摘要:

The theory for a spherical collisionless planetary corona is extended to include charge exchange collisions between H+and H, which are assumed to constitute intermingled gases with different kinetic temperatures. The treatment is based on the conventional concept of a critical level (or exobase), above which the only collisions considered in the Boltzmann equation are those that resonantly exchange charge. Satellite orbits are not included. Although the geometry treated is an oversimplification for a real planet, numerical examples are given for an idealized earth and Venus. For earth an ion temperature of 4 times the neutral temperature, an ion density at the exobase of 1.4 × 104cm−3, and a plasmapause at 1.5REwill raise the escape flux of H by a factor of 6. The total H above the exobase is changed by less than 1%. For Venus the conditions are examined that would account for the peculiar H distribution observed from Mariner 5. The plasma conditions required are not obviously outrageous by terrestrial standards, but the Mariner 5 ionosphere measurements did not show a high plasmapause at, say, 1.25 or 1.5 planetary radii, a fact that might argue against a charge exchange mod

ISSN:0148-0227    

DOI:10.1029/JA082i001p00001

年代:1977

数据来源: WILEY

摘要:

We examine the plasma and magnetic field changes occurring across 1359 directional discontinuities taken from interplanetary data spanning almost four solar rotations. The plasma field characteristics of these events exhibit a distinct variation with large‐scale solar wind velocity. At low velocities, tangential discontinuities appear to predominate. At higher velocities a substantial and increasing fraction of directional discontinuities exhibits the plasma field properties expected of outwardly propagating rotational discontinuities. The results of Sari (1972, 1975) and of the present study suggest that in the calculation of propagation diffusion coefficients for low‐energy cosmic rays, the effects of directional discontinuities should be subtracted from the magnetic fluctuation spectrum during relatively quiet wind conditions. It is not clear that such subtraction is necessary during more disturbed peri

ISSN:0148-0227    

DOI:10.1029/JA082i001p00010

年代:1977

数据来源: WILEY

摘要:

Air radiation (N, O, N2) is present in major amounts in the spectra of three high‐geocentric‐velocity photographic meteor spectra. These spectra are high‐definition spectra with over 50 identifiable features in each spectrum. These meteor spectra are compared with N2radiation from a Geissler tube and with calculated N2first‐positive band intensities. An ‘effective vibrational temperature’ of about 20,000 K is obtained from the nitrogen first‐positive band relative intensities. Electron excitation is indicated as the primary excit

ISSN:0148-0227    

DOI:10.1029/JA082i001p00015

年代:1977

数据来源: WILEY

摘要:

The roles of rapid flow tube divergence and heat and momentum addition in one‐fluid models of the solar wind and stellar winds and the role of heat addition in two‐fluid models of the solar wind are explored. It is found that under certain circumstances heat addition, momentum addition, or the rapid divergence of a flow tube can produce more than one critical point in the solution topologies of the solar and stellar wind equations. For the solar wind, additional critical points associated with rapid flow tube divergence (e.g., in coronal holes) and/or with momentum addition can lead to high expansion speeds near the coronal base, and these high speeds, in conjunction with a rapid flow tube divergence, may in certain cases produce an increased conductive energy supply to the solar wind. If such an increased conductive energy supply is produced, the need for energy addition above the coronal base is correspondingly reduced. In addition, the high flow speeds at low altitudes make it possible for any required energy addition to occur relatively near the coronal base, so that the need for extended heating of the solar wind may be substantially less than has been suggested in the past. For radiation‐driven stellar winds the additional critical points associated with rapid flow tube divergence can lead to supersonic flow much deeper in the stellar atmosphere than is predicted by radial, spherically symmetric flow models, and this might resolve the apparent conflict between radiation‐driven wind models and certain observations of Of stars. In two‐fluid solar wind models including proton heat addition it is shown that the radial electron temperature profile has a sufficiently important dynamical influence that the accurate treatment of electron energy transport is a primary prerequisite to obtaining quantitatively significan

ISSN:0148-0227    

DOI:10.1029/JA082i001p00023

年代:1977

数据来源: WILEY

摘要:

The Atmosphere Explorer‐C satellite (AE‐C) is uniquely suited for correlative studies with ground‐based stations because its on‐board propulsion system enables a desired ground station overflight condition to be maintained for a period of several weeks. It also provides the first low‐altitude (below 260 km) comparison of satellite and incoherent scatter electron and ion temperatures. More than 40 comparisons of remote and in situ measurements were made by using data from AE‐C and four incoherent scatter stations (Arecibo, Chatanika, Millstone Hill, and St. Santin). The results indicate very good agreement between satellite and ground measurements of the ion temperature, the average satellite retarding potential analyzer temperatures differing from the average incoherent scatter temperatures by −2% at St. Santin, +3% at Millstone Hill, and +2% at Arecibo. The electron temperatures also agree well, the average satellite temperatures exceeding the average incoherent scatter temperatures by 3% at St. Santin, 2% at Arecibo, and 11% at Millstone Hill. Several temperature comparisons were made between AE‐C and Chatanika. In spite of the highly variable ionosphere often encountered at this high‐latitude location, good agreement was obtained between the in situ and remote measurements of electron and ion temperatures. Longitudinal variations are found to be very important in the comparisons of electron temperature in some locations. The agreement between the electron temperatures is considerably better than that found in some earlier comparisons involving satellites at

ISSN:0148-0227    

DOI:10.1029/JA082i001p00036

年代:1977

数据来源: WILEY

摘要:

Electron energy spectra from 10 eV to 25 keV have been obtained from steady diffuse auroral forms at altitudes above 150 km by the Atmosphere Explorer C and D spacecraft. Overlapping coverage of the energy range was provided by the photoelectron spectrometer experiment (10–500 eV) and the low‐energy electron experiment (0.2–25 keV). The spectral shape between 10 and 20 eV is independent of altitude between 150 and 270 km, has variable energy dependence between ∼20 and 150 eV, and above ∼150 eV has energy dependence determined primarily by the details of the energy spectrum of electrons incident on the atmosphere. The observed results are in satisfactory agreement with two recently published model cal

ISSN:0148-0227    

DOI:10.1029/JA082i001p00043

年代:1977

数据来源: WILEY

摘要:

The electron population in and near the loss cone comprises trapped electrons, electrons that have diffused into the loss cone since their last bounce, and electrons that have interacted one or more times with the atmosphere. The distribution function of these electrons has been calculated by stepwise integrating the local pitch angle diffusion equation for wave‐particle interactions along the magnetic field line. Above the atmosphere the diffusion mechanism is wave‐particle interactions. At the atmosphere the scattering and energy loss collisions with atoms were included in the calculation. The results show that the pitch angle distributions of loss cone electrons depend strongly on the wave‐particle diffusion coefficients and that measurements of electron fluxes can be used to derive values of these coefficients. Comparisons of the theoretical distributions with presently available data show the promise of the procedure but demonstrate the need for additional experimental

ISSN:0148-0227    

DOI:10.1029/JA082i001p00048

年代:1977

数据来源: WILEY

摘要:

The magnetospheric compression associated with the very large magnetic storm of August 4–5, 1972, provided an opportunity for Explorer 45 to observe plasma waves in the magnetosphere and the magnetosheath during extremely disturbed conditions. Electrostatic noise bursts were observed near the plasmapause in electric field channels from 35 Hz to 5.62 kHz. In the outer magnetosphere, electric field noise bands apparently harmonically related to the electron gyrofrequency with components as low as 3 kHz and as high as 50 kHz were observed. The electric field of the fundamental was perpendicular toB0. A mechanism including the electron cyclotron instability may generate the noise band. Hiss of 100–1000 Hz was observed in the outer magnetosphere. The electromagnetic hiss was generally weak and was observed in the magnetic wide band data only when it was strong. In the magnetosheath broad band, incoherent noise (hiss) was observed from 1 Hz to 100 kHz. This magnetosheath hiss was the strongest phenomenon observed by the plasma wave detectors during the lifetime of Explorer 45. The highest intensities of magnetosheath hiss occurred at the magnetopause. Its broad band nature suggests that magnetosheath hiss was generated locally. Broad band noise bursts and short bursts of chorus were also observed in the magnetoshe

ISSN:0148-0227    

DOI:10.1029/JA082i001p00055

年代:1977

数据来源: WILEY

摘要:

During December 1974 and January 1975 the northern magnetospheric cleft was monitored by ionosondes at Cape Parry and Sachs Harbor, Northwest Territories, Canada, in support of rocket shots into the cleft. Ionograms were taken nominally at 15‐min intervals but as rapidly as two per minute during times of particular interest. Analysis of 5 days of data shows the ionosphere at cleft latitudes to be very complex and dynamic. The ionograms often show considerable structure and can change appearance significantly in a minute or two. The cleft at times appears to move equatorward in response either to a southward turning of the interplanetary magnetic field or to the occurrence of geomagnetic disturbances. This response is in agreement with the conclusions of previous satellite studies. Behavior contrary to this generalization is not uncommon, however, and therefore it may not always hold on time scales considerably shorter than the satellite orbital period of ≳ 1 hour. The rate of the cleft's motion may vary from ∼0.05 to ∼0.5

ISSN:0148-0227    

DOI:10.1029/JA082i001p00067

年代:1977

数据来源: WILEY

摘要:

In order to study the relationship between substorm occurrence and magnetospheric compression caused by solar wind discontinuities, 125 storm sudden commencements (ssc's) observed during the 4 years 1967–1970 were examined by using ground magnetograms, AE indices, and magnetic field data obtained by Explorer 33, 34, and 35 and OGO 5. Statistical and case studies confirm that geomagnetic activity and interplanetary magnetic field conditions before the ssc's are important factors for the subsequent triggering of substorms and that the triggering probability tends to increase with increase in ssc magnitude. Negative bays at auroral latitudes followed 43% of the ssc and si (sudden impulse) events examined. In approximately 90% of these cases the AE indices showed appreciable activity (AE>100 γ) during an interval of 15 min before the ssc. When the previous AE is small (<100 γ), the probability of triggering is very low (∼8%) and is almost independent of ssc magnitude. An examination of interplanetary magnetic field data also revealed that the north‐south component was negative or decreasing over a period of 30 min before the passage of the discontinuity when negative bays immediately followed the ssc. These results suggest that preconditions are required for triggering of a substorm by magnetospheric compression. In other words, the triggering probability is high when the magnetosphere is in a metastable or favorable state for substorm occurrence, as is expected during the growth phase. When a substorm is in progress, a further enhancement of the auroral electrojet immediately follows a large‐scale magnetospheric compression. A careful case study is made of several apparent exceptions to this conclusion. It is found that an unusually large enhancement of an SqP‐like current system sometimes occurs in association with the southward interplanetary magnetic field behind the shock. Magnetic perturbations caused by this polar cap current system can cause extremely large disturbances at auroral zone stations. Since the sense of these perturbations is the same as that of perturbations due to substorm expansions in the morning and afternoon auroral zone, it is possible to confuse the two. Reports of the apparent triggering of substorm expansions without the expected preconditions can usually be attributed to thi

ISSN:0148-0227    

DOI:10.1029/JA082i001p00074

年代:1977

数据来源: WILEY