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Showing papers in "Geophysical Research Letters in 1979"


Journal ArticleDOI
TL;DR: In this paper, the authors examined magnetic field measurements from the ISEE 1 and 2 spacecraft in the vicinity of the magnetopause near local noon on a typical pass when the magnetosheath field is southward.
Abstract: Magnetic field measurements from the ISEE 1 and 2 spacecraft are examined in the vicinity of the magnetopause near local noon on a typical pass when the magnetosheath field is southward. The data clearly show evidence for patchy impulsive reconnection. The flux transfer rate for these events is at least of the order of 1-2 times 10 to the 12th Maxwells per second, and possibly greater. This rate is similar to rates deduced for magnetopause erosion events. Not only are these observations relevant to the substorm process, but the impulsive nature of the flux transfer events leads to boundary oscillations that could also be the source of long period magnetic pulsations in the outer magnetosphere.

709 citations


Journal ArticleDOI
TL;DR: In this article, the power delivered by the solar wind dynamo to the open magnetosphere is calculated based on the concept of field line reconnection, independent of the MHD steady reconnection theories.
Abstract: The power delivered by the solar wind dynamo to the open magnetosphere is calculated based on the concept of field line reconnection, independent of the MHD steady reconnection theories. By recognizing a previously overlooked geometrical relationship between the reconnection electric field and the magnetic field, the calculated power is shown to be approximately proportional to the Akasofu-Perreault energy coupling function for the magnetospheric substorm. In addition to the polar cap potential, field line reconnection also gives rise to parallel electric fields on open field lines in the high-latitude cusp and the polar cap regions.

502 citations


Journal ArticleDOI
TL;DR: In this paper, the authors suggest that anomalous reversals of the zonal equatorial electric field component are associated with a sudden change in the convection electric field in the magnetosphere and present measurements to support this explanation.
Abstract: Anomalous reversals of the zonal equatorial electric field component have some- times been observed when the interplanetary mag- netic field turns northward from a steady south- erly direction. We suggest that this reversal is associated with a sudden change in the convection electric field in the magnetosphere and present measurements to support this explanation. Al- though slower variations in the convection field are shielded from the low latitude ionosphere by polarization charges at the inner edge of the ring current, these charges may require an hour or more to vary. A sudden decrease in the cross- tail electric field will thus be accompanied by a dusk-dawn perturbation electric field across the inner magnet o s phe re.

440 citations


Journal ArticleDOI
TL;DR: In this article, the formation of HNO2 was investigated by long path optical absorption at three sites in Western Europe and it vas definitely identified and measured in moderately polluted air at Julich.
Abstract: HNO2 was investigated by long path optical absorption at three sites in Western Europe. It vas definitely identified and measured in moderately polluted air at Julich. Mixing ratios as high as 0.8 ppb were observed before sunrise. After sunrise the HNO2 is photolyzed and considerable amounts of OH are produced. The formation of HNO2 is unclear and possible reactions are discussed.

372 citations


Journal ArticleDOI
TL;DR: In this paper, the authors measured attenuation and velocities in resonating bars of Massilon sandstone at various degrees of saturation and found that shear energy loss simply increases with degree of saturation, whereas bulk compressional energy loss increases to ∼95% saturation and then rapidly decreases as total saturation is achieved.
Abstract: Seismic attenuation and velocities were measured in resonating bars of Massilon sandstone at various degrees of saturation. Whereas shear energy loss simply increases with degree of saturation, bulk compressional energy loss increases to ∼95% saturation and then rapidly decreases as total saturation is achieved. This behavior is analogous to the behavior of shear and compressional velocities, but the effect on attenuation is larger by an order of magnitude. Our observations are in excellent agreement with the predictions of several models of energy loss involving partial or total saturation. Pore fluid attenuation mechanisms are expected to be dominant at least in the shallow crust.

352 citations


Journal ArticleDOI
TL;DR: In this paper, a reduced set of cross-section and flux data is presented for the wavelength range below 1027A, consisting of 37 wavelength intervals, for various dates exhibiting notably different levels of solar activity.
Abstract: Increases in the solar ultraviolet flux (wavelengths shorter than 1250A) over the past five years of rising solar activity have been larger than anticipated. This increase in UV flux dramatically affects the production of ionization of the various constituents in the thermosphere. Measurements of the solar UV flux by the Atmosphere Explorer satellites are used to determine ionization frequencies for the major thermospheric species for various dates exhibiting notably different levels of solar activity. For the convenience of users of such data, a reduced set of cross-section and flux data is presented for the wavelength range below 1027A, consisting of 37 wavelength intervals

341 citations


Journal ArticleDOI
TL;DR: Polar cap electric fields were measured from times when the S3-2 Satellite was near the dawn-dusk meridian and IMF data were available as mentioned in this paper, and two characteristic types of electric field patterns were measured in the polar cap.
Abstract: Polar cap electric fields patterns are presented from times when the S3-2 Satellite was near the dawn-dusk meridian and IMF data were available. With Bz ≥ 0.7 γ, two characteristic types of electric field patterns were measured in the polar cap. In the sunlit polar cap the convection pattern usually consisted of four cells. Two of the cells were confined to the polar cap with sunward convection in the central portion of the cap. The other pair of cells were marked by anti-sunward flow along the flanks of the polar cap and by sunward flow in the auroral oval. These observations are interpreted in terms of a model for magnetic merging at the poleward wall of the dayside polar cusp. The sunward flow in the auroral zone is not predicted by the magnetic model and may be due to a viscous interaction between the solar wind and magnetosphere. The second type, which was observed in some of the summer hemisphere passes and all of the winter ones, was characterized by an electric field pattern which was very turbulent, and may be related to inhomogeneous merging.

313 citations


Journal ArticleDOI
TL;DR: In this paper, the auroral kilometric radiation (AKR) was observed from Isis 1 above the nighttime auroral zone over a wider extent in longitude than in latitude with an intense source region observed most often near 2200 LMT and 70 deg invariant latitude.
Abstract: Observations of auroral kilometric radiation (AKR) were made by Isis 1 in the source region. The radiation is found to be generated in the extraordinary mode just above the local cut-off frequency and to emanate nearly perpendicular to the magnetic field. It occurs within local depletions of electron density, where the ratio of plasma frequency to cyclotron frequency is less than 0.2. The density depletion is restricted to altitudes above about 2000 km, and the upper AKR frequency limit corresponds to the extraordinary cut-off frequency at this altitude. AKR is observed from Isis 1 above the nighttime auroral zone over a wider extent in longitude than in latitude with an intense source region observed most often near 2200 LMT and 70 deg invariant latitude. It is directly related to inverted V electron precipitation events with an electron-to-wave energy conversion efficiency of the order of 0.1 to 1%.

269 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated the rapid subauroral ion drift features using data obtained over a nearly five-year period from the ion RPA/drift meter on the Atmosphere Explorer-C.
Abstract: Results are presented for an investigation of rapid subauroral ion drift features using data obtained over a nearly five-year period from the ion RPA/drift meter on Atmosphere Explorer-C. These latitudinally narrow features are found to be confined predominantly to the local time sector between 18:00 and 02:00 hr. They occur either singly or as multiple events, one of which almost always straddles the equatorward edge of the auroral zone. Their occurrence probability suggests a dependence of magnetic substorm activity.

266 citations


Journal ArticleDOI
TL;DR: In this paper, the LASL/MPI plasma instruments and the UCLA magnetometers on ISEE-1 and 2 have revealed a striking relationship between the presence of low-frequency fluctuations in solar wind density and field strength and the different types of distribution functions of upstream ions.
Abstract: Observations obtained upstream of the earth's bowshock with the LASL/MPI plasma instruments and the UCLA magnetometers on ISEE-1 and 2 have revealed a striking relationship between the presence of low-frequency fluctuations in solar wind density and field strength and the different types of distribution functions of upstream ions. Waves are absent when the ions have the beamlike distribution of the 'reflected' ions. Large-amplitude waves are present only in conjunction with the 'diffuse' ions, which are characterized by flat energy spectra and broad angular distributions. The waves are largely compressive, showing very good correlation between oscillations in magnetic field strength and plasma density.

238 citations


Journal ArticleDOI
TL;DR: Magnetic data for mantle derived rocks: peridtites from St Pauls rocks, dunite xenoliths from the kaupulehu flow in Hawaii, as well as peridolite, Dunite and eclogite Xenoid, from Roberts Victor, Dutoitspan, Kilbourne Hole, and San Carlos diatremes are presented in this article.
Abstract: Magnetic data are presented for mantle derived rocks: peridtites from St. Pauls rocks, dunite xenoliths from the kaupulehu flow in Hawaii, as well as peridolite, dunite and eclogite xenoliths from Roberts Victor, Dutoitspan, Kilbourne Hole, and San Carlos diatremes. The rocks are paramagnetic or very weakly ferromagnetic at room temperature. Saturation magnetization values range from 0.013 emu/gm to less than 0.001 emu/gm. A review of pertinent literature dealing with analysis of the minerals in mantle xenoliths provides evidence that metals and primary Fe3O4 are absent, and that complex CR, Mg, Al, and Fe spinels dominate the oxide mineralogy. All of the available evidence supports the magnetic results, indicating that the seismic MOHO is a magnetic boundary.

Journal ArticleDOI
TL;DR: Recently discovered hydrothermal vents at 21°N on the East Pacific Rise are discharging turbid waters at up to 400°C; mixtures of the plumes with ambient seawater contain significant amounts of dissolved H2 and CH4as well as He as discussed by the authors.
Abstract: Recently discovered hydrothermal vents at 21°N on the East Pacific Rise are discharging turbid waters at up to 400°C; mixtures of the plumes with ambient seawater contain significant amounts of dissolved H2 and CH4as well as He. The first grab samples of these waters were diluted 50-100 foldbut they contained as much as 20 × 10−5 cc(STP) of H2 and 2 × 10−5 cc(STP) of CH4 per gram of water. H2/CH4 ratios in the vents increase with temperaturea result that is tentatively attributed to chemical equilibrium and/or the redox state of the individual waters. The phase diagram for the NaCl-H2O "surrogate-seawater" system shows that liquid-vapor separation may take place prior to dischargeand mixing of a vapor phase with entrained cooler sea-water would profoundly alter original concentrations of volatiles as well as dissolved salts. H2 and CH4 ratios to basalt-derived helium are respectively about 550 and 70 in these waters. The total fluxes from the world-ocean ridge systemestimated from the He-3 fluxare of the order of 1.3 × 109 m³/y for H2 and 1.6 × 108 m³/y for CH4. The CH4 flux so calculated is sufficient to replace the deep-sea methane in ∼ 30 yearsimplying a very rapid bacterial consumption rate below the thermocline.

Journal ArticleDOI
TL;DR: It is possible that tidal dissipation in an ice crust on Europa preserved a liquid water layer beneath it, provided that the three-body orbital resonance for Io, Europa, and Ganymede is ancient as discussed by the authors.
Abstract: It is possible that tidal dissipation in an ice crust on Europa preserved a liquid water layer beneath it, provided that the three-body orbital resonance for Io, Europa, and Ganymede is ancient. The liquid water layer could be a continuing source of the observed surface frost. If Europa's water mantle were ever completely frozen, heating by tidal dissipation would not exceed that produced by radioactive elements, and the mantle would remain frozen.

Journal ArticleDOI
TL;DR: In this article, phase coding techniques have been applied to such measurements with a height resolution of 300 m during 6 days in summer, 5 days in autumn and 3 days in winter 1978 within the height range between 51 and 118 km.
Abstract: The SOUSY-VHF-Radar has been used to study the diurnal variation of the echo power received from mesospheric structures in different seasons. For the first time phase coding techniques have been applied to such measurements with a height resolution of 300 m during 6 days in summer, 5 days in autumn and 3 days in winter 1978 within the height range between 51 and 118 km. The various structures observed are classified according to characteristic features such as thickness and apparent lifetime. The results indicate the existence of four main types of mesospheric structures — blobs, sheets, thin and thick layers. Their spatial and temporal occurrence, which depends on season, is discussed.

Journal ArticleDOI
TL;DR: In this paper, surface NO mixing ratios were measured in the equatorial Pacific region using a chemiluminescent detector, and the average NO mixing ratio was about 4 pptv during noontime conditions for nine days of measurements.
Abstract: Surface nitric oxide mixing ratios were measured in the equatorial Pacific region using a chemiluminescent detector. The average NO mixing ratio was about 4 pptv during noontime conditions for nine days of measurements. These NO mixing ratios, which are much lower than any previously reported, imply that the O/sub 3/ production rate due to CO and CH/sub 4/ oxidation may be less than previously believed. They also imply smaller OH/HO ratios as a consequency of the lower HO/sub 2/ to OH/sup 2/ conversion by NO.

Journal ArticleDOI
TL;DR: In this article, the authors investigated a simple plasma fluid model and found that instability results for -kxV/sub d/>kx (cE/sub o/B/sub O/) (..nu../sub i//..cap omega../sub I/) where V/subd/ is the relative drift (precipitation current) between ions and electrons along B/subO/, E/sub
Abstract: A stable E x B gradient drift geometry can become destabilized by a current along the magnetic field. This type of instability is generically called the current convective instability. This instability may be responsible for the diffuse auroral scintillation causing F region irregularities observed by the DNA Wideband satellite. In these phenomena the northward TEC gradient dominates the altitude electron density gradient. We have investigated a simple plasma fluid model and found that instability results for -kxV/sub d/>kx (cE/sub o//B/sub o/) (..nu../sub i//..cap omega../sub i/) where V/sub d/ is the relative drift (precipitation current) between ions and electrons along B/sub o/, E/sub o/ is the westward ambient electric field (perpendicularB/sub o/), and ..nu../sub i/ and ..cap omega../sub i/ are the F region ion-neutral collision frequency and ion gyrofrequency.

Journal ArticleDOI
TL;DR: In this article, the authors proposed that these earthquakes are induced by the removal of the Pleistocene glacial loads which extended onto the continental shelf and reactivated basement faults remaining from rifting associated with the opening of the Labrador Sea.
Abstract: An active seismic zone extends along the passive margin of eastern North America from Baffin Island to the Grand Banks of Newfoundland. We have determined the focal mechanisms of several of the earthquakes, including the 1933 Ms 7.3 Baffin Bay earthquake, the largest event ever recorded along the eastern North American margin. The mechanisms show thrust faulting for earthquakes seaward of the 1000 m contour, and primarily normal faulting for earthquakes landward. We propose that these earthquakes are induced by the removal of the Pleistocene glacial loads which extended onto the continental shelf. The deglaciation reactivated basement faults remaining from rifting associated with the opening of the Labrador Sea. Baffin Bay and the Atlantic. A simple flexure calculation yields horizontal extension (normal faulting) in the previously glaciated region, and horizontal compression (thrust faulting) farther seaward, in good general agreement with the observed earthquake mechanisms. The magnitude of the stresses, 100 to 150 bars, is sufficient to reactivate preexisting basement faults. Large passive margin earthquakes may occur as far south along the coast as glaciation extended.

Journal ArticleDOI
TL;DR: In this article, the solubility of fluorapatite in magmatic liquids ranging in composition from olivine melilitite to andesite was determined by fusion of powdered rock samples in fluoratite capsules and subsequent analysis of the quenched glasses with an electron microprobe.
Abstract: The solubility of fluorapatite in magmatic liquids ranging in composition from olivine melilitite to andesite was determined by fusion of powdered rock samples in fluorapatite capsules and subsequent analysis of the quenched glasses with an electron microprobe. Over the temperature range 1165° - 1275°C at 1 atmosphere pressure, saturation of the melts in apatite is controlled by three primary variables: 1) concentration of P2O5, 2) concentration of SiO2, and 3) temperature. As SiO2 concentration increases from 30 to 55 wt% at 1250°C, the amount of dissolved P2O5 required to saturate a melt in apatite decreases from 12 to less than 4 wt%. At 1165°, the saturation level is uniformly ∼ 36% lower than at 1250°C. By comparison of these results with P2O5 concentrations in natural basalts, it is clear that few basic lavas are saturated in apatite at the time of extrusion. Extrapolation of the data to high-pressure conditions in the upper mantle is tenuous at the present time, but the low-pressure data suggest that any apatite present in regions of basalt production may be consumed during melting.

Journal ArticleDOI
TL;DR: In this article, the authors show that energetic electrons are injected into the region upstream from the earth's bow shock in a thin sheet which lies just behind the sheet of interplanetary magnetic field lines that are tangent to the shock surface.
Abstract: ISEE spacecraft observations show that energetic (not less than 16 keV) electrons are injected into the region upstream from the earth's bow shock in a thin sheet which lies just behind the sheet of interplanetary magnetic field lines that are tangent to the shock surface. Lower energy electrons leave the shock over a much broader region. Although the energetic electron intensity varies, the sheet is nearly always present and may be a quasi-steady state feature of the bow shock. The electron velocity distribution in the thin sheet is strongly peaked and is responsible for excitation of electron plasma waves.

Journal ArticleDOI
TL;DR: In this article, a clear hysteresis of emission numbers related to the stress history (Kaiser effect) was observed below dilatancy onset stress, and the recovery process was over one month under room humidity and temperature conditions.
Abstract: In acoustic emission studies on granite under uniaxial compression, clear hysteresis of emission numbers related to the stress history (Kaiser effect) was observed below dilatancy onset stress. The maximum stress loaded in the past is memorized in rocks. Above dilatancy, we could not observe such a hysteresis. These features are explained by the nature of irreversible sudden advances of microcrack tips. Recovery process time of this hysteresis is over one month under room humidity and temperature conditions. The results in this paper cast foundation for the applicability of geostress measurements by the acoustic emission method.

Journal ArticleDOI
TL;DR: The upper mantle transition region is usually considered to be peridotite which undergoes a series of phase changes involving spinel and post-spinel assemblages.
Abstract: The upper mantle transition region is usually considered to be peridotite which undergoes a series of phase changes involving spinel and post-spinel assemblages. There are difficulties associated with attempts to explain the 220, 400 and 670 km discontinuities in terms of phase changes in a peridotitic mantle. Moreover, in a differentiated earth there should be large quantities of eclogite in the upper mantle. Eclogite is denser than Al2O3-poor mantle to depths of 670 km, but it stays in the garnet stability field to pressures in excess of those required to transform depleted mantle to denser phases such as ilmenite and perovskite. Eclogite, therefore, remains above 670 km. The seismic properties of the transition region are more consistent with eclogite than peridotite. Most of the mantle's inventory of incompatible trace elements may be in this layer, which is a potential source region for some basalt magmas. The radioactivity in this layer is the main source of mantle heat flow, 0.7 microcalorie/sq cm-sec, and drives upper mantle convection.

Journal ArticleDOI
TL;DR: In this paper, a class of partial melt distributions is considered where melt forms is one place and accumulates elsewhere; a case modelled by a simple modification of Archie's Law for porous media.
Abstract: The presence of partial melt can profoundly affect the bulk electrical properties of composite materials. A class of melt distributions is considered where melt distributions is considered where melt forms is one place and accumulates elsewhere; a case modelled by a simple modification of Archie's Law for porous media. This relation provides values for the bulk conductivity intermediate to those for a thoroughly connected melt distribution and those for isolated melt pockets. Thus, if melt is tortously distributed, larger amounts are required to produce a given increase of the bulk conductivity, than if it is thoroughly interconnected along grain boundaries.

Journal ArticleDOI
TL;DR: In this article, the authors show that the calculated whistler-mode travel times from Jupiter to the spacecraft are in good agreement with the measured dispersion characteristics, thereby confirming that the signals are caused by lightning on Jupiter and substantiating the Voyager 1 photographic evidence for lightning on the planet.
Abstract: During the Voyager 1 encounter with Jupiter a number of discrete signals were identified in the wideband plasma wave data with characteristics similar to whistlers generated by lightning. In this paper we show that the calculated whistler-mode travel times from Jupiter to the spacecraft are in good agreement with the measured dispersion characteristics, thereby confirming that the signals are caused by lightning on Jupiter and substantiating the Voyager 1 photographic evidence for lightning on Jupiter. A quantitative estimate of the north-south thickness of the Io plasma torus is also obtained from the measured whistler dispersion.

Journal ArticleDOI
TL;DR: In this article, the structures and thermal evolutions of the large icy-satellites of the outer solar system are considered. And it is shown (for bodies comparable in size and mass to the Galilean satellites, having a sizeable mass fraction of H2O, and with meteoritic abundances of radioactive materials contained within their silicate fractions) that the crust of solid ice over a liquid mantle predicted by conductive heat transfer calculations is unstable to large-scale solid-state convection.
Abstract: The structures and thermal evolutions of the large icy-satellites of the outer solar system are considered. It is shown (for bodies comparable in size and mass to the Galilean satellites, having sizeable mass fraction of H2O, and with meteoritic abundances of radioactive materials contained within their silicate fractions) that the crust of solid ice over a liquid mantle predicted by conductive heat-transfer calculations is unstable to large-scale solid-state convection. For appropriate material parameters, convective heat-transfer rates are sufficient to freeze a large liquid mantle on a time scale that is short compared to the lifetime of the body. It is also concluded that the ice layer is convecting at the present time. A reevaluation of previous work, using improved values for material parameters and boundary conditions, reverses earlier conclusions and implies a rigid outer crust with resulting long-term stability of surface features to creep deformation. The combination of a rigid crust with active internal convection presents the additional possibility of surface features that are produced and maintained by dynamic internal processes.

Journal ArticleDOI
TL;DR: In this paper, in situ direct measurements of regularly observed thermosphere neutral particle (i.e., N2) temperature maxima that occur predominantly after midnight were made using the Neutral Atmosphere Temperature Instrument aboard the Atmosphere Explorer-E in circular orbit at about 275 km.
Abstract: The paper reports in situ direct measurements of regularly observed thermosphere neutral particle (i.e., N2) temperature maxima that occur predominantly after midnight. The measurements were made using the Neutral Atmosphere Temperature Instrument aboard Atmosphere Explorer-E in circular orbit (inclination 19 deg) at about 275 km. Hundreds of midnight temperature maxima were observed, some having values exceeding the well-known afternoon maximum. Simultaneous in situ direct measurements of the wind component normal to the orbit plane have also been obtained and observed to correlate in a systematic way with the temperature maxima.

Journal ArticleDOI
TL;DR: The Pioneer Venus Orbiter ultraviolet spectrometer has seen variable disk brightness features similar to the well-known "UV markings" seen at longer wavelengths as discussed by the authors, which are consistent with a homogeneous cloud of H2SO4 aerosols.
Abstract: The Pioneer Venus Orbiter ultraviolet spectrometer sees variable disk brightness features similar to the well-known 'UV markings' seen at longer wavelengths. The bright features are consistent with a homogeneous cloud of H2SO4 aerosols. The darker features show the presence of a broad-band absorber, which is at some depth in the cloud layer. Additional contrast arises from SO2 absorption. The observed strength of the SO2 absorption as a function of wavelength rules out a uniform mixing ratio for the SO2. The data are well fitted by an inhomogeneous light scattering model in which the SO2 scale height is one-fifth of the CO2 scale height, and the mixing ratio of SO2 at 40 mb is 10 to the -7th. A model of the oxidation of sulfur dioxide in the upper cloud reproduces the observed vertical distribution of SO2 and indicates that SO2 alone is sufficient to produce the observed amount of H2SO4 in this region.

Journal ArticleDOI
TL;DR: In this paper, the results from a gas kinetics -aerosol laboratory study involving the OH induced oxidation of SO/sub 2/ radical at tropospheric and lower stratospheric pressures were reported.
Abstract: Reported in this study are the results from a gas kinetics--aerosol laboratory study involving the OH induced oxidation of SO/sub 2/. At tropospheric and lower stratospheric pressures, reaction (1) is neither a third order process nor is it a simple bimolecular reaction. The effective bimolecular k value at one atmosphere (N/sub 2/) pressure has been estimated by these authors to be 9 x 10/sup -13/cm/sup 3//molec/s. Based on estimated k values and concentrations for several trace gases, it is suggested here that the resulting HSO/sub 3/ radical from reaction (1) under atmospheric conditions would react predominantly with O/sub 2/ in both the lower stratosphere and the troposphere. It is further suggested that the product HSO/sub 5/ radical would undergo hydration in both atmospheric regions.

Journal ArticleDOI
TL;DR: In this article, a multiconstituent circulation model was used to analyze the midnight temperature anomaly observed on Atmosphere Explorer-E. The model showed that this feature and associated variations in composition are the result of a complex interaction between the semidiurnal tide generated in the lower atmosphere and ion-neutral momentum coupling associated with the diurnal variation of the ion density.
Abstract: Spectral analysis of the midnight temperature anomaly observed on Atmosphere Explorer-E indicates that the phenomenon can be adequately represented with wave numbers between 1 and 5. Results from a multiconstituent circulation model suggest that this feature and associated variations in composition are the result of a complex interaction between the semidiurnal tide generated in the lower atmosphere and ion-neutral momentum coupling associated with the diurnal variation of the ion density which, in turn, also generates higher order tidal models.

Journal ArticleDOI
TL;DR: In this article, the authors identify the broad absorption feature below 3300 A in the Venus UV spectrum is primarily due to SO2 absorption based on new higher resolution spectra of the 3000-3400 A region showing broad (10 A), unresolved absorptions in the regions at all SO2 band origins between 3000 and 3300A.
Abstract: The broad absorption feature below 3300 A in the Venus UV spectrum is identified as primarily due to SO2 absorption based on new higher resolution spectra of the 3000-3400 A region showing broad (10 A), unresolved absorptions in the regions at all SO2 band origins between 3000 and 3300 A. SO2 mixing ratios vary from 5 x 10 to the -7th down to an upper limit of 2 x 10 to the -8th at a phase angle of 138 deg. Previous observational determinations of the SO2 mixing ratio were biased toward large phase angles, and consequently did not detect any SO2 absorption at the 10 to the -8th level. The upper limit derived from the CS2 band head at 3206 A is not greater than 5 x 10 to the -8th. The observed range of SO2 mixing ratios is consistent with model predictions based on the sulfur photochemistry at the cloud tops. Ground-based observations of SO2 mixing ratio will provide constraints on models and check on the Venera and Pioneer Venus measurements of the mixing ratios of SO2 and other sulfur-bearing gases with altitude.

Journal ArticleDOI
TL;DR: In this article, the spectral hardening is seen to be produced by a large increase in the ≳ 1 MeV electron flux; by contrast, electrons with E < 1 MEV show flux increases several days earlier than the high-energy component and this lower energy component is in close time synchronism with high solar wind speeds.
Abstract: Using energetic electron data (30 keV - 2 MeV) from instruments onboard spacecraft 1976-059A at synchronous orbit (6.6 RE), we have been able to study relatively long-term electron flux variations. Recurrently, and often with a 27-day periodicity, the daily average 0.2-2.0 MeV electron spectrum hardens dramatically. This change, wherein the power law spectral index goes from γ ∼ 3-4 to γ ≲ 2, occurs during quiet geomagnetic (low Kp) periods usually several days after the leading edge of high-speed solar wind streams have gone past the earth. The spectral hardening is seen to be produced by a large increase in the ≳ 1 MeV electron flux; by contrast, electrons with E < 1 MeV show flux increases several days earlier than the high-energy component and this lower energy component is in close time synchronism with high solar wind speeds. Based on nearly 2.5 years of available data, it also appears that the high-energy electron flux may undergo an ∼ 13-month periodicity, and for many recurrent peak intensity events we see that the flux maximum at 6.6 RE occurs ∼2 days after Jovian electron intensities have peaked outside the magnetosphere at IMP 7/8. Thus we suggest the possibility that Jovian electrons might contribute significantly at times to the terrestrial electron radiation belt population.