摘要:

A time‐varying model of neutral gas expansion in a nonuniform environment is developed. The model includes diffusion in a multicomponent atmosphere, chemical reactions between the diffusing gases and the atmosphere, thermal diffusion effects, and transport due to altitude‐dependent winds. The three‐dimensional diffusion equation governing the neutral gas flow is solved numerically using Fourier transform and finite difference techniques. Examples of H2, OH, and CO2diffusion illustrate the effects of chemical reactions and wind shears on the neutral expansion. The model may be applied to chemical releases which produce ionospheric depletions or luminescent t

ISSN:0148-0227    

DOI:10.1029/JA084iA03p00793

年代:1979

数据来源: WILEY

摘要:

A formalism is developed for approximating tidal structures in a spherical, rotating, viscous atmosphere by ‘equivalent gravity waves’ (EGW's) on anfplane. The frequency and zonal wave number of the EGW is chosen to match that of the simulated tidal mode. Then, for a given planar rotation ratefthe meridional wave number of the EGW is determined by matching the vertical structure (equivalent depth) of the tidal mode in the absence of dissipation. Simulations are performed for the thermospheric extensions of the first two symmetric and antisymmetric semidiurnal tidal modes and compared to a full numerical treatment of the inseparable tidal equations in the thermosphere. Development of this technique forms the basis for investigation of a number of problems associated with thermospheric tides which might otherwise be precluded by computer limitati

ISSN:0148-0227    

DOI:10.1029/JA084iA03p00803

年代:1979

数据来源: WILEY

摘要:

For application to planetary ionospheres we have derived diffusion and heat flow equations for a fully ionized three‐component plasma and for a partially ionized three‐component plasma using a formulation that is valid for arbitrarily large temperature differences between the interacting species. These equations can be applied to ionospheric situations where steady state, collision‐dominated conditions prevail and where the species drift velocities are much less than the species thermal speeds (low Mach numbers). The application of the diffusion and heat flow equations to theFregion and topside terrestrial ionosphere indicates that the various transport coefficients can exhibit significant variation with the different species temperature r

ISSN:0148-0227    

DOI:10.1029/JA084iA03p00811

年代:1979

数据来源: WILEY

摘要:

An artificial auroral experiment, Precede, was performed in the 80‐ to 120‐km altitude range above the White Sands Missile Range, New Mexico, in October 1974. A 2‐kW rocket‐borne electron accelerator, square wave modulated at 0.5 Hz, was activated at 95 km on payload ascent, was pulsed continuously through apogee (120 km) to a descent altitude of approximately 80 km, and provided a total of 90 pulses of a 2.5‐kV 0.8‐A electron beam over a period of 180 s. A ground‐based dual channel telephotometer recorded the time‐dependent photon emission rate of the N2+(B²Σu+→X²Σg+) first negative (0–0) band at 3914 Å and the O(¹S→ ¹D) transition at 5577 Å induced in the night atmosphere by the pulsed electron source. An electron‐induced luminous efficiency of (4.5±0.4) × 10−3was determined for the N2+1N (0–0) transition at 3914 Å in the 80‐ to 100‐km altitude range. The photon emission rates of several bright stars were measured to calibrate the telephotometer and to correct for the effects of atmospheric extinction. The time‐dependent O(¹S) 5577‐Å photon emission rate has been fitted with a model calculation providing insight into O(¹S) production and loss processes resulting from the deposition of energetic electrons in the 90‐ to 116‐km altitude range. At altitudes in excess of approximately 110 km the O(¹S) time‐dependent photon emission profiles indicate that consecutive reactions involving energy transfer from N2(A³Σu+) to O(³P) is the dominant O(¹S) production process. A rate coefficient of 5.7 × 10−12cm³ s−1representing an O(¹S) yield of 0.29 has been inferred from the data for the reaction of N2(A³Σu+) and O(³P). The dissociative recombination of O2+has been established as the dominant O(¹S) production process at altitudes less than 96 km with an O(¹S) yield of 4.5–6.0% per dissociation. Other processes account for approximately 20% or less of the total O(¹S) production at 90 km with smaller contributions indicated at higher altitudes. Collisional deactivation by O(³P) accounts for approximately 50% of the total O(¹S) depopulation rate in the 95‐ to 116‐km altitude range with a rate coefficient of 6.0 × 10−11e−305/Tcm³ s−1. Quenching by O2dominates as an O(¹S) loss mechanism at altitudes less than 94 km with an estimated rate coefficient of 1.2 × 10−11e−850/Tcm³ s−1. The rate coefficients determined for O(¹S) produced by the reaction of N2(A³Σu+) and O and the collisional deactivation processes have a probable error of approximately 25% i

ISSN:0148-0227    

DOI:10.1029/JA084iA03p00823

年代:1979

数据来源: WILEY

摘要:

The ionospheric electron density at discrete heights is obtained with a 1‐min sampling interval using the Arecibo radar for several runs in May 1974. These values are treated as time series in a spectral analysis. Assuming the ionization fluctuations are random traveling ionospheric disturbances, hence are excited by random gravity waves in the neutral atmosphere, the observed spectra are used (1) to compare with the theoretically computed transmittivity functions, where satisfactory agreement has been obtained, and (2) to make inference about the nature of the gravity wave velocity spectrum at the source, which suggests broad bandedness. At least in one case the data suggest the continuous cascading of energy into higher frequency components through a nonlinear process as the spectrum of waves propagates upward into the thermospher

ISSN:0148-0227    

DOI:10.1029/JA084iA03p00834

年代:1979

数据来源: WILEY

摘要:

Recently, atomic nitrogen has been measured in the upper thermosphere with a mass spectrometer carried on the Atmosphere Explorer satellites. Only a small fraction of N atoms are directly measured by the mass spectrometer, however. The majority appear as NO, formed within the ion source. Occasionally a relatively large NO2signal has also been observed, showing a strong dependence on the ion source surface temperature. Comparison of a numerical simulation of the reactions leading to NO2with data obtained in circular orbits on AE‐C provides insight into the pertinent chemical reactions. It demonstrates that the techniques used in open source neutral mass spectrometer operation—warmup and outgassing of the source before measurements—were successful in minimizing the effects of this contam

ISSN:0148-0227    

DOI:10.1029/JA084iA03p00839

年代:1979

数据来源: WILEY

摘要:

Radio pulses have been used as a probe to investigate scattering characteristics of ionospheric irregularities in the D‐ region at a frequency of 1.98 MHz, at Adelaide, South Australia (35°S). The angular distribution of the returned energy was investigated as a function of time and height. Distinct layers of strong scatter have frequently been detected, the heights of which differ on different days. The layers appear to be of two distinct types—those occurring above 80 km and those below—the two groups having different temporal and angular characteristics. The higher layers exhibit scatter from a much larger range of off‐vertical angles, and the power returned from them varies less in time than for the lower layers, which tend to show short ‘bursts

ISSN:0148-0227    

DOI:10.1029/JA084iA03p00845

年代:1979

数据来源: WILEY

摘要:

The magnetic signatures of field‐aligned and ionospheric currents can be used to determine the geometry and strength of the electrical current systems which couple the ionosphere to the outer regions of the earth's magnetosphere. It is now recognized that the currents flowing in the evening sector are an important clue to the understanding of processes leading to explosive substorm instabilities and episodes of intense ionospheric disruption. In this report we have used a combination of ground‐based magnetometer data and Isis 2 satellite data in the form of energetic particles, auroral luminosity, and electromagnetic and/or electrostatic noise measurements to provide a comprehensive picture of processes which are taking place on field lines penetrating the auroral oval in the evening and midnight sectors. We shall show that noise measurements in the frequency range 100

ISSN:0148-0227    

DOI:10.1029/JA084iA03p00853

年代:1979

数据来源: WILEY

摘要:

In a set of 17 low‐ to mid‐latitude crossings of the dayside and near‐dayside magnetopause, Imp 6 plasma measurements show 11 cases of decreases in magnetosheath density just outside the boundary which are consistent with plasma depletion owing to magnetic flux tube compression as the field becomes draped against the magnetopause. Pressure anisotropies in the sensep⊥>p∥are a predicted result of the plasma depletion and field compression, and such anisotropies are observed. Application of the mirror instability criterion, which predicts growth of slow mode magnetoacoustic waves for values ofp⊥/p∥greater than a critical value, suggests that dayside magnetosheath plasma is usually unstable. One of the seventeen cases shows long‐period waveforms in the 100‐s density data that are 180° out of phase with simultaneous waveforms in the magnetic field strength. We interpret these data as the signature of slow mode mag

ISSN:0148-0227    

DOI:10.1029/JA084iA03p00869

年代:1979

数据来源: WILEY

摘要:

Three groups of indices were studied as indicators for quiet day geomagnetic field level determinations: one was theAEindex, and the other two were the positive and negative value groups of theDstindex. A comparison of the behaviors of these three indices for 17 years showed their solar cycle changes and the differences in distribution of index levels between the times of high and low sunspot numbers. Two selections of the quietest days were made to provide at least 19 and 30 chosen days per year. These selections required the correspondence of equivalent fractional portions of the distribution of days in which all hourly values of indices were below specified levels. Lists of these days are given for the years 1958–1974. A comparison of these lists with the 5 days per month selection derived from the geomagnetic activity indexKpshows that for the same total number of quiet days per year only about one third to one half of the low‐Kpdays would be quiet byAEandDstindex standa

ISSN:0148-0227    

DOI:10.1029/JA084iA03p00875

年代:1979

数据来源: WILEY