摘要:

Using data from the University of New Hampshire cosmic ray experiment on the Pioneer 8 and 9 space probes at radial distances from 0.75 to 1.10 AU from the sun, we have made a detailed examination of the spectrum, time variations, and interplanetary gradients of cosmic ray electrons from ∼0.3 to 8 Mev. These data cover the time period from December 1967 to April 1969. Obvious solar flare electron increases have been removed from the data, so that the remaining data should represent quiet time electron behavior. We observe a strong and direct correlation between changes in electron intensity over the entire 0.3‐ to 8‐Mev range on Pioneers 8 and 9 and those for 3‐ to 12‐Mev electrons observed simultaneously on the Imp satellites. We find that, when an intensity change occurs, the electron spectrum simply moves bodily up and down, maintaining very nearly the same spectral exponent; in effect, the electron modulation is found to be essentially rigidity independent throughout the 0.3‐ to 8‐Mev range. This behavior appears to be an average property of quiet time electron changes during the time we have studied them and extends as well to the quiet time electron increases that we also observe in direct conjunction with those reported from Imp. The average quiet time day to day changes in electron intensity show very little correlation with day to day changes in higher‐energy nuclei, however, except during Forbush decreases when the observed modulation of electrons is found to be directly correlated with, but ∼2.5 × larger than the>60‐Mev nuclei changes. The average electron spectrum we measure isdJ/dE= 170/E1.7particles cm² ster sec Mev between 0.2 and 8 Mev. The average quiet time interplanetary electron gradient is observed to be +25 ± 20%/AU from Pioneer 8 data in 1968 and +3% ± 5%/AU from Pioneer 9 data in 1969 over the radial ran

ISSN:0148-0227    

DOI:10.1029/JA078i010p01487

年代:1973

数据来源: WILEY

摘要:

Balloon exposures of hodoscope instruments at Churchill, Manitoba, Minneapolis, Minnesota, and Sioux Falls, South Dakota, have established that the flux of return albedo electrons does not depend upon launch latitude and varies with solar modulation in proportion to the intensity of atmospheric secondary electrons. Only one flight out of 21 showed any indication of a magnetospheric electron flux significantly in excess of that attributable to albedo. Diurnal changes in geomagnetic cutoffs exhibit marked variability from day to day, as was illustrated by one flight in which a low cutoff was observed at Churchill throughout the daytime hours. The intensity increase of 15 to 65 Mev primary cosmic ray electrons due to solar modulation was no more than a factor of 2 from 1969–1970 to 197

ISSN:0148-0227    

DOI:10.1029/JA078i010p01502

年代:1973

数据来源: WILEY

摘要:

We report a high‐statistics magnetic spectrometer measurement of the geomagnetic cutoff rigidity and related effects at Palestine, Texas. The effective cutoffs we observe are in agreement with computer‐calculated cutoffs. We also report measured spectra of albedo and atmospheric secondary particles that come below geomagnetic cut

ISSN:0148-0227    

DOI:10.1029/JA078i010p01515

年代:1973

数据来源: WILEY

摘要:

A hydrodynamic model describing the generation and propagation of high‐speed plasma streams in the solar wind is presented. The model is based upon numerical integrations of the conservation equations for a time‐dependent, spherically symmetric, radial flow of interplanetary plasma. The nearly radial nature of the solar wind flow justifies the use of the model to approximate ‘corotating streams,’ e.g., nonspherically symmetric flows that are steady in a frame of reference rotating with the sun. The predicted variations in solar wind properties are in good agreement with those observed at 1 AU for a reasonable choice of parameters characterizing a ‘coronal disturbance’ at the heliocentric distance of 28Rs. This choice must include a perturbation of the coronal temperature but need not include perturbations of the coronal density or mass efflux. The streams produced by such a disturbance ‘steepen’ in transit to the orbit of the earth, with formation of a pair of shocks predicted at slightly larger heliocentric distances. The average dependencies of density and temperature upon the solar wind speed deduced from the model resemble those inferred from solar wind observations. This suggests that the major density changes associated with high‐speed streams are the products of interplanetary compression and rarefaction within the evolving stream structure. The same processes explain the deviations of proton temperature from their average dependence on solar wind speed; however, that basic dependence appears to reflect the temperature changes imposed on the pla

ISSN:0148-0227    

DOI:10.1029/JA078i010p01528

年代:1973

数据来源: WILEY

摘要:

Observations of interplanetary scintillations are compared with predictions based on a spatial electron density spectrum extrapolated from the power law shape at wave numbers 10−6–10−5rad/km measured from spacecraft. The influences of the power law exponent, a high wave number cutoff, and the Fresnel filter are examined with respect to scintillation index and pattern scale. The comparison suggests a model in which the high wave number density spectrum lies below the extrapolated power law but has a relatively flat part before the c

ISSN:0148-0227    

DOI:10.1029/JA078i010p01543

年代:1973

数据来源: WILEY

摘要:

Two types of magnetic field changes are repeatedly observed in the high‐latitude nightside magnetosphere in association with magnetic substorms. One type of field change occurs on field lines associated with the high‐latitude part of the auroral oval and is characterized by a sudden decrease in the field strength accompanied by an abrupt perturbation in the field declination angle. These changes are attributed to field‐aligned sheet currents flowing on the high‐latitude boundary of an expanding plasma sheet following substorms. Single sheets of field‐aligned currents on this boundary tend to flow toward the earth in the morning quadrant and away from the earth in the evening quadrant. Multiple sheets of current may also occur, the direction of the high‐latitude sheet generally being the same as that of a single sheet. A second type of field change observed on polar cap field lines is a decrease in field inclination during substorms. This type of change is regarded as a further manifestation of the changing field configuration during substorms and can be described in terms of azimuth

ISSN:0148-0227    

DOI:10.1029/JA078i010p01553

年代:1973

数据来源: WILEY

摘要:

A balloon observation of sudden commencement X rays (up to 2 times background) was made near Macquarie Island (λ = −61°) at 0423 UT on February 28, 1969. A synoptic study of this event, using riometer data, reveals that in the morning sector of the auroral zone the pattern of sudden commencement absorption (sca) is similar to that inferred from previous statistical studies. The situation in the afternoon sector is not clear. The sca at College was 10 times greater than that at Macquarie Island, and thus an asymmetry in sca between stations occupying positions of near conjugacy is indicated. A restricted period of data from the conjugate stations Great Whale River and Byrd reveals two other asymmetrical sca events. It is suggested that asymmetries in conjugate sca, and perhaps variations in the longitudinal distribution of sca, occur when a solar wind shock normal makes a large angle with the geomagnetic equatorial plane or the sun‐earth

ISSN:0148-0227    

DOI:10.1029/JA078i010p01563

年代:1973

数据来源: WILEY

摘要:

Observations of nighttime phase disturbances to long‐distance mid‐latitude (2 ≲L≲ 4) VLF transmissions during a magnetospheric substorm on January 2, 1971, are presented. The onset of the phase disturbances to a number of VLF paths began at the time of the substorm expansion. Whistler measurements during this event indicate that all the paths were below the plasmapause. Bremsstrahlung X rays and VLF emissions were observed above the plasmapause, nearL= 4, simultaneously with the VLF propagation disturbances. A previous analysis of the X ray and VLF emission data indicates that electron precipitation atL= 4 was caused by cyclotron resonance between energetic trapped electrons and whistler mode VLF waves near the equatorial plane. The data presented here suggest that the mid‐latitude ionospheric disturbances are due to energetic electron precipitation, which is possibly caused by this same mechanism. For this event it is estimated that a flux of electronsJ(>40 kev) ≲ 300/cm² sec ster withe‐folding energy equal to 45 kev will account for the measured phase change along a path nearly parallel toL= 3. Calculations illustrate that nighttime VLF phase is very sensitive to values of incident electron flux that are only marginally detectable, if at all, with the more conventional indirect indicators of electron precipitation, e.g., X rays and riometer absorption. This suggests that VLF propagation can serve as a useful tool for the detection of low‐intensity electr

ISSN:0148-0227    

DOI:10.1029/JA078i010p01572

年代:1973

数据来源: WILEY

摘要:

A relatively steady band of ELF hiss has been detected by the Ogo 5 search coil magnetometer on almost every passage through the plasmasphere; except for an anomalous region on the dayside at high geomagnetic latitudes, the emissions terminate abruptly at the plasmapause, and we therefore refer to them as ‘plasmaspheric hiss.’ A preliminary statistical study of the properties of the observed whistler mode turbulence has yielded the following characteristics: the waves are band limited with a sharp lower‐frequency cutoff and a more diffuse upper‐frequency cutoff; power spectra show a well‐defined maximum near a few hundred hertz, the peak intensities generally ranging between 10−7and 10−5γ²/Hz; the wave energy is spread over a bandwidth of a few hundred hertz, and corresponding wide band amplitudes are 5–50 mγ; the waves are highly turbulent in nature and show little tendency of definite polarization. The above properties remain essentially constant throughout the plasmasphere. Observed properties of the hiss are consistent with generation at all local times in a restrictedLrange just within the plasmapause. Waves subsequently propagate on complex paths to fill the plasmasphere. The most probable generation mechanism is cyclotron resonant instability with low‐energy electrons that continually diffuse inward from the outer radiation zone. At lowerL, hiss resonates with higher‐energy electrons, and thus the electrons are scattered in pitch angle and hence lost to the atmosphere throughout the ‘slot’ between the inner

ISSN:0148-0227    

DOI:10.1029/JA078i010p01581

年代:1973

数据来源: WILEY

摘要:

We use Ogo 5 measurements made within the plasmapause on May 15, 1969, to investigate the possible association between changes in lightning whistler dispersion characteristics and local density fluctuations. It is shown that groups of whistlers with relatively constant dispersions tended to be detected in regions where the local ion concentration was significantly enhanced. It is assumed that these local density fluctuations represent characteristics of large‐scale field‐aligned variations. The results are then compared with ray refraction estimates appropriate for low‐frequency whistler mode propagation (wave components with frequencies comparable to the local lower hybrid frequency) in a nonuniform m

ISSN:0148-0227    

DOI:10.1029/JA078i010p01597

年代:1973

数据来源: WILEY