Global mode of Pi2 waves in the equatorial region - Difference of Pi2 mode between high and equatorial latitudes.

Kitamura, Teitaro; Saka, O.; Shimoizumi, M.; Tachihara, H.; Oguti, Takasi; Araki, Tohru; Sato, Natsuo; Ishitsuka, Mutumi; Veliz, O.; Nyobe, J. B.

doi:10.5636/jgg.40.621

Cited by 44 publications

(33 citation statements)

References 17 publications

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“…This is consistent with the result of Kitamura et al (1988) and Nosé et al (2003). From m≈0 and result 4, we think that these Pi2 pulsations are likely to be caused by the global plasmaspheric cavity mode.…”

Section: Discussionsupporting

confidence: 81%

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Longitudinal dependence of characteristics of low-latitude Pi2 pulsations observed at Kakioka and Hermanus

2006

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We statistically investigated longitudinal dependence of characteristics of low-latitude Pi2 pulsations to find the longitudinal structure of the plasmaspheric cavity mode. We used the geomagnetic field data from two ground stations, Kakioka (27.2• geomagnetic latitude, 208.5• geomagnetic longitude) and Hermanus (−33.9• geomagnetic latitude, 82.2• geomagnetic longitude), and auroral image data acquired by the ultraviolet imager onboard the Polar satellite for the period of December 4, 1996 to March 3, 1997. Our findings include the following: (1) Pi2 amplitude is the largest around the magnetic local time of the auroral breakup site and decreases away from it; (2) when a nightside Pi2 pulsation has large amplitude, a dayside Pi2 pulsation can be observed with a similar waveform; (3) Pi2 pulsations generally have no clear phase differences (mean phase difference of 3.3• ) between Kakioka and Hermanus, except for some events; and (4) the phase difference is independent on MLT (difference of magnetic local time between a station and the auroral breakup). These observations suggest that the plasmaspheric cavity mode can be excited globally with a very small value of the azimuthal wave number (m ≈ 0).

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Section: Discussionsupporting

confidence: 81%

“…On the other hand, Kitamura et al (1988) found a very small number of m ( 1) for equatorial and low-latitude (L<1.3) Pi2 pulsations. showed an event of low-latitude (L<1.5) Pi2 pulsation having no phase delay among three local time sectors (0200 MLT, 0700 MLT, and 1500 MLT), suggesting m∼0.…”

Section: Introductionmentioning

confidence: 99%

Longitudinal dependence of characteristics of low-latitude Pi2 pulsations observed at Kakioka and Hermanus

2006

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“…As the delay times between KUJ and other ground stations are between −6 and 5 s, the difference between the ground stations is within 11 s. The oscillations on the ground after the onsets are almost inphase. The small onset time delay and phase delay among the nightside low latitudes are consistent with previous studies (Kitamura et al 1988;Shinohara et al 1997;Nosé et al 2006). Figure 1b shows the filtered H-component at KUJ without a time shift and the P-component data at ETS-VIII with a 42-s positive time shift.…”

Section: Event Examplessupporting

confidence: 77%

Analysis of propagation delays of compressional Pi 2 waves between geosynchronous altitude and low latitudes

et al. 2014

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The propagation of compressional Pi 2 waves in the inner magnetosphere is investigated by analyzing the onset delay times between the ground and the geosynchronous altitude. We use the compressional component (northward) of magnetic data from low-latitude stations and the geosynchronous satellite ETS-VIII (GMLat. = −10.8°, GMLon. = 217.5°). The onset delays are determined by a cross-correlation analysis, and we analyzed the events with high waveform correlations (correlation coefficient greater than 0.75). Some of these high-correlation events have the properties of propagating waves; Pi 2 waveforms at the ground stations and the satellite were synchronized with each other when the data were shifted by onset delays. The results of the statistical analysis show that 87% of the Pi 2 onsets at a ground station (Kuju, GMLat. = 26.13°, GMLon. = 202.96°) were delayed from the Pi 2 onsets at ETS-VIII, and the average of the delay times was 29 sec. This clearly shows Pi 2 onsets (initial perturbations of Pi 2) propagated from the geosynchronous altitude to the low-latitude ground. The delay times tended to be larger around the midnight sector than around the dawn and dusk sectors. These results are consistent with two-dimensional propagation of fast waves estimated by the model of Uozumi et al. (J Geophys Res 114:A11207, 2009). The delay times are nearly identical to the travel time of fast waves from geosynchronous altitude to the low-latitude ground, and the local time variation of the delay shows the azimuthal propagation along the geosynchronous orbit. We conclude that the initial compressional perturbations of Pi 2 waves propagate radially and longitudinally as a fast wave in the inner magnetosphere.

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“…Although the source (or the energy source) of Pi2 is believed to be localized in the magnetotail region (e.g., Uozumi et al 2007;Chi et al 2009;Keiling et al 2014), Pi2 pulsations have been observed in low-latitude and equatorial regions on the dayside ground (e.g., Yanagihara and Shimizu 1966;Kitamura et al 1988;Sutcliffe and Yumoto 1989). The amplitude of dayside Pi2 is enhanced near the magnetic equator, in a way similar to other disturbances that propagate from a source in the magnetosphere (e.g., Yanagihara and Shimizu 1966;Sastry et al 1983;Shinohara et al 1997).…”

Section: Introductionmentioning

confidence: 99%

Solar terminator effects on middle- to low-latitude Pi2 pulsations

et al. 2016

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To clarify the effect of the dawn and dusk terminators on Pi2 pulsations, we statistically analyzed the longitudinal phase and amplitude structures of Pi2 pulsations at middle-to low-latitude stations (GMLat = 5.30°-46.18°) around both the dawn and dusk terminators. Although the H (north-south) component Pi2s were affected by neither the local time (LT) nor the terminator location (at 100 km altitude in the highly conducting E region), some features of the D (east-west) component Pi2s depended on the location of the terminator rather than the LT. The phase reversal of the D component occurred 0.5-1 h after sunrise and 1-2 h before sunset. These phase reversals can be attributed to a change in the contributing currents from field-aligned currents (FACs) on the nightside to the meridional ionospheric currents on the sunlit side of the terminator, and vice versa. The phase reversal of the dawn terminator was more frequent than that of the dusk terminator. The D-to-H amplitude ratio on the dawn side began to increase at sunrise, reaching a peak approximately 2 h after sunrise (the sunward side of the phase reversal region), whereas the ratio on the dusk side reached a peak at sunset (the antisunward side). The dawn-dusk asymmetric features suggest that the magnetic contribution of the nightside FAC relative to the meridional ionospheric current on the dusk side is stronger than that on the dawn side, indicating that the center of Pi2-associated FACs, which probably corresponds to the Pi2 energy source, tends to be shifted duskward on average. Different features and weak sunrise/sunset dependences at the middle-latitude station (Paratunka, GMLat = 46.18°) can be attributed to the larger annual variation in the sunrise/sunset time and a stronger magnetic effect because of closeness from FACs. The D-to-H amplitude ratio decreased with decreasing latitude, suggesting that the azimuthal magnetic field produced by the FACs in darkness and the meridional ionospheric current in sunlight also decreased with decreasing latitude.

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Global mode of Pi2 waves in the equatorial region - Difference of Pi2 mode between high and equatorial latitudes.

Cited by 44 publications

References 17 publications

Longitudinal dependence of characteristics of low-latitude Pi2 pulsations observed at Kakioka and Hermanus

Longitudinal dependence of characteristics of low-latitude Pi2 pulsations observed at Kakioka and Hermanus

Analysis of propagation delays of compressional Pi 2 waves between geosynchronous altitude and low latitudes

Solar terminator effects on middle- to low-latitude Pi2 pulsations

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