摘要:

Coronal transients are believed to involve the expulsion of magnetic ‘bubbles’ or loops into interplanetary space. The close relationship of coronal transients with other forms of solar activity suggests a variation in their frequency of occurrence by a factor of 3–10 over the solar cycle. As magnetic ‘inclusions’ in the interplanetary magnetic field, transients should then lead to a solar cycle dependent scattering of cosmic rays entering the inner solar system. The power spectrum of a model of the transverse magnetic fluctuations and its solar cycle dependence is compared to the observed power spectra. Coronal transients are tentatively identified as the solar origin of the low‐frequency power in the interplanetary field and, as such, an important factor in cosmic ray

ISSN:0148-0227    

DOI:10.1029/JA086iA07p05387

年代:1981

数据来源: WILEY

摘要:

Data from the low‐altitude polar orbiting satellite Ogo 6 showed that the ratio north/south (N/S) of the intensity of solar protons (Ep>50 Mev) over the earth's north (N) polar cap (λ>70°) to that over its south (S) polar cap (−λ>70°) was about 1.61±0.04 for the solar particle event of November 2, 1969, and 1.00±0.03 for the event of December 18, 1969, while the ratio N/S was 0.64±0.02 for the solar particle event of December 19, 1969. These results, considered together with the interplanetary magnetic field polarities and the interplanetary proton anisotropies, favor the open model of the magnetosphere. The data also showed a clear evidence of periodic temporal variations of the proton flux over the polar caps; the pulsation effects had frequencies in the same range as the Pc4 and Pc5 geomagnetic micropulsations and were attributed to magnetohydromagn

ISSN:0148-0227    

DOI:10.1029/JA086iA07p05397

年代:1981

数据来源: WILEY

摘要:

Vela heavy ion and IMP solar wind data are used to identify the coronal origins of the interstream, low‐speed solar wind as well as to understand the causes of the long‐term trends in solar wind densities and electron temperatures observed at 1 AU. Several lines of evidence suggest a strong association between interstream flows and the extensions of the near equatorial band of coronal streamers into interplanetary space. This evidence includes (1) the moderate to high plasma density and oxygen freezing in temperatures measured at 1 AU which match similar conditions within coronal streamers close to the sun, (2) the strong association between sector boundaries and/or general field polarity reversals with both interstream flows at 1 AU and the photospheric footpoints of coronal streamers, and (3) the correlation between the long‐term trend in coronal morphology and the long‐term variation in the occurrence frequency of noncompressive density enhancements (NCDE's) which occur often within interstream flows. Our study further indicates that high electron temperatures at 1 AU result from a lower temperature gradient in the corona rather than an overall higher coronal temperature. Such conditions hold preferentially at the edges of NCDE's at 1 AU and hence by inference, the edges of coronal streamers near the sun. The observed flattening of the streamer belt about the solar equator near solar minimum, then led to a concurrent preferential sampling of streamer associated solar wind at 1 AU and hence a higher average density and electron temp

ISSN:0148-0227    

DOI:10.1029/JA086iA07p05408

年代:1981

数据来源: WILEY

摘要:

We examined the interplanetary magnetic field behavior in the field enhancement regions associated with the high velocity stream fronts observed during the primary mission of Helios 2 (January–April 1976). The principal conclusions of our investigation are the following: (1) The relative variation of the field magnitude ranges between 1.3 and 1.8 and is independent of heliocentric distance at least between 0.5 and 1 AU; (2) Close to the sector boundaries the field enhancements are consistent with a field perturbation occurring in a plane perpendicular to both the solar equator and the radial direction; (3) The field line has occasionally the form of a cylindrical helix rather than a simple planar geometry; (4) There is no compelling evidence to relate, in the inner solar system and in the period of interest, the field enhancements with the shape and location of the sector boundary surfac

ISSN:0148-0227    

DOI:10.1029/JA086iA07p05417

年代:1981

数据来源: WILEY

摘要:

We have used a superposed epoch analysis to examine the variation in solar wind properties observed in 1974 in a ‘heliomagnetic’ coordinate system tilted with respect to the solar equator. A tilt of 30°±10° was found to produce the best ‘organization’ of these properties in such a coordinate system. The solar wind speed increased with heliomagnetic latitude, while the proton density and the proton flux density decreased. These variations are qualitatively consistent with those inferred from coronal hole and other interplanetary ob

ISSN:0148-0227    

DOI:10.1029/JA086iA07p05423

年代:1981

数据来源: WILEY

摘要:

The propagation of large‐amplitude hydromagnetic waves of a collisionless anisotropic plasma is treated by using the Chew‐Goldberger‐Low equations. The generalization of the usual theory of characteristics as applied to this treatment has been developed. It is shown that in such a plasma there are six different types of waves. They incorporate all modes considered in a small‐amplitude theory. For a special case of a magnetic field almost parallel to the direction of propagation a fast magnetosonic wave has small density variations proportional to the variations of the square of a magnetic field intensity. A wave equation similar to one used in an isotropic plasma describes the behavior of nonplanar Alfvén waves. The simple relation obtained for the averaged large‐amplitude perturbations in the transverse Alfvén wave is identical to the equation derived on the basis of the WKB ap

ISSN:0148-0227    

DOI:10.1029/JA086iA07p05431

年代:1981

数据来源: WILEY

摘要:

Examination of solar wind plasma data obtained by the Los Alamos experiments on Imp 6, 7, and 8 during the 1971–1978 interval has revealed a frequent association between minimums in helium abundance and maximums in proton density. These events occur at low flow speeds and are strongly correlated with polarity reversals in the interplanetary magnetic field. A large fraction of these high proton density‐low helium abundance events are examples of noncompressive density enhancements (NCDE), i.e., large positive density signals not readily associated with stream‐stream interactions. The cleanest examples of these events often occur at well defined sector boundaries; complex, multiple events with 2 or more peaks in proton density and lasting ∼3–7 days are, however, common, and are associated with multiple field polarity reversals. When mapped back to the sun, assuming constant speed along a stream tube, these high proton density ‐ low helium abundance events associated with magnetic field reversals usually correspond to intersections of the spacecraft trajectory with the mid line of a coronal streamer belt that encircles the sun. The duration or multiplicity of these 1 AU events is generally correlated with the local tilt of the middle of the streamer belt to the solar equator. These events thus appear to be the 1 AU extensions of coronal streamers. A fine scale warping of the streamer belt on a longitudinal scale of ∼10° and varying thickness and density of the streamer belt at 1 AU adequately account for the variety of low helium abundance ‐ high proton density events observed. It is not yet understood why the helium abundance is low within coronal s

ISSN:0148-0227    

DOI:10.1029/JA086iA07p05438

年代:1981

数据来源: WILEY

摘要:

A systematic analysis of low‐energy anisotropy data derived from nonimpulsive energetic (0.3–0.5 MeV) proton events has been carried out with the APL/JHU detectors on board the IMP 7 and 8 spacecraft during 1972–1975. After reducing to a minimum any magnetospheric influence by applying various selection criteria, 1289 hourly anisotropy averages survived for which we also had simultaneous hourly averaged solar wind and magnetic field observations. These anisotropy vectors were resolved into components parallel and perpendicular to the measured magnetic field. Analysis of the resulting anisotropy distributions leads directly to the following conclusions: (1) The average perpendicular anisotropy component is nearly entirely accounted for in terms of theE × Bdrift, and hence interplanetary transverse diffusion is negligible at these energies. (2) Application of diffusion‐convection theory to our data yields an estimate of a representative value for the ratio of mean free paths transverse and parallel toBwhich is consistent with zero but bounded above, i.e., 0 ≤λ1/λ∥<0.05. (3) The parallel anisotropy component averages nearly to zero over many events, consistent with virtually no net particle streaming along the field line in nonimpulsive particle events at 1 AU. Therefore the net event‐averaged anisotropy of 0.3‐ to 0.5‐MeV protons observed by spacecraft located at 1 AU is outward away from the sun in a direction approximately perpendicular to the nominal magnetic field, implying that this population of protons is, on the average, being removed from the vicinity of 1 AU simply by ‘cross‐field convecti

ISSN:0148-0227    

DOI:10.1029/JA086iA07p05449

年代:1981

数据来源: WILEY

摘要:

The dependence of the occurrence probability of Pc 3 pulsations (frequency of 0.022–0.100 Hz) at synchronous orbit on factors such as local time and solar wind parameters is studied. Power spectra calculated from the magnetic field observed at the ATS 6 satellite for a 1‐year period from June 1974 to May 1975 were examined to identify Pc 3 pulsation occurrence. Pc 3 pulsations are usually observed in the dayside magnetosphere. The average diurnal occurrence pattern is a maximum at 0900 LT, with the pattern shifting to earlier local times in winter and to later local times in summer. Solar wind velocity VSWand the direction of the interplanetary magnetic field with respect to the sun‐earth line, θXB, significantly affect the occurrence probability. Large VSWand small θXBare favorable for the occurrence of Pc 3 pulsations. The average occurrence probability over 0600–1600 LT changes from 10% for VSW≲400 km/s and θXB≳60° to 80% for VSW≳600 km/s and θXB≲20°. The result suggests that the solar wind controls Pc 3 occurrence. However, the study of the occurrence probability alone is not sufficient to distinguish between the most likely sources, that is, the magnetosheath turbulence and the Kelvin‐Helmholtz instabil

ISSN:0148-0227    

DOI:10.1029/JA086iA07p05472

年代:1981

数据来源: WILEY

摘要:

Magnetospheric processes at Mercury are investigated to determine how they affect the source and loss rates of the neutral He and H atmosphere. The atmospheric source rate caused by direct impact of the solar wind on the planetary surface is estimated by using a model that included the effect of the large planetary core upon the compressibility of the magnetosphere. As the nonconducting planetary surface could inhibit Birkeland currents that cause erosion of the dayside magnetosphere, the impact of the solar wind on the surface is modeled with and without the effects of erosion. The solar wind impacts the surface, at most, only about 6% of the time, and the resulting atmospheric supply rate is negligible. The flux on closed dayside field lines is estimated to be roughly comparable to the flux to the surface along open dayside field lines in the polar cap region. The flux to the surface from the plasma sheet is estimated as being about three times either of these sources, provided that all sunward convected particles in the tail precipitate to the surface. A comparison of the flux available from convection with the flux that would precipitate to the ‘auroral zones’ under the assumption of strong pitch angle scattering shows that the strong pitch angle scattering assumption may be invalid at Mercury, owing to the large size of the loss cone. Observations of a correlation between the lunar atmosphere He content andKp, and consideration of surface processes, suggest that a significant fraction of the He striking the surface eventually enters the atmosphere. Loss mechanisms are also investigated. The extent to which magnetospheric convection recycles photoions (created at both high and low latitudes) back to the planetary surface, and to a lesser extent the uncertainty in the number of atoms exposed to sunlight, leads to considerable uncertainty in atmospheric loss estimates. An examination of atmospheric losses caused by electron impact ionization in the ‘auroral zone’ indicates that this mechanism does not compete with photoionization. The estimated solar wind supply of He to the surface is in the range 3.9 × 1022−2.3 × 1023s−1, the estimated radiogenic supply is between 6.9 × 1021and 4.6 × 1022s−1, and the loss rate is estimated as between 1.2 × 102

ISSN:0148-0227    

DOI:10.1029/JA086iA07p05485

年代:1981

数据来源: WILEY