428 research outputs found
Convective plumes and the scarcity of Titan's clouds
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94936/1/grl19061.pd
Titan's lakes chemical composition: sources of uncertainties and variability
Between 2004 and 2007 the instruments of the CASSINI spacecraft discovered
hydrocarbon lakes in the polar regions of Titan. We have developed a
lake-atmosphere equilibrium model allowing the determination of the chemical
composition of these liquid areas. The model is based on uncertain
thermodynamic data and precipitation rates of organic species predicted to be
present in the lakes and seas that are subject to spatial and temporal
variations. Here we explore and discuss the influence of these uncertainties
and variations. The errors and uncertainties relevant to thermodynamic data are
simulated via Monte-Carlo simulations. Global Circulation Models (GCM) are also
employed in order to investigate the possibility of chemical asymmetry between
the south and the north poles, due to differences in precipitation rates. We
find that mole fractions of compounds in the liquid phase have a high
sensitivity to thermodynamic data used as inputs, in particular molar volumes
and enthalpies of vaporization. When we combine all considered uncertainties,
the ranges of obtained mole fractions are rather large (up to ~8500%) but the
distributions of values are narrow. The relative standard deviations remain
between 10% and ~300% depending on the compound considered. Compared to other
sources of uncertainties and variability, deviation caused by surface pressure
variations are clearly negligible, remaining of the order of a few percent up
to ~20%. Moreover no significant difference is found between the composition of
lakes located in north and south poles. Because the theory of regular solutions
employed here is sensitive to thermodynamic data and is not suitable for polar
molecules such as HCN and CH3CN, our work strongly underlines the need for
experimental simulations and the improvement of Titan's atmospheric models.Comment: Accepted in Planetary and Space Scienc
Methane storms as a driver of Titan's dune orientation
Titan's equatorial regions are covered by eastward propagating linear dunes.
This direction is opposite to mean surface winds simulated by Global Climate
Models (GCMs), which are oriented westward at these latitudes, similar to trade
winds on Earth. Different hypotheses have been proposed to address this
apparent contradiction, involving Saturn's gravitational tides, large scale
topography or wind statistics, but none of them can explain a global eastward
dune propagation in the equatorial band. Here we analyse the impact of
equinoctial tropical methane storms developing in the superrotating atmosphere
(i.e. the eastward winds at high altitude) on Titan's dune orientation. Using
mesoscale simulations of convective methane clouds with a GCM wind profile
featuring superrotation, we show that Titan's storms should produce fast
eastward gust fronts above the surface. Such gusts dominate the aeolian
transport, allowing dunes to extend eastward. This analysis therefore suggests
a coupling between superrotation, tropical methane storms and dune formation on
Titan. Furthermore, together with GCM predictions and analogies to some
terrestrial dune fields, this work provides a general framework explaining
several major features of Titan's dunes: linear shape, eastward propagation and
poleward divergence, and implies an equatorial origin of Titan's dune sand.Comment: Published online on Nature Geoscience on 13 April 201
Indication of intrinsic room-temperature ferromagnetism in Ti1-xCoxO2-d thin film: An x-ray magnetic circular dichroism study
Soft x-ray magnetic circular dichroism (XMCD) measurements at the Co L2,3
edges of Co doped rutile TiO2 at room temperature have revealed clear multiplet
features characteristic of ferromagnetic Co2+ ions coordinated by O2- ions,
being in sharp contrast to the featureless XMCD spectrum of Co metal or
metallic clusters. The absorption and XMCD spectra agree well with a full
atomic-multiplet calculation for the Co2+ high-spin state in the D2h-symmetry
crystal field at the Ti site in rutile TiO2. The results indicate that the
ferromagnetism arises from the Co2+ ions substituting the Ti4+ ions.Comment: 11 pages including 3 figure
Recommended from our members
ExoMars entry, descent and landing science
The entry, descent and landing of ExoMars offer a rare (once-per-mission) opportunity to perform in situ investigation of the martian environment over a wide altitude range. Entry, Descent and Landing System (EDLS) measurements can provide essential data for atmospheric scientific investigations.
We intend to perform atmospheric science measurements by exploiting data from EDLS engineering sensors and exploiting their readings beyond the expected engineering information
Lightning detection in planetary atmospheres
Lightning in planetary atmospheres is now a well-established concept. Here we
discuss the available detection techniques for, and observations of, planetary
lightning by spacecraft, planetary landers and, increasingly, sophisticated
terrestrial radio telescopes. Future space missions carrying lightning-related
instrumentation are also summarised, specifically the European ExoMars mission
and Japanese Akatsuki mission to Venus, which could both yield lightning
observations in 2016.Comment: Accepted for publication in Weather as part of a special issue on
Advances in Lightning Detectio
Temporal observations of a linear sand dune in the Simpson Desert, central Australia: Testing models for dune formation on planetary surfaces
Effect of Ventricular Shock Strength on Cardiac Hemodynamics
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75115/1/j.1540-8167.1998.tb00118.x.pd
Long-Term Evaluation of the Ventricular Defibrillation Energy Requirement
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74692/1/j.1540-8167.1998.tb00132.x.pd
The water cycle and regolith-atmosphere interaction at Gale crater, Mars
We perform mesoscale simulations of the water cycle in a region around Gale crater, including the diffusion of water vapour in and out of the regolith, and compare our results with measurements from the REMS instrument on board the Curiosity rover. Simulations are performed at three times of year, and show that diffusion in and out of the regolith and adsorption/desorption needs to be taken into account in order to match the diurnal variation of relative humidity measured by REMS. During the evening and night, local downslope flows transport water vapour down the walls of Gale crater. When including regolith-atmosphere interaction, the amount of vapour reaching the crater floor is reduced (by factors of 2–3 depending on season) due to vapour diffusing into the regolith along the crater walls. The transport of vapour into Gale crater is also affected by the regional katabatic flow over the dichotomy boundary, with the largest flux of vapour into the regolith initially occurring on the northern crater wall, and moving to the southern wall by early morning. Upslope winds during the day transport vapour desorbing and mixing out of the regolith up crater walls, where it can then be transported a few hundred metres into the atmosphere at convergence boundaries. Regolith-atmosphere interaction limits the formation of surface ice by reducing water vapour abundances in the lower atmosphere, though in some seasons ice can still form in the early morning on eastern crater walls. Subsurface ice amounts are small in all seasons, with ice only existing in the upper few millimetres of regolith during the night. The results at Gale crater are representative of the behaviour at other craters in the mesoscale domain
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