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It has been known that high-speed solar wind streams associated with coronal holes lead to quasi-periodic substorms that occur approximately every 2˜4 hours. In this paper we examined 222 repetitive substorms that occurred during high-speed stream periods in July through December in 2003 to quantitatively determine a range of energy input from the solar wind into the magnetosphere between two consecutive substorms. For this study, we have used the Akasofu \varepsilon-parameter to time-integrate it for the interval between two consecutive substorms, and have applied this method to the 222 substorms. We find that the average amount of solar wind input energy between two adjacent substorms is 1.28×10^{14}J and about 85% out of the 222 substorms occur after an energy input of 2×10^{13}˜2.3×10^{14}J. Based on these results, we suggest that it is not practical to predict when a substorm will occur after a previous one occurs purely based on the solar wind-magnetosphere energy coupling. We provide discussion on several possible factors that may affect determining substorm onset times during high-speed streams.

We have studied energetic neutral atom (ENA) disturbances during the magnetic storm main phase that occurred on October 3,2001, using the ENA data from the HENA instrument onboard the IMAGE spacecraft. We find that the main phase is characterized by five ENA enhancement events that occurred quasi-periodically. The repetitive ENA enhancements are most significant in the highest energy (138-222 keV) oxygen channel and become less significant for hydrogen and in lower energies. Also they are separated by ~1.2 to ~1.7 hrs, which is well below an average period usually seen for other repetitive injection events.

Ion acoustic solitary wave in a plasma consisting of electrons and ions with an external magnetic field is reinvestigated using the Sagdeev's potential method. Although the Sagdeev potential has a singularity for n

We have carried out a statistical analysis on solar wind dynamic pressure pulses during geomagnetic storms. The Dst index was used to identify 111 geomagnetic storms that occurred in the time interval from 1997 through 2001. We have selected only the events having the minimum Dst value less than --50 nT. In order to identify the pressure impact precisely, we have used the horizontal component data of the magnetic field H (northward) at low latitudes as well as the solar wind pressure data themselves. Our analysis leads to the following results: (1) The enhancement of H due to a pressure pulse tends to be proportional to the magnitude of minimum Dst value; (2) The occurrence frequency of pressure pulses also increases with storm intensity. (3) For about 30% of our storms, the occurrence frequency of pressure pulses is greater than 0.4 #/hr, implying that for those storms the pressure pulses occur more frequently than do periodic substorms with an average substorm duration of 2.5 hrs. In order to understand the origin of these pressure pulses, we have first examined responsible storm drivers. It turns out that 65% of the studied storms are driven by coronal mass ejections (CMEs) while others are associated with corotating interaction regions (6.3%) or Type II bursts (7.2%). Out of the storms that are driven by CMEs, over 70% show that the main phase interval overlaps with the sheath, namely, the region between CME body and the shock, and with the leading region of a CME. This suggests that the origin of the frequent pressure pulses is often due to density fluctuations in the sheath region and the leading edge of the CME body.

In this paper we report some properties of inner magnetospheric structure inferred from the T01s code, one of the latest magnetospheric models by Tsyganenko. We have constructed three average storms representing moderate, strong, and severe intensity storms using 95 actual storms. The three storms are then modelled by the T01s code to examine differences in magnetic structure among them. We find that the magnetic structure of intense storms is strikingly different from the normal structure. First, when the storm intensity is large, the field lines anchored at dayside longitudinal sectors become warped tailward to align to the solar wind direction. This is particularly so for the field lines anchored at the longitudinal sectors from postnoon through dusk. Also while for the moderate storm the equatorial magnetic field near geosynchronous altitude is found to be weakest near midnight sector, this depression region expands into even late afternoon sector during the severe storm. Accordingly the field line curvature radius at the equator in the premidnight geosynchronous region becomes unusually small, reaching down to a value less than 500 km. We attribute this strong depression and the dawn-dusk asymmetry to the combined effect from the enhanced tail current and the westward expansion/rotation of the partial ring current.

Magnetic storms are almost always accompanied with substorms or substorm-like disturbances. Understanding the nature of the storm-time substorm is important for the currently critical issue of the storm-substorm relation. In this work we have done a statistical analysis in a straightforward way to see whether the storm-time substorms are preferably spontaneous or triggered. On the basis of 301 storm-time substorms selected for this work, we have found that the occurrence of about 28% of them was spontaneous while only 6.5% were associated with a clear trigger(s). The rest of the events were mostly associated with complex variations of IMF. The significant percentage for the spontaneous substorms implies that the possibility of finding a storm without a substorm is greatly reduced due to the spontaneous occurrence of the substorm even when the solar wind and IMF condition remains completely steady during the storm time.

The magnetometer is one of the most important payloads of scientific satellites to monitor the near-earth space environment. The electromagnetic variations of the space environment can be observed with the electric and magnetic field measurements. In practice, it is well known that the measurement of magnetic fields needs less technical complexities than that of electric fields in space. Therefore the magnetometer has long been recognized as one of the basic payloads for the scientific satellites. In this paper, we discuss the scientific fluxgate magnetometer which will be on board the KITSAT-3. The main circuit design of the present magnetometer is based on that of KISAT-1 and -2 but its facilities have been re-designed to improve the resolution to about 5nT for scientific purpose. The calibration and noise level test of this circuit have been performed at the laboratory of the Tierra Tecnica company in Japan.

We installed a pair of geomagnetic ground station in Ichon branch of Radio Research Laboratory(Ichon station, N3T.1447,5127.5509) and Kyunghee University(Yongin station, N37.1419, Bl27.0454). We have successfully finished test operation, arid we are now setting up a data base for the real time monitoring of the geomagnetic field. We are also going to have another geomagnetic station for the southward direction at Cheju in summer of 1997. By that time, we will have a set of geomagnetic data base for the near earth solar-terrestrial environment in real time In this paper, we compare and analyze the results of geomagnetic field observation: from our stations, Kakioka observatory, Wind and Geotail satellites when the corona mass ejections(CME) occurred on Dec. 2, 1996.

Solar wind dynamic pressure enhancements are known to cause various types of disturbances to the magnetosphere. In particular, dynamic pressure enhancements may affect the evolution of magnetic storms when they occur during storm times. In this paper, we have investigated the statistical significance and features of dynamic pressure enhancements during magnetic storm times. For the investigation, we have used a total of 91 geomagnetic storms for 2001-2003, for which the Dst minimum (Dst_min) is below -50 nT. Also, we have imposed a set of selection criteria for a pressure enhancement to be considered an event: The main selection criterion is that the pressure increases by ≥50% or ≥3nPa within 30 min and remains to be elevated for 10 min or longer. For our statistical analysis, we define the storm time to be the interval from the main Dst decrease, through Dst_min, to the point where the Dst index recovers by 50%. Our main results are summarized as follows. (i) ~81% of the studied storms indicate at least one event of pressure enhancements. When averaged over all the 91 storms, the occurrence rate is 4.5 pressure enhancement events per storm and 0.15 pressure enhancement events per hour. (ii) The occurrence rate of the pressure enhancements is about three times higher for CME-driven storm times than for CIR-driven storm times. (iii) Only 21.1% of the pressure enhancements show a clear association with an interplanetary shock. (iv) A large number of the pressure enhancement events are accompanied with a simultaneous change of IMF By and/or Bz: For example, 73.5% of the pressure enhancement events are associated with an IMF change of either |∆Bz|>2nT or |∆By|>2nT. This last finding suggests that one should consider possible interplay effects between the simultaneous pressure and IMF changes in many situations.