Abstract. The advanced energetic particle spectrometer RAPID on board Cluster can provide a complete description of the relevant particle parameters velocity, V , and atomic mass, A, over an energy range from 30 keV up to 1.5 MeV. We present the first measurements taken by RAPID during the commissioning and the early operating phases. The orbit on 14 January 2001, when Cluster was travelling from a perigee near dawn northward across the pole towards an apogee in the solar wind, is used to demonstrate the capabilities of RAPID in investigating a wide variety of particle populations. RAPID, with its unique capability of measuring the complete angular distribution of energetic particles, allows for the simultaneous measurements of local density gradients, as reflected in the anisotropies of 90 • particles and the remote sensing of changes in the distant field line topology, as manifested in the variations of loss cone properties. A detailed discussion of angle-angle plots shows considerable differences in the structure of the boundaries between the open and closed field lines on the nightside fraction of the pass and the magnetopause crossing. The 3 March 2001 encounter of Cluster with an FTE just outside the magnetosphere is used to show the first structural plasma investigations of an FTE by energetic multi-spacecraft observations.Correspondence to: U. Mall (mall@linmpi.mpg.de) Key words. Magnetospheric physics (energetic particles, trapped; magnetopause, cusp and boundary layers; magnetosheath) The instrumentThe RAPID spectrometer (Research with Adaptive Particle Imaging Detectors), described in detail by Wilken et al. (1995), is an advanced particle detector for the analysis of suprathermal plasma distributions in the energy range from 20-400 keV for electrons, 30 keV-1500 keV for hydrogen, and 10 keV/nucleon-1500 keV for heavier ions. Innovative detector concepts, in combination with pinhole acceptance, allow for the measurement of angular distributions over a range of 180 • in the polar angle for electrons and ions. Identification of the ion species is based on a two-dimensional analysis of the particle's velocity and energy. Electrons are identified by the well-known energy-range relationship. Table 1 list the main parameters of the RAPID instrument.The energy signals in RAPID are analyzed in 8 bit ADCs. With a mapping process the 256 channels are reduced to 8 channels in the case of the ion sensor and into 9 channels in the case of the electron sensor. The resulting energy channel limits are listed in Table 2.

A detailed study of energetic (Ep ≳ 0.29 MeV; Ee ≳ 0.22 MeV) proton and electron bursts in the vicinity of the magnetosphere over a 1‐year period (day 270 of 1972 to day 270 of 1973) using the Johns Hopkins University/Applied Physics Laboratory (JHU/APL) experiment on board the near‐circular (∼32 RE by ∼38 RE) orbiting Explorer 47 (Imp 7) satellite has been performed with greater sensitivity (jp ≳ 10−2 cm−2 s−1 sr−1 MeV−1) than has previously been possible at these energies. The results reveal that bursts of electrons and protons at these energies are a semipermanent feature of the near‐earth environment both within and outside the magnetotail with intensities ranging from 10−2 to 104 (cm² s sr MeV)−1 for protons and 0.5 to 5 × 10³ (cm² s sr)−1 for electrons and energies up to 4.5 MeV and >1 MeV for protons and electrons, respectively. The proton energy spectrum is soft and characterized by spectral indices 5 ≲ γ ≲ 7. The bursts are found in and about the magnetosheath, plasma sheet, and magnetotail boundary layer and outside the bow shock; however, they rarely appear at large distances (≳ 10 RE) north or south of the neutral sheet. Dawn‐dusk asymmetries are present in intensity (most intense proton bursts occur in the dusk magnetotail) but not necessarily in frequency of occurrence. Proton bursts are highly anisotropic (typical amplitude C ≳ 1) upstream from the bow shock and in the magnetosheath (moving away from the earth). In the magnetotail, proton anisotropies are somewhat reduced and are directed either toward or away from the earth but with a substantial dawn to dusk component. Electron bursts are anisotropic (and field aligned) only in the upstream solar wind, where differences in the proton and electron anisotropy vectors can exceed 90°. A unique class of ‘impulsive’ bursts has been identified in the dusk magnetotail having intensities of up to 105 (cm² s sr MeV)−1, a duration of 10–30 s, and field‐aligned anisotropies of up to 5 × 104 to 1 (sunward to antisunward ratio) and exhibiting inverse velocity dispersion (i.e., low‐energy protons arrive before higher‐energy ones). No electrons are observed in association with these bursts. The observed bursts are consistent with a nonthermal origin, in association with other magnetospheric phenomena. The implications of the results with regard to the origin of the bursts, acceleration mechanisms, and magnetospheric processes in general are discussed.

Comprehensive energy density studies provide an important measure of the participation of various sources in energization processes and have been relatively rare in the literature. We present a statistical study of the energy density of the near-Earth magnetotail major ions (H +, O +, He ++, He +) during substorm expansion phase and discuss its implications for the solar wind/magnetosphere/ionosphere coupling. Our aim is to examine the relation between auroral activity and the particle energization during substorms through the correlation between the AE indices and the energy density of the major magnetospheric ions. The data we used here were collected by the charge-energy-mass (CHEM) spectrometer on board the AMPTE/CCE satellite in the near-equatorial nightside magnetosphere, at geocentric distances ~7-9 RE. CHEM provided the opportunity to conduct the first statistical study of energy density in the near-Earth magnetotail with multispecies particle data extending into the higher energy range (>_ 20 keV/e). The use of 1-min AE indices in this study should be emphasized, as the use (in previous statistical studies) of the (3-hour) Kp index or of long-time averages of AE indices essentially smoothed out all the information on substorms. Most distinct feature of our study is the excellent correlation of O + energy density with the AE index, in contrast with the remarkably poor He ++ energy density -AE index correlation. Furthermore, we examined the relation of the ion energy density to the electrojet activity during substorm growth phase. The O + energydensity is strongly correlated with the pre-onset A U index, that is the eastward electrojet intensity, which represents the growth phase current system. Our investigation shows that the near-Earth magnetotail is increasingly fed with energetic ionospheric ions during periods of enhanced dissipation of auroral currents. The participation of the ionosphere in the substorm energization processes seems to be closely, air, hough not solely, associated with the solar wind/magnetosphere coupling. That is, the ionosphere influences actively the substorm energization processes by responding to the increased solar wind/magnetosphere coupling as well as to the unloading dissipation of stored energy, with the increased feeding of new material into the magnetosphere.

Energetic (E o • 0.21, 0.29 MeV) proton bursts have been observed simultaneously by the Johns Hopkins University Applied Physics Laboratory experiments on three earth-orbiting (Imp 6, 350 km X 432 RE; Imp 7, 432 RE X 38 RE; Imp 8, 425 RE X 43 RE) spacecraft, separated by several earth radii both inside and outside the earth's magnetosphere over the period October 1972 through August 1974. It is shown that proton bursts are present nearly simultaneously in the vicinity of the outer belt trapping boundary, in the low-latitude magnetotail, in the magnetosheath, and upstream from the bow shock. Large intensity differences (up to 108 ) are seen among the three spacecraft, with the highest fluxes generally observed near the neutral sheet and outside the outer belt and the lowest inside the tail lobes at ]ZsM[ > 10 RE. However, intensity gradients can change sign between successive bursts a few minutes apart, a new or moving source being suggested. Time delays in burst onset from one spacecraft to the nextranging up to 30 min are observed and are attributed to propagation effects from the source to the point of observation. In some cases, particle onsets upstream from the bow shock precede those inside the magnetosphere. The energy spectra for a given burst are shown to be harder outside the magnetosphere than inside, a feature suggesting a rigidity-dependent mechanism for particle escape into the interplanetary medium. Energetic (Ee • 0.22 MeV) electron bursts were generally, but not always, seen to be associated with the protons; intensity differences in the electrons were very large (410 8) between points within the plasma sheet and outside the magnetosphere; a finding reenforcing the suggestion for rigidity dependence in the propagation process. It is suggested that energetic protons and electrons most likely are accelerated inside the plasma sheet and propagate to various regions both inside and outside the magnetosphere.It is our intent in the present study to establish the interrelationship among energetic proton bursts appearing in the magnetosphere, magnetosheath, and upstream solar wind. We will do so by using simultaneous observations from two and sometimes three spacecraft (Imp 6, 7, and 8) separated by large distances in the near-earth environment. Measurements of the proton {ntensities, energy spectra, anisotropies, and time delays are reported, and their implications about the origin are discussed. Complementary measurements of energetic electrons are also shown in some cases, although the morphology of electron bursts is relatively well established. Detailed corre: lation of the proton bursts with magnetic activity will not be attempted here, although it is known to exist. In a forthcoming publication [$arris et al., 1978] we will discuss specific events from closely spaced (•< 10 Rs) spacecraft and address the question of source presence and/or motion and its •elation to the development of the geomagnetic substorm.The events shown in this paper are separated into (1) events which are seen close to the ...

During the interval 2012 March 7-11 the geospace experienced a barrage of intense space weather phenomena including the second largest geomagnetic storm of solar cycle 24 so far. Significant ultra-low-frequency wave enhancements and relativistic-electron dropouts in the radiation belts, as well as strong energetic-electron injection events in the magnetosphere were observed. These phenomena were ultimately associated with two ultra-fast (>2000 km s −1 ) coronal mass ejections (CMEs), linked to two X-class flares launched on early 2012 March 7. Given that both powerful events originated from solar active region NOAA 11429 and their onsets were separated by less than an hour, the analysis of the two events and the determination of solar causes and geospace effects are rather challenging. Using satellite data from a flotilla of solar, heliospheric and magnetospheric missions a synergistic Sun-to-Earth study of diverse observational solar, interplanetary and magnetospheric data sets was performed. It was found that only the second CME was Earth-directed. Using a novel method, we estimated its near-Sun magnetic field at 13 R e to be in the range [0.01, 0.16] G. Steep radial fall-offs of the near-Sun CME magnetic field are required to match the magnetic fields of the corresponding interplanetary CME (ICME) at 1 AU. Perturbed upstream solar-wind conditions, as resulting from the shock associated with the Earth-directed CME, offer a decent description of its kinematics. The magnetospheric compression caused by the arrival at 1 AU of the shock associated with the ICME was a key factor for radiation-belt dynamics.