摘要:

A balloon‐borne measurement of the cosmic ray electron spectrum from 10 to 200 Gev is reported in which two new techniques have been used to remove proton background contamination. First, the depth of the spectrometer was more than 40 radiation lengths, the equivalent of more than 3 mean free paths of material, enabling hadronically and electromagnetically induced cascades to be differentiated for a subset of the data. Second, electromagnetic cascade starting points were determined to within ±0.1 radiation lengths on the basis of a calibration with electrons from 5.4 to 18 Gev at the Stanford Linear Accelerator, greatly reducing the chances for a proton to simulate an electron. The resulting spectrum, when fitted with a power law, is quite steep, −3.2 ± 0.1, but the fit to a power law is mar

ISSN:0148-0227    

DOI:10.1029/JA078i031p07165

年代:1973

数据来源: WILEY

摘要:

The diurnal variations of underground cosmic ray intensities are analyzed on a day‐to‐day basis. At the depths of the London and Torino stations an anisotropy in the direction of the interplanetary magnetic field is observed in addition to the corotation effect, which varies in relation to the perturbations produced by the sun. This effect is not recorded in the Hobart data during the same period of observat

ISSN:0148-0227    

DOI:10.1029/JA078i031p07174

年代:1973

数据来源: WILEY

摘要:

In an earlier paper (McKibben, 1972) observations were presented of solar proton fluxes at an energy of ∼17 Mev, which showed that after some large solar flares the proton flux at the orbit of the earth became approximately independent of solar longitude within about 4 days. Flux differences at these late times were typically less than a factor of ∼2 at spacecraft separated by as much as 180° in solar longitude. These observations were found to be consistent with an effective κ⊥≅ 7 × 1020cm²/sec at the orbit of the earth. In this paper this conclusion is examined more closely, and the possible interpretations of the results presented earlier are discussed. An attempt is made by using simple physical arguments to derive an estimate of the effective κ⊥in the interplanetary field from known properties of the field, including the effects of the random walk of field lines as proposed by Jokipii and Parker (1969), the result being that for the cases considered the effective κ⊥is found to be much smaller than the κ⊥required by the solar flare observations. Observations of 17‐Mev protons in corotating regions are presented, and they also are found to lead to upper limits on the effective κ⊥that are significantly less than the κ⊥required by the solar flare results. Alternative models of azimuthal propagation are discussed that do not require a large κ⊥in near‐earth interplanetary space. Models are considered in which azimuthal propagation takes place primarily in a spherical shell far outside the orbit of the earth, in a region above and below the ecliptic plane, and in the upper solar corona. Some experimental evidence is found in support of the hypothesis that azimuthal propagation takes place primar

ISSN:0148-0227    

DOI:10.1029/JA078i031p07184

年代:1973

数据来源: WILEY

摘要:

The most recent (September 1–2, 1971) of the rare ground level events signaling the arrival at the earth of relativistic solar cosmic rays arising from a flare on the sun's invisible hemisphere displayed marked anisotropy for several hours. Application of newly developed analytical procedures has made it possible to study in detail the evolution of the anisotropic pitch angle distribution. Throughout the anisotropic phase the solar particle flux is proportional to the cosine of the angle between the weighted mean asymptotic direction of viewing and an axis of symmetry corresponding to the spiral interplanetary magnetic field line that connects the sun to the earth. Furthermore, the degree of anisotropy deduced from the ratio of the fluxes in the garden hose direction toward and away from the sun decays exponentially. The results of this analysis and the reexamination of the three previously observed invisible hemisphere ground level events have demonstrated that propagation along the spiral interplanetary field line connecting the sun to the earth occurs even when the source lies far beyond the limb of the sun. In one case (January 28, 1967) the anisotropy near onset was 100% (i.e., no particles traveling toward the sun), a situation that had only been reported twice previously and then in association with visible flares that occurred within 10° of the foot of the nominal garden hose field line. These results bespeak the operation of an efficient transport mechanism in the solar corona that enables relativistic protons to travel over distances at least as great as 70° in heliolongitude in about 15

ISSN:0148-0227    

DOI:10.1029/JA078i031p07205

年代:1973

数据来源: WILEY

摘要:

This paper presents a theoretical study of the Alfvén waves in the spiral interplanetary magnetic field. The Alfvén waves under consideration are arbitrary large‐amplitude nonmonochromatic microscale waves of any polarization. They superpose on a mesoscale background flow of thermally anisotropic plasma. When the WKB approximation is used, an analytical solution for the amplitude vectors is obtained as a function of the background flow properties: density, velocity, Alfvén speed, thermal anisotropy, and the spiral angle. The necessary condition for the validity of the WKB approximation is discussed. The intensity of fluctuations is calculated as a function of heliocentric distance. The relative intensity of fluctuations compared with the magnitude of the background field has its maximum in the region near 1 AU. Thus outside of this region the solar wind is less turbulent. Owing to attenuation of microscale Alfvén waves, fluctuation energy is converted into the kinetic energy of the solar wind. Its contribution amounts to about 20% of the kinetic energy at

ISSN:0148-0227    

DOI:10.1029/JA078i031p07221

年代:1973

数据来源: WILEY

摘要:

The solar wind properties at the earth are computed for a variety of values of the density and temperature at the base of the corona. For the electron thermal conductivity the expression derived by Perkins is adopted. Good agreement with observations is obtained for values of the density and temperature at the base of the corona equal to ∼9 × 107cm−3and ∼1.7 × 106°K, resp

ISSN:0148-0227    

DOI:10.1029/JA078i031p07229

年代:1973

数据来源: WILEY

摘要:

The shock system observed in the solar wind by Pioneer 9 and Ogo 5 on February 2, 1969, consisted of the following major discontinuities: a forward slow shock, a forward fast shock, a tangential discontinuity at which the density dropped sharply and the flow direction changed, a tangential discontinuity at which the magnetic field strength jumped to an unusually high value, two closely spaced tangential discontinuities that bracketed a region of even greater field strength and that fronted a region of very cool, very dense, helium‐enriched plasma, a reverse fast shock of low Mach number, and a second reverse fast shock of very low Mach number. The event had aspects of both corotating and flare‐induced shock systems; it is suggested that the source of the disturbances was a flare occurring at or near anMregion. The Ogo 5 search coil magnetometer detected a high level of turbulence throughout the event; a local enhancement of this turbulence at the front of the helium enrichment is believed to have been caused by a magnetic drift wave instability. Data are also presented for two other shock pair systems, both of which had density and flow direction profiles similar to those observed on February 2, 1

ISSN:0148-0227    

DOI:10.1029/JA078i031p07237

年代:1973

数据来源: WILEY

摘要:

At the distance of the Vela satellite orbits (r ≈ 18RE) there are three distinct plasma environments associated with the earth's magnetotail: the plasma sheet, the high‐latitude tail (or tail lobes), and the magnetotail boundary layer. This paper reports measurements of the plasma properties in these three regions made with electrostatic analyzers on Vela satellites 5A, 5B, 6A, and 6B. Evidence presented suggests that the plasma temperature profile across the thickness of the plasma sheet may be nearly uniform and very cool (proton average energy ≈1 kev) after long geomagnetically quiet periods; the profile may be nearly uniform and very hot (proton average energy ≈20–30 kev) immediately after a substorm. Except during these extreme cases the central part of the plasma sheet is hottest, and there is a gradual but substantial cooling toward the upper and lower edges. The magnetotail boundary layer, containing plasma less dense than that in the magnetosheath and flowing antisunward at less than magnetosheath flow speeds, is often very thin near the tail's magnetic midplane, but it is thousands of kilometers thick away from the midplane. We suggest that it may extend completely around the top and the bottom surfaces of the tail. The very low density plasma in the tail lobes is rather uniform over that portion of the height of the lobes explored with the Vela satellites. Comparisons of these observations with a magnetospheric model suggest that the boundary layer is the magnetic projection of the dayside cusps and may be a site of injection of magnetosheath plasma into the pla

ISSN:0148-0227    

DOI:10.1029/JA078i031p07257

年代:1973

数据来源: WILEY

摘要:

Observations of geomagnetically trapped α particles over the energy range 1.18 ≤Eα≲ 8 Mev obtained with the Injun 5 polar‐orbiting satellite during the period September 1968 to May 1970 are presented. The time history atL≃ 3 andB≃ 0.19 is dominated by the large intensity increase following the magnetic storm on October 31, 1968, during which the α particle intensity reached 2 × 10³ (cm² sec ster)−1and the intensity ratio of α particles to protons (jα/jp) attained values of ≳2 × 10−3. The short‐term decay of both α particles and protons in the same energy per nucleon range is similar, decay constants being ∼40 days. The α particle fluxes and thejα/jpratio attained minimum values in mid‐1969 and in early 1970 of ∼20 (cm² sec ster)−1and ∼2 × 10−4, respectively, indicating that α particles are not replenished as readily as protons. The period February 11–28, 1970, was selected for detailed study, as representing the ‘quiet time’ trapped α particle population. During this period, it was found that (1) the α particle intensity versusLprofile is most similar to the proton profile at the same energy per nucleon interval, (2) thejα/jpratio is nearly constant as a function ofLin the same energy per nucleon representation but rises sharply withLwhen it is computed in the same total energy interval, (3) the variation of α particle intensity withBsuggests a steep (j(α) ∝ sinnα,n≳ 10) angular distribution at small (∼10°–15°) equatorial pitch angles but thejα/jpratio shows little dependence onB, and (4) the α particle spectral parameterE0shows a markedly different dependence onLL from the equivalent one for protons. It is concluded on the basis of the observations that the source of the observed α particles during quiet times must be the solar wind or the upper ionosphere (via the polar wind) or some combination of the two but not directly captured solar particles. Further, the particle velocity appears to be the most physically plausible parameter in organizing the data for geomagnetically trapped nuclei. The data are compared with the theoretical model of Cornwall (1972), and it is found that rea

ISSN:0148-0227    

DOI:10.1029/JA078i031p07275

年代:1973

数据来源: WILEY

摘要:

Isis 1 satellite observations of the cleft position during magnetospheric substorms show that the cleft shifts equatorward as the interplanetaryBzcomponent turns southward and substorm activity increases and that it shifts back toward higher latitudes as substorm activity subsides andBzreturns northward. Also, unusually low latitudes for the cleft (less than 70° invariant latitude) were found during geomagnetic storms with significantDstvalues and large negativeBzvalues. Significant shifts occur in the cleft location with no accompanying effect seen in theAEindex; however,Bzis observed to be southward during these periods

ISSN:0148-0227    

DOI:10.1029/JA078i031p07286

年代:1973

数据来源: WILEY