Measurements from the MASS instrument on the WIND spacecraft from late Dec. 94 through Aug. 95 are reported for 20Ne, 16O, and 4He. The average 4He/20Ne density ratio is 566±87 with considerable variability. The average 16O/20Ne density ratio is 8.0±0.6 and is independent, within experimental uncertainty, of solar wind speed. The 20Ne/4He and 16O/4He temperature ratios at the lowest solar wind speeds are consistent with unity, increasing with increasing speed to values exceeding that expected from mass proportionality. 20Ne, 16O, and 4He distribution functions exhibit high energy tails which are well‐fit by a kappa function.

Abstract. The Charge and Mass Magnetospheric Ion Composition Experiment(CAMMICE) on board the Polar spacecraft observed 75 energetic particle events in 1996 while the satellite was at apogee. All of these events were associated with a decrease in the magnitude of the local magnetic field measured by the Magnetic Field Experiment (MFE) on Polar. These new events showed several unusual features: (1) They were detected in the dayside polar cusp near the apogee of Polar with about 79% of the total events in the afternoonside and 21% in the morningside; (2) an individual event could last for hours; (3) the measured helium ion had energies up to and many times in excess of 2.4 MeV; (4) the intensity of 1-200 KeV/e helium was anticorrelated with the magnitude of the local geomagnetic field but correlated with the turbulent magnetic energy density; (5) the events were associated with an enhancement of the low-frequency magnetic noise, the spectrum of which typically extends from a few hertz to a few hundreds of hertz as measured by the Plasma Wave Instrument (PWI) on Polar; and (6) a seasonal variation was found for the occurrence rate of the events with a maximum in September. These characterized a new phenomenon which we are calling cusp energetic particle (CEP) events. The observed high charge state of helium and oxygen ions in the CEP events indicates a solar source for these particles. Furthermore, the measured 0.52-1.15 MeV helium flux was proportional to the difference between the maximum and the minimum magnetic field in the event. A possible explanation is that the energetic helium ions are energized from lower energy helium by a local acceleration mechanism associated with the high-altitude dayside cusp. These observations represent a potential discovery of a major acceleration region of the magnetosphere.

Abstract. New, coordinated measurements from the International Solar-TerrestrialPhysics (ISTP) constellation of spacecraft are presented to show the causes and effects of recurrent geomagnetic activity during recent solar minimum conditions. It is found using WIND and POLAR data that even for modest geomagnetic storms, relativistic electron fluxes are strongly and rapidly enhanced within the outer radiation zone of the Earth' s magnetosphere. Solar wind data are utilized to identify the drivers of magnetospheric acceleration processes. Yohkoh solar soft X-ray data are also used to identify the solar coronal holes that produce the high-speed solar wind streams which, in turn, cause the recurrent geomagnetic activity. It is concluded that even during extremely quiet solar conditions (sunspot minimum) there are discernible coronal holes and resultant solar wind streams which can produce intense magnetospheric particle acceleration. As a practical consequence of this Sun-Earth connection, it is noted that a long-lasting E> 1MeV electron event in late March 1996 appears to have contributed significantly to a major spacecraft (Anik E 1) operational failure.

We have studied the transport and loss of ions in the Earth's quiet time ring current, comparing the standard radial diffusion model developed for the higher‐energy radiation belt particles with measurements of the lower‐energy ring current ions. We compiled a data set with full local time coverage from the quietest days seen by the AMPTE/CCE/CHEM instrument in near‐equatorial orbit at L=2‐9 RE. This data set provides, for the first time, ionic composition information in an energy range that includes the bulk of the ring current energy density, 1‐300 keV/e. Protons were found to dominate the quiet time energy density at all altitudes, peaking near L∼4 at 60 keV cm−3, with much smaller contributions from O+ (1‐10%), He+ (1‐5%), and He++ (<1%). The proton densities were azimuthally symmetric excepting a small dawn‐dusk distortion caused by the cross‐tail electric field, and a plasma sheet contribution for L>6 near midnight. Thus the standard radial diffusion model, which incorporates an outer source boundary at 7.5 RE from the Earth, and diffuses ions earthward while undergoing charge exchange and Coulomb energy loss, should fit the data. We improved on previously used model loss processes by incorporating the latest atomic physics cross sections from the literature, updating the last survey done 15 years ago. We also included the effects of finite electron temperature on Coulomb drag. A χ² minimization procedure was used to fit the amplitudes of the standard electric radial diffusion coefficient, giving DLLE = 5.8 × 10−11 RE²/s. Yet the model was unable to fit the data (to within a factor of 10) over 50% of the energy and radial ranges of the data set, particularly at L<4 or E<30 keV. Assuming that the loss terms in the model are correct, the data can be inverted to extract a radial diffusion coefficient that had nearly constant amplitude from 2‐7 RE. This suggests that another transport mechanism is operating in the ring current region, which is strongest at smaller radial distances. We speculate that fluctuating ionospheric electric fields may be the source of this additional diffusion.

[1] From a study of the 4 May 1998 storm event, Chang et al. [2001] (hereinafter referred to as CETAL01) suggested that ''ions are accelerated at the quasi-parallel bow shock to energies as high as 1 MeV and subsequently transported into the magnetosheath during this event'' and mentioned that ''This is confirmed by a comparison of energetic ion fluxes simultaneously measured in the magnetosheath and at the quasi-parallel bow shock when both regions are likely connected by the magnetic field lines'' (see their Abstract). After an inspection of the measured energetic ion data, however, one finds that CETAL01 have misplotted the observed ion energy spectrum in the ''magnetosheath'' (near the cusp) to lower energy which brings it in closer agreement to the flux measured near the quasi-parallel bow shock, making their analysis suspect. In fact, simultaneous measurements at this time indicate that (1) the energetic ion flux near the cusp was about one order of magnitude higher than that near the quasi-parallel bow shock, (2) the energetic ion time signatures were seen first near the cusp then near the bow shock, and (3) the energetic ion flux observed near the bow shock was independent of bow shock geometry. Each of these three facts is sufficient to demonstrate that the quasi-parallel bow shock was not the main source of the energetic ions near the cusp during this event.[2] CETAL01 stated that ''A comparison of Interball and Polar ion spectra can potentially falsify our bow shock source hypothesis and is now the focus of our analysis.'' In Figure 11 of CETAL01, accordingly, they compared the energetic ion flux measured by Interball near the quasiparallel bow shock with that measured by Polar near the cusp during the interval 1101 -1142 UT on 4 May 1998, where their Polar/CEPPAD energetic ion data (open circles in their Figure 11) were taken only from the ion sensor that was looking 90°from the Polar spin axis. Our Figure 1 replots the Interball data (stars) and the Polar/CEPPAD data (open squares) for the same time interval. Comparing Figure 11 of CETAL01 to our Figure 1, we find that they have misplotted the CEPPAD ion energy spectrum near the cusp to the lower energies which reduces the difference between Interball and Polar ion fluxes. A closer inspection of their Figure 11 suggests that for each energy interval (channel) near the cusp they used the lower energy threshold to represent it without taking into account the effective energy passband [McKinnon and Fritz, 1976] of the steep energy spectrum, and the resulting energy spectrum near the cusp shown in their Figure 11 is thus lower than the actually observed spectrum as shown in our Figure 1.[3] This is not the only case where CETAL01 misplotted the observed ion energy spectrum around the cusp to lower than the actually observed spectrum, for in an earlier paper, Chang et al. [1998] (hereinafter referred to as CETAL98) misplotted the MICS (Magnetospheric Ion Composition Sensor) lower energy limit from 1 keV/e to 0.6 keV/e which brought the cusp fluxes int...