摘要:

A review of the ionospheres of the major planets is given from the pre‐Voyager 1 encounter perspective of Jupiter. Ion chemistry, recombination, and sources are individually discussed. It is concluded that material sputtered off the surfaces of the Galilean satellites, ionized by electron impact, and accelerated by magnetic field capture and inward radial diffusion by flux tube interchange may dissipate sufficient energy in Jupiter's upper atmosphere to completely dominate the solar column production of ionization and Lyman α radiation and heating by dissipation of upward propagating inertia‐gravity waves. These precipitating ions may also be a source of the pronounced layers observed by the Pioneer 10 and 11 radio occultation experiments in Jupiter's lower ionosphere. If Saturn has a strong magnetic field, similar conclusions also apply to hydrogen escaping Titan's atmosphere. Cosmic rays are probably the most important ionization source on Nep

ISSN:8755-1209    

DOI:10.1029/RG017i008p01913

年代:1979

数据来源: WILEY

摘要:

Observations of nonequilibrium phenomena on the Saturn satellite Titan indicate the occurrence of organic chemical evolution. Features taken from various models of Titan's atmosphere are combined in a working composite model that provides environmental constraints within which different pathways for organic chemical synthesis are assessed. Experimental results and theoretical modeling studies suggest that the organic chemistry of the satellite is dominated by two atmospheric processes: photochemistry and energetic particle bombardment. Photochemical reactions of CH4in the upper atmosphere can account for the presence of C2hydrocarbons. Reactions initiated in various levels of the atmosphere by cosmic ray, Saturn ‘wind,’ and solar wind particle bombardment of a CH4‐N2atmospheric mixture can account for the ultraviolet‐visible absorbing stratospheric haze, the reddish appearance of the satellite, and some of the C2hydrocarbons. In the lower atmosphere, photochemical processes will be important if surface temperatures are sufficiently high for gaseous NH3to exist. Hot H atom reactions initiated by photodissociation of NH3can couple the chemical reactions of NH3and CH4; if 0.1% of the incident ultraviolet light from 1600 to 2270 Å reaches the lower atmosphere, these reactions will be capable of producing organic matter at a rate comparable to or higher than that resulting from particle‐initiated reactions. Electric discharges are highly improbable on Titan; if they occurred at all, they would be restricted to the lower atmosphere and clouds. Their yield of organic matter might approach that of hot H atom reactions if the conversion of solar to electrical discharge energy on Titan was as efficient as that on earth. These assessments indicate that future missions to Titan should include organic chemical analyses of its atmosphere and surface among the prime science

ISSN:8755-1209    

DOI:10.1029/RG017i008p01923

年代:1979

数据来源: WILEY

摘要:

Considerable evidence for the existence of large‐scale (zonal wave numbers 1, 2, and 3) traveling Rossby waves, or waves of the second class, has been published. Analyses indicate that these observed waves disperse according to theory, the largest longitudinal and latitudinal scales moving fastest toward the west. Zonal wave numbers 1 and 2 in the geopotential or pressure fields nearly always propagate westward, wave number 3 propagates both eastward and westward, and wave number 4 nearly always propagates eastward. For zonal wave number 1 the largest latitudinal scale disturbances move around the earth in about 5 days. Smaller latitudinal scales range in period from 1 to 3 weeks. The most often reported period is near 16 days. For zonal wave number 2, most frequent periods reported are near 4 and 15 days. Vertical structures of the traveling large‐scale waves that have been studied so far resemble those of external waves with very small phase change with height and some indication of an amplitude increase with height. These large‐scale traveling waves may be important in furthering our understanding of time variations in the general circulation and in efforts to improve the skill of numerical weather prediction m

ISSN:8755-1209    

DOI:10.1029/RG017i008p01935

年代:1979

数据来源: WILEY

摘要:

Advances in the theory of atmospheric tides since the monograph by Chapman and Lindzen (1970) are comprehensively reviewed. Major developments include investigations of the effects of mean zonal winds and meridional temperature gradients, molecular viscosity and thermal conductivity, radiative damping, composition variations, and hydromagnetic coupling, including seasonal and solar cycle effects. Linearized inviscid and viscid equations of general applicability are documented in this review, and a number of quantitative studies of atmospheric tides are considered as simplifications or modifications of these equations. Recent calculations of thermal excitation due to insolation absorption by H2O and O3below 80 km, UV and EUV absorption in the lower thermosphere, and latent heat release in the tropical troposphere are presented. Although no attempt is made to exhaustively review incoherent scatter, meteor radar, and satellite mass spectrometer contributions to the study of atmospheric tides, representative wind, temperature, and composition data from these sources are interpreted within the framework of the most recent quantitative models, and the current status of our understanding of atmospheric tides is assessed. Some potentially fruitful areas of future research are also presented.

ISSN:8755-1209    

DOI:10.1029/RG017i008p01951

年代:1979

数据来源: WILEY

摘要:

Information pertaining to aerosols and to microparticles preserved in snow and ice on the high plateau of Antarctica is assembled and interpreted with a diffusive transport model. The boundary conditions for the problem involve the existence of a two‐mode microparticle size distribution function. The smaller (Aitken) mode likely consists of converted products from nucleation of trace gases; the particles are less than 2.3 days old and are produced locally over the ice caps at a production rate of 4 × 10−21g cm−3s−1. The Aitken particles are present in concentrations of 10²–10³ cm−3throughout the troposphere, except in the lowest few hundred meters within the turbulent boundary layer, where they are depleted. The Aitken particles are probably composed of converted sulfates and hydrocarbons. Large particles ∼0.4 µm in radius are also found in Antarctica, in concentrations of 0.5 cm−3; these particles dominate the aerosol mass. They are of great interest because they have apparently come from long distances and because they precipitate onto the surface and are incorporated into the polar ice in varying rates that can show a connection with past changes in terrestrial climate. The large particles are estimated to have come from (1) unidentified sulfate sources, (2) oceanic sources surrounding the continent, (3) arid regions in the southern hemisphere (Australia, Kalahari Desert, Atacama Desert), (4) extraterrestrial sources, and (5) oases on the continent—in that order of importance. Turbulent diffusion seems to be the primary particle transport mechanism, and diffusion models support the plausibility of the mentioned terrestrial sources and quantify their contributions. The transport by eddy diffusion from continental sources apparently is operating mainly within the middle and upper troposphere. Particles are removed over Antarctica by diffusing into the turbulent boundary region or by encountering clouds or hydrometeors. The major removal mechanisms are impaction on the surface (2.0 × 10−14g cm−2s−1), impaction onto snowflakes (1.6 × 10−14g cm−2s−1), impaction onto ice crystals (0.2 × 10−14g cm−2s−1), and nucleation (0.6 × 10−14g cm−2s−1). The Aitken particles are removed predominantly by diffusing to ice crystals (0.006 × 10−14g cm−2s−1) and by diffusing across the laminar layer to the surface (0.015 × 10−14g cm−2s−1). The many near‐surface removal mechanisms deplete aerosol mass loading by a factor of 5–10 in the turbulent boundary layer (making it a poor place to collect samples from). Changes in atmospheric circulation during the last third of the latest Wisconsin ice age may have increased desertification in the southern hemispheric mid‐latitude zones an

ISSN:8755-1209    

DOI:10.1029/RG017i008p01983

年代:1979

数据来源: WILEY

摘要:

Near most coastlines the vertical component of the geomagnetic variation field is abnormally large and correlates positively with the inland horizontal component. This phenomenon is known as the geomagnetic coast effect. The few coastal locations at which it is absent are tectonically anomalous. The ratio of vertical to horizontal components decreases inland at a rate which depends on the geological nature of the continent. The effect varies only slightly with period, reaching a broad maximum between periods of 30 and 90 min. A number of models have been investigated by either calculation or analogue modeling, but the complete problem dealing with finitely conducting irregular oceans overlying a less conducting lithosphere has not yet been solved. Eddy currents flowing entirely in the seawater would be induced only by the vertical component of the magnetic field. Observations, combined with analogue model experiments, suggest that induction by horizontal components is also important. This requires flow of current in the lithosphere beneath the oceans.

ISSN:8755-1209    

DOI:10.1029/RG017i008p01999

年代:1979

数据来源: WILEY

摘要:

The existence of an opening on the dayside of the earth's magnetic field through which solar plasma could penetrate was noted by Chapman and Ferraro in 1931, and although observational evidence of its auroral and ionospheric effects accumulated steadily over the years, the dayside cleft (or cusp) was not accepted as a real magnetospheric feature until 1971. The history of this development is described, and some reasons for the long delay in recognizing this profound ionospheric influence are given. The entry of magnetosheath plasma to ionospheric levels provides an essentially permanent dayside energy source for theFregion that generates a rather constant 1–2 kR of 6300‐Å atomic oxygen emission, a weak hydrogen emission, and some other emissions. It also produces ionospheric irregularities and enhanced electron temperatures that can be detected by a variety of methods, all of this in a region normally centered at noon and 78° in invariant coordinates, with a latitude extent of a few degrees and a longitude extent of a few hours. The cleft ionization is an important source for the polar cap ionosphere, and the detailed nature of its effect depends upon the interplanetary field and on magnetospheric influences on the polar cap convection pattern. Some questions for further study are given in concl

ISSN:8755-1209    

DOI:10.1029/RG017i008p02017

年代:1979

数据来源: WILEY

摘要:

The availability of in situ solar wind observations from the complete sunspot cycle 20 (1964–1976) suggests an examination of the changes in the character of the solar wind related to the solar cycle and comparison of these observed changes with those expected from earlier studies of solar‐terrestrial physics. In many ways the observations correspond to these expectations; flare‐associated shock waves were probably most important near sunspot maximum, while long‐lived streams of high‐speed wind, now known to originate in coronal holes, were clearly most important in the declining years of the cycle. However, one important pattern of deviation from the expected behavior must be emphasized. The largest elevations of solar wind speed and the highest level of geomagnetic activity, associated with coronal holes and long‐lived streams, occurred very late in the cycle rather than near sunspot maximum. The implications of this ‘anomalous’ behavior are not

ISSN:8755-1209    

DOI:10.1029/RG017i008p02034

年代:1979

数据来源: WILEY

摘要:

In recent years, there has been increasing awareness of the importance of large‐scale electric fields in the earth's magnetosphere. Much attention has been directed to the quasi‐static electric field associated with charge separations generated by solar wind‐magnetosphere interaction, but these seem inadequate to explain many important processes. This paper reviews the evidence for the inclusion of electric fields of inductive origin, i.e., those due to time‐dependent currents in the magnetosphere‐ionosphere system. Attention is focused on processes associated with magnetospheric substorms, as they are well characterized by various types of evidence and do involve events such as energetic particle precipitation which require explanation beyond that provided by static electric field models. It is found that inductive electric fields are significant at times and should be included for a proper description of observ

ISSN:8755-1209    

DOI:10.1029/RG017i008p02049

年代:1979

数据来源: WILEY

摘要:

The theory of resonance absorption of plane gravitational waves incident on a layered earth is developed and applied in the analysis of the response of various crustal models. In comparison with a homogeneous half‐space model, crustal layering is found to enhance, greatly, the radiation‐generated surface seismic motions at certain resonant frequencies. Under particular conditions the resonance qualityQis limited only by the absorption of elastic energy in the crustal materials. These results suggest that well‐located seismograph systems might provide an effective means for the detection of gravitational radiation in the 0.1‐ to 10‐Hz band. The possibility of the incidental discovery of gravitational wave bursts by the community of seismologists is discussed. Furthermore, the response of the earth to gravitational radiation with very long and ultralong periods is discussed in terms of the current understanding of the earth's elastic and fluid mechanical motions. Experiments in seismic detection of gravitational radiation are

ISSN:8755-1209    

DOI:10.1029/RG017i008p02057

年代:1979

数据来源: WILEY