JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 97, NO. A6, PAGES 8231-8237, JUNE 1, 1992 Absence of Upstream Energetic IonsUnder Turbulent Radial Interplanetary Magnetic Field E. T. Sguus' Applied Physics Laboratory, Johns Hokpins University, Laurel, Maryland G. C. ANAGNOSTOPOULOS Department of ElectricalEngineering, Demokritos University of Thrace,Xanthi, Greece S. M. Kmmais Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland According to Fermi models as applied to the Earth's bow shock energetic particles are accelerated most efficientlyunder radial interplanetary magnetic field (IMF) conditions. In an earlier paper (Sarrisand Krimigis, 1988) we tested the Fermimechanism for cases of radialIMF whenno detectable ambient ener- getic particle fluxes werepresent. We concluded thatthe above mechanism could not account for the ob- servations in the vicinity of the bow shock. In this work we extend the previous testby examining cases observed by the IMP 8 spacecraft where, in addition to the radial IMF, the following particle and field conditions were present: (I) in situ cyclotron-resonant wave activity,(2) a seed energetic particle popula- fion, and O) small (•<25 ø) OBn atthepoints of connection of thespacecraft to the bowshock. Examination of datafrom days 67, 1979, and303, 1980, show that despite the fact that all of the above conditions were satisfied, no ion enhancements (mS0 keV) attributable to the Fermi process couldbe discerned. We con- chde that,even with the addition of criteria much morestringent thanthose applied in all previously pub- lishedupstream events, whichprovided the observational underpinning for the development of the Fermi model, the effects of the Fermi process in accelerating ions to energies greater than--50keV are essentially undetectable (• < 10 -3) in theregion upstream of Earth's bow shock. INTRODUCTION The Fermi theoryfor the diffusiveacceleration of energetic particles by scattering in the environment of shock waveshas been widely applied in a variety of cosmic shock scales, rang- ing from interstellar shocks and supernova envelopes to plan- etary bow shocks [seeBlandford and Eichler, 1987]. In par- ticular, in a large numberof publications basedprimarily on measurements by the ISEE 1 and2 spacecraft, the originof the energetic ions observed upstream from the Earth's bow shock has been explained in termsof the Fermi acceleration model for ions with energies up to ~200 keV [Scholeret al., 1980; lpavich et al., 1981a, b; Eichler, 1981; Terasawa, 1981; Lee, 1982; Skadron and Lee, 1983; Ellison, 1981, 1985; Wibberenz et al., 1985]. However, simultaneous multispacecraft observations inside and outside the magnetosphere duringupstream ion events, in- cluding all the cases cited as the underpinning of the Fermi modelin thatregion[lpavich et al., 1979; Scholer et al., 1979; lpavich et al., 1981b; Skadron and Lee, 1983; Ellison, 1985; Wibberenz et al., 1985], haveshown that the energetic particles 'Permanently at Demokritos University of Thrace, Xanthi, Greece. Copyright 1992by the American Geophysical Union. Paper number 92JA00133. 0148-0227/92/92JA-00133505.00 (E > 50 keV) observed upstream are most likely of magneto- spheric origin. Furthermore, detailed analysis has shown that a number of fundamental predictions of the Fermi model (i.e., energyextent, spectral shape, anisotropies, velocity dispersion, interplanetary magnetic field (IMF) connection times, etc.) were in directdisagreement with the observations, thusraising grave doubts on the viability of the Fermi mechanism as applied to the Earth's bow shock [Sarriset al., 1978;Krimigis and Sarris, 1979; Anagnostopoulos et al., 1986, 1987; Krirnigis et al., 1986; Sarris et al., 1987; Sibecket al., 1987, 1988; Baker et al., 1988]. A similarsituation obtains at otherplanetary magne- tospheres [Krimigis, 1992]. In all applications of the Fermi modelto the Earth's bow shock, greatemphasis was given to radialIMF connections to that regionof the front with X > 0, sincethese conditions wouldprovide for the long (at leastseveral minutes) connec- tion times thought to be necessary for the acceleration of ener- getic ions to E > 50 keV. Sarris and Krirnigis [1988] have tested this hypothesis and foundno evidence of particle accel- erationat E -> 50 keV under extended (several hours)periods with radial IMF connections to that part of the bow shock. This test was performed duringtimeswhen the ambient ener- getic particle population was at background levels so as to test the model [e.g., Lee, 1982] that upstream ions are accelerated to >-50 keV out of the superthermal tail of the shocked solar wind plasma under radialIMF conditions. Some issues regard- ing the adequacy of this testhavebeendiscussed in the litera- ture [Fuselier, 1989; Sarrisand Krirnigis, 1989]. 8231