摘要:

The characteristics of the cosmic ray produced secondary background encountered in X‐ray astronomy experiments by balloon‐borne scintillation telescopes using NaI(Tl) in the energy range 20–200 kev at small atmospheric depths is derived and discussed in detail. For equatorial latitudes almost all background originates from the electromagnetic interactions, especially through Compton scattering, of photons of energy greater than 200 kev with the scintillation crystal as well as shielding materials. The background originating from nuclear interactions like π° decay gammas, radiative capture, and star production of neutrons is found to be negligible. At high latitudes the atmospheric X rays in the 20‐ to 200‐kev interval also contribute significantly to the background. These features of the background lead to the conclusion that by suitable detector design, particularly by reducing the thickness of the scintillation crystal, it is possible to appreciably improve the sensitivity to cosmic X rays for X‐ray telescopes flown on equatorial balloon flights compared with h

ISSN:0148-0227    

DOI:10.1029/JA076i016p03527

年代:1971

数据来源: WILEY

摘要:

An extensive study of the dynamic nonshock properties of the microscale fluctuations (scale lengths of 0.01 AU and less) in the interplanetary medium was made by using plasma and magnetic field data from Mariner 5 (Venus 1967). The observational results of the study are: (1) Large‐amplitude, nonsinusoidal Alfvén waves propagating outward from the sun with a broad wavelength range from 103to 5×106km dominate the microscale structure at least 50% of the time; the waves frequently have energy densities comparable both to the unperturbed magnetic field energy density and to the thermal energy density. (2) The purest examples of these outwardly propagating Alfvén waves occur in high‐velocity solar wind streams and on their trailing edges (where the velocity decreases slowly with time). In low‐velocity regions Alfvén waves are also outwardly propagating but usually have smaller amplitudes than in the fast streams and tend to be less pure in the sense that they are more strongly intermixed with structures of a non‐Alfvénic and possibly static nature. (3) The largest amplitude Alfvénic fluctuations are found in the compression regions at the leading edges of high‐velocity streams where the velocity increases rapidly with time; these regions may contain significant amounts of inwardly propagating or non‐Alfvénic wave modes. (4) Power spectra of the interplanetary magnetic field in the frequency range from 1/(107 min) to 1/(25.2 sec) have frequency dependencies of ƒ−1.5to ƒ−2.2; the spectra with slower falloffs tend to be associated with higher temperature regions. (5) The microscale magnetic field fluctuations have on the average a 5∶4∶1 power anisotropy in an orthogonal coodinate system whose axes are (eB×eR, eB×(eB×eR), eB), where eBis a unit vector in the average field direction and eRis a unit vector radially away from the sun; this anisotropy tends to be strongest (6∶3∶1) in the compression regions at the leading edges of high‐velocity streams. (6) Presumably magnetoacoustic wave modes occur, but they have not been identified and, if present, have a small average power of the order of 10% or less of that in the Alfvén mode.These observations are organized on the basis of a model of the solar wind velocity structure. Most Alfvén waves in the interplanetary medium are likely the undamped remnants of waves generated at or near the sun. The high level of wave activity in high‐velocity high‐temperature streams can be interpreted as evidence for the extensive heating of these streams by wave damping near the sun. The highest level of Alfvénic wave activity in the compression regions at the leading edges of high‐velocity streams may be due to either the amplification of ambient Alfvén waves in high‐velocity streams as they are swept into the compression regions or the fresh generation of waves in these regions by the stream‐stream interactions. The observed absence of the magnetoacoustic modes is evidence for their strong damping. The eB×eRanisotropy is viewed as due to the partial conversion of the Alfvén waves to the damped magnetoacoustic modes as they are convected away from the sun; this process continually transfers energy from the microscale fi

ISSN:0148-0227    

DOI:10.1029/JA076i016p03534

年代:1971

数据来源: WILEY

摘要:

The accurate in situ measurement of the weak magnetic fields in interplanetary space and near the moon and planets by satellites has often been limited more by the spacecraft generated magnetic field than by the zero level stability of the magnetometer or the quantization uncertainty of the telemetry data readout system. A new method is proposed for obtaining improved results even in the presence of a large and variable spacecraft field. The method uses simultaneous data from two magnetometers whose sensors are placed at different positions along a moderately long boom. The analysis of the data yields a continuous estimate of the spacecraft field and the unknown field in space. The accuracy is determined by the validity of assumptions concerning the spacecraft field and the zero level drifts of the sensors. It is assumed that the external field to be measured is spatially uniform on the distance scale of the sensors' separation distance. This method can be used on both spin stabilized and fixed attitude spacecraft. Specific application to the future NASA‐JPL Manner Venus Mercury mission in 1973 is presented, with an estimated accuracy of ±0.5 to ±1.0 gammas using a 6‐meter

ISSN:0148-0227    

DOI:10.1029/JA076i016p03564

年代:1971

数据来源: WILEY

摘要:

Observations of electron fluxes between 25 ev and several kev by the triaxial electron spectrometer and of the magnetic field by the fluxgate magnetometer on the satellite Ogo 5 are used to study the structure and movement of the magnetopause. The observations were made at both quiet and fairly disturbed times between 6.4 and 7.6 hours local time and at geomagnetic latitudes between 16° and 40°. The boundary layer electron fluxes forV<8000 km/sec (energy8000 km resemble those observed in the magnetosphere. The magnetic field in the boundary layer has either magnetospheric or transitional characteristics. These observations suggest the possibility of mixing of the magnetosheath plasma with the magnetospheric plasma, which would be important in determining the structure of the boundary layer. It is inferred from pressure balance across the magnetopause, in agreement with previous work, that β (=plasma energy density/magnetic field energy density) is close to or exceeds unity in the region of the magnetosphere immediately adjacent to the dawn magnetopause. Values of βccalculated from the observed electron spectra indicate substantial contributions to β from other particle popul

ISSN:0148-0227    

DOI:10.1029/JA076i016p03574

年代:1971

数据来源: WILEY

摘要:

Equatorial observations by the geostationary satellite ATS 5 of the charged particles on auroral lines of force reveal the frequent injection of plasma into this region of the magnetosphere. These intrusions of hot plasma are found to have a one‐to‐one correspondence with magnetospheric substorms. An injection is assumed to correspond to an inward flow from the plasma sheet in the magnetotail. This flow seems to subside gradually so that injection eventually ceases. The net result is the insertion of a relatively discrete set of particles, i.e., a ‘plasma cloud,’ on lines of force that are not normally involved in the flow of the plasma sheet particles. The clouds of freshly injected plasma are dispersed by the earth’s magnetic and electric fields such that complicated energy structure is

ISSN:0148-0227    

DOI:10.1029/JA076i016p03587

年代:1971

数据来源: WILEY

摘要:

An array of sensitive electrostatic analyzers was borne on the earth satellite Injun 5 in a nearly polar low‐altitude orbit. The energy spectrums and angular distributions of proton and electron intensities over the energy range 5≲E≲50,000 ev were measured separately and simultaneously with good temporal and energy resolutions over the auroral zones and polar cap regions and within the outer radiation zone. Fully color‐coded energy‐time (E‐t) spectrograms are utilized to present and effectively digest a massive body of individual intensity measurements. Several of the principal observational results were: (1) In the late evening sector the electron precipitation patterns are usually characterized by two or more bands of low‐energy electron precipitation during periods of relative magnetic quiescence,Kp≃0 to 2. (2) With increasing magnetic activity,Kp≃3 to 4+, these ‘bands’ of precipitated electron intensities become more intense, and often less well defined, relative to those observed during quiescent periods. (3) During these periods of relative magnetic disturbance, a persistent inverted ‘V’ substructure in theE‐tspectrograms is evident. This substructure displays a well‐defined increase of the electron energy for peak differential intensities with time to a maximum energy usually ∼kiloelectron volts followed by a subsequent decrease of this energy. (4) Occasionally a relatively structureless, broad precipitation pattern is observed at late local evening during magnetically disturbed periods. (5) In the late local evening sector the dominant band of proton precipitation is often located just inside, i.e., equatorward of, the termination of low‐energy electron precipitation. (6) Energy influxes into the earth's upper atmosphere during late evening have been observed to be as low as ≲1 erg (cm2sec)−1during magnetic quiescence and as high as ≃250 ergs (cm2sec)−1for disturbed periods. (7) The over‐all features of electron precipitation in the late‐morning sector are generally more diffuse and less intense relative to those observed during local evening. (8) The late‐morning precipitation patterns are often characterized by a subtructure, not spanning the width of the entire precipitation region, that displays decreasing average electron energies with increasing invariant latitudes. (9) The electron precipitation in the late morning sector is often bounded at its high‐latitude edge by a remarkably intense, narrow band of low‐energy electron intensities. Typical widths of this intense, unique structure are ∼20 to 30 km. The electron spectrums and densities are similar to those observed in the distant magnetosheath. These observations are discussed in terms of previous results gained with similar instrumentation at great distances within the earth's magnetosphere near the magnetic equator and the implications concerning the

ISSN:0148-0227    

DOI:10.1029/JA076i016p03612

年代:1971

数据来源: WILEY

摘要:

Ogo 2 and Ogo 4 VLF data on plasmapause crossings were compared with SAR arc observations reported on September 29, 1967, and on October 31 and November 1, 1968. The positions of the plasmapause and SAR arcs were found to agree within ±1° in invariant latitude. Ogo 4 evidence from the 0900–2100 MLT (magnetic local time) plane showed that the known local‐time asymmetry in plasmapauseLvalue (evening maximum, dawn minimum) could explain some of the apparent motions of the arcs as viewed from ground stations. Some other details of the arc motions are apparently due to substorm‐related convection events in the outer plasm

ISSN:0148-0227    

DOI:10.1029/JA076i016p03644

年代:1971

数据来源: WILEY

摘要:

Fluctuations of the magnetospheric electric field with periods between 1 minute and 1 day have been studied by analyses of more than 200 power spectra generated from about 700 hours of electric field data obtained by flight of 44 balloons at sites ranging inLfrom 2.8 to 23. Arguments that include the variations of these power spectra with magnetic activity, local time, and latitude are advanced to show that fluctuations of ionospheric and not weather‐associated electric fields have been measured. The variations of the ionospheric power spectra with latitude and local time are consistent with a uniform power (independent of local time andLfor 8≥L≥3) in the equatorial electric field of magnitudePi(ν) = (100−70+200)(exp 0.4Kp) (ν−1.6±0.3), wherePi(ν) is the power (millivolts2/meter2hertz) of theith perpendicular component of the equatorial electric field at a frequency of ν cycles/hour. The uncertainties in this expression are standard deviations in single determinations of power spectra from 6‐hour segments of data and represent real variations in the electric field power. The fluctuations in the two perpendicular components are anticorrelated such that the power in the total field is generally less than that of the larger component. The broadband root mean square equatorial electric field strength of either component obtained from the above equation is about 0.6 mvolts/m forKp=2, a value indicating that a significant fraction of the quasistatic magnetospheric electric field arises from long‐period fluctuations and that the field is therefore extremely turbulent. Since the equatorial power does not decrease inside the plasmapause, magnetospheric electric field fluctuations must penetrate efficiently into the outer plasmasphere. The measured power in the electric field fluctuations is at least an order of magnitude larger than that which would be obtained in a completely open magnetosphere from fluctuations of the interplanetary electric field if it convected freely through the magnetosphere. The measured power spectra are adequate to drive the radial diffusion of trapped energetic charged particles in the Van Allen belts although detailed comparisons between electric field power spectra and particle diffusion rates require further information on scale lengths over which the fluctuating fields are corre

ISSN:0148-0227    

DOI:10.1029/JA076i016p03651

年代:1971

数据来源: WILEY

摘要:

The Dodge satellite detected regular and irregular micropulsations and a variety of other temporal variations in the vector geomagnetic field at 6.25RE. The regular micropulsations with periods between 3 and 240 sec are Alfvén waves, transverse to the ambient field, with amplitudes usually between 1 and 20 γ that increase with period. The polarization is linear or elliptical. Toroidal, poloidal, and mixed modes are observed. It is suggested that the dominant eigenmode of the outer magnetosphere has a period of about 40 se

ISSN:0148-0227    

DOI:10.1029/JA076i016p03668

年代:1971

数据来源: WILEY

摘要:

In summer 1969 a line of 7 magnetic stations was set up in western Canada between the geomagnetic latitudes of 59° and 77°N and within ∼2° of 302°E corrected geomagnetic longitude. This paper concerns the analysis of the horizontal components of quasi‐monochromatic, geomagnetic micropulsations recorded at these stations over 3 days. Both the amplitude spectra and the sense of polarization of the micropulsations exhibit marked latitude dependence, thus implying that much of the micropulsation energy is distributed in the toroidal mode of eigenoscillations of the geomagnetic lines of force. A switch in the sense of polarization around 1200–1400 LT strongly suggests that Pc micropulsations are generated through the development of Kelvin‐Helmholtz instabilities at the m

ISSN:0148-0227    

DOI:10.1029/JA076i016p03675

年代:1971

数据来源: WILEY