摘要:

Observations with a stereo television system show that many pulsating auroras have vertical extents of less than 2 km. This is significantly less than has been calculated based on collisions between precipitating electrons and the atmosphere. Assuming that the pulsating auroras are caused by precipitating electrons, the data suggest that noncollisional interactions, localized in the lowerEregion (90–107 km), where most of the pulsations are observed, may play a dominant role in thermalizing the particles. Proximate pulsating forms may be at different altitudes, but invariably, the pulsating auroras appear at lower altitudes than interspersed nonpulsating forms. The altitude is essentially constant during an individual pulsation as well as between succeeding similar pulses in a series, but the average altitude of all pulsations appears to increase toward daw

ISSN:0148-0227    

DOI:10.1029/JA084iA07p03257

年代:1979

数据来源: WILEY

摘要:

A detailed absorption cross section for molecular oxygen in the region of the Schumann‐Runge bands has been calculated using data about the molecular constants for oxygen, the band strengths and linewidths for the Schumann‐Runge system, and the absorption continua of oxygen in this region. The accuracy of the cross section is demonstrated by comparison with a range of experimental measurements. An absorption model for the mean transmission and effective local cross section for oxygen over 1.0‐nm and 0.2‐nm intervals in the wavelength region 175–205 nm has been based on the detailed cross section, and the coefficients of the model are given. The model incorporates an atmospheric temperature profile and is suitable for the calculation of photodissociation rates of oxygen and minor constituents in the a

ISSN:0148-0227    

DOI:10.1029/JA084iA07p03272

年代:1979

数据来源: WILEY

摘要:

We have made a thorough re‐examination of the Rayleigh‐Taylor instability in the nighttime equatorial ionosphere from ∼100 km to the bottomsideFregion. We have taken into account explicitly the following effects which have been ignored by other workers in various combinations: (1) The eastward drift of the ionosphere caused by the nighttime polarization electric field, (2) the eastward nighttime neutral wind, and (3) recombination in theFandEregions. We found that, well below the bottomsideFregion, the Rayleigh‐Taylor mode can be unstable and is driven by an eastward neutral wind rather than by gravitational drift. Formation of ionospheric bubbles below the bottomsideFregion is consistent with the observation of lower ionospheric ions inFregion ionospheric holes; furthermore, seasonal and shorter term variations in spread‐Foccurrence may be associated with variations in the neutral wind and polarization elect

ISSN:0148-0227    

DOI:10.1029/JA084iA07p03283

年代:1979

数据来源: WILEY

摘要:

A model of global atmospheric electricity is constructed and used to examine the electrical coupling between the earth's upper and lower atmospheric regions. The main sources of electric current within the model are thunderstorms, which are considered as dipolar electric generators with a net positive charge at the top of the thundercloud and a net negative charge at the bottom of the cloud. The thunderstorms are assumed to be distributed in geographic areas that are in accordance with the known statistical distribution of thunderstorm frequency at a given universal time. The electric potential at the surface of the earth is assumed to be zero along the earth's orographic surface. Calculations are made with and without the earth's orography. The electrical conductivity increases exponentially with altitude, and electrical effects are eventually coupled into the magnetosphere along geomagnetic field lines. Also, the electrical conductivity is assumed to vary with latitude, simulating the latitudinal variation of known cosmic ray production. The electrostatic model calculates the global distribution of electric potential and current for model conductivities and an assumed spatial distribution of thunderstorm current sources. The results show that large positive electric potentials are generated over thunderstorms and that these perturbations penetrate upward to ionospheric heights. The effect of a thunderstorm region in one hemisphere can be transmitted along geomagnetic field lines into the conjugate hemisphere; however, the potential perturbation in the conjugate hemisphere is damped below stratospheric altitudes. Electric fields over thunderstorm regions may approach 0.25–0.50 mV m−1at ionospheric heights for nighttime conditions. The return current at the earth’s surface in the fair weather region is greater over mountainous regions than at sea level. The perturbation of the calculated electric potential and current distributions due to an increase in cosmic rays during a solar flare increase and the subsequent Forbush decrease in cosmic ray ionization is also disc

ISSN:0148-0227    

DOI:10.1029/JA084iA07p03291

年代:1979

数据来源: WILEY

摘要:

A model of the compression of the Hermaean magnetosphere by the solar wind is presented. The model considers the consequences of the finite electrical conductivity of the planetary interior on the magnetopause standoff distance under varying solar wind conditions. Although for average conditions the standoff distance is almost identical to that obtained for a point dipole source embedded in an insulating interior, for periods of above‐average solar wind dynamic pressure the compression of the planetary field between the magnetopause and the conducting interior will increase the standoff distance. From these considerations the solar wind would be expected to impact the dayside surface directly only a very small fraction of the time. Magnetic reconnection may erode the dayside magnetosphere and increase the rate of direct impact upon the surface. However, this effect is not included in the model calculation

ISSN:0148-0227    

DOI:10.1029/JA084iA07p03306

年代:1979

数据来源: WILEY

摘要:

In this paper we discuss errors in lunar magnetic field data obtained by the Apollo 12, 15, and 16 surface and the orbiting Explorer 35 Ames and Goddard magnetometers and the implications of these errors on investigations of electromagnetic induction in the moon. The Apollo surface instruments measure fields up to 300 γ with fluctuations of about 15 γ and the Explorer magnetometers measure fields of about 10 γ with 5 γ fluctuations. Typical errors of these field measurements are found to be on the order of 1 γ or 1% of the largest fields measured. Comparison of data from the Apollo 12 and Explorer 35 Ames and Goddard magnetometers has allowed measurement of the relative gains and offsets of these three instruments between day 323 of 1969 and day 179 of 1970. During the first half of this period, (i.e., the first four lunations of Apollo 12 magnetometer operation), all three instruments generally are in good agreement with the gains and offsets differing by 1 to 2% and 0.5 γ, respectively. Commencing with the fifth Apollo 12 lunation the two Explorer magnetometer gains and offsets are significantly different. The degraded operation of one or both magnetometers results in gain differences increasing up to 60% and offset differences over 1 γ by the eighth Apollo 12 lunation. Neither Explorer 35 magnetometer agrees well with the Apollo 12 instrument during this later period. The ApolloxAlsep axis gain coincides better with that of the Ames instrument but theyAlsep axis gain corresponds to the Goddard magnetometer. It is probable that both Explorer magnetometers begin to malfunction by the fifth lunation. Coincident with the increase in gain and offset errors an additional data anomaly appears which is associated with exit of the spacecraft from the lunar sun shadow. This error in the spin plane attains a maximum value of 7 γ, which decays monotonically within approximately 3 hours of shadow exit. This malfunction probably results from orientation error in the spin plane sensors. Three other errors in the Apollo surface magnetometer data are also discussed. The effects of magnetic data errors on electrical conductivity are estimated by determining the envelope of conductivity profiles resulting from the errors delineated by this study. Adjustment of previously published bulk lunar magnetic permeability results to account for magnetometer gain uncertainties, yields a lunar permeability of µ=1.012±0.011. We conclude that careful selection of magnetic data used in any study of the moon or its environment is the best procedure for minimizing the effects of the

ISSN:0148-0227    

DOI:10.1029/JA084iA07p03313

年代:1979

数据来源: WILEY

摘要:

In the Martian ionosphere the dominant solar ionization products are O+and CO2+. These ions are rapidly converted to O2+by ion neutral reactions resulting in O2+as the dominant ion. As O2+has a lower ionization potential, each reaction results in approximately 1.2 eV of energy to be shared by the reaction products. The kinetic energy given to the O2+will affect the ion temperatures. Calculations have been made of the ion heating rates and temperatures which result from the degradation of these energetic ions for various energy production distributions for conditions similar to those encountered by Viking 1. It is shown that the thermalization of the energetic O2+can greatly increase the ion temperatures above 200 km compared to those calculated using only the ambient electron heating source. The effect of small horizontal magnetic fields, as predicted by current solar wind interaction models on the ion thermal balance was also investigated. These fields act to restrict the ion thermal conductivity and thus also increase the upper altitude ion temperatures. The combination of the heating by the energetic O2+and the effect of the magnetic field provide a partial agreement with the Viking 1 measurements.

ISSN:0148-0227    

DOI:10.1029/JA084iA07p03327

年代:1979

数据来源: WILEY

摘要:

Photometric keograms from South Pole Station are used to investigate dayside auroral precipitation. Identification of cusp auroral signatures allows cusp movements to be monitored and correlated with substorm activity and interplanetary magnetic field direction. We conclude that any erosion of dayside field is not a direct result of southward turningBz. On the other hand, cusp position is intimately related to substorm timing and intensity. We suggest the associated dayside field reconfiguration results from diversion of near‐tail magnetopause currents through the nightside electrojet because of enhanced auroral ionosphere conductivity. This interpretation implies that substorms result from increased efficiency of the extraction of energy from the solar wind rather than from a release of internally stored magnetic energy in the tai

ISSN:0148-0227    

DOI:10.1029/JA084iA07p03339

年代:1979

数据来源: WILEY

摘要:

Over the past decade, several models have been developed which describe the diurnal behavior of molecular and atomic ions in the altitude range where the atomic and molecular densities are comparable. However, no complete set of diurnal measurements has been available in the past with which to compare these theoretical results, because the altitude regime (130–220 km) lies below the reach of conventional satellites and rocket results give only a transient picture. The Atmosphere Explorer C, D, and E satellites have been taking measurements of ion concentrations together with related aeronomic parameters in the thermosphere for over 4 years. These data have been analyzed to extract the average diurnal variation (i.e., for solar zenith angles less than 105°) of the ion species NO+, O2+, N2+, and O+as functions of altitude. The AE data have been used in a number of separate studies which have reduced the uncertainties associated with key reaction rate coefficients. As a test of the overall consistency of the photochemistry of theF1layer we compare the measured ion concentrations with those calculated by using a model which incorporates our latest understanding of the chemistry and which uses, as input parameters, the measured neutral concentrations and temperature, the solar extreme ultraviolet flux, and electron and ion temperatures. The results show that a fairly simple model, in which the free parameters are minimized, reproduces the measurements to a satisfactory degr

ISSN:0148-0227    

DOI:10.1029/JA084iA07p03360

年代:1979

数据来源: WILEY

摘要:

The Stare (Scandinavian twin auroral radar experiment) auroral radar system has been used to measure ionospheric electric fields associated with Pc 5 geomagnetic pulsations. With this system, electric fields are derived from the drift velocity of radar auroral irregularities. The spatial resolution is 20 km over a 200,000‐km² grid, and the temporal resolution is 20 s. It has been found that the oscillating electric field associated with a hydromagnetic field line resonance produces poleward moving, bandlike regions of radar aurora, which are aligned in the east‐west direction. The drift of the irregularities within these bands is alternately eastward and westward. The Stare electric field data have been used in conjunction with the Biot‐Savart Law and an assumed height‐integrated conductivity of 8–10 Ω−1to calculate the ground magnetic disturbance. It has been found that theHandZare well predicted, whereasDis generally underestimated. These results are consistent with a 90° rotation of the magnetic polarization ellipse in the ionosphere. By Fourier analyses of the Stare data it is found that the half‐power latitudinal width of the field line resonance is typically 100 km in the ionosphere. Moreover, the north‐south electric field undergoes a 180° phase shift about the resonance as predicted by theory. The data have been used to estimate equatorial plasma densities for 6

ISSN:0148-0227    

DOI:10.1029/JA084iA07p03373

年代:1979

数据来源: WILEY