摘要:

We derive a simple expression for the escape flux which takes into account horizontal winds at the exobase. The escape flux is shown to increase with the wind velocity and becomes much larger than the Jeans escape flux for velocities approaching the thermal velocity. This model is applied to terrestrial4He, where we determine the conditions required for wind‐enhanced escape to contribute to the overall4He budget. For completeness, we also derive an expression for the escape flux when only a vertical wind is present at the exobas

ISSN:0148-0227    

DOI:10.1029/JA081i007p01207

年代:1976

数据来源: WILEY

摘要:

Lyman α measurements of the exosphere of Venus made by the ultraviolet photometer on Mariner 5 on October 19, 1967, are analyzed. Radiative transfer models for a spherical isothermal hydrogen atmosphere with carbon dioxide present as a pure absorber are used to determine the exospheric temperature and density at the bright limb and on the dark disc. It is found that (1) the bright limb data have two components with exospheric temperatures of 275° ± 50°K and 1020° ± 100°K and densities 2 ± 1 × 105cm−3and 1.3 × 10³ cm−3, respectively, (2) the dark disc data are best fit by a two‐component density model with exospheric temperatures of 150° ± 50°K and 1500° ± 200°K and densities 2 ± 1 × 105cm−3and 10³ cm−3, respectively, and (3) the dark limb exhibits only a hot component because of the very low temp

ISSN:0148-0227    

DOI:10.1029/JA081i007p01213

年代:1976

数据来源: WILEY

摘要:

An analysis of the generation and propagation characteristics of infrasonic pressure waves excited during meteor entry into the earth's atmosphere is presented. Possible line source sound producing regions are determined for an assumed range of meteor entry parameters, gross fragmentation phenomena being neglected. A pressure wave model of a line source cylindrical blast wave produced by a high‐velocity meteoroid in a continuum gas is then formulated by using similarity theory. It is found that the strong shock behavior of the blast wave is confined to a cylindrical region whose radiusR0is proportional to the product of the meteor's Mach number and its diameter. By using the numerical blast wave solutions of Plooster as initial conditions a description of the wave form far from the source is obtained. Both refraction and attenuation of the airwaves are then calculated separately in an approximate manner. For meteors with an associatedR0≲ 10 m for source altitude regions determined earlier, predicted attenuation is very severe. Dominant wave periods predicted for arrivals at the ground are 0.4–2.5 s for sources with 10 ≤R0≤ 100 m. Finally, infrasonic data from Goerke, from Shoemaker, and from Johnson and Wilson for four recent events are analyzed. Kinetic energy estimates which are obtained range from 1017to 1022ergs, each with an uncertainty of about 2 orders of

ISSN:0148-0227    

DOI:10.1029/JA081i007p01217

年代:1976

数据来源: WILEY

摘要:

Observations of auroral forms by meteorological satellites, detailed thermospheric density response to auroral heating and wind fields at thermospheric altitudes, indicate that both phenomena exhibit structures whose spatial scales are in the synoptic planetary range. In order to study the propagation of these planetary scale disturbances, proper account of the wave vorticity transport must be taken. We have formulated and solved the approximate Green's function response problem of atmospheric waves in a spherically rotating atmosphere valid for the full wave spectrum, which ranges continuously from acoustic‐gravity to Rossby waves. Numerical examples of wave response to an impulsive auroral band are given for a set of planetary surface mode

ISSN:0148-0227    

DOI:10.1029/JA081i007p01231

年代:1976

数据来源: WILEY

摘要:

The linear dispersion properties of proton temperature anisotropy instabilities in a homogeneous infinite Vlasov plasma are studied by using a configuration appropriate to the solar wind at 1 AU. The proton distribution is taken to consist of two components, a coolerT⊥>T∥‘core’ and a hotterT∥>T⊥‘halo.’ For the parameters considered thek∥B0fire hose and ion cyclotron instabilities are the most important modes. Resonant proton effects enhance both instabilities, and the presence of the cooler component can substantially reduce the threshold anisotropy of the halo

ISSN:0148-0227    

DOI:10.1029/JA081i007p01241

年代:1976

数据来源: WILEY

摘要:

The flux density of ions created by ionization of interstellar neutral particles in the solar system and picked up by the solar wind is calculated as a function of the neutral particles. A very broad maximum occurs at an angle of 0 and a distance that depends on the density and speed of the neutral particles and on the ionization time but is typically in the general region of 10 AU. For atomic hydrogen the flux density is estimated to exceed 104cm−2s−1over the distance range from a few to nearly 100 AU. The velocity space distribution of the interstellar ions is calculated under the assumption of no significant energy diffusion but with inclusion of adiabatic effects as well as a possible strong pitch angle diffusion. The energy spectrum is highly nonthermal and much broader than that of the solar wind ions; under the assumed conditions, interstellar protons are easily distinguishable from solar wind protons by their location in velocity space. If charge exchange is an important contributor to the ionization of hydrogen, the observed local intensity of interstellar protons should exhibit time variations correlated with the density changes of the solar wind stream struct

ISSN:0148-0227    

DOI:10.1029/JA081i007p01247

年代:1976

数据来源: WILEY

摘要:

Calculations have been made of the 10,830‐Å column emission rates from metastable He(2³S) atoms in the upper atmosphere, and these have been compared with other calculations and observations. The dawn/dusk intensity ratio is accounted for mainly by changes in the ambient thermal electron concentration for the observations in Peru and Brazil and by changes in plasmasphere opacity to conjugate point photoelectrons for the New Mexico and to some extent the Brazilian data. The large enhancement of the New Mexico intensities at local solar zenith angle 100° by a factor of 10 or more in winter is due partly to the presence at that time of conjugate point photoelectrons, which increase the excitation rate to up to 3 times that due to the local photoelectrons alone. The change in ambient helium concentration from summer to winter by a factor of 3 or more accounts for the remainder of the enhancements. There is a discrepancy by a factor of 6 in absolute intensities, which could be removed by a rather improbable conjunction of errors all acting in the right direction. Alternatively, increasing the photoelectron flux calculated by a factor of 2 and decreasing by an order of magnitude the recently measured cross section for loss of He(2³S) by Penning ionization on atomic oxygen (Cook et al., 1974) would remove the discre

ISSN:0148-0227    

DOI:10.1029/JA081i007p01253

年代:1976

数据来源: WILEY

摘要:

An auroral ion charge spectrometer was flown into a hydrogen aurora on a Javelin sounding rocket launched from Churchill, Manitoba. The instrument contained an electrostatic analyzer which selected particles with incident energy per unit charge up to 20 keV/charge and an 80‐kV power supply which accelerated these ions onto an array of solid state detectors. Ions tentatively identified as H+, He++, and O+were detected from 225 to 820 km in altitude. The experiment did not discriminate between H+and He+, or between O+, N+, and C+. Upper limits of highly charged heavy ion abundances have been set at 20% of the He++and 0.15% of the H+. It is concluded that both terrestrial and solar wind sources play significant roles in auroral ion precipitatio

ISSN:0148-0227    

DOI:10.1029/JA081i007p01264

年代:1976

数据来源: WILEY

摘要:

A detector designed to search for modulation of auroral electron fluxes in the frequency range 50 kHz to 10 MHz and energy range 5–7 keV was flown on a Nike‐Tomahawk sounding rocket payload launched from Poker Flat, Alaska, at 0722 UT on February 25, 1972. Data from the flight show no obvious peaks in the frequency spectra. However, cross‐correlation analysis of the data shows low‐level modulation near the detection threshold of the instrument. The 5% modulation occurs at frequencies from 4.2 to 5.6 MHz at 211–218 s into the flight. The indicated modulation occurred near the boundary of two oppositely directed Birkeland sheet currents whose position was determined by the use of an on‐board vector magnetometer. Also, accompanying the boundary was a large increase in the flux of electrons in the 0.5‐ to 20‐keV range and strong pitch angle anisotropy peaked at 0°–10°. Lack of modulation at other times suggests that the observed modulation is relate

ISSN:0148-0227    

DOI:10.1029/JA081i007p01269

年代:1976

数据来源: WILEY

摘要:

The fluxes of electrons that precipitate through the day side clefts of the magnetosphere are intense enough and deposit their energy at a high enough altitude to heat and ionize theFlayer and top side ionosphere substantially. Relevant synoptic results from bottom side and top side sounder measurements are reviewed, and new data from the Isis satellites are presented. The effects of precipitation through the cleft can be seen in bottom side ionograms, but the diurnal variations that appear in routine monthly median plots are probably due primarily to other effects. As seen from above theFlayer by the top side sounders on Alouette and Isis spacecraft, the most obvious effects are an expansion (increase in scale height) of the top side ionosphere due to heating and the presence of small‐scale spatial fluctuations in density. The electron density at theFlayer peak is often, but not always, increased. The increased electron density at satellite altitudes associated with top side expansion is often seen at a slightly higher latitude than the precipitation, and this displacement in latitude (of ∼1°) is interpreted in terms of an antisunward drift due to magnetospheric convec

ISSN:0148-0227    

DOI:10.1029/JA081i007p01279

年代:1976

数据来源: WILEY