Geng‐Xiong Chen

Evidence of strong energetic ion acceleration in the near-Earth magnetotail

Until now it is still questionable whether ions are accelerated to energies above 100 keV in the near-Earth current sheet (CS), in the vicinity of a possible near-Earth neutral line. By using 11 years of 3-D energetic ion flux data for protons, helium, and oxygen (~150 keV–1 MeV) from the RAPID instrument on board Cluster 4, we statistically study the energetic ion acceleration by investigating ion anisotropies in the near-Earth magnetotail (−20 RE  150 keV) ions (protons, He+, and O+) tend to become higher as the earthward (tailward) plasma bulk flows (measured by Cluster Ion Spectrometry experiment) become stronger. During such periods the presence of a strong acceleration source tailward (earthward) of Cluster spacecraft (S/C) is confirmed by the hardening energy spectra of the earthward (tailward) energetic ion flows. A good statistical correlation between tailward bulk flow, negative Bz, and the tailward anisotropy of energetic ions indicates that the strong ion acceleration might be related to a near-Earth reconnection, which occurred earthward of the Cluster S/C. The energetic ion anisotropies do not show a clear dependence on the AE index, which may indicate that the acceleration source(s) for the energetic ions could be spatially localized.

Magnetic survey and ChinaGRF 2000

The magnetic survey in China carried out in resent years is briefly introduced. On the basis of the magnetic data at 119 repeat stations, 39 permanent observatories and 20 grid values of the IGRF 2000, the magnetic charts and models of China for 2000, called China Geomagnetic Reference Field 2000 (or ChinaGRF 2000) have been compiled.

Generation of traveling convection vortices and field-aligned currents in the magnetosphere by response to an interplanetary tangential discontinuity

Three-dimensional global magnetohydrodynamic simulations are conducted to study the response of the magnetosheath and the magnetosphere to an interplanetary tangential discontinuity (TD), across which the plasma density increases. A fast mode wave and a transmitted TD are generated in the magnetosheath by the interaction between the interplanetary TD and the bow shock. These waves further propagate and disturb the dayside magnetosphere. The fast mode compressional wave propagates downstream out of the dayside region in about 1 minute. The pressure enhancement associated with the transmitted TD later compresses the magnetopause significantly for several minutes. The generation of traveling convection vortices, shear Alfven waves, and the associated field-aligned currents (FACs) in the dayside magnetosphere by these pressure pulses is identified in the simulation.

Auroral electrojet oval

The auroral electrojet is enhanced in the polar ionosphere associated with charged particle precipitation and field-aligned currents during substorms. In this paper the geometry of the elctrojet is determined by using the ionospheric equivalent current systems for every 5 minutes during March 18 and 19, 1978. The latitudinal and local time shifts of the oval are examined. Possible relationship of the electrojet oval with expansion of the auroral oval and the field-aligned current belts during substorms are discussed. The electrojet oval in the polar region consists of westward and eastward electrojets, varying with AE index. As the magnetic activity increases, the westward electrojet has distinct latitudinal shifts in different local time sectors: it shifts poleward around the midnight (23:00-03:00 MLT), while moves equatorward in the morning sector (03:00-10:00 MLT) and afternoon sector (20:00-23:00 MLT. The eastward electrojet includes two insulated parts: a higher-latitude part around 80° latitude in the nighttime sector (21:00-03:00 MLT) and a lower-latitude part between 60°–70° latitudes in other local time sectors. As AE index increases, the higher-latitude part of the eastward electrojet expands eastward from 03:00 to 08:00 MLT, while the lower-latitude part shows a equatorward shift in the afternoon sector, which is more or less similar to the westward electrojet.

IMF dependence of energetic oxygen and hydrogen ion distributions in the near‐Earth magnetosphere

Energetic ion distributions in the near-Earth plasma sheet can provide important information for understanding the entry of ions into the magnetosphere and their transportation, acceleration, and losses in the near-Earth region. In this study, 11 years of energetic proton and oxygen observations (> similar to 274 keV) from Cluster/Research with Adaptive Particle Imaging Detectors were used to statistically study the energetic ion distributions in the near-Earth region. The dawn-dusk asymmetries of the distributions in three different regions (dayside magnetosphere, near-Earth nightside plasma sheet, and tail plasma sheet) are examined in Northern and Southern Hemispheres. The results show that the energetic ion distributions are influenced by the dawn-dusk interplanetary magnetic field (IMF) direction. The enhancement of ion intensity largely correlates with the location of the magnetic reconnection at the magnetopause. The results imply that substorm-related acceleration processes in the magnetotail are not the only source of energetic ions in the dayside and the near-Earth magnetosphere. Energetic ions delivered through reconnection at the magnetopause significantly affect the energetic ion population in the magnetosphere. We also believe that the influence of the dawn-dusk IMF direction should not be neglected in models of the particle population in the magnetosphere.

Multipoint observations of Pi2 pulsations and correlation with dynamic processes in the near-Earth magnetotail on March 18, 2009

Simultaneous measurements from THEMIS spacecraft, GOES-11 and ground stations (Canadian Array for Realtime Investigations of Magnetic Activity or CARISMA, and 210° magnetic meridian or MM) on March 18, 2009 allow the study of dynamic processes in the near-Earth magnetotail and corresponding Pi2 pulsations on the ground in great detail. Fast earthward flows along with traveling Alfvén waves and fast mode waves in the Pi2 band were observed by three Time History of Events and Macroscale Interactions during Substorms (THEMIS) probes (P3, P4 and P5) in the near-Earth plasmasheet. At the mid- to high-latitude nightside, the CARISMA stations located near the foot points of the three probes recorded Pi2s with two periods, about 80 s after the earthward fast flows observed by the P4 probe. The long-period Pi2 (140–150 s) belongs to the transient response Pi2 (TR Pi2), since the travel time of the Alfvén waves between the plasma sheet and CARISMA stations is very close to half the period of the long-period Pi2. The short-period Pi2 (60–80 s) has the same period band as the perpendicular velocity of the fast flows, which indicates that it may relate to the inertial current caused by periodic braking of the earthward fast flows. The 210° MM stations located at the low-latitude duskside also observed Pi2s with the same start time, waveform and frequency, about ∼120 s after the earthward fast flows. Strong poloidal oscillations are shown by GOES-11 (∼23 MLT) and the compressional component (Bb) is highly correlated with H components of the 210° MM stations, whereas the other two components (Br and Be) are not. These results confirm that the low-latitude Pi2s are generated by cavity mode resonance, which is driven by an impulsive broadband source in the near-Earth magnetotail.

THE LOWEST POSSIBLE LATITUDE OF THE WESTWARD ELECTROJET DURING SEVERELY DISTURBED PERIODS

Abstract. It has been reported that the AE index cannot, at times, adequately monitor the auroral electrojets because as magnetic activity increases, it shifts equatorward from the standard AE stations, resulting in a serious underestimation of the auroral electrojet intensity. To evaluate quantitatively the equatorial shift of the westward electrojet, an extensive database obtained from CANOPUS, Alaska and IMAGE chains of magnetometers are utilized in this study. The data thus assembled enable us to determine how the westward electrojet shifts equatorward with increased magnetic activity. We are particularly interested in the latitude of the center of the westward electrojet during intense magnetic storms. The tendency of equatorward shift is confirmed from this study. However, the peak of the westward electrojet seems to shift only approximately 60° in magnetic latitude, regardless of magnetic activity levels. Therefore the current AE network, which covers as low as about 62°, does not have any serious problems in monitoring the auroral electrojet. The relative location of the westward electrojet with respect to the global auroral image taken from the Polar satellite is also examined. It is found that the center of the westward electrojet does not flow over the brightest auroral region but slightly poleward of it, with less luminous region. It indicates that the electric field is more important in intensifying the auroral electrojet than the ionospheric conductivity.