摘要:

The two‐fluid model for the solar wind of Hollweg (1970) is reconsidered with the inclusion of the spiral structure of the interplanetary magnetic field. In the present model, the protons are assumed to become collisionless beyond 0.1 AU from the sun, whereas the electrons are treated hydrodynamically and the electron temperature is supposed to obey the polytropic law. The electric field established from the charge separation, which is assumed to be derivable from a potential, tends to enhance the velocity of the solar wind at 1 AU to a value over 300 km/sec. The proton thermal anisotrophyT∥/T⊥at the orbit of the earth is reduced from the value of 50 in the model with the radial magnetic field to the value of 11 in the present

ISSN:0148-0227    

DOI:10.1029/JA077i001p00001

年代:1972

数据来源: WILEY

摘要:

An autocorrelation analysis has been performed on the Vela 2 and 3 solar‐wind speed data obtained from July 1964 through December 1967 with two goals: to establish the degree to which speed structures recur from one solar rotation to the next, and to examine the duration and origin of ‘persistence’ in the solar‐wind speed. The average correlation between speed measurements separated in time by 1 solar rotation is 0.3, thus implying that most speed structures during the period under consideration do not endure for 28 days; however, the amplitude of the correlation varies with time from less than 0.1 to greater than 0.7. Differential solar rotation serves to weaken the correlation at any particular lag; the data suggest that a wide variety of solar latitudes contribute to the solar wind observed near the earth. Recurrence periods ranging from about 27 to 29 days were observed; these periods differed from those determined from interplanetary‐field measurements for the same interval by as much as a day. Correlations associated with the solar rotation are questionable after about August 1966; this fact may be related to increased solar activity associated with the advance of the solar cycle. High‐speed streams are not the primary source of correlations between speed measurements separated by about 28 days; rather, low‐speed (<400 km sec−1) streams make the major contribution to the correlations observed. Those speed structures which do recur for more than 1 solar rotation have variable lifetimes, but few endure for more than 2 solar rotations. Measurements of the solar‐wind speed separated by a day or less are usually highly correlated; the average correlation is 0.94 and 0.64 at lags of 3 hours and 1 day, respectively. It is found that this positive correlation, or persistence, extends out to about 3 days on the average; it is argued that about half this interval is the time over which the solar wind can be considered as ‘steady.’ Persistence is limited by both the spatial scale of coherent emission from the sun and the temporal evolution of the solar atmosphere. It is suggested that 4 days is a typical time interval over which significant changes occur in the flow speed of the wind emanating fro

ISSN:0148-0227    

DOI:10.1029/JA077i001p00012

年代:1972

数据来源: WILEY

摘要:

An analysis is given of five stream‐stream interaction events observed in the Pioneer 6 plasma and field data. That the time profiles of all the parameters are consistent among the events and with previous descriptions given in the literature substantiates the notion of a common interaction type. The velocity variations in four of the events tend to lie in planes approximately parallel to the corotation spiral; thus it is implied that the events are reasonably stationary in time in the corotating frame. The data are interpreted in terms of a corotating interaction front, which is a ridge of high pressure parallel to a corotating spiral. The increased pressure is due to radial compression of the streams. The east‐west (zonal) flow directions also occur in the front and are shown to be produced by the zonal pressure gradient of the pressure ri

ISSN:0148-0227    

DOI:10.1029/JA077i001p00027

年代:1972

数据来源: WILEY

摘要:

The problem of the solar‐wind structure resulting from long‐lived inhomogeneities in the solar corona has been extended within the framework of a linearized hydrodynamic approach to allow for arbitrary perturbations in the plasma parameters, namely, velocity, density, and temperature. By using a Parker model for the zero‐order flow speed, solutions are given for perturbations imposed at the zero‐order critical point. Using the restriction that the solutions must be regular at the critical point, it is possible to express all situations as a linear sum of the solutions for pure velocity, density, and temperature perturbations at the critical point. The results of the integrations for the three inner‐boundary conditions can be used as the elements of matrices that map arbitrary perturbations at one heliocentric distance to any other distance. One interesting feature of the solutions is that the amplitudes at earth for the pure initial temperature situation are larger than for the other two situations. Thus, if the perturbation amplitudes at the critical point are all of the same order of magnitude, the temperature perturbation will dominate the structure at earth. In fact, the phases between the perturbations at earth given by the pure initial temperature situation are similar to the obs

ISSN:0148-0227    

DOI:10.1029/JA077i001p00035

年代:1972

数据来源: WILEY

摘要:

Actively collimated balloon‐borne scintillation counters employing a special phoswich anticoincidence technique were flown a total of 5 times from Palestine, Texas. Jupiter was observed for a total of 133 min, and an upper limit to the flux of X rays present at the observation time is 1.6 × 10−2X rays/cm² sec in the energy range 30‐100 kev. Three separate calculations are made to estimate the flux of Jovian X rays at the earth; the first two calculations involve scaling up terrestrial precipitating electron fluxes by factors that depend on the energy intercepted by Jupiter's magnetosphere and the Jovian magnetic‐field strength, whereas the third estimate is based on a model of Jovian decametric emission. These estimates range from 10−9to 10−1X rays/cm² sec in the energy range 30‐100 kev. It is concluded that, since there was no decametric emission at the time of the flight and there had been no significant solar activity for several days prior to the flight, no X rays were being generated at the time of

ISSN:0148-0227    

DOI:10.1029/JA077i001p00046

年代:1972

数据来源: WILEY

摘要:

The Mariner 6 and 7 ultraviolet spectrometer experiments observed intense emissions from CO, O, and CO2+in the Martian airglow. Analysis shows that they are excited predominantly by the absorption of solar EUV photons by CO2and constitute a major energy‐loss mechanism for the thermosphere. Models of the thermospheric temperature profile and the airglow layer that demonstrate the effects of neutral chemistry and ionospheric composition are developed. With their aid, the observed CO Cameron‐band emission scale height of 19 ± 4½ km is shown to suggest an exospheric temperature of 315 ± 75°K. Consideration of other data suggests a ‘best’ value of about 350°K. The emissions from CO2+are consistent with a topside ionosphere containing about 30% CO2+. The abundance of O necessary to convert the rest to O2+is about 2% at 135 km, in good accord with an independent determination. Within the uncertainties in the excitation efficiencies and in the thermospheric cooling mechanisms, the observations are consistent with the measured electron density. Eddy cooling may be important if the eddy diffusion coefficient is large, but it is difficult to reconcile the heating effects of CO3with the small observed airglow scale heights. There is no indication in the data that the ionosphere is modified by the solar wind

ISSN:0148-0227    

DOI:10.1029/JA077i001p00054

年代:1972

数据来源: WILEY

摘要:

The dissociative excitation of CO(a³Π) and other metastable fragments such as O(5S0) produced by electron impact on CO2has been investigated from threshold to 50 ev. The observed threshold for CO(a³Π) production at 11.9 ± 0.5 ev was near the minimum required energy of 11.5 ev. If an isotropic distribution of CO(a³Π) fragments after dissociation was assumed, the cross section for dissociative excitation of CO(a³Π) from CO2was found to be about 3.6 × 10−17cm² at 20 ev, which is 3 times smaller than the maximum cross section for the direct excitation of CO(a³Π) from CO. We also used our time‐of‐flight data to infer a value for the CO(a³Π) dissociative excitation cross section from Ajello's relative cross section measurements, and we obtained a slightly lower value of 1.6 × 10−17cm² at 20 ev. These experiments imply a maximum cross section value of (4.1 ± 3.0) × 10−17cm² at 27 ev. The differential cross section for the dissociative excitation of CO(a³Π) at right angles to the electron beam was found to bedσ/dΩ = (3.0 ± 2.2) ×

ISSN:0148-0227    

DOI:10.1029/JA077i001p00069

年代:1972

数据来源: WILEY

摘要:

It is shown that the contribution of higher harmonics to the lunar transfer functions for the tangential components of the surface magnetic field is significant at frequencies greater than 0.01 Hz (Apollo 12 and Explorer 35 magnetometer data extend to frequencies as high as 0.04 Hz). The inclusion of the higher harmonics shows that there are two distinct transfer functions corresponding to the components of the tangential surface magnetic field perpendicular and parallel to the direction of the wave vector of the external disturbance forcing the lunar induction. The dependences of these transfer functions on frequency and location are determined. The effects of the higher harmonics can (1) account for a hitherto unexplained feature in the Apollo 12 and Explorer 35 transfer functions, namely the rolloff at high frequencies, and (2) offer a possible explanation for the frequency dependence of the difference between the transfer functions for the two orthogonal components of the surface magnetic field. The harmonic response of a simple current layer model of the moon is derived and shown to provide a reasonable fit to the experimental data.

ISSN:0148-0227    

DOI:10.1029/JA077i001p00076

年代:1972

数据来源: WILEY

摘要:

Two types of circularly polarized hydromagnetic waves that can propagate upstream in the solar wind exist. One type is right‐hand polarized with respect to the ambient magnetic field and has both its phase and group velocities directed upstream. It is a Doppler‐shifted whistler mode that in a stationary frame has a much larger phase velocity than the solar‐wind velocity. The other is left‐hand polarized with respect to the ambient field and has its phase velocity directed downstream, but its group velocity is directed upstream. It is shown that the latter mode, which is also a Doppler‐shifted whistler mode but which propagates backward in the moving frame, can be excited at the bow shock through a two‐stream type instability between the solar wind and the magnetosheath plasma. The instability occurs around the local proton cyclotron frequency, and the generated wave can be convected upstream by this mode with a group velocity approximately equal to the solar‐wind velocity. This instability, because of its scale size, is shown also to be a possible candidate for the sh

ISSN:0148-0227    

DOI:10.1029/JA077i001p00084

年代:1972

数据来源: WILEY

摘要:

A study of the internal structure of the neutral sheet in the geomagnetic tail has been made from data obtained by the NASA‐GSFC magnetic‐field experiment on the Explorer 34 spacecraft during its tail passage in the first half of 1968. The data used in the analysis are individual measurements of the vector magnetic field at 2.56‐sec intervals. The experimental results consist of statistical studies of relevant properties of the magnetic field as a function of field magnitude. The results do not support nearly one‐dimensional field models with characteristic lengths for field variation parallel to the neutral sheet much larger than the neutral‐sheet width. The principal conclusion from the data points toward consistency with a quasi‐periodic (possibly turbulent) structure with a tendency to formation of magnetic loops as one might expect from stability studies. Numerical results obtained using a simple model with a periodic field pattern in the field reversal region are compared with the observed interna

ISSN:0148-0227    

DOI:10.1029/JA077i001p00091

年代:1972

数据来源: WILEY