Observations And Analysis Of The Earth's Magnetosphere By DSP And ClusterⅡ

The magnetosphere is the important region for space environment of the Earth, is also one of the active objects of space physics. On the basis of the observations, some key problems of the magnetospheric physics were analysed, following the inversion and modeling techniques.We analyse the vertical structure of the magnetotail current sheet withir 2011 -2030 UT on 19 August 2001, during which the Clusterâ…¡spacecrafts crossed the current sheet in a quiet time. In the intervals, the current sheet moved slowly, and the value of the AE index was relatively small, about 40-130 nT. In the quiet time, without fast plasma flow and without significant flapping motion, we also directly observed the bifurcated current sheet. Ion density, velocity and temperature, measured by Clusterâ…¡spacecrafts in the current sheet during 2011-2030 UT 19 August 2001 arc discussed. It is shown that ion density was comparatively bigger near the neutral line, presented non-symmetric distribution, but the distribution of temperature was uniform. And it is observed that in the y direction, the proton bulk velocity is opposite on the both sides of the neutral line. Finally we discuss a possible mechanism for the bifurcated current sheet in a quiet time, which is nonlinear evolution of the lower-hybrid drift instability in the current sheet. These may be important for perfecting the formation mechanism of current sheet bifurcation.We analyze the magnetic structures in the near-tail at X_GSM=-17.5 R_E on September 19, 2003 by Clusterâ…¡. During the course of a substorm event, the earthward propagating plasmoid and flux ropes in the near-tail are observed. The earthward propagating plasmoid is associated with the bipolar B_z and B_y signatures. The two flux ropes are embedded within the earthward plasma flows, which might be referred to the population as "BBF-type" flux ropes. The first flux rope diameter is about 0.7 R_E and duration based upon the B_z signature is -20 s, while the second one diameter is about 1.4 R_E and duration is -30 s. The earthward propagating plasmoid and flux ropes could have influence upon the dipolarization and injection in inner magnetosphere.The Clusterâ…¡observations of earthward propagating plasmoid and flux ropes can be interpreted as strong evidence for multiple X-lines. Our observations are consistent with that multiple plasmoids or flux ropes are formed repeatedly and ejected tailward in the course of geomagnetically active time. We present observations of a substorm on 13 March 2008 by THEMIS in the neartail during the plasma sheet (PS) expansion evidenced by increase in the plasma density and temperature. The main features of the event are: (1) The cross-tail current reduction or disruption (CD) initiates in the near-Earth tail at X--8.0 R_E and Y--2.0 R_E, which is marked by a sharp drop of |B_x| with sharp increases in the plasma density and temperature, manifesting a rapid expansion of the local plasma sheet. During the course of the PS expansion, the progression speed of the CD is -48 km·s^-1 in tailward direction and -35 km·s^-1 in azimuthal direction. (2) In the inner edge of the plasma sheet, the slow flux pileup is observed. The evident magnetic flux pileup characterized by continuous enhancement of B_z and B_y with the trend of reduction of the plasma density, the plasma pressure P_th and p is observed in the flow brake region. And, the tailward CD is also passing across the flow brake region. In short, the dipolarization in the inner edge of the plasma sheet may mainly be attributed to CD, while the tailward progression of dipolarization in the flow brake region may mainly be attributed to magnetic flux pileup. (3) A sharp decrease in the magnitude of B_x prior to the substorm expansion onset is difficult to explain as part of the evolution of the CD. The rapid change in the magnetic field topology may be caused by magnetic reconnection in mid-tail (20-30 R_E). Tail reconnection before substorm expansion onset can lead to a sudden change of the near-Earth configuration, which may lead to instabilities in this region then trigger the CD.We present Clusterâ…¡observations of the dusk-side magnetosheath (MSH) during the storm main phase on 20 November 2003, which was associated with the passage of a large magnetic cloud past the Earth. During the interval, the B_z of magnetic field in the magnetosheath was observed to be about-60 nT, which is basically consistent with the one observed by ACE. And, ion flow velocity in the magnetosheath has a strong dependence on the magnetosheath magnetic field orientation. The IMF electric field E_y in the magnetosheath is -50 mV/m. These extreme field and flows in the magnetosheath drove the secondary geomagnetic storm to date in the solar cycle 23 with a Dst minimum of -472 nT. The ion number density in the magnetosheath is lower than the magnetospheric in our study, which is cause by the lower ion number density in solar wind when a large magnetic cloud past the Earth. The number densities of H⁺, He⁺ and He⁺⁺ with an energy of 1-10 keV in the magnetosheath are dependent on the density of solar wind in the magnetosheath. The magnetopause is strongly compressed for the extremely large southward magnetic field. The abundant energetic oxygen ions with an energy of 1-10 keV cross the magnetopause into the magnetosheath, because of their finite gyroradius (>1000 km), provided the MSH convection and magnetic field orientation are taken accordingly into consideration. This is the indication of the magnetospheric response to the extreme IMF condition. These may be important for us to more understand the large geomagnetic storm.We present energetic neutral atom (ENA) images in the energy range 45 to 50 keV for H and 92 to 138 keV for O measured by the Neutral Atom De(?)ector Unit (NUADU) onboard Double Star TC-2 during a geomagnetic storm on 8 May 2005. We compare the ion fluxes deduced from inversion of the NUADU image with those calculated using the Comprehensive Ring Current Model (CRCM). This comparison shows that the two approaches are consistent when used to derive the configuration of the corresponding global ion distribution and the peak ion fluxes. The deduced peak ion flux is located in the premidnight sector at 1540 UT, while the deduced ion peak flux is located in the midnight sector at 1610 UT. There are strong ion fluxes in the region between L=2 and L = 4 which form a closed loop configuration. The ion peak flux is about 2.2×10⁵s^-1cm^-2sr^-1keV^-1. The deduced ion distribution agrees well with the NUADU measurement. The agreement between the inverted ion distributions and the CRCM results give us confidence in applying our ENA imaging and modeling techniques to the study of the evolution of the inner magnetosphere plasma distribution and the global dynamics of the ring current during magnetic storms.