Search results for " Convection"

The Impact of a Very Weak and Thin Upper Asthenosphere on Subduction Motions

2019

Recent geophysical observations report the presence of a very weak and thin upper asthenosphere underneath subducting oceanic plates at convergent margins. Along these margins, trench migrations are significantly slower than plate convergence rates. We use numerical models to assess the role of a weak upper asthenospheric layer on plate and trench motions. We show that the presence of this layer alone can enhance an advancing trend for the motion of the plate and hamper trench retreat. This mechanism provides a novel and alternative explanation for the slow rates of trench migration and fast-moving plates observed globally at natural subduction zones.

Lagrangian Description of Air Masses Associated with Latent Heat Release in Tropical Storm Karl (2016) during Extratropical Transition

2019

Abstract Extratropical transition (ET) of tropical cyclones involves distinct changes of the cyclone’s structure that are not yet well understood. This study presents for the first time a comprehensive Lagrangian description of structure change near the inner core. A large sample of trajectories is computed from a convection-permitting numerical simulation of the ET of Tropical Storm Karl (2016). Three main airstreams are considered: those associated with the inner-core convection, inner-core descent, and the developing warm conveyor belt. Analysis of these airstreams is performed both in thermodynamic and physical space. Prior to ET, Karl is embedded in weak vertical wind shear and its int…

Mean Radiant Temperature Measurements through Small Black Globes under Forced Convection Conditions

2021

One of the most critical variables in the field of thermal comfort measurements is the mean radiant temperature which is typically measured with a standard 150 mm black globe thermometer. This is also the reference instrument required for the assessment of heat stress conditions by means of the well-known Wet Bulb Globe Temperature index (WBGT). However, one of the limitations of this method is represented by the relatively long response time. This is why in recent years there has been a more and more pressing need of smart sensors for controlling Heating Ventilation and Air Conditioning (HVAC) systems, and for pocket heat stress meters (e.g., WBGT meters provided with table tennis balls). …

Variability of the African convection centre as viewed by outgoing longwave radiation records and relationships with sea-surface temperature patterns

1995

International audience; The main African convection centre (ACC) is delimited by the 5"-square areas with outgoing longwave radiation less than 235 W m-' in the domain 17.5°N-17.5"S and 18"W-46"E. Four parameters (latitude and longitude of the centre of gravity, mean intensity, and extension) were analysed during the period June 1974 to December 1991. The relationships between the variability of the ACC and the main sea-surface temperature (SST) patterns were then studied. Correlation and composite analyses demonstrate that the first principal component of SST, representing mainly the variability of the eastern and the central tropical Pacific, is associated strongly with the extension and …

Adaptive discontinuous evolution Galerkin method for dry atmospheric flow

2014

We present a new adaptive genuinely multidimensional method within the framework of the discontinuous Galerkin method. The discontinuous evolution Galerkin (DEG) method couples a discontinuous Galerkin formulation with approximate evolution operators. The latter are constructed using the bicharacteristics of multidimensional hyperbolic systems, such that all of the infinitely many directions of wave propagation are considered explicitly. In order to take into account multiscale phenomena that typically appear in atmospheric flows nonlinear fluxes are split into a linear part governing the acoustic and gravitational waves and a nonlinear part that models advection. Time integration is realiz…

Thermomagnetic Materials: Thermomagnetic Properties Improved by Self-Organized Flower-Like Phase Separation of Ferromagnetic Co2Dy0.5Mn0.5Sn (Adv. Fu…

2012

Theoretical study of a Bénard Marangoni problem

2011

[EN] In this paper we prove the existence of strong solutions for the stationary Benard-Marangoni problem in a finite domain flat on the top, bifurcating from the basic heat conductive state. The Benard-Marangoni problem is a physical phenomenon of thermal convection in which the effects of buoyancy and surface tension are taken into account. This problem is modelled with a system of partial differential equations of the type Navier-Stokes and heat equation. The boundary conditions include crossed boundary conditions involving tangential derivatives of the temperature and normal derivatives of the velocity field. To define tangential derivatives at the boundary, intended in the trace sense,…

Thermomagnetic Properties Improved by Self-Organized Flower-Like Phase Separation of Ferromagnetic Co2Dy0.5Mn0.5Sn

2012

A thermodynamically stable phase separation of Co2Dy0.5Mn0.5Sn into the Heusler compound Co2MnSn and Co8Dy3Sn4 is induced by rapid cooling from the liquid phase. The phase separation forms an ordered flower-like structure on the microscale. The increased scattering of phonons at the phase boundaries reduces the thermal conductivity and thus improves thermoelectric and spincaloric properties.

Efficient parallel computations of flows of arbitrary fluids for all regimes of Reynolds, Mach and Grashof numbers

2002

This paper presents a unified numerical method able to address a wide class of fluid flow problems of engineering interest. Arbitrary fluids are treated specifying totally arbitrary equations of state, either in analytical form or through look‐up tables. The most general system of the unsteady Navier–Stokes equations is integrated with a coupled implicit preconditioned method. The method can stand infinite CFL number and shows the efficiency of a quasi‐Newton method independent of the multi‐block partitioning on parallel machines. Computed test cases ranging from inviscid hydrodynamics, to natural convection loops of liquid metals, and to supersonic gasdynamics, show a solution efficiency i…

Tropical–extratropical interactions related to upper-level troughs at low latitudes

2007

Abstract Momentum and kinetic energy fluxes associated with low-latitude transient disturbances at upper-levels play an important role in the general circulation of the atmosphere. They are related to eastward and equatorward propagating, positively tilted wave trains from the extratropics. Theoretical, modelling and observational studies show that this particular kind of tropical–extratropical interaction is most common in regions of mean upper-level westerlies at low latitudes, i.e. over the central and eastern Pacific and Atlantic Oceans during boreal winter and spring. The penetration of an upper-level trough into the Tropics is often associated with enhanced convection and the formatio…