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1.
Meridional circulation in stellar convection zones is not generally well observed, but may be critical for the workings of MHD dynamos operating in these domains. Coriolis forces from differential rotation play a large role in determining what the meridional circulation is. Here, we consider the question of whether a stellar differential rotation that is constant on cylinders concentric with the rotation axis can drive a meridional circulation. Conventional wisdom says that it can not. Using two related forms of the governing equations that respectively estimate the longitudinal components of the curl of the meridional mass flux and the vorticity, we show that such differential rotation will drive a meridional flow. This is because to satisfy anelastic mass conservation, non-spherically symmetric pressure contours must be present for all differential rotations, not just ones that depart from constancy on cylinders concentric with the rotation axis. Therefore, the fluid is always baroclinic if differential rotation is present. This is because, in anelastic systems, the perturbation pressure must satisfy a Poisson type equation, as well as an equation of state and a thermodynamic equation. We support our qualitative reasoning with numerical examples, and show that meridional circulation is sensitive to the magnitude and form of departures from rotation constant on cylinders. The effect should be present in 3D global anelastic convection simulations, particularly those for which the differential rotation driven by global convection is nearly cylindrical in profile. For solar-like differential rotation, Coriolis forces generally drive a two-celled circulation in each hemisphere, with a second, reversed flow at high latitudes. For solar like turbulent viscosities, the meridional circulation produced by Coriolis forces is much larger than observed on the Sun. Therefore, there must be at least one additional force, probably a buoyancy force, which opposes the meridional flow to bring its amplitude down to observed values.  相似文献   
2.
Solar magnetic indices are used to model the solar irradiance and ultimately to forecast it. However, the observation of such indices is generally limited to the Earth-facing hemisphere of the Sun. Seismic maps of the far side of the Sun have proven their capability to locate and track medium–large active regions at the non-visible hemisphere. We present here the possibility of using the average signal from these seismic far-side maps, combined with similarly calculated near-side maps, as a proxy to the full-Sun magnetic activity.  相似文献   
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The relatively stable concentrations of calcium (42.2–122.3 mg/l) and magnesium (48.9–88.1 mg/l) between 2012 and 2013 and their possible weathering paths identified by mass balance models for both soil solutions and stream water from a small salted (regular applications of winter road deicing salt) watershed in New Jersey, USA indicate that the weathering of feldspars and dissolution of carbonates are the primary sources for these cations. However, the relatively stable and lower concentrations of sodium and chloride in soil solutions (19.6–46.1 mg/l for Na and 12.7–88.3 mg/l for Cl) and their fluctuating and higher concentrations in stream water (14.6–103.1 mg/l for Na and 15.2–260.4 mg/l)) from the same watershed during the same period also indicate that road deicing salt is the primary source for sodium and chloride in stream water. Furthermore, positive correlations between calcium and sulfur concentrations (correlation coefficient r = 0.77) and magnesium and sulfur concentrations (r = 0.73) in stream water between 2009 and 2013, as well as positive correlations between sulfur and iron concentrations in soil compositions (r = 0.27), indicate that both the dissolution of gypsum and the oxidation of pyrite into hematite might be the primary sources of sulfate in the watershed. Analyses of water chemistry from the related and much larger Delaware River Watershed (DRW) show that sodium and chloride concentrations have increased steadily (2.7 times for Na and 4.56 times for Cl for 10-year average) due to the regular application of winter deicing salt from 1944 to 2011 for which data are available. The greater increase of stream water chloride concentrations compared with sodium concentrations also results in the steady decline of Na+/Cl molar ratios from 1.51 to 0.92 for the 10-year average during that time in the DRW and approximately 78% of the chloride in the DRW now being anthropogenic. In addition, the decline of sulfate concentration from 22.08 to 14.59 mg/l (∼34%) for the 10-year average from 1980 to 2011 in the DRW stream water may be attributed to the decline of sulfate levels in atmospheric deposition resulting from enhanced national and state environmental regulations and a shift in local economic activities. There also are more periods of low silica stream water concentrations in the DRW than in the past, perhaps as a result of recent increases in summer stream temperatures combined with an increase of impervious surface area in the region. Warmer stream water might cause the temporary bloom of biota requiring silica, particularly plankton, increasing its uptake from stream water, while an expanded impervious surface area increases the contribution of low-silica runoff water to total stream discharge, thereby lowering the silica concentration in stream water. The combined results of this study illustrate the possible changing anthropogenic factors that can control stream water chemistry in salted watersheds and that these factors need to be taken into account when future water quality regulations and policy are considered.  相似文献   
5.
In this study we map the methane gas in the Martian atmosphere. The main goal of this work is to show the methane behaviour across the planet seasonally. To this aim, we analyze the strongest methane band in the short wavelength channel of the Planetary Fourier Spectrometer (PFS) on board ESA Mars Express (MeX) spacecraft. The optical line depth is used to derive the column density of methane. The maps thus obtained show the spatial variability of this non-condensable gas and how the gas is transported in the atmosphere due to the cycle of carbon dioxide. Moreover, the increase of methane over the north polar cap during local summer, which cannot be explained by global circulation, strongly suggests that there could be methane reservoir associated with the polar cap.  相似文献   
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Demands for a broad range of integrated geospatial data-analysis tools and methods for planetary data organization have been growing considerably since the late 1990s when a plethora of missions equipped with new instruments entered planetary orbits or landed on the surface. They sent back terabytes of new data which soon became accessible for the scientific community and public and which needed to be organized. On the terrestrial side, issues of data access, organization and utilization for scientific and economic analyses are handled by using a range of well-established geographic information systems (GIS) that also found their way into the field of planetary sciences in the late 1990s. We here address key issues concerning the field of planetary mapping by making use of established GIS environments and discuss methods of addressing data organization and mapping requirements by using an easily integrable datamodel that is—for the time being—designed as file-geodatabase (FileGDB) environment in ESRI's ArcGIS. A major design-driving requirement for this datamodel is its extensibility and scalability for growing scientific as well as technical needs, e.g., the utilization of such a datamodel for surface mapping of different planetary objects as defined by their respective reference system and by using different instrument data. Furthermore, it is a major goal to construct a generic model which allows to perform combined geologic as well as geomorphologic mapping tasks making use of international standards without loss of information and by maintaining topologic integrity. An integration of such a datamodel within a geospatial DBMS context can practically be performed by individuals as well as groups without having to deal with the details of administrative tasks and data ingestion issues. Besides the actual mapping, key components of such a mapping datamodel deal with the organization and search for image-sensor data and previous mapping efforts, as well as the proper organization of cartographic representations and assignments of geologic/geomorphologic units within their stratigraphic context.  相似文献   
7.
Condensed water particles are known to exist in the high latitude upper mesosphere during the summer months. However, the mechanism or mechanisms through which they nucleate remains uncertain. It is postulated here that particles of amorphous solid water (ASW, condensed water with a non-crystalline structure) may nucleate homogeneously in the summer mesosphere. Using classical nucleation theory and a one-dimensional model, it is shown that more than 105 cm?3 amorphous solid water particles can nucleate homogeneously under mesopause conditions. Furthermore, it is shown that homogeneous nucleation competes with heterogeneous nucleation on meteoric smoke particles when the cooling rate is >0.5 K/h. The homogeneous nucleation of amorphous solid water could provide an explanation for the high density of ice particles (many thousands per cm3) thought to be required for electron depletions in the upper mesosphere. A parameterisation for homogeneous nucleation is presented which can be used in other mesospheric cloud models.  相似文献   
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Corwin J. Wright 《Icarus》2012,219(1):274-282
Temperature measurements from the Mars Climate Sounder on NASA’s Mars Reconnaissance Orbiter are examined for gravity wave signals using the Stockwell transform, a technique previously applied to terrestrial temperature profiles. An analysis is presented for internal-gravity waves throughout the martian atmosphere for the period July 2007–May 2009, representing a full martian year of data, divided by season. Momentum fluxes observed in the altitude range 200–20 Pa are measured as ~10?5–10?3 Pa, significantly higher than at equivalent altitudes on Earth, and are primarily peaked around the tropics. Observed orographic effects are minimal; the primary observed effects are seasonal. Waves are shown to vary significantly in wavelength with latitude, but are generally approximately zonally symmetric. Horizontal wavelengths are consistently much shorter in the northern hemisphere than the southern.  相似文献   
10.
Several independent lines of observational evidence of the existence of kinetic Alfvén waves (KAWs) in the solar wind are briefly reviewed. Each piece of evidence is inconclusive when considered separately, but when taken together, it is reasonable to conclude from these observations that KAWs in the form of kinetic Alfvén turbulence are almost always present in the free-flowing solar wind near 1 AU and, by inference, perhaps throughout much of the heliosphere.  相似文献   
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