摘要:

A sequence of 236 varve thickness measurements by Perkins and Sims from proglacial Skilak Lake in southern Alaska is shown to contain spectral features similar to those of the sunspot index. In general, the varve spectrum qualitatively mimics that of the sunspot index, with discrepancies perhaps arising from the misinterpretation of random summer layers as annual increments (varves). These discrepancies may be largely removed through maximization of the sunspot index‐varve cross correlation whereby a time‐scale factor increment is applied to the varve series measurements. Varve thickness is positively correlated with the sunspot index and with vanishing lag (insofar as can be resolved). As varve thickness and meteorological variables have previously been shown to be strongly correlated, a direct link between the sunspot index and varve thickness is suggested by way of climate response to solar variati

ISSN:0148-0227    

DOI:10.1029/JA090iA12p12019

年代:1985

数据来源: WILEY

摘要:

When Voyager 2 was near 11 AU, the counting rate of nuclei ≳75 MeV/nucleon decreased during the interval from July 1982 to November 1982, and it increased thereafter until August 1983. The counting rate fluctuated within this “minicycle” with short‐term decreases lasting 1 to 4 days and recoveries lasting several days. A decrease in cosmic ray flux was generally associated with the passage of an “interaction region” in which the magnetic field strengthBwas higher than that predicted by the spiral field model,Bp. Several large enhancements inB/Bpwere associated with “merged interaction regions” which probably resulted from the interaction of two or more distinct flows. During the passage of interaction regions the cosmic ray intensity decreased at a rate proportional to (B/Bp‐ 1), and during the passage of rarefaction regions (whereB/Bp<1) the cosmic ray intensity increased at a constant rate. The general form of the cosmic ray intensity profile during this ∼13 month minicycle can be described by integrating these relations using the observedB(t), and it can be understood in terms of the sizes and separations of interaction regions. Latitudinal variations of the interaction regions and of the short‐term cosmic ray variations were identified by comparing Voyager 2 observations with Voyager 1 observations made at higher latitudes (14° to 20°). The interaction regions were turbulent, with anf−5/3spectrum from at least 3×10−4Hz tofc= (1 to 2) × 10−6Hz. A break in the spectrum atfccorresponds to the characteristic width of the interaction regions, and it represents a “stirring scale” for the solar wind. The interaction regions, including merged interaction regions, may be viewed as “turbulent boundary layers” which grow in size with increasing distance from the sun. They act as barriers which impede the

ISSN:0148-0227    

DOI:10.1029/JA090iA12p12027

年代:1985

数据来源: WILEY

摘要:

We use a time‐dependent, one‐dimensional, spherically symmetric, one‐fluid solar wind model to investigate the heating of the solar wind by an interaction with the interstellar neutral hydrogen. The interaction is modeled through particle, momentum, and energy source terms equivalent to those of T. E. Holzer (1972). The equations are solved using a flux‐corrected transport algorithm which incorporates stream‐stream heating directly into the model. We input solar wind data at 1 AU for the time between October 12, 1978, and February 25, 1980, and generate 52‐day averages of solar wind temperature as functions of radius out to 10 AU for values of the interstellar hydrogen densityNH= 0.0, 0.03, and 0.1 cm−3. The radial dependence of temperature, averaged over the entire time period, yields power law exponents α = 0.714, 0.597, and 0.428 for the three densities, respectively. A more detailed comparison between the temperature measurements of Voyager 1 and Pioneer 11, and the model solar wind temperatures at the positions of these spacecraft indicates that the observations are consistent with solar wind heating by the interstellar neutral hydrogen, at least within the context of the model. We close with a suggestion for further data analysis to determine the radial gradient of proton temperatu

ISSN:0148-0227    

DOI:10.1029/JA090iA12p12040

年代:1985

数据来源: WILEY

摘要:

Small scale (∼10 km) magnetic field structures or “flux ropes” observed in the ionosphere of Venus can be interpreted as the result of a kinematic dynamo process acting on weak seed fields. The seed fields result from the prevailing downward convection of magnetic flux from the vicinity of the ionopause, while small scale fluctuations in the velocity of the ionospheric plasma, which can be caused by collisional coupling to gravity waves in the neutral atmosphere, provide the mechanism by which the field is twisted and redistributed into features of similar scale. This mechanism naturally explains some of the average properties of flux ropes such as the variation of their characteristics with altitude and solar zenith angle. It also elucidates the relationship between the large scale and small scale ionospheric magnetic f

ISSN:0148-0227    

DOI:10.1029/JA090iA12p12047

年代:1985

数据来源: WILEY

摘要:

Suprathermal electron fluxes measured in the ionosphere of Mars by the retarding potential analyzer (RPA) on Viking lander 1 are presented and compared with the photoelectron flux that is produced by the absorption of the solar EUV. The calculation of the equilibrium photoelectron population on Mars is based on the multistream electron transport theory and a model neutral atmosphere and ionosphere that was actually observed by Viking lander 1. From the theoretical equilibrium photoelectron population we compute the expected RPA volt‐ampere characteristic curves and compare them with those recorded by the instrument. The theoretical and the observed RPA currents below ≃170 km are in agreement, confirming that the solar EUV is the main source of suprathermal electrons at these altitudes. Above ≃170 km an additional source of suprathermal electrons is required to explain the observations. We suggest that this source is supplied by the solar wind, either by direct particle entry or by wave‐particle coupling. The rate of attenuation of the topside suprathermal electron flux with altitude indicates that the ionosphere is permeated by a substantially horizontal (dip angle ≃15°) magn

ISSN:0148-0227    

DOI:10.1029/JA090iA12p12057

年代:1985

数据来源: WILEY

摘要:

Calculations of ion partitioning in the hot outer Io torus have failed to account for certain observed features. Notably, the low concentration of OIII measured in the first half of 1981 has been difficult to reconcile with abundances of other ions inferred from Voyager 1 and 2 measurements in 1979. One possible explanation invokes a two‐state plasma torus and suggests time‐dependent changes of bulk composition. In this paper we propose an alternative time‐independent model (time‐independent in a mean‐value sense) but introduce the ratio of sulfur to oxygen in the neutral source as a free parameter. The recent evidence that there exist distinct sources of S2and SO2justifies this introduction of independent sources of S and O. In our calculations, we also varied the relative abundances of hot (1 keV) and thermal electrons, the neutral injection rate and characteristic radial diffusion time scale, and the characteristic ion temperatures. We integrated the rate equations over time until a steady state was achieved. For a pure SO2source, we found no solutions qualitatively compatible with observations. A solution in qualitative agreement with observations emerges when the injection rate of neutral S2is about 60% the rate of SO2. The deficiency of OIII observed in 1981 is obtained in a model consistent with other aspects of composition and dynamical features of the torus observed in 1979 at the time of the Voyager encounter by including of order 0.05% of 1 keV electrons and using a radial diffusion time of order 35 days. The intensity of EUV spectral lines attributed to OII and OIII can be produced by our sulfur‐rich torus model if collision strengths of lines near 833 Å are taken near the upper limit of their range of

ISSN:0148-0227    

DOI:10.1029/JA090iA12p12065

年代:1985

数据来源: WILEY

摘要:

Using the Voyager 1 and 2 (V1 and V2) planetary radio astronomy experiment, we have analyzed the data in the kilometric wavelength range from January to December 1979, the period which includes the Jupiter encounters for V1 and V2. Statistical studies of the broadband kilometric radiation (bKOM) reveal new results on the polarization and beaming of the emission. The northern and southern components are right‐hand and left‐hand, respectively polarized, without reversal at encounter. The central meridian longitude occurrence of these two components is dependent on the zenographic latitude of the observer. The shadowing by the Io plasma torus is confirmed, the boundaries of the emission beam have been deduced, and it is shown that the latitudinal beaming of the emission is dependent on local time, from dayside to nightside observations. Our results are discussed in terms of a source radiating in the extraordinary mode. It is suggested that the source regions are at the inner boundary of the Io torus all around the planet and that the emission is beamed into a hollow conical sheet whose axis coincides with the magnetic dipole of the planet. Radiation mechanisms are briefly discussed; the maser synchrotron instability and the non linear conversion of electrostatic waves could contribute to bKOM, each one in a limited frequency ra

ISSN:0148-0227    

DOI:10.1029/JA090iA12p12073

年代:1985

数据来源: WILEY

摘要:

Frequently, a detector on a spinning spacecraft measures the flux of charged particles whose velocities lie in a plane containing the magnetic field. This flux may be Fourier analyzed as a function of the spacecraft roll angle. Relationships among the Fourier coefficients are derived using the adiabatic solution of the Vlasov equation. These relationships depend only on the fact that the lowest order (in gyroradius) of the distribution function is a function of the magnetic moment and that the first‐order term is a function of the lowest order. These relationships may be used to separate the proton from the electron counts registered in Saturn's inner magnetosphere by the University of California's Cerenkov counter on Pioneer 1

ISSN:0148-0227    

DOI:10.1029/JA090iA12p12081

年代:1985

数据来源: WILEY

摘要:

The University of California Cerenkov detector on Pioneer 11 previously observed cosmic ray albedo neutron decay (CRAND) protons above 600 MeV in Saturn's inner magnetosphere, mixed with a poorly understood background of energetic electrons (Fillius and McIlwain, 1980). Here we separate the electron from the proton counts and establish the first‐order angular distributions for each species. To do this, we use the theoretical relationships among the harmonic coefficents of the count rate as a function of spacecraft roll angle derived by Northrop (1985). The majority of the counts were electrons with energy above several MeV, i.e., with drift periods shorter than the satellite orbital resonance. The electrons have isotropic pitch angle distributions, and the protons pancake over most of the region between Mimas and the rings, although there is a small region of dumbbell proton distributions in the vicinity of Janus and Epimetheu

ISSN:0148-0227    

DOI:10.1029/JA090iA12p12085

年代:1985

数据来源: WILEY

摘要:

Some model distributions based on recent observations and simulations of the plasma at the earth's bow shock are found to be unstable to obliquely propagating electrostatic instabilities. The model distributions consist of either an ion beam or an ion velocity ring accompanied by a bi‐Maxwellian background ion distribution and a flattop electron distribution. Ion anisotropies and nonthermal electrons are capable of significantly lowering the threshold of the ion beam instability. The generated waves share many properties in common with the ion acoustic waves that have been observed at the earth's bow shock. The results also indicate the importance of an anisotropy in the background ion velocity distribution in identifying sources of the ion‐acoustic‐like waves observed in the ion foreshock and the solar

ISSN:0148-0227    

DOI:10.1029/JA090iA12p12095

年代:1985

数据来源: WILEY