Highly relativistic electrons (3–10 MeV) at times are observed to populate the earth's magnetosphere near the geostationary orbit (r ∼ 6.6 RE). Electron fluxes and energy spectra are shown which were measured by two high‐energy electron sensor systems at 6.6 RE from 1979 to the present. Large, persistent increases in this electron population were found to be relatively infrequent and sporadic in 1979–1981 around solar maximum. This situation contrasts markedly with the frequent occurrence of very large flux increases from late 1981 to the present. Furthermore, in this latter period, which constitutes the approach to solar minimum, it is observed that the highly relativistic electrons occur with a relatively regular 27‐day periodicity and are well associated with the reestablished solar wind stream structures. On the basis of an examination of long‐term flux variations as a function of solar rotation we find strongly periodic behavior beginning with Bartels rotation ∼2035. Through a superposed epoch analysis technique we study empirical particle lifetimes as a function of particle energy. An energetic electron enhancement typically rises on a 2‐ to 3‐day time scale and decays on a 3‐ to 4‐day time scale at essentially all energies above ∼3 MeV. The present analysis suggests either that a regular pulsing by high‐speed solar wind streams makes the magnetosphere an efficient relativistic electron accelerator or else that the Jovian magnetosphere is a recurrent source of a significant electron population in the outer terrestrial magnetosphere.

In a follow‐up study to the earlier work of Webber and Higbie (2003) on 10Be production in the Earth's atmosphere by cosmic rays, we have calculated the atmospheric production of the cosmogenic isotopes 3H, 7Be, 10Be, and 36Cl using the FLUKA Monte Carlo code. This new calculation of atmospheric yields of these isotopes is based on 107 vertically incident protons at each of 24 logarithmically spaced energies from 10 MeV to 10 GeV, 102 times the number used in the earlier calculation, along with the latest cross sections. This permits a study of the production due to solar cosmic rays as well as galactic cosmic rays at lower energies where isotope production is a very sensitive function of energy. Solar cosmic ray spectra are reevaluated for all of the major events occurring since 1956. In terms of yearly production of 10Be, only the February 1956 solar event makes a major contribution. For 36Cl these yearly SCR production contributions are 2–5 times larger depending on the solar cosmic ray energy spectra. We have determined the yearly production of 10Be, 36Cl, and other cosmogenic isotopes above 65° geomagnetic latitude for the time period 1940–2006 covering six solar 11‐year (a) cycles. The average peak‐to‐peak 11‐a amplitude of this yearly production is 1.77. The effects of latitudinal mixing alter these direct polar production values considerably, giving an average peak‐to‐peak 11‐a amplitude of 1.48 for the global average production.

[1] Recent work by McCracken [2001] shows that 10 Be production rates by cosmic rays on the polar plateau are little affected by geomagnetic field changes in the last few hundred years. Also, the 10 Be observed in ice cores on the polar plateau probably originated at high latitudes and precipitated to the Earth in about 1 year, according to McCracken. As a result of this assumption, ice core records of 10 Be concentration extending back several hundred years, including the Maunder minimum, have the potential to study the solar modulation of cosmic rays on a time scale extending back several hundred years. These ice core records indicate that the Be production in the atmosphere using new data related to the interstellar cosmic ray spectrum and the effects of solar modulation as determined from Voyager spacecraft data in the outer heliosphere. We have used the FLUKA Monte Carlo program along with new cross-section data to calculate the production of nucleons and 10 Be nuclei in the atmosphere. These calculations show that 10 Be temporal variations are sensitive indicators of low-energy solar modulation. Our calculations of 10 Be production are able to reproduce well the factor $1.5-2.0 change in 10 Be observed in the ice core data as a result of the 11-year solar modulation. We are also able to show that starting as recently as the sunspot minimum of 1954, the cosmic ray intensity at the Earth was higher than it was during more recent minima. The cosmic ray intensity during these minima time periods represents the residual modulation between the Earth and interstellar space. The 10 Be measurements are consistant with the fact that given the interstellar cosmic ray spectrum used in this analysis, this residual modulation was small or zero at the time of the Maunder minimum. Citation: Webber, W. R., and P. R. Higbie, Production of cosmogenic Be nuclei in the Earth's atmosphere by cosmic rays: Its dependence on solar modulation and the interstellar cosmic ray spectrum,

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At 0027 UT on July 29, 1977 an interplanetary shock wave arrived at the front side magnetosphere and triggered substantial geomagnetic activity throughout the day. The propagation of the resulting MHD wave within the magnetosphere has been studied with measurements from a total of six satellites in (or near) the geostationary orbit and the interplanetary space and groundbased magnetometers. At the time of the SSC the European spacecraft GEOS 1 was located at R --6.7 RE and 1300 LT providing accurate reference measurements for the hydromagnetic impulse spreading out in the magnetosphere. The signal transmission from the front side magnetopause down to the equatorial ionosphere corresponded to an average wave speed of v = 600 km/s. A propagation speed of v = 910 km/s was found for the signal transmission in the outer magnetosphere in and beyond the geostationary altitude.The results compared reasonably well with model calculations.sphere was strongly compressed. The sudden increase in solar wind pressure pushed the subsolar point from an estimated preshock location at R0 = 7.8 RE [Knott et al., 1982] down to R0 = 6.3 RE and triggered substantial magnetic activity with repeated occurrences of major substorms. The SSC event occurred after a quiet period of several days in which Kp was equal to or smaller than 1 +.The focus of this paper is on the immediate effects of the shock arrival on the state of the magnetosphere as observed by energetic particle distributions and magnetic field signatures. The propagation of these effects throughout the magnetosphere is determined from ground-based magnetograms, particles, and field data from five satellites in and near the geostationary altitude and one spacecraft in the interplanetary region. INSTRUMENTATIONThe present analysis is based mainly on energetic particle measurements obtained from a set of similar instruments flown on the synchronous satellites ATS 6, 1976-059, 1977-007, and on the elliptical ESA spacecraft GEOS 1. Instrumental details of the various particle spectrometers are given by Fritz and Cessna [1975] for ATS 6, Higbie et al. [1978], and Baker et al. [1979a, b] for the satellites 1976-059 and 1977-007 and by Wilken et al. [1977] for GEOS 1. In addition, magnetic field and solar wind data are used from GEOS 1 and IMP 8. The instrumentation available for this study, the energy coverage for ions and electrons, and the local time positions of the various satellites at the time of the SCC are summarized in Table 1.The different particle spectrometers employed on the various satellites use essentially the same detection techniques. Electron/ion discrimination is achieved by combining simple broom magnets or more sophisticated magnetic spectrometers with solid state detectors. Significant differences, however, exist in the overall measuring geometry resulting from the principle used for the spacecraft attitude 5901