Embayed intermediate volcanoes on Venus: Implications for the evolution of the volcanic plains     

I. López 《Icarus》2011,213(1):73-85

Volcanoes on Venus are classified according to size with studies on the stratigraphic position of large volcanoes proposing that most of the large volcanoes postdate the regional volcanic materials. Some studies regarding intermediate volcanoes proposed that some of these volcanic features could be large volcanoes with embayed flow aprons, a situation that would alter the previous stratigraphic considerations about large volcanoes on Venus.In this work I analyze the global population of embayed intermediate-size volcanoes and compare their summits with that of other edifices classified as large volcanoes. Intermediate-size volcanoes are considered embayed when: (1) flows from another source clearly overlap the volcano slopes, and (2) display scarps related to flank-failure processes but with the associated collapse deposits being absent (i.e. interpreted as covered). As result of the survey 88 embayed intermediate-size volcanoes have been catalogued and integrated into a Geographic Information System. These embayed volcanoes have summit sizes and characteristics similar to large volcanoes and, therefore, could be interpreted as possible large volcanoes with their flow aprons embayed. Embayment materials for these volcanoes include all the units present in the history of the volcanic plains and would indicate that this type of central volcanic edifice would occur throughout the geologic history recorded in the venusian plains.  相似文献   

A bulk cloud parameterization in a Venus General Circulation Model     

Christopher Lee  Stephen R. Lewis 《Icarus》2010,206(2):662-668

A condensing cloud parameterization is included in a super-rotating Venus General Circulation Model. A parameterization including condensation, evaporation and sedimentation of mono-modal sulfuric acid cloud particles is described. Saturation vapor pressure of sulfuric acid vapor is used to determine cloud formation through instantaneous condensation and destruction through evaporation, while pressure dependent viscosity of a carbon dioxide atmosphere is used to determine sedimentation rates assuming particles fall at their terminal Stokes velocity. Modifications are described to account for the large range of the Reynolds number seen in the Venus atmosphere.Two GCM experiments initialized with 10 ppm-equivalent of sulfuric acid are integrated for 30 Earth years and the results are discussed with reference to “Y” shaped cloud structures observed on Venus. The GCM is able to produce an analog of the “Y” shaped cloud structure through dynamical processes alone, with contributions from the mean westward wind, the equatorial Kelvin wave, and the mid-latitude/polar Mixed Rossby/Gravity waves. The cloud top height in the GCM decreases from equator to pole and latitudinal gradients of cloud top height are comparable to those observed by Pioneer Venus and Venus Express, and those produced in more complex microphysical models of the sulfur cycle on Venus. Differences between the modeled cloud structures and observations are described and dynamical explanations are suggested for the most prominent differences.  相似文献   

Sulfur chemistry in the Venus mesosphere from SO₂ and SO microwave spectra     

Brad J. Sandor  R. Todd Clancy  Gerald Moriarty-Schieven 《Icarus》2010,208(1):49-60

First measurements of SO₂ and SO in the Venus mesosphere (70-100 km) are reported. This altitude range is distinctly above the ∼60-70 km range to which nadir-sounding IR and UV investigations are sensitive. Since July 2004, use of ground-based sub-mm spectroscopy has yielded multiple discoveries. Abundance of each molecule varies strongly on many timescales over the entire sub-Earth Venus hemisphere. Diurnal behavior is evident, with more SO₂, and less SO, at night than during the day. Non-diurnal variability is also present, with measured SO₂ and SO abundances each changing by up to 2× or more between observations conducted on different dates, but at fixed phase, hence identical sub-Earth Venus local times. Change as large and rapid as a 5σ doubling of SO on a one-week timescale is seen. The sum of SO₂ and SO abundances varies by an order of magnitude or more, indicating at least one additional sulfur reservoir must be present, and that it must function as both a sink and source for these molecules. The ratio SO₂/SO varies by nearly two orders of magnitude, with both diurnal and non-diurnal components. In contrast to the strong time dependence of molecular abundances, their altitude distributions are temporally invariant, with far more SO₂ and SO at 85-100 km than at 70-85 km. The observed increase of SO₂ mixing ratio with altitude requires that the primary SO₂ source be upper mesospheric photochemistry, contrary to atmospheric models which assert upward transport as the only source of above-cloud SO₂. Abundance of upper mesospheric aerosol, with assumption that it is composed primarily of sulfuric acid, is at least sufficient to provide the maximum gas phase (SO + SO₂) sulfur reported in this study. Sulfate aerosol is thus a plausible source of upper mesospheric SO₂.  相似文献   

Oxidation of CO on surface hematite in high CO₂ atmospheres     

John Lee Grenfell  Joachim W. Stock  Stefanie Gebauer 《Planetary and Space Science》2010,58(10):1252-1257

We propose a mechanism for the oxidation of gaseous CO into CO₂ occurring on the surface mineral hematite (Fe₂O₃(s)) in hot, CO₂-rich planetary atmospheres, such as Venus. This mechanism is likely to constitute an important source of tropospheric CO₂ on Venus and could at least partly address the CO₂ stability problem in Venus’ stratosphere, since our results suggest that atmospheric CO₂ is produced from CO oxidation via surface hematite at a rate of 0.4 petagrammes (Pg) CO₂ per (Earth) year on Venus which is about 45% of the mass loss of CO₂ via photolysis in the Venusian stratosphere. We also investigated CO oxidation via the hematite mechanism for a range of planetary scenarios and found that modern Earth and Mars are probably too cold for the mechanism to be important because the rate-limiting step, involving CO(g) reacting onto the hematite surface, proceeds much slower at lower temperatures. The mechanism may feature on extrasolar planets such as Gliese 581c or CoRoT-7b assuming they can maintain solid surface hematite which, e.g. starts to melt above about 1200 K. The mechanism may also be important for hot Hadean-type environments and for the emerging class of hot Super-Earths with planetary surface temperatures between about 600 and 900 K.  相似文献   

���ʽ���̽��ƻ���չ���ҹ����������ݶȼƻ���ʵʩ     

郑伟  许厚泽  钟敏  刘成恕 《大地测量与地球动力学》2014,34(1):8-14

????????????????????ù????????????????????????????????????????????????????????????????????SST-HL/SGG-Doppler-VLBI????????????????????50~100 km??  相似文献   

Latitudinal variations of CO and OCS in the lower atmosphere of Venus from near-infrared nightside spectro-imaging     

Emmanuel Marcq  Bruno Bézard  Mirel Birlan 《Icarus》2005,179(2):375-386

Spectro-imaging of Venus' nightside in the 2.3-μm window provides a powerful means of probing the lower atmosphere in the 25-40 km altitude range. We present observations recorded at the NASA/IRTF in February 2003 and August 2004, using the SpeX spectro-imager in the 2.1-2.5-μm region. Abundances of CO and OCS have been derived as a function of latitude for different longitudes. The CO abundance increases by about 15% between the equatorial region and higher latitudes (±40°). No longitudinal or temporal variations are observed. The OCS abundance shows the opposite variation in observational sets with sufficient S/N. These variations and anticorrelation are consistent with upwelling motions in the equatorial region and downwelling at higher latitudes.  相似文献   

Maintenance of equatorial superrotation in the atmospheres of Venus and Titan     

Xun Zhu 《Planetary and Space Science》2006,54(8):761-773

This paper extends Leovy's theory on Venus’ equatorial superrotation by analytically examining additional terms in the mean zonal momentum equation that stably balances the momentum source of pumping by thermal tides. The general analytical solution is applied to the atmospheres of both Venus and Saturn's moon Titan. The main results are: (i) Venus’ equatorial superrotation of 118 m s⁻¹ results primarily from a balance between the momentum source of pumping by thermal tides and the momentum sink of meridional advection of wind shear by horizontal branches of the Hadley circulation; (ii) no solution is found for Titan's stratospheric equatorial superrotation centered at the 1-hPa level; (iii) however, if the main solar radiation absorption layer in Titan's stratosphere is lifted from 1 hPa (∼185 km) to 0.1 hPa (∼288 km), an equatorial superrotation of ∼110 m s⁻¹ centered at 0.1-hPa could be maintained. Titan's equatorial superrotation results mainly from a balance between the momentum source of tidal pumping and the momentum sink of frictional drag.  相似文献   

High-resolution imaging spectroscopy of planetary atmospheres     

《Comptes Rendus Geoscience》2015,347(3):145-152

Imaging spectroscopy at high resolution, in the infrared range, is a powerful tool for monitoring the behavior of minor species in planetary atmospheres and their evolution with latitude and longitude, season or local hour. Using the TEXES imaging spectrometer at the Infrared Telescope Facility (IRTF), this method has been applied for detecting and monitoring hydrogen peroxide and water vapor (using its proxy HDO) on Mars, then for monitoring sulfur dioxide and water (again using HDO) above the H₂SO₄ cloud deck (z = 65 km on Venus). Observations of Mars have shown that its atmosphere and climate are well reproduced by the Global Climatic Models. In contrast, strong spatio-temporal variations of SO₂, observed above the Venus clouds, are not understood by the models. As a support of the forthcoming Juno space mission, a similar program has started on Jupiter to monitor its dynamics through 3-D maps of ammonia and phosphine.  相似文献   

Rayleigh-Taylor instability as a mechanism for corona formation on Venus     

Trudi Hoogenboom  Gregory A. Houseman 《Icarus》2006,180(2):292-307

In this study we explore the idea that coronae have formed on Venus as a result of gravitational (Rayleigh-Taylor) instability of the lithosphere. The lithosphere is represented by a system of stratified homogeneous viscous layers (low-density crust over high density mantle, over lower density layer beneath the lithosphere). A small harmonic perturbation imposed on the base of the lithosphere is observed to result in gravitational instability under the constraint of assumed axisymmetry. Topography develops with time under the influence of dynamic stress associated with downwelling or upwelling, and spatially variable crustal thickening or thinning. Topography may therefore be elevated or depressed above a mantle downwelling, but the computed gravity anomaly is always negative above a mantle downwelling in a homogeneous asthenosphere. The ratio of peak gravity to topography anomaly depends primarily on the ratio of crust to lithospheric viscosity. Average observed ratios are well resolved for two groups of coronae (∼40 mgal km⁻¹), consistent with models in which the crust is perhaps 5 times stronger than the lithosphere. Group 3a (rim surrounding elevated central region) coronae are inferred to arise from a central upwelling model, whereas Group 8 (depression) coronae are inferred to arise from central downwelling. Observed average coronae radii are consistent with a lithospheric thickness of only 50 km. An upper low-density crustal layer is 10-20 km thick, as inferred from the amplitude of gravity and topography anomalies.  相似文献   

Atomic oxygen distribution in the Venus mesosphere from observations of O₂ infrared airglow by VIRTIS-Venus Express     

Jean-Claude Gérard  Adem Saglam  Pierre Drossart  Jean-Loup Bertaux 《Icarus》2009,199(2):264-272

This VIRTIS instrument on board Venus Express has collected spectrally resolved images of the Venus nightside limb that show the presence of the (0,0) band of the infrared atmospheric system of O₂ at 1.27 μm. The emission is produced by three-body recombination of oxygen atoms created by photodissociation of CO₂ on the dayside. It is consistently bright so that emission limb profiles can be extracted from the images. The vertical distribution of O₂() may be derived following Abel inversion of the radiance limb profiles. Assuming photochemical equilibrium, it is combined with the CO₂ vertical distribution to determine the atomic oxygen density. The uncertainties on the O density caused by the Abel inversion reach a few percent at the peak, increasing to about 50% near 120 km. We first analyze a case when the CO₂ density was derived from a stellar occultation observed with the SPICAV spectrometer simultaneously with an image of the O₂ limb airglow. In other cases, an average CO₂ profile deduced from a series of ultraviolet stellar occultations is used to derive the O profile, leading to uncertainties on the O density less than 30%. It is found that the maximum O density is generally located between 94 and 115 km with a mean value of 104 km. It ranges from less than 1×¹⁰¹¹ to about 5×¹⁰¹¹ cm⁻³ with a global mean of 2.2×¹⁰¹¹ cm⁻³. These values are in reasonable agreement with the VIRA midnight oxygen profile. The vertical O distribution is generally in good agreement with the oxygen profile calculated with a one-dimensional chemical-diffusive model. No statistical latitudinal dependence of the altitude of the oxygen peak is observed, but the maximum O density tends to decrease with increasing northern latitudes. The latitudinal distribution at a given time exhibits large variations in the O density profile and its vertical structure. The vertical oxygen distribution frequently shows multiple peaks possibly caused by waves or variations in the structure of turbulent transport. It is concluded that the O₂ infrared night airglow is a powerful tool to map the distribution of atomic oxygen in the mesosphere between 90 and 115 km and improve future Venus reference atmosphere models.  相似文献