摘要:

The 2.29 GHzSband carrier signals of the two Helios spacecraft are used to probe the magnetic and density structures of the solar corona inside 0.05 AU. In this paper we analyze the observed fluctuations of the electron content and Faraday rotation. A simple statistical ray analysis is employed. We conclude that (1) the observed Faraday rotation fluctuations cannot be solely due to electron density fluctuations in the corona unless the coronal magnetic field is some 5 times stronger than suggested by current estimates, and (2) the observed Faraday rotation fluctuations are consistent with the hypothesis that the sun radiates Alfvén waves with sufficient energies to heat and accelerate high‐speed solar wind strea

ISSN:0148-0227    

DOI:10.1029/JA087iA01p00001

年代:1982

数据来源: WILEY

摘要:

A new statistical modeling approach is used to fit models to 200 years of sunspot data and the adequate models for yearly, monthly, and daily sunspot numbers are employed to obtain the minimum mean squared error forecasts. The analysis of new models revealed a long‐term 76‐year period, a short‐term 27‐year period, and a 2.5‐year period due to stratospheric winds in addition to a commonly known 11‐year periodicity of the sunspots. The forecasting charts are developed in a format that can be easily read to obtain the long‐term (yearly average) and short‐term (daily average) predictions of

ISSN:0148-0227    

DOI:10.1029/JA087iA01p00009

年代:1982

数据来源: WILEY

摘要:

The plasma wave instrument on ISEE 3 has detected regions of plasma turbulence that extend several tenths of an astronomical unit upstream or downstream of inteplanetary shocks. The plasma waves fall into four categories. Highly impulsive 1‐ 10‐kHz electric field bursts were found hours upstream of quasi‐parallel interplanetary shocks. On occasion their average and peak amplitudes increased monotonically until the shock crossing, at which time they were suppressed. A lower frequency electric field (0.1–1 kHz) component was enhanced at nearly all shocks and persisted downstream. Broadband low‐frequency (typically<178 Hz) magnetic fluctuations increased at, and persisted hours downstream of, every interplanetary shock in our sample. A smooth high‐frequency continuum, near and above the local electron plasma frequency, was enhanced at, and persisted well downstream of, every interplanetary shock we studied. Impulsive electron plasma wave bursts were occasionally found near the shocks. The shock‐associated plasma waves we found to extend over large spatial scales are similar to those found previously in local studies of interplanetary shocks. While no single interplanetary shock showed every effect, the ensemble of shocks contained at least one example of each type of plasma wave found upstream of the earth's bow shock. The 1‐ to 10‐kHz spectra upstream of interplanetary shocks and the earth's bow shock are similar. The low‐frequency electric and magnetic fluctuations downstream of interplanetary shocks and the bow shock have similar spectra. They seem to be ubiquitous features of flowing plasmas made t

ISSN:0148-0227    

DOI:10.1029/JA087iA01p00017

年代:1982

数据来源: WILEY

摘要:

A survey of solar wind helium ion velocity distributions and derived parameters as measured by the Helios solar probes between 0.3 and 1 AU is presented. Nonthermal features like heat fluxes or He2+double streams and temperature anisotropies have been frequently observed. Fairly isotropic distributions have only been measured close to sector boundaries of the interplanetary magnetic field. At times in slow solar wind, persistent double‐humped helium ion distributions constituting a temperature anisotropyT∥α/T⊥α>1 have been reliably identified. Distributions in high‐speed wind generally have small total anisotropies (T∥α/T⊥α≳ 1) with a slight indication that in the core part the temperatures are larger parallel than perpendicular to the magnetic field, in contrast to simultaneous proton observations. The anisotropy tends to increase with increasing heliocentric radial distance. The average dependence of helium ion temperatures on radial distance from the sun is described by a power law ∼R−βwith 0.7 ≲ β ≲ 1.2 forT∥αand 0.87 ≲ β ≲ 1.4 forT⊥α. In fast solar wind theT⊥αprofile is compatible with nearly adiabatic cooling. Pronounced differential ion speeds Δvαphave been observed with values of more than 150 km/s near perihelion (0.3 AU). In fast streams Δvαptends to approach the local Alfvén velocity vA, whereas in slow plasma values around zero are obtained. Generally, the differential speed increases with increasing proton bulk speed and (with the exception of slow plasma) with increasing heliocentric radial distance. The role of Coulomb collisions in limiting Δvαpand the ion temperature ratioTα/Tpis investigated. Collisions are shown to play a negligible role in fast solar wind, possibly a minor role in intermediate speed solar wind and a distinct role in low‐speed wind in lim

ISSN:0148-0227    

DOI:10.1029/JA087iA01p00035

年代:1982

数据来源: WILEY

摘要:

A survey of solar wind three‐dimensional proton velocity distributions as measured by the Helios solar probes between 0.3 and 1 AU is presented. A variety of nonthermal features like temperature anisotropies, heat fluxes, or proton double streams has been observed. The relative speed of the second proton component increases on the average with increasing wind speed and decreasing heliocentric radial distance and shows a correlation with the local Alfvén speed. A marked anisotropy in the core of proton distributions with a temperature larger perpendicular than parallel to the magnetic field (T∥c1 frequently caused by ‘high‐energy shoulders’ or a resolved second proton component. No clear radial gradient of the temperature anisotropy could be established in these cases. The average dependence of the proton temperature on heliocentric radial distance is given by a power lawR−α, where α ≈ 1 forT⊥pand 0.7<α<1 forT⊥pare compatible neither with isothermal nor adiabatic expansion. Flattest radial temperature profiles are obtained in high‐speed streams. These observations indicate that local heating or considerable proton heat conduction occurs in the solar wind. Some consequences of nonthermal features of proton distributions for plasma instabilities are discussed as well as kinetic processes that may s

ISSN:0148-0227    

DOI:10.1029/JA087iA01p00052

年代:1982

数据来源: WILEY

摘要:

The Vlasov theory for an electrostatic instability driven by a parabolic density gradient is considered. The magnetic field is taken as uniform, and the local approximation is used. The instability grows only for a sufficiently large, positive second derivative of the density. The parametric dependences of the linear growth rate are reported, as well as weakly nonlinear calculations on wave‐particle transport due to this instabilit

ISSN:0148-0227    

DOI:10.1029/JA087iA01p00073

年代:1982

数据来源: WILEY

摘要:

Synchronous orbit measurements from the University of New Hampshire ATS 6 instrument have been compared with several other types of space and ground data in a study of the plasma effects related to SI and SC (positive excursions ofDst) magnetic perturbations. It is found that plasma injections at synchronous orbit, related to SI and SC, are very similar to plasma injections associated with substorms, except that the former occur at all local times. These injections can be interpreted as the co‐location of particle boundaries on an inward propagating front. The boundaries are those due to magnetospheric convection and precipitation losses and normally are spatially dispersed as a function of energy. The compression magnetic pulse associated with SI and SC events is apparently responsible for the co‐location of these boundaries and their inward propagation. The +Dstmagnetic pulse plays a role similar to that of the magnetic tail reconfiguration pulse associated with substorms. Theories of convection in steady state magnetic fields cannot account for the dispersionless character of the injection front. The electron plasma behind the injection front is a hot Maxwellian for local evening +Dstplasma events as is the case for substorms. +Dst‐related injections observed on the dayside have enhanced low‐energy electron intensities, perhaps owing to an ionospheric component. The plasma observed behind the front appears to be hot tail plasma convected to its point of observation. We show evidence that +Dstenhances magnetospheric convection independent of interplanetary magnetic field direction. Since +Dstdoes not necessarily trigger substorms, enhanced convection is apparently not a sufficient condition for substorm gen

ISSN:0148-0227    

DOI:10.1029/JA087iA01p00077

年代:1982

数据来源: WILEY

摘要:

The characteristics and transport of>200 keV electrons upstream of Earth's bow shock and in the outer magnetosheath are studied using nearly 4 years of data from the California Institute of Technology Electron/Isotope Spectrometer aboard IMP 8. In the upstream region, elevated electron intensities ranging from near the background level ∼0.1 (cm² s sr)−1up to ∼100 (cm² s sr)−1are observed about 2% of the time and typically persist for less than 5 min. These burst electrons stream intensely (ξ ∼ 0.5 to 1.5) sunward along the interplanetary magnetic field line. With the aid of a new coordinate system, it is demonstrated that the upstream bursts are most frequently seen on interplanetary field lines that trace to the inner magnetosheath, and that the total energy transported sunward by>200 keV upstream electrons averages ∼1.6 × 1014ergs/s, a figure comparable to the tailward energy flow observed in the permanent layer of energetic electrons adjacent to the magnetopause. Bursts of energetic electrons in the outer magnetosheath have time scales similar to those observed upstream, but they are typically ∼10 times more intense and much less anisotropic (ξ ≲ 0.4). The net flow of these electrons is toward the shock and very nearly equals the net flow away from the shock in the adjacent upstream region. The magnetosheath data suggest that energetic electron transport in this region may be described by a leaky box model with a scattering mean free path ∼0.6RE. It is concluded that the energetic (>200 keV) component of upstream electrons originates downstream of the bow shock. Energetic electrons in the upstream region, in the outer magnetosheath, and in the magnetopause electron layer appear to be closely related and probably have a common origin in the inner magnetosheath or poss

ISSN:0148-0227    

DOI:10.1029/JA087iA01p00085

年代:1982

数据来源: WILEY

摘要:

Observations aboard GEOS 1 and 2 show a correlation between generation of strong ion‐cyclotron ULF waves below the proton gyrofrequency and an increase in the cold He+ion concentration. The amplification process due to one cold species seems to be well understood and has been thoroughly discussed. Nevertheless, the amplification process when two cold species are present has not been so far properly studied. The GEOS experiments have also shown a close association between the occurrence of ion‐cyclotron ULF waves and the presence of thermal He+ions in the equatorial region of the magnetosphere (Young et al., 1979). Thus we study here the combined effect of cold H+and He+ions on the proton cyclotron electromagnetic instabil

ISSN:0148-0227    

DOI:10.1029/JA087iA01p00095

年代:1982

数据来源: WILEY

摘要:

Extensive spatial and temporal measurements of plasma pressurenkTe, magnetic force densityJ × B, and ion velocities v have been performed in a laboratory experiment undergoing magnetic field line reconnection. The pressure is found to peak at the two edges of the neutral sheet. It exhibits large transverse gradients, causing space charge fields and Hall currents. The magnetic force density arises mainly from induced axial neutral sheet currents and transverse magnetic fields but also from transverse currents and a magnetic field component along the separator. The total force density on the fluid,J × B‐ ▽p, is compared with direct measurements of the fluid acceleration by using differential particle detectors. It is found that the ion acceleration is strongly modified by scattering off wave turbulence. After several Alfvén times the fluid develops the classic flow pattern, with jetting from the edges of the neutral sheet to velocities close to the Alfvé

ISSN:0148-0227    

DOI:10.1029/JA087iA01p00101

年代:1982

数据来源: WILEY