Relative contributions of sublimation and volcanoes to Io's atmosphere inferred from its plasma interaction during solar eclipse     

Joachim Saur  Darrell F. Strobel 《Icarus》2004,171(2):411-420

We present a model that describes Io's delayed electrodynamic response to a temporal change in Io's atmosphere. Our model incorporates the relevant physical processes involved in Io's atmosphere-ionosphere-magnetosphere electrodynamic interaction to predict the far-ultraviolet (FUV) radiation as Io enters Jupiter's shadow and re-emerges into sunlight. The predicted FUV brightnesses are highly nonlinear as the strength of the electrodynamic interaction depends on the ratios of ionospheric conductances to the torus Alfvén conductance, but the former are functions of electrodynamics and the atmospheric density, which decays rapidly upon entering eclipse. Key factors governing the time evolution are the column density due to sublimation and the column density due to volcanoes, which maintain the background atmosphere during eclipse. The plasma interaction does not react instantaneously, but lags to a temporarily changing atmosphere. We find three qualitatively different scenarios with two of them including a post-eclipse brightening. The brightness ratio of in-sunlight/in-eclipse coupled with the existence of a sub-jovian equatorial spot constrains the volcanic column density to several times 10¹⁸ m⁻², based on the currently available observations. Thus in sunlight, the sublimation driven part of Io's atmosphere dominates the volcanically driven contribution by roughly a factor of 10 or more.  相似文献   

Spectro-imaging observations of Jupiter's 2-μm auroral emission. I. H₃ distribution and temperature     

E. Raynaud  J.-P. Maillard  J.H. Waite Jr.  P. Drossart 《Icarus》2004,171(1):133-152

We report on spectro-imaging infrared observations of Jupiter's auroral zones, acquired in October 1999 and October 2000 with the FTS/BEAR instrument at the Canada-France-Hawaii Telescope. The use of narrow-band filters at 2.09 and 2.12 μm, combined with high spectral resolution (0.2 cm⁻¹), allowed us to map emission from the H₂S₁(1) quadrupole line and from several H₃⁺ lines. The H₂ and H₃⁺ emission appears to be morphologically different, especially in the north, where the latter notably exhibits a “hot spot” near 150°-170° System III longitude. This hot spot coincides in position with the region of increased and variable hydrocarbon, FUV and X-ray emission, but is not seen in the more uniform H₂S₁(1) emission. We also present the first images of the H₂ emission in the southern polar region. The spectra include a total of 14 H₃⁺ lines, including two hot lines from the 3ν₂-ν₂ band, detected on Jupiter for the first time. They can be used to determine H₃⁺ column densities, rotational (T_rot) and vibrational (T_vib) temperatures. We find the mean T_vib of the v₂=3 state to be lower (960±50 K) than the mean T_rot in v₂=2 (1170±75 K), indicating an underpopulation of the v₂=3 level with respect to local thermodynamical equilibrium. Rotational temperatures and associated column densities are generally higher and lower, respectively, than inferred previously from ν₂ observations. This is a likely consequence of a large positive temperature gradient in the sub-microbar auroral atmosphere. While the signal-to-noise is not sufficient to take full advantage of the 2-D capabilities of the observations, the search for correlations between line intensities, T_vib and column densities, indicates that variations in line intensities are mostly due to correlated variations in the H₃⁺ column densities. The thermostatic role played by H₃⁺ at ionospheric levels may provide an explanation. The exception is the northern “hot spot,” which exhibits a T_vib about 250 K higher than other regions. A partial explanation might invoke a homopause elevation in this region, but a fully consistent scenario is not yet available. The different distributions of the H₂ and H₃⁺ emission are equally difficult to explain.  相似文献   

Climatic and biological simulations in a two-way coupled atmosphere–biosphere model (CABM)     

Li Dan  Jinjun Ji  Yinpeng Li 《Global and Planetary Change》2005,47(2-4):153

Today, most land surface process models have prescribed seasonal change of vegetation with regard to the exchange processes between land and the atmosphere. However, in order to consider the real interaction between vegetation and atmosphere and represent it best in a climate model, the vegetation growth process should be included. In other words, “life” should be brought into climate models. In this study, we have coupled the physical and biological components of AVIM (Atmosphere–Vegetation Interaction Model), a land surface model including plant ecophysiological processes, into the IAP/LASG L9 R15 GOALS GCM. To exhibit terrestrial vegetation information, the vegetation is given a high resolution of 1.5° by 1.5° to nest and couple the fine grid cells of land with the coarse grid cells of atmosphere, which is 7.5° longitude and 4.5° latitude. The simulated monthly mean surface air temperature and precipitation is close to the observations. The monthly mean Leaf Area Index (LAI) is consistent with the observed data. The global annual mean net primary production (NPP) simulation is also reasonable. The coupled model is stable, providing a good platform for research on two-way interaction between land and atmosphere, and the global terrestrial ecosystem carbon cycle.  相似文献   

Dynamical implications of Jupiter's tropospheric ammonia abundance     

Adam P. Showman  Imke de Pater 《Icarus》2005,174(1):192-204

Groundbased radio observations indicate that Jupiter's ammonia is globally depleted from 0.6 bars to at least 4-6 bars relative to the deep abundance of ∼3 times solar, a fact that has so far defied explanation. The observations also indicate that (i) the depletion is greater in belts than zones, and (ii) the greatest depletion occurs within Jupiter's local 5-μm hot spots, which have recently been detected at radio wavelengths. Here, we first show that both the global depletion and its belt-zone variation can be explained by a simple model for the interaction of moist convection with Jupiter's cloud-layer circulation. If the global depletion is dynamical in origin, then important endmember models for the belt-zone circulation can be ruled out. Next, we show that the radio observations of Jupiter's 5-μm hot spots imply that the equatorial wave inferred to cause hot spots induces vertical parcel oscillation of a factor of ∼2 in pressure near the 2-bar level, which places important constraints on hot-spot dynamics. Finally, using spatially resolved radio maps, we demonstrate that low-latitude features exceeding ∼4000 km diameter, such as the equatorial plumes and large vortices, are also depleted in ammonia from 0.6 bars to at least 2 bars relative to the deep abundance of 3 times solar. If any low-latitude features exist that contain 3-times-solar ammonia up to the 0.6-bar ammonia condensation level, they must have diameters less than ∼4000 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   

Variations in dissolved CO2 and CH4 in a first‐order stream and catchment: an investigation of soil–stream linkages     

Diane Hope  Sheila M. Palmer  Michael F. Billett  Julian J. C. Dawson 《水文研究》2004,18(17):3255-3275

Spatial and seasonal variations in CO₂ and CH₄ concentrations in streamwater and adjacent soils were studied at three sites on Brocky Burn, a headwater stream draining a peatland catchment in upland Britain. Concentrations of both gases in the soil atmosphere were significantly higher in peat and riparian soils than in mineral soils. Peat and riparian soil CO₂ concentrations varied seasonally, showing a positive correlation with air and soil temperature. Streamwater CO₂ concentrations at the upper sampling site, which mostly drained deep peats, varied from 2·8 to 9·8 mg l^?1 (2·5 to 11·9 times atmospheric saturation) and decreased markedly downstream. Temperature‐related seasonal variations in peat and riparian soil CO₂ were reflected in the stream at the upper site, where 77% of biweekly variation was explained by an autoregressive model based on: (i) a negative log‐linear relationship with stream flow; (ii) a positive linear relationship with soil CO₂ concentrations in the shallow riparian wells; and (iii) a negative linear relationship with soil CO₂ concentrations in the shallow peat wells, with a significant 2‐week lag term. These relationships changed markedly downstream, with an apparent decrease in the soil–stream linkage and a switch to a positive relationship between stream flow and stream CO₂. Streamwater CH₄ concentrations also declined sharply downstream, but were much lower (<0·01 to 0·12 mg l^?1) than those of CO₂ and showed no seasonal variation, nor any relationship with soil atmospheric CH₄ concentrations. However, stream CH₄ was significantly correlated with stream flow at the upper site, which explained 57% of biweekly variations in dissolved concentrations. We conclude that stream CO₂ can be a useful integrative measure of whole catchment respiration, but only at sites where the soil–stream linkage is strong. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Microwave observations of Saturn's rings: anisotropy in directly transmitted and scattered saturnian thermal emission     

David E. Dunn  Lawrence A. Molnar  Imke de Pater 《Icarus》2004,171(1):183-198

We present a new Very Large Array (VLA) image of Saturn, made from data taken in October 1998 at a wavelength of λ3.6 cm. The moderate ring opening angle (B≈15°) allows us to explore direct transmission of microwave photons through the A and C rings. We find a strong asymmetry of photons transmitted through the A ring, but not in the C ring, a new diagnostic of wake structure in the ring particles. We also find a weak asymmetry between east and west for the far side of the ansae. To facilitate quantitative comparison between dynamic models of the A ring and radio observations, we extend our Monte Carlo radiative transfer code (described in Dunn et al., 2002, Icarus 160, 132-160) to include idealized wakes. We show the idealized model can reproduce the properties of dynamic simulations in directly transmitted light. We examine the model behavior in directly transmitted and scattered light over a range of physical and geometric wake parameters. Finally, we present a wake model with a plausible set of physical parameters that quantitatively reproduces the observed intensity and asymmetry of the A ring both across the planet and in the ansae.  相似文献   

Optimal orbits for Mars atmosphere remote sensing   总被引：1，自引：0，他引：1  

Michel Capderou  François Forget 《Planetary and Space Science》2004,52(9):789-798

Most of the spacecrafts currently around Mars (or planned to reach Mars in the near future) use Sun-synchronous or near-polar orbits. Such orbits offer a very poor sampling of the diurnal cycle. Yet, sampling the diurnal cycle is of key importance to study Mars meteorology and climate. A comprehensive remote sensing data set should have been obtained by the end of the MRO mission, launched in 2005. For later windows, time-varying phenomena should be given the highest priority for remote sensing investigations. We present possible orbits for such missions which provide a rich spatial and temporal sampling with a relatively short repeat cycle (50 sols). After computation and determination of these orbits, said “optimal orbits”, we illustrate our results by tables of sampling and comparison with other orbits.  相似文献   

The Nippon/Norway Svalbard Meteor Radar: First results of small-scale structure observations     

BO Husφy 《极地研究(英文版)》2002,13(1)

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Search for spatial variation in the jovian N/N ratio from Cassini/CIRS observations     

Thierry Fouchet  Patrick G.J. Irwin  Simon B. Calcutt  Conor A. Nixon 《Icarus》2004,172(1):50-58

We have used the spectra obtained by the Composite Infrared Spectrometer (CIRS) onboard the Cassini spacecraft to search for latitudinal variation in the ¹⁵N/¹⁴N ratio on Jupiter. We found no variations statistically significant given the observational and model uncertainties. The absence of latitudinal variations demonstrates that ¹⁵NH₃ is not fractionated in Jupiter's atmosphere, and that the measured ¹⁵N/¹⁴N represents Jupiter's global value. Our mean value for the global jovian ¹⁵N/¹⁴N ratio of (2.22±0.52)×10⁻³ agrees with previous measurements made by Fouchet et al. (2000, Icarus 143, 223-243) and Owen et al. (2001, Astrophys. J. 553, L77-L79). We argue that the jovian isotopic ¹⁵N/¹⁴N ratio must represent the solar nitrogen isotopic composition. The solar ¹⁵N/¹⁴N ratio hence significantly differs from the terrestrial value: (¹⁵N/¹⁴N)_⊕=3.68×10⁻³. This supports the proposition that terrestrial nitrogen originates from a nitrogen reservoir isolated from the main nitrogen reservoir in the proto-solar nebula. The origin and carrier of this isolated reservoir are still unknown.  相似文献