摘要:

A dynamical model is developed for interaction of solar wind with Martian ionosphere. It is assumed that Mars has a negligible magnetic moment, and a radiative equilibrium model, characterized by an exospheric temperature of 490°K, is adopted for the neutral atmosphere. The ionospheric structure is determined by integration of Maxwell's equations for a 3‐component fluid, in combination with the equations for conservation of mass, momentum, and energy. It is demonstrated that a standing bow shock wave is required by the interaction of solar wind with the ionosphere. Profiles of various flow parameters, as well as electric and magnetic field profiles, are calculated, and the problem of how to extrapolate present results, which are strictly applicable only at the subsolar point, to other locations on the planet is discussed. The computed ionospheric structure is compared with the ionospheric profile observed by Mariner 4 and is found to agree satisfactorily. In particular, the dynamic model predicts a constant scale height of 29 km over an extensive altitude regime, in excellent agreement with the observed value. The dynamic scale height is smaller by a factor of 2 than the value computed under assumptions of photochemical equilibrium, a consequence of the pressure exerted on the ionosphere by the solar wind plas

ISSN:0148-0227    

DOI:10.1029/JA074i026p06215

年代:1969

数据来源: WILEY

摘要:

Numerical solutions of the time‐dependent equations of motion for spherically symmetric flow are obtained to study the propagation and modification of the forward‐reverse shock pair in the region between the sun and 1 AU. For cases where the duration of the disturbance is long compared toT, the shock transit time to 1 AU, a double shock pair that resembles those predicted by similarity theory occurs at 1 AU. In cases where the duration of the solar disturbance is less than about 0.45T, the shock pair structure is appreciably altered by a rarefaction, initiated at the end of the solar disturbance, which has caught up with the shock pair. In cases where the duration is less than about 0.1T, the rarefaction completely destroys the reverse shock, leaving a single shock. This analysis indicates that a forward‐reverse shock pair will not be observed at 1 AU unless the time duration of the solar disturbance is greater than about 5 hours. Since solar flares that last this long are quite rare, it is concluded that observation of a flare‐associated forward‐reverse shock pair at 1 AU is

ISSN:0148-0227    

DOI:10.1029/JA074i026p06229

年代:1969

数据来源: WILEY

摘要:

Charged particle detectors on the Alouette 2 satellite have been used to study various features of solar proton (1–8 Mev) latitude profiles during relatively quiet magnetic conditions, One feature of these profiles that is observed frequently is a flux enhancement close to the cutoff latitude for these particles. The high‐latitude limit of the enhancement, denoted by Λϵ, shows a good correlation with Λb, the background boundary for outer‐zone electrons (E>35 kev). The region of enhanced flux, when it occurs, usually extends down to the latitude cutoff or ‘knee’, which exhibits approximately the same dependence on local time as Λϵ(or Λb) but is displaced 6° or 7° toward lower latitudes. Arguments are given that indicate the enhanced fluxes occur on closed field lines, and it is suggested that solar protons from the tail scatter across closed field lines and the flux enhancements may result from small differences in the probabilities for scattering into and out of the closed field line region. The position of the latitude ‘knee’ as a function of local time and the pitch‐angle distributions close to the ‘knee’ are discussed in

ISSN:0148-0227    

DOI:10.1029/JA074i026p06239

年代:1969

数据来源: WILEY

摘要:

Cosmic‐ray total ionization measurements made in space near the earth with the OGO 1 and OGO 3 ion chambers (cutoff = 12 Mev per nucleon for protons and helium nuclei) during the period September 1964 to December 1967 are compared with other cosmic‐ray measurements in space and on the ground. The findings are: (1) As compared to the recovery phase (before May 1965) the apparent long‐term modulation of the low‐energy (>12 Mev per nucleon) particles was relatively less during the early decreasing phase (June 1965 to December 1966) giving rise to the ‘hysteresis’ effect. The observed effect, which was maximum (∼13%) from June 30, 1966, to July 4, 1966, disappeared completely by April 22–28, 1967. (2) The hysteresis effect is probably a characteristic of the modulation mechanism. It is not likely to be due to the time variation of a quiescent flux of energetic solar particles. (3) The observations in 1964–1965 are consistent with a heliocentric gradient of ∼0% per AU in the range 1.0–1.28 AU and probably also in

ISSN:0148-0227    

DOI:10.1029/JA074i026p06247

年代:1969

数据来源: WILEY

摘要:

Observations have been made of Lyman‐alpha auroral emissions during January and February 1967. The observations were made with a narrow band sky‐scanning photometer mounted on an earth‐oriented satellite in polar orbit. Auroras in the southern hemisphere were usually single in structure, whereas those in the north were complex. The single auroral emissions show a typical latitude spread of about 6.5°. Intensities up to 60 kR were observed at times of high magnetic activity, implying energy deposition up to 20 ergs cm−2sec−1. The intensities show a correlation with high‐latitude geomagnetic activity, with a breakdown during extremely ac

ISSN:0148-0227    

DOI:10.1029/JA074i026p06257

年代:1969

数据来源: WILEY

摘要:

The rate of energy injection into the geomagnetic ring current has been determined for the years 1958 and 1964 using a method based onDstand knowledge of the decay rate for the ring current energy. At all levels of magnetic activity, the temporal behavior of the energy injection is similar toDpin that it is burst‐like; also there is a positive but imperfect correlation betweenDpand the rate of energy injection into the ring current. The onset times of energy‐injection bursts typically occur during the same hour or after the onset times ofDpbursts, and it is often possible to identify an injection burst as being associated with a particularDpburst and then the peaks in both types of activity are simultaneous within one hour. During the quiet year of 1964, the average injection rate, on a monthly basis, was fairly constant and was near 1.2 × 1017ergs sec−1. The rate during the active year 1958 was highly variable with the over‐all average being 1.7 × 1017ergs sec−1. Maximum hourly average injection rates of 1 × 1019ergs sec−1occurred during great magnetic storms. Although the injection of energy into the ring current, averaged over the entire ring, increases during a magnetospheric substorm, examination of longitudinal differences in the injection indicate temporary losses from the midnight and morning sectors at the onset of some substorms. Also it is found that when a magnetic storm follows a prolonged period of magnetic quiet, there is often precursor activity lasting

ISSN:0148-0227    

DOI:10.1029/JA074i026p06266

年代:1969

数据来源: WILEY

摘要:

In a magnetosphere with a magnetic tail and a perfect neutral sheet, the steady‐state field line configuration is found to depend on two variables: the magnetic flux in the tail and the solar wind momentum flux. Thus, changes in solar wind momentum flux, or transport of magnetic field lines into and from the tail cause a large‐scale magnetospheric flow toward the new equilibrium configuration. The solutions to the two‐dimensional case are used to study the flows and indicate the following: (1) Changes of the momentum flux of the solar wind are important in producing convective flow, only if they are an order of magnitude in a short time. (2) The large‐scale convective flow is usually determined to first order by the rate at which field lines are being carried into the tail and is probably not dependent on occurrences at the neutral sheet. (3) Reconnection and collapse of tail field lines to a dipolar‐like configuration could produce significant magnetosphere‐wide flow only if it was burst‐like in occurrence. The magnetospheric response to forces that produce flows depends on the relative size of three time constants: The time constant of the driving force, the time to set up a stressed magnetosphere, and the time to relax it by motion of field line feet through the conducti

ISSN:0148-0227    

DOI:10.1029/JA074i026p06275

年代:1969

数据来源: WILEY

摘要:

An Argo D‐4 (Javelin) rocket was launched from Wallops Island, Virginia, at 1828 GMT, Aug. 15, 1966, to rendezvous with a pass of the Explorer 31 and Alouette 2 satellites. The rocket reached an altitude of 720 km while the satellites were at 970 km. Identical magnetic mass spectrometers on the rocket and Explorer 31 satellite measured the composition of the ionosphere while the Alouette 2 topside sounder provided electron concentration profiles. Ten different ion species were observed. O+is the dominant constituent from 200 km to 1000 km with H+5% and He+less than 1% of the O+. The chemical equilibrium relation between H+and O+gives a value for the neutral hydrogen concentration of 6.2 × 104at 250 km and a neutral gas temperature of 940°K. From the He+concentration at 400 km a rate coefficient for the He+loss reaction with N2of 1.2 × 10−9cm³ sec−1is calculated. The NO+and O2+scale heights from 200 to 300 km agree with those of N2and O2giving credence to the ion chemistry involved. In comparing the results from this rocket flight with those of other types of mass spectrometers flown in a similar time period, it is seen that the major discrepancy lies in then(H+) measurements, the present result being lowest. The in‐flight calibration tends to indicate that a mass spectrometer is more sensitive to light mass ions than to O+. This phenomenon may account for the discre

ISSN:0148-0227    

DOI:10.1029/JA074i026p06281

年代:1969

数据来源: WILEY

摘要:

Data obtained from the Alouette 2 Langmuir probe experiment during a 3‐month period in the fall of 1966 have been examined for effects due to electron concentration irregularities (fine structure). Irregularities occur in patches hundreds of kilometers in horizontal extent, and individual irregularities have amplitudes between 5% (limit of resolution) and 70% and dimensions of less than 2 km along the satellite path. These irregularities appear more often at night than during the day, and they occur in a region that contains the auroral oval and extends to both higher and lower latitudes. Comparison of the probe data with Alouette 2 ionograms obtained simultaneously shows that spreadFoccurred at the height of the satellite whenever fine structure was observed. However, particularly at mid latitudes, spreadFoften occurs at the satellite even when the probe does not detect irregularities. When spreadFoccurs, but the probe does not observe fine structure, the irregularities are less than 5% in amplitude (i.e., below the probe’s resolution). Calculations using an irregularity model indicate that spreadFis often caused by irregularities less than 0.5 km thick. Several irregularity production mechanisms that could account for the results are discus

ISSN:0148-0227    

DOI:10.1029/JA074i026p06291

年代:1969

数据来源: WILEY

摘要:

Problems relating to steady, ambipolar flow of plasma are discussed with application to the terrestrial ionosphere. It is shown that steady flow, either accretion or escape, must be a general condition in the absence of a constraining magnetic field and that diffusive equilibrium results only for one particular value of the asymptotic boundary plasma pressure. With regard to plasma escape, subsonic and supersonic flows act to reduce ion densities below the values found for diffusive equilibrium. The usual diffusion equation appropriate to low‐speed plasma transport leads to two linearly independent density distributions corresponding to diffusive equilibrium and full flow. For any model, linear combinations of these two solutions must be used to match density and velocity boundary conditions. The equations appropriate to high‐speed plasma transport are developed, and boundary conditions appropriate to supersonic and subsonic flow are discus

ISSN:0148-0227    

DOI:10.1029/JA074i026p06304

年代:1969

数据来源: WILEY