摘要:

Two types of temporal variations in the solar UV spectral irradiance, caused by solar rotation and active region evolution, are presented and discussed. These particular UV variations differ markedly from the concurrent variations in the 10.7‐cm radio flux and sunspot number. The temporal variations of the modeled UV flux based on Ca‐K plage data are similar to the observed UV flux. The first type of dissimilar temporal behavior occurs when concentrations of solar active regions evolve at solar longitudes nearly 180° apart. Both the UV observations and modeled UV fluxes based on Ca‐K plage data then show strong 13‐day periodicity, while the 10.7‐cm solar radio flux and sunspot number exhibit quite dissimilar temporal variations. This type of dissimilarity is related to the modeled UV flux, having a dependence on the solar central meridian distance that is narrower than that for the 10.7‐cm radio flux or for sunspot numbers. A second case of marked dissimilarity occurs when major new solar active regions arise and dominate the full‐disk fluxes for several rotations. The strongest peaks in 10.7 cm and sunspot numbers tend to occur on their first rotation, for example, during major dips in the total solar irradiance, while the Ca‐K plages and UV enhancements peak on the next rotation and then decay more slowly on subsequent rotations. This type of dissimilarity is related to major active regions having a more rapid growth, peak and decay of sunspots, their strong magnetic fields and related coronal radio emission at centimeter wavelengths than for the Ca‐K plages and their relat

ISSN:0148-0227    

DOI:10.1029/JA088iA12p09883

年代:1983

数据来源: WILEY

摘要:

Latitudinal and field‐aligned cosmic ray gradients have been measured separately by inter‐normalization of the similar integral response (greater than approximately 30 MeV/nucleon) and high counting rates of approximately 60 counts per second of the anticoincidence detectors of the LECP experiment on Voyagers 1 and 2 and the CPME experiment on IMP 8. The unambiguous separation of latitudinal from field‐aligned gradients in long‐lived (greater than 10 days) cosmic ray structures is possible because during their Earth‐Jupiter transits, the two Voyagers are never separated by more than a few degrees in latitude or longitude, or by more than 8% of the helioradius of either spacecraft, and because the Voyagers remain magnetically well‐connected to Earth, which allows a direct estimate of field‐aligned gradients. The IMF connection is estimated by using the solar wind velocities measured by the PLS experiment on Voyager 1. Latitudinal gradients of approximately 2 to 5%/deg are found in short‐lived (10 to 30 days) structures, while they are approximately 1 to 2%/deg in structures recurring over several solar rotations. Radial gradients, except in the onsets of Forbush decreases, are commonly approximately 2%/AU, although there are rotations on which neither a radial nor a latitudinal gradient is measurable above 1%/AU or 1%/deg. Application of diffusion‐convection theory to these gradients shows that if one assumes that diffusion dominates transport transverse to the magnetic field, one obtains an upper bound on the transverse mean free path for scattering λ⊥much less than 10−3AU at 1 GeV/nucleon, which is inconsistent with values predicted by diffusion theory. The contrary hypothesis of very weak scattering is theoretically self‐consistent and is also supported by the observation of the effects expected from small‐scale (a few degrees) latitudinal gradients upon the diurnal variation of high

ISSN:0148-0227    

DOI:10.1029/JA088iA12p09889

年代:1983

数据来源: WILEY

摘要:

The structure of the heliospheric magnetic field changes substantially during the 11‐year sunspot cycle. We have calculated its configuration for the period 1976–1982 by using a potential field model, continuing our earlier study near solar minimum in 1976–1977 (Hoeksema et al., 1982). In this paper we concentrate on the structure during the rising phase, maximum, and early decline of sunspot cycle 21, from 1978 to 1982. Early in this interval there are four warps in the current sheet (the boundary between interplanetary magnetic field toward and away from the sun) giving rise to a four‐sector structure in the interplanetary magnetic field observed at earth. The location of the current sheet changes slowly and extends to a heliographic latitude of approximately 50°. Near maximum the structure is much more complex, with the current sheet extending nearly to the poles. Often there are multiple current sheets. As solar activity decreases, the structure simplifies until, in most of 1982, there is a single, simply shaped current sheet corresponding to a two‐sector interplanetary magnetic field structure in the ecliptic plane. The sun's polar fields, not fully measured by magnetographs such as that at the Stanford Solar Observatory, substantially influence the calculated position of the current sheet near sunspot minimum. We have determined the strength of the polar field correction throughout this period and include it in our model calculations. The lower latitude magnetic fields become much stronger as the polar fields weaken and reverse polarity near maximum, decreasing the influence of the polar field correction. The major model parameter is the radius of the source surface, the spherical surface at which the field lines become radial. Correlations of interplanetary magnetic field polarity observed by spacecraft with that predicted by the model calculated at various source surface radii indicate that the optimum source surface radius is not significantly different from 2.5RSduring this part of the s

ISSN:0148-0227    

DOI:10.1029/JA088iA12p09910

年代:1983

数据来源: WILEY

摘要:

We have studied one of the rare occasions when the same piece of solar wind plasma passed both Helios 1 (at 0.507 AU) and Helios 2 (at 0.72 AU). Our particular example occurred in the middle of a fairly smooth and typical high‐speed stream. We find clear indications that the ion behavior during this transit did not conserve the particles' adiabatic invariants and that some heating is required for the proton and alpha perpendicular temperature. The situation regarding the parallel temperature is less clear. The decreasing alpha‐proton differential speed does not appear to release very much free energy owing to a natural “adiabatic” cooling process. A very strong radial dependence of the electromagnetic energy flux, along with other factors, suggests the possibility of strong dissipation of Alfvenic fluctuations. Our conclusions are weakened somewhat by the many sources of inaccuracy that we have found and that seem unavoidable in a study of th

ISSN:0148-0227    

DOI:10.1029/JA088iA12p09919

年代:1983

数据来源: WILEY

摘要:

The effects of coulomb collisions on solar wind ion velocity distributions are investigated by using Helios data obtained between 0.3 and 1 AU. The mean free path of ions moving at thermal speed (in the solar wind frame) varies by three orders of magnitude in dependence on the plasma parameters. The number of collisions (roughly defined as collision frequency times the solar wind expansion time) can easily exceed one in low‐speed wind near the heliospheric current sheet. In these regions, almost Maxwellian distributions are observed. In solar wind with intermediate speeds (ranging from 400–600 km/s) one usually finds distributions with a nearly isotropic core which again can be understood by the action of coulomb collisions. On the other hand, the major part of high‐speed solar wind ion distributions can, by good reason, be called collisionless on local s

ISSN:0148-0227    

DOI:10.1029/JA088iA12p09933

年代:1983

数据来源: WILEY

摘要:

ISEE 1 and ISEE 3 three‐dimensional solar wind plasma measurements are used together with magnetic field measurements across five previously studied interplanetary shocks to test the accuracy of the mixed‐mode shock‐normal determination technique and to test whether the shock properties are best approximated with a ratio of specific heats of 5/3 or 2. In the shocks examined, the assumption that the velocity jump was along the normal provided an estimate of the shock normal within 15° of our best fit normal 50% of the time and within 50°, 90% of the time. The mixed‐mode normals lay within 12° of our best fit normal 50% of the time and within 36°, 90% of the time. Part of this deviation may be due to differences in the orientation of the local normal from that of the average normal. Finally, the jump in plasma and field across the shock is better predicted from the Rankine‐Hugoniot equations using a ratio of specific heats (γ) of 5/3

ISSN:0148-0227    

DOI:10.1029/JA088iA12p09941

年代:1983

数据来源: WILEY

摘要:

Solar wind electron velocity distributions measured across interplanetary shocks using the Los Alamos plasma analyzer on ISEE 3 have been studied to understand electron heating mechanisms for weak and intermediate strength collisionless shocks. This study thus complements earlier studies of electron heating at the earth's bow shock, an example of a highly supercritical collisionless shock. At the weakest interplanetary shocks (downstream to upstream density ratioN(d/u) ≲ 2 and velocity differenceV(d‐u) ≲ 70 km/s), heating perpendicular to the magnetic fieldBpredominates over parallel heating. Such heating may be a consequence of conservation of magnetic moment across the shock. At the stronger interplanetary shocks (N(d/u) ≳ 2 andV(d‐u) ≳ 70 km/s), heating parallel toBis dominant and the downstream velocity distributions are flat‐topped, similar to what is observed downstream of the earth's bow shock. This similarity suggests that electron heating in all collisionless shocks withN(d/u) ≳ 2 andV(d‐u) ≳ 70 km/s results in part from an acceleration parallel toBproduced by the macroscopic shock electric field, followed by beam driven p

ISSN:0148-0227    

DOI:10.1029/JA088iA12p09949

年代:1983

数据来源: WILEY

摘要:

This paper is an analysis of how shock‐spike particle events are formed by single‐encounter “shock‐drift” acceleration at quasi‐perpendicular fast‐mode interplanetary shocks. A set of time‐reversed equations, valid in the upstream or downstream solar wind frames, express a particle's initial or pre‐shock‐interaction kinetic energy and pitch angle as functions of its final or post‐shock‐interaction kinetic energy and pitch angle. These equations and particular forms of the initial or ambient energy spectrum and angular distribution yield model‐predicted intensity enhancements, energy spectra, and pitch angle distributions for comparison with spacecraft observations. It is shown that the final energy spectrum can be harder than, softer than, or equal to the ambient spectrum, depending upon, for example, the point along the final spectrum one chooses to examine, whether one looks at the upstream of downstream spectrum, and how rapidly the ambient spectrum decreases with increasing energy. It is shown that for a given form of the ambient energy spectrum, an upstream ambient angular distribution peaked toward (away from) the shock along the magnetic field yields a final energy spectrum that is harder (softer) in both the upstream and downstream regions than the spectrum produced for an isotropic ambient distribution. The single‐encounter scheme is shown to account for many features observed in the short‐lived, impulsive shock‐spike events. In particular, the existence of the high‐intensity spike in close temporal association (of the order of minutes) with the shock passage is consistent with a kinematical accumulation of particles accelerated and transmitted downstream of the shock. The single‐encounter acceleration process is also consistent with some features of energetic storm particle events observed at radial

ISSN:0148-0227    

DOI:10.1029/JA088iA12p09959

年代:1983

数据来源: WILEY

摘要:

We examine the origin of the intensity‐time profile characteristic of diffuse ion events upstream of the earth's bow shock. This profile is believed to result from a rotation of the interplanetary magnetic field which produces a systematic variation in the connection time of field lines with the bow shock. A plateau in the ion intensity is formed if the connection time exceeds the time needed to reach equilibrium between the shock acceleration and ion loss processes. This scenario is tested using the October 31, 1977, upstream diffuse ion event for which simultaneous magnetic field and ion intensity data have been published. We analyze this event using a two‐dimensional Gleeson‐Axford equation to describe the shock acceleration process and a model bow shock whose nose serves as a uniform source of ions injected into the acceleration process. Intensity‐time profiles are calculated for 30‐keV and 120‐keV protons for a range of diffusion coefficients,K∥andK⊥, using connection times based upon the shock geometry and the magnetic field data. It is found that the calculated and observed profiles are in good general agreement during the growth phase but diverge during the decay. The best overall fit is achieved with diffusion coefficients,K∥(30 keV) ∼ 4×1017cm² s−1,K∥(120 keV) ∼ 1.2×1018cm² s−1, andK⊥(120 keV) ∼ 1016cm² s−1. These values also produce cross‐field anisotropies at 0430 UT which are in satisfactory

ISSN:0148-0227    

DOI:10.1029/JA088iA12p09975

年代:1983

数据来源: WILEY

摘要:

Second‐order effects are calculated for a low‐frequency electromagnetic instability due to an ion beam in a plasma. This instability is a characteristic of a parallel shock model that includes an ion reflecting electrostatic subshock. The analysis is similar to that done by S. P. Gary, but a counterstreaming configuration is chosen that is homogeneous in time and that has specially growing modes. Among other effects, energy is transferred from the incoming main plasma ions to the beam ions. Electron pressure effects are calculated and are small for low frequencies. The application of this model to the earth's bow shock is discus

ISSN:0148-0227    

DOI:10.1029/JA088iA12p09981

年代:1983

数据来源: WILEY