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101.
Bruch William Piazzola Jacques Branger Hubert van Eijk Alexander M. J. Luneau Christopher Bourras Denis Tedeschi Gilles 《Boundary-Layer Meteorology》2021,180(3):477-505
Boundary-Layer Meteorology - We investigate the effects of wind–wave interactions on the surface sea-spray-generation flux. To this end, the Marine Aerosol Tunnel Experiment (MATE2019) was... 相似文献
102.
Planets form in circumstellar discs as dust grains collide together and form ever larger bodies. However a major bottleneck
occurs for bodies with sizes around a few centimetres or larger. These rocks and boulders have very poor sticking properties
and spiral into the star in a few hundred years due to friction with the slower rotating gas. A possible way to overcome this
“meter-barrier” is to have local concentrations of rocks and boulders that become gravitationally unstable and contract to
form planetesimals of several kilometers in size. We present the results of numerical simulations of the coupled motion of
gas and rocks in protoplanetary disc mid-planes. The gas rotates slightly sub-Keplerian due to the global, radial pressure
gradient of the disc, causing a net velocity difference between the gas and the solids. This relative motion is in turn unstable
to streaming instabilities, and the saturated state of the turbulence is characterised by dense particle clumps that are fed
by the radial drift of isolated rocks. For realistic protoplanetary disc parameters the clumps are gravitationally unstable
and contract on the time-scale of a few orbits to form bodies of several hundred kilometers in size. Magnetic fields may further
augment the particle concentrations due to relatively long-lived high pressure bumps that form in magnetorotational turbulence.
However, magnetic fields are not crucial to the gravoturbulent formation of planetesimals, rather magnetised turbulence allows
collapse to occur for flows that are on the average less affected by the particles, i.e. for lower particle column densities. 相似文献
103.
104.
Sensitivity of coastal polynyas and high-salinity shelf water production in the Ross Sea,Antarctica, to the atmospheric forcing 总被引:1,自引:1,他引:0
Pierre Mathiot Nicolas C. Jourdain Bernard Barnier Hubert Gallée Jean Marc Molines Julien Le Sommer Thierry Penduff 《Ocean Dynamics》2012,62(5):701-723
Coastal polynyas around Antarctica are the place of intense air–sea exchanges which eventually lead to the formation of high-salinity shelf waters (HSSW) over continental shelves. Here, the influence of atmospheric forcing on coastal polynyas in the Ross Sea is studied by contrasting the response of a regional ocean/sea-ice circulation model to two different atmospheric forcing sets. A first forcing (DFS3) is based on ERA40 atmospheric surface variables and satellite products. A second forcing (MAR) is produced on the basis of ERA40 with a dynamical downscaling procedure. As compared to DFS3, MAR forcing is shown to improve substantially the representation of small-scale patterns of coastal winds with stronger katabatic winds along the coast. The response of the ocean/sea-ice model to the two forcing sets shows that the MAR forcing improves substantially the geographical distribution of polynyas in the Ross Sea. With the MAR forcing, the polynya season is also shown to last longer with a greater ice-production rate. As a consequence, a greater flow of dense water out of the polynyas is found with the MAR forcing and the properties of HSSW are notably improved as compared to the DFS3 forcing. The factors contributing to the activity of Terra Nova Bay and Ross Ice Shelf polynyas in the model are studied in detail. The general picture that emerges from our simulations is that the properties of HSSW are mostly set by brine rejection when the polynya season resume. We found that coastal polynyas in the Ross Sea export about 0.4 Sv of HSSW which then flows along three separate channels over the Ross Shelf. A 6-month time lag is observed between the peak of activity of polynyas and the maximum transport across the sills in the channels with a maximum transport of about 1 Sv in February. This lag corresponds to the time it takes to the newly formed HSSW to spread from the polynya to the sills (at a speed of nearly 2 cm s−1). 相似文献
105.
A two-dimensional equation governing the steady state spatial concentration distribution of a reactive constituent within a heterogeneous advective–dispersive flow field is solved analytically. The solution which is developed for the case of a single point source can be generalized to represent analogous situations with any number of separate point sources. A limiting case of special interest has a line source of constant concentration spanning the domain’s upstream boundary. The work has relevance for improving understanding of reactive transport within various kinds of advection-dominated natural or engineered environments including rivers and streams, and bioreactors such as treatment wetlands. Simulations are used to examine quantitatively the impact that transverse dispersion (deviations from purely stochastic-convective flow) can have on mean concentration decline in the direction of flow. Results support the contention that transverse mixing serves to enhance the overall rate of reaction in such systems. 相似文献
106.
Knowledge of river gain from or loss to a hydraulically connected water table aquifer is crucial in issues of water rights and also when attempting to optimize conjunctive use of surface and ground waters. Typically in groundwater models this exchange flow is related to a difference in head between the river and some point in the aquifer, through a “coefficient.” This coefficient has been defined differently as well as the location for the head in the aquifer. This paper proposes a new coefficient, analytically derived, and a specific location for the point where the aquifer head is used in the difference. The dimensionless part of the coefficient is referred to as the SAFE (stream‐aquifer flow exchange) dimensionless conductance. The paper investigates the factors that influence the value of this new conductance. Among these factors are (1) the wetted perimeter of the cross‐section, (2) the degree of penetration of the cross‐section, and (3) the shape of the cross‐section. The study shows that these factors just listed are indeed ordered in their respective level of importance. In addition the study verifies that the analytical correct value of the coefficient is matched by finite difference simulation only if the grid system is sufficiently fine. Thus the use of the analytical value of the coefficient is an accurate and efficient alternative to ad hoc estimates for the coefficient typically used in finite difference and finite element methods. 相似文献
107.
Hubert Krivine 《Comptes Rendus Geoscience》2017,349(3):91-95
The history of the determination of the Earth's age is interesting in two ways. First, it is a great school for understanding the genesis of a scientific theory. It stands at the crossroads of almost all scientific disciplines, and also philosophy or even theology. This history shows how what one may well call a “scientific truth” was established through polemics. Second, that age of 4.567 billion years is not just another figure in the series of ages that would be of concern only to astrophysicists; this scale is the only one that makes it possible to understand the genesis of the marvelous order of the solar system (that Newton attributed to God) and the fantastic complexity of Life on Earth. 相似文献
108.
A detailed field study was carried out on a tidal bore to document the turbulent processes and sediment entrainment which occurred. The measured bore, within the Arcins Channel of the Garonne River (France), was undular in nature and was followed by well‐defined secondary wave motion. Due to the local river geometry a collision between the Arcins channel tidal bore and the bore which formed within the main Garonne River channel was observed about 800 m upstream of the sampling site. This bore collision generated a transient standing wave with a black water mixing zone. Following this collision the bore from the main Garonne River channel propagated ‘backward’ to the downstream end of the Arcins channel. Velocity measurements with a fine temporal resolution were complemented by measurements of the sediment concentration and river level. The instantaneous velocity data indicated large and rapid fluctuations of all velocity components during the tidal bore. Large Reynolds shear stresses were observed during and after the tidal bore passage, including during the 'backward' bore propagation. Large suspended sediment concentration estimates were recorded and the suspended sediment flux data showed some substantial sediment motion, consistent with the murky appearance of the flood tide waters. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
109.
110.
Typical auroral events in the Martian atmosphere, such as discrete and diffuse auroral emissions detected by UV spectrometers onboard ESA Mars Express and NASA MAVEN, are investigated. Auroral electron kinetic energy distribution functions and energy spectra of the upward and downward electron fluxes are obtained by electron transport calculations using the kinetic Monte Carlo model. These characteristics of auroral electron fluxes make it possible to calculate both the precipitation-induced changes in the atmosphere and the observed manifestations of auroral events on Mars. In particular, intensities of discrete and diffuse auroral emissions in the UV and visible wavelength ranges (Soret et al., 2016; Bisikalo et al., 2017; Gérard et al., 2017). For these conditions of auroral events, the analysis is carried out, and the contribution of the fluxes of precipitating electrons to the heating and ionization of the Martian atmosphere is estimated. Numerical calculations show that in the case of discrete auroral events the effect of the residual crustal magnetic field leads to a significant increase in the upward fluxes of electrons, which causes a decrease in the rates of heating and ionization of the atmospheric gas in comparison with the calculations without taking into account the residual magnetic field. It is shown that all the above-mentioned impact factors of auroral electron precipitation processes should be taken into account both in the photochemical models of the Martian atmosphere and in the interpretation of observations of the chemical composition and its variations using the ACS instrument onboard ExoMars. 相似文献