magnetometer measurements from the MM100 array to relate SW and IMF measurements to the occurrence of Pc3 activity. Multiple linear regression and artificial neural network models are used in iterative processes in order to identify sets of SW-based input parameters, which optimally reproduce a set of Pc3 activity data. The inclusion of SW density in the parameter set significantly improves the models. Not only the density itself, but other density related parameters, such as the dynamic pressure of the SW, or the standoff distance of the magnetopause work equally well in the model. The disappearance of Pc3s during lowdensity events can have at least four reasons according to the existing upstream wave theory: 1. Pausing the ion-cyclotron resonance that generates the upstream ultra low frequency waves in the absence of protons, 2. Weakening of the bow shock that implies less efficient reflection, 3. The SW becomes sub-Alfvénic and hence it is not able to sweep back the waves propagating upstream with the Alfvén-speed, and 4. The increase of the standoff distance of the magnetopause (and of the bow shock). Although the models cannot account Correspondence to: B. Heilig (heilig@elgi.hu) for the lack of Pc3s during intervals when the SW density is extremely low, the resulting sets of optimal model inputs support the generation of mid latitude Pc3 activity predominantly through upstream waves.

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“…This process can be implemented in real time to identify Pi2 pulsations, and consequently substorm onsets and enhancements, as they occur. Many years ago Saito et al (1976) proposed that by continuously monitoring Pi2 pulsations from three low-latitude ground stations evenly spaced in longitude, the onset of most substorms could be identi®ed. Although this suggestion had signi®cant merit, the technology at the time was not adequate to implement easily the idea in practice.…”

Section: Applicationsmentioning

confidence: 99%

“…frequency band 6±25 mHz, oscillations of the geomagnetic ®eld which occur at the time of magnetospheric substorm onsets and intensi®cations. Two decades ago, Saito et al (1976) pointed out that Pi2 pulsations recorded at low latitudes, where amplitudes typically lie in the range 0.25±2.5 nT, are one of the clearest indicators of substorm onsets. They also pointed out the shortcomings of some of the other methods of identifying substorms.…”

Section: Introductionmentioning

confidence: 99%

Substorm onset identification using neural networks and Pi2 pulsations

Sutcliffe¹

1997

Ann. Geophys.

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Abstract. The pattern recognition capabilities of arti®-cial neural networks (ANNs) have for the ®rst time been used to identify Pi2 pulsations in magnetometer data, which in turn serve as indicators of substorm onsets and intensi®cations. The pulsation spectrum was used as input to the ANN and the network was trained to give an output of +1 for Pi2 signatures and A1 for non-Pi2 signatures. In order to evaluate the degree of success of the neural-network procedure for identifying Pi2 pulsations, the ANN was used to scan a number of data sets and the results compared with visual identi®cation of Pi2 signatures. The ANN performed extremely well with a success rate of approximately 90% for Pi2 identi®ca-tion and a timing accuracy generally within 1 min compared to visual identi®cation. A number of potential applications of the neural-network Pi2 scanning procedure are discussed.

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Magnetic pulsation Pi2 as a sensitive indicator of magnetospheric substorm

Cited by 100 publications

References 16 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

Empirically modelled Pc3 activity based on solar wind parameters

Substorm onset identification using neural networks and Pi2 pulsations

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