[1] Energetic electron and proton fluxes measured by geosynchronous satellites often show sawtooth-like variations during magnetic storms. We examine whether the sawtooth oscillations and relevant magnetospheric-ionospheric disturbances are caused by periodic substorms or driven by a series of enhancements in the solar wind pressure. We show that there are significant differences between periodic substorms and solar wind-induced variations. The energetic fluxes at geosynchronous orbit may increase by orders of magnitude after each onset of periodic substorms and by 10-50% in response to a large solar wind pressure impulse. The sudden increases of the energetic fluxes during periodic substorms show significant time delays of 30-50 min at different longitudes/local times, indicating that the fluxes are injected on the nightside and then drift to the dayside. In contrast, the small flux increases caused by solar wind pressure enhancements occur almost simultaneously at all local times. The periodic substorms always have a strong spectrum peak at 2-3 hours, no matter whether the solar wind pressure and/or IMF have similar spectrum peaks. The nightside magnetospheric magnetic elevation angle shows a large (30-60°) increase at each onset of periodic substorms through dipolarization and a small (<10°) decrease in response to a solar wind pressure impulse. Each cycle of periodic substorms can cause a deviation of 40-60 nT in the midlatitude geomagnetic field; the midlatitude geomagnetic deviations caused by solar wind pressure enhancements are proportional to the square root of the pressure change. The increase of the polar cap index caused by substorms is $4 times that caused by solar wind pressure enhancements. We conclude that the sawtooth-like flux oscillations represent flux injections during periodic substorms and that the period of substorms is determined by the magnetosphere.Citation: Huang, C.-S., G. D. Reeves, G. Le, and K. Yumoto (2005), Are sawtooth oscillations of energetic plasma particle fluxes caused by periodic substorms or driven by solar wind pressure enhancements?,

in the east Asian sector. We have used the ionospheric sounding observations at Ho Chi Minh City (Vietnam) and Okinawa, Yamagawa, Kokubunji, and Wakkanai (Japan) in the present investigations. Also, GPS observations in the east Asian sector (several longitude zones) have been used to study the effect in the F region during the intense geomagnetic disturbances. The ion density versus latitudinal variations obtained by the DMSP F15 satellite orbiting at about 800 km altitude in the east Asian sector and the magnetic field data obtained at several stations in the Japanese meridian are also presented. Several important features from these observations in both the sectors during this extended period of intense geomagnetic disturbances are presented. The east Asian sector showed very pronounced effects during the second superstorm, which was preceded by two storm enhancements. It should be mentioned that around the beginning of the night on 10 November, ionospheric irregularities propagating from higher midlatitude region to low-latitude region were observed in the Japanese sector. The most intense geomagnetic field H component in that sector was observed on 10 November at L = 2.8, indicating that the auroral oval and the heating got further to low latitudes and the ionospheric irregularities observed in the Japanese sector on this night are midlatitude ionospheric disturbances associated with the second superstorm. The absence of ionospheric irregularities in the Japanese sector during the 8 November superstorm suggests that the magnetosphere-ionosphere system was possibly preconditioned (primed) when the second interplanetary structure impacted the magnetosphere.

This paper reports latitudinal and longitudinal movements of four low-latitude auroras observed by a meridian scanning photometer and an all-sky TV camera at Moshiri and Rikubetsu (L = 1.6) in Japan during magnetic storms. It is observationally found that the low-latitude auroras occur in the region of L -2 even during moderate magnetic storms. The auroras which are characterized by 6300-A emissions of several kR are also found to take place associated with magnetospheric substorm activity during the maximum phase of magnetic storms. The auroras and associated current systems inferred from ground magnetic field fluctuations tend to expand from midnight toward both the dawnside and the duskside. It is suggested that the observed low-latitude auroras are excited by precipitating low-energy electrons originated in the plasmasphere. We discuss generation mechanisms of these electrons based on the observations.

[1] We report ground and satellite observations of unique low-latitude red auroras that appear at the initial phase of geomagnetic storms. For two events on 21 October 2001, and 6 April 2000, the low-latitude red auroras appeared at~45 MLAT (L $ 2) $ 1.5 h after the storm sudden commencement in the postmidnight sector in Japan. Comprehensive satellite data were available for the former event. The energetic neutral atom images obtained by the Imager for Magnetopause-to-Aurora Global Exploration satellite show rapid enhancement of ring current hydrogen and oxygen fluxes at radial distances of $ 2-8 R E after the storm sudden commencement and associated with several storm-time substorms. The hydrogen ring-current enhancement occurred particularly in the postmidnight sector where the red aurora was observed. The timing of oxygen flux enhancement associated with a storm-time substorm coincided with the red aurora appearance. This rapid and significant enhancement of energetic neutral atom flux was also confirmed by energetic ion data obtained by the NOAA/POES-16 satellite. Extreme ultraviolet plasmaspheric images obtained by Magnetopause-to-Aurora Global Exploration indicate that the plasmapause was located at L = 2.3-2.5 in the postmidnight sector during the event, indicating that a spatial overlap occurs between the plasmasphere and the enhanced ring current ions at L $ 2. Based on these observations, we suggest that large energization of high-energy ring-current ions in the postmidnight inner magnetosphere caused the spatial overlap of these ring-current ions with the low-energy plasmaspheric plasmas at L $ 2, producing the low-latitude red auroras at the very beginning of the storms.Citation: Shiokawa, K., Y. Miyoshi, P. C. Brandt, D. S. Evans, H. U. Frey, J. Goldstein, and K. Yumoto (2013), Ground and satellite observations of low-latitude red auroras at the initial phase of magnetic storms,

[1] We have compared two quantities which were simultaneously observed by two different instruments at the same point of the plasmaspheric plume. One quantity is the field-line eigenfrequency, which was obtained by applying the dual-station H-component power ratio method to geomagnetic data obtained from two ground magnetometers (at Tixie and Chokurdakh) of the Circum-pan Pacific Magnetometer Network (CPMN). The other is the He + column abundance obtained by the IMAGE satellite Extreme Ultraviolet Imager (IMAGE/EUV). We used the EUV He + column abundance data mapped to the equatorial footpoint of the field-line whose eigenfrequency we obtained from the ground data. The mapped EUV He + column abundance is roughly proportional to the equatorial density of He + . The result of the IMAGE/EUV analysis showed an increase-then-decrease pattern of the He + column abundance. On the other hand, as a result of analyzing the simultaneously observed ground magnetometer data, we found that the eigenfrequency showed a coherent decrease-then-increase pattern. Since this pattern takes place if the equatorial plasma density along the field line increased and then decreased, these two results are qualitatively consistent. In addition, the H-power ratio showed an offset when either Tixie or Chokurdakh (these stations are longitudinally separated) stayed inside the plume. This feature can be explained if the overall ULF wave power was weaker in the plume than in the surrounding trough. With the above findings, this paper is the first to identify a plume from both the spacecraft image and the ground magnetometer ULF waves.