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1
Hughes, Graham O., and Ross W. Griffiths. "Horizontal Convection." Annual Review of Fluid Mechanics 40, no. 1 (January 2008): 185–208. http://dx.doi.org/10.1146/annurev.fluid.40.111406.102148.
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Hazewinkel, J., F. Paparella, and W. R. Young. "Stressed horizontal convection." Journal of Fluid Mechanics 692 (January 5, 2012): 317–31. http://dx.doi.org/10.1017/jfm.2011.514.
Повний текст джерелаАнотація:
AbstractWe consider the problem of a Boussinesq fluid forced by applying both non-uniform temperature and stress at the top surface. On the other boundaries the conditions are thermally insulating and either no-slip or stress-free. The interesting case is when the direction of the steady applied surface stress opposes the sense of the buoyancy driven flow. We obtain two-dimensional numerical solutions showing a regime in which there is an upper cell with thermally indirect circulation (buoyant fluid is pushed downwards by the applied stress and heavy fluid is elevated), and a second deep cell with thermally direct circulation. In this two-cell regime the driving mechanisms are competitive in the sense that neither dominates the flow. A scaling argument shows that this balance requires that surface stress vary as the horizontal Rayleigh number to the three-fifths power.
3
Barkan, Roy, Kraig B. Winters, and Stefan G. Llewellyn Smith. "Rotating horizontal convection." Journal of Fluid Mechanics 723 (April 16, 2013): 556–86. http://dx.doi.org/10.1017/jfm.2013.136.
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Abstract‘Horizontal convection’ (HC) is the generic name for the flow resulting from a buoyancy variation imposed along a horizontal boundary of a fluid. We study the effects of rotation on three-dimensional HC numerically in two stages: first, when baroclinic instability is suppressed and, second, when it ensues and baroclinic eddies are formed. We concentrate on changes to the thickness of the near-surface boundary layer, the stratification at depth, the overturning circulation and the flow energetics during each of these stages. Our results show that, for moderate flux Rayleigh numbers ($O(1{0}^{11} )$), rapid rotation greatly alters the steady-state solution of HC. When the flow is constrained to be uniform in the transverse direction, rapidly rotating solutions do not support a boundary layer, exhibit weaker overturning circulation and greater stratification at all depths. In this case, diffusion is the dominant mechanism for lateral buoyancy flux and the consequent buildup of available potential energy leads to baroclinically unstable solutions. When these rapidly rotating flows are perturbed, baroclinic instability develops and baroclinic eddies dominate both the lateral and vertical buoyancy fluxes. The resulting statistically steady solution supports a boundary layer, larger values of deep stratification and multiple overturning cells compared with non-rotating HC. A transformed Eulerian-mean approach shows that the residual circulation is dominated by the quasi-geostrophic eddy streamfunction and that the eddy buoyancy flux has a non-negligible interior diabatic component. The kinetic and available potential energies are greater than in the non-rotating case and the mixing efficiency drops from ${\sim }0. 7$ to ${\sim }0. 17$. The eddies play an important role in the formation of the thermal boundary layer and, together with the negatively buoyant plume, help establish deep stratification. These baroclinically active solutions have characteristics of geostrophic turbulence.
4
Feng, Tao, Jia-Yuh Yu, Xiu-Qun Yang, and Ronghui Huang. "Convective Coupling in Tropical-Depression-Type Waves. Part II: Moisture and Moist Static Energy Budgets." Journal of the Atmospheric Sciences 77, no. 10 (October 1, 2020): 3423–40. http://dx.doi.org/10.1175/jas-d-19-0173.1.
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AbstractThe companion of this paper, Part I, discovered the characteristics of the rainfall progression in tropical-depression (TD)-type waves over the western North Pacific. In Part II, the large-scale controls on the convective rainfall progression have been investigated using the ERA-Interim data and the TRMM 3B42 precipitation-rate data during June–October from 1998 to 2013 through budgets of moist static energy (MSE) and moisture. A buildup of column-integrated MSE occurs in advance of deep convection, and an export of MSE occurs following deep convection, which is consistent with the MSE recharge–discharge paradigm. The MSE recharge–discharge is controlled by horizontal processes, whereby horizontal moisture advection causes net MSE import prior to deep convection. Such moistening by horizontal advection creates a moist midtroposphere, which helps destabilize the atmospheric column, leading to the development of deep convective rainfall. Following the heaviest rainfall, negative horizontal moisture advection dries the troposphere, inhibiting convection. Such moistening and drying processes explain why deep convection can develop without preceding shallow convection. The advection of moisture anomalies by the mean horizontal flow controls the tropospheric moistening and drying processes. As the TD-type waves propagate northwestward in coincidence with the northwestward environmental flow, the moisture, or convective rainfall, is phase locked to the waves. The critical role of the MSE import by horizontal advection in modulating the rainfall progression is supported by the anomalous gross moist stability (AGMS), where the lowest AGMS corresponds to the quickest increase in the precipitation rate prior to the rainfall maximum.
5
Straughan, B. "Horizontally isotropic double porosity convection." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 475, no. 2221 (January 2019): 20180672. http://dx.doi.org/10.1098/rspa.2018.0672.
Повний текст джерелаАнотація:
We analyse instability and nonlinear stability in a layer of saturated double porosity medium. In a double porosity or bidisperse porous medium, there are normal pores which give rise to a macroporosity. But, there are also cracks or fissures in the solid skeleton and these give arise to another porosity known as micro porosity. In this paper, the macropermeability is horizontally isotropic, in the sense that the vertical component of permeability is different to the horizontal one which is the same in all horizontal directions. Thus, the permeability is transversely isotropic with the isotropy axis in the vertical direction of gravity. We also allow the micro permeability to be horizontally isotropic, but the permeability ratios of vertical to horizontal are different in the macro- and micro-phases. The effect of the difference of ratios is examined in detail.
6
Zhang, Nan, Yan Wang, and Xiaomeng Lin. "Mesoscale Observational Analysis of Isolated Convection Associated with the Interaction of the Sea Breeze Front and the Gust Front in the Context of the Urban Heat Humid Island Effect." Atmosphere 13, no. 4 (April 9, 2022): 603. http://dx.doi.org/10.3390/atmos13040603.
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An isolated convection was unexpectedly initiated in the evening of 1 August 2019 around the Tianjin urban region (TUR), which happened at some distance from the shear line at lower level and the preexisting convection to the South, analyzed by using ERA5 reanalysis data and observations from surface weather stations, and a S-band radar. The results show that, 42 min before the initiation of the convection, the atmospheric thermodynamic conditions around TUR were favorable for the initiation of the isolated convection, although the southerly and vertical shear of the horizontal wind at the lower level was weak. A sea-breeze front approached the TUR and continued to move West, leading to the triggering of the isolated convection in the context of the urban humid heat island (UHHI) effect. Subsequently, the gust front, which was formed between the cold pool away from the TUR and the warm and humid air of the UHHI, moved northward, approached the convection, and collided with sea breeze front, resulting in five reflectivity centers of isolated convection being merged and the convection’s development. Finally, the isolated convection split into two convections that moved away from the TUR and disappeared at 20:36 Beijing Time. The isolated convection was initiated and developed by the interaction of the sea breeze front and gust front in the context of the UHHI effect. The sea breeze front triggered the isolated convection around TUR in the context of the UHHI effect, and the gust front produced by the early convective storms to the south played a vital role in the development of the isolated convection.
7
SIGGERS, J. H., R. R. KERSWELL, and N. J. BALMFORTH. "Bounds on horizontal convection." Journal of Fluid Mechanics 517 (October 25, 2004): 55–70. http://dx.doi.org/10.1017/s0022112004000497.
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Simpkins, P. G., and K. S. Chen. "Convection in horizontal cavities." Journal of Fluid Mechanics 166, no. -1 (May 1986): 21. http://dx.doi.org/10.1017/s0022112086000022.
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CHIU-WEBSTER, S., E. J. HINCH, and J. R. LISTER. "Very viscous horizontal convection." Journal of Fluid Mechanics 611 (September 25, 2008): 395–426. http://dx.doi.org/10.1017/s0022112008002942.
Повний текст джерелаАнотація:
‘Horizontal convection’ arises when a temperature variation is imposed along a horizontal boundary of a finite fluid volume. Here we study the infinite-Prandtl-number limit relevant to very viscous fluids, motivated by the study of convection in glass furnaces. We consider a rectangular domain with insulating conditions on the sides and bottom, and a linear temperature gradient on the top. We describe steady states for a large range of aspect ratio A and Rayleigh number Ra, and find universal scalings for the transition from small to large Rayleigh numbers. At large Rayleigh number, the top boundary-layer thickness scales as Ra−1/5, with the circulation and heat flux scaling as Ra1/5. These scalings hold for both rigid and shear-free boundary conditions on the top or on the other boundaries, which is initially surprising, but is because the return flow is dominated by a horizontal intrusion immediately beneath the top boundary layer. A downwelling plume also forms on one side, but because of strong stratification in the interior, the volume flux it carries is much smaller than that of the horizontal intrusion, decaying as the inverse of the depth below the top boundary. The fluid in the plume detrains into the interior and then returns to the top boundary, thus forming a ‘filling box’. We find analytic solutions for the interior temperature and streamfunction and match them to a similarity solution for the plume. At depths comparable to the length of the top boundary the streamfunction has O(1) values and the temperature variations scale as 1/Ra. Transient calculations with a large, but finite, Prandtl number, show how the steady state is reached from hot and cold initial conditions.
10
Takemi, Tetsuya. "Importance of the Numerical Representation of Shallow and Deep Convection for Simulations of Dust Transport over a Desert Region." Advances in Meteorology 2012 (2012): 1–13. http://dx.doi.org/10.1155/2012/413584.
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This study examines the representations of shallow and deep convection under two distinct stability conditions over a desert region with the use of the numerical outputs from large-eddy simulations at the 100 m horizontal resolution. The numerical experiments were set up under idealized conditions of a horizontally uniform basic state over a homogeneous and flat surface, which was aimed at representing fair-weather convective situations over the Gobi Desert. Spatial spectra were used in order to examine how small scales are reproduced and how representative scales appear at various heights. From the results of the spectral analyses, a grid scale required to properly represent shallow and deep convection in convection-resolving simulations is identified. It is indicated that the adequate representations of shallow and deep convection are critically important in simulating the transport of dust aerosols under convective conditions.
11
Fiedler, R., and J. O. Murphy. "Preferred Horizontal Scale for Thermal Convection." Publications of the Astronomical Society of Australia 6, no. 4 (1986): 439–43. http://dx.doi.org/10.1017/s1323358000018336.
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AbstractLinear stability theory for Rayleigh-Benard convection shows that for a specified Rayleigh number, greater than some critical value, only a finite range of horizontal wave numbers support convective instability in a horizontal layer of fluid heated from below. However, it is not possible to predict the preferred horizontal scale of established motions from this approach although it is clear from observations, particularly of the solar surface, that a preferred cell size does prevail. In an endeavour to establish a preferred horizontal scale appropriate non-linear modal equations have been integrated forward in time, initially incorporating a discrete band of wave numbers equally spaced across the range that supports convection, for a specific Rayleigh number. The horizontal resolution was improved in subsequent integrations by first deleting modes that had substantially decayed and then introducing new modes on a finer horizontal mesh in the vicinity of what appeared to be the evolutionary dominant mode. Finally, the multimode integrations were continued in time until the evolution of a dominant horizontal mode from within the restricted range was evident. Both the model characteristics and numerical scheme adopted placed limits on the degree of horizontal refinement that could be undertaken with confidence.
12
Frajka-Williams, Eleanor, Peter B. Rhines, and Charles C. Eriksen. "Horizontal Stratification during Deep Convection in the Labrador Sea." Journal of Physical Oceanography 44, no. 1 (January 1, 2014): 220–28. http://dx.doi.org/10.1175/jpo-d-13-069.1.
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Abstract Deep convection—the process by which surface waters are mixed down to 1000 m or deeper—forms the primary downwelling of the meridional overturning circulation in the Northern Hemisphere. High-resolution hydrographic measurements from Seagliders indicate that during deep convection—though water is well mixed vertically—there is substantial horizontal variation in density over short distances (tens of kilometers). This horizontal density variability present in winter (January–February) contains sufficient buoyancy to restratify the convecting region to observed levels 2.5 months later, as estimated from Argo floating platforms. These results highlight the importance of small-scale heterogeneities in the ocean that are typically poorly represented in climate models, potentially contributing to the difficulty climate models have in representing deep convection.
13
Boos, William R., Alexey Fedorov, and Les Muir. "Convective Self-Aggregation and Tropical Cyclogenesis under the Hypohydrostatic Rescaling." Journal of the Atmospheric Sciences 73, no. 2 (January 27, 2016): 525–44. http://dx.doi.org/10.1175/jas-d-15-0049.1.
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Abstract The behavior of rotating and nonrotating aggregated convection is examined at various horizontal resolutions using the hypohydrostatic, or reduced acceleration in the vertical (RAVE), rescaling. This modification of the equations of motion reduces the scale separation between convective- and larger-scale motions, enabling the simultaneous and explicit representation of both types of flow in a single model without convective parameterization. Without the RAVE rescaling, a dry bias develops when simulations of nonrotating radiative–convective equilibrium are integrated at coarse resolution in domains large enough to permit convective self-aggregation. The rescaling reduces this dry bias, and here it is suggested that the rescaling moistens the troposphere by weakening the amplitude and slowing the group velocity of gravity waves, thus reducing the subsidence drying around aggregated convection. Separate simulations of rotating radiative–convective equilibrium exhibit tropical cyclogenesis; as horizontal resolution is coarsened without the rescaling, the resulting storms intensify more slowly and achieve lower peak intensities. At a given horizontal resolution, using RAVE increases peak storm intensity and reduces the time needed for tropical cyclogenesis—effects here suggested to be caused at least in part by the environmental moistening produced by RAVE. Consequently, the RAVE rescaling has the potential to improve simulations of tropical cyclones and other aggregated convection in models with horizontal resolutions of order 10–100 km.
14
Deng, Liping, and Xiaoqing Wu. "Physical Mechanisms for the Maintenance of GCM-Simulated Madden–Julian Oscillation over the Indian Ocean and Pacific." Journal of Climate 24, no. 10 (May 15, 2011): 2469–82. http://dx.doi.org/10.1175/2010jcli3759.1.
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Abstract The kinetic energy budget is conducted to analyze the physical processes responsible for the improved Madden–Julian oscillation (MJO) simulated by the Iowa State University general circulation models (ISUGCMs). The modified deep convection scheme that includes the revised convection closure, convection trigger condition, and convective momentum transport (CMT) enhances the equatorial (10°S–10°N) MJO-related perturbation kinetic energy (PKE) in the upper troposphere and leads to a more robust and coherent eastward-propagating MJO signal. In the MJO source region, the Indian Ocean (45°–120°E), the upper-tropospheric MJO PKE is maintained by the vertical convergence of wave energy flux and the barotropic conversion through the horizontal shear of mean flow. In the convectively active region, the western Pacific (120°E–180°), the upper-tropospheric MJO PKE is supported by the convergence of horizontal and vertical wave energy fluxes. Over the central-eastern Pacific (180°–120°W), where convection is suppressed, the upper-tropospheric MJO PKE is mainly due to the horizontal convergence of wave energy flux. The deep convection trigger condition produces stronger convective heating that enhances the perturbation available potential energy (PAPE) production and the upward wave energy fluxes and leads to the increased MJO PKE over the Indian Ocean and western Pacific. The trigger condition also enhances the MJO PKE over the central-eastern Pacific through the increased convergence of meridional wave energy flux from the subtropical latitudes of both hemispheres. The revised convection closure affects the response of mean zonal wind shear to the convective heating over the Indian Ocean and leads to the enhanced upper-tropospheric MJO PKE through the barotropic conversion. The stronger eastward wave energy flux due to the increase of convective heating over the Indian Ocean and western Pacific by the revised closure is favorable to the eastward propagation of MJO and the convergence of horizontal wave energy flux over the central-eastern Pacific. The convection-induced momentum tendency tends to decelerate the upper-tropospheric wind, which results in a negative work to the PKE budget in the upper troposphere. However, the convection momentum tendency accelerates the westerly wind below 800 hPa over the western Pacific, which is partially responsible for the improved MJO simulation.
15
Folkins, Ian, S. Fueglistaler, G. Lesins, and T. Mitovski. "A Low-Level Circulation in the Tropics." Journal of the Atmospheric Sciences 65, no. 3 (March 1, 2008): 1019–34. http://dx.doi.org/10.1175/2007jas2463.1.
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Abstract Deep convective tropical systems are strongly convergent in the midtroposphere. Horizontal wind measurements from a variety of rawinsonde arrays in the equatorial Pacific and Caribbean are used to calculate the mean dynamical divergence profiles of large-scale arrays (≥1000 km in diameter) in actively convecting regions. Somewhat surprisingly, the magnitude of the midtropospheric divergence calculated from these arrays is usually small. In principle, the midlevel convergence of deep convective systems could be balanced on larger scales either by a vertical variation in the radiative mass flux of the background clear sky atmosphere, or by a divergence from shallow cumuli. The vertical variation of the clear sky mass flux in the midtroposphere is small, however, so that the offsetting divergence must be supplied by shallow cumuli. On spatial scales of ∼1000 km, the midlevel convergent inflow toward deep convection appears to be internally compensated, or “screened,” by a divergent outflow from surrounding precipitating shallow convection. Deep convective systems do not induce a large-scale inflow of midlevel air toward actively convecting regions from the rest of the tropics, but instead help generate a secondary low-level circulation, in which the net downward mass flux from mesoscale and convective-scale downdrafts is balanced by a net upward mass flux from precipitating shallow cumuli. The existence of this circulation is consistent with observational evidence showing that deep and shallow convection are spatiotemporally coupled on a wide range of both spatial and temporal scales. One of the mechanisms proposed for coupling shallow convection to deep convection is the tendency for deep convection to cool the lower troposphere. The authors use radiosonde temperature profiles and the Tropical Rainfall Measuring Mission (TRMM) 3B42 gridded rainfall product to argue that the distance over which deep convection cools the lower troposphere is approximately 1000 km.
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Zavolgenskiy, M. V., and P. B. Rutkevich. "Tornado funnel-shaped cloud as convection in a cloudy layer." Advances in Science and Research 3, no. 1 (April 2, 2009): 17–21. http://dx.doi.org/10.5194/asr-3-17-2009.
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Abstract. Analytical model of convection in a thick horizontal cloud layer with free upper and lower boundaries is constructed. The cloud layer is supposed to be subjected to the Coriolis force due to the cloud rotation, which is a typical condition for tornado formation. It is obtained that convection in such system can look as just one rotating cell in contrast to the usual many-cells Benard convection. The tornado-type vortex is different from spatially periodic convective cells because their amplitudes vanish with distance from the vortex axis. The lower boundary at this convection can substantially move out of the initially horizontal cloud layer forming a single vertical vortex with intense upward and downward flows. The results are also applicable to convection in water layer with negative temperature gradient.
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Santellanes, Sean R., George S. Young, David J. Stensrud, Matthew R. Kumjian, and Ying Pan. "Environmental Conditions Associated with Horizontal Convective Rolls, Cellular Convection, and No Organized Circulations." Monthly Weather Review 149, no. 5 (May 2021): 1305–16. http://dx.doi.org/10.1175/mwr-d-20-0207.1.
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AbstractTypical environmental conditions associated with horizontal convective rolls (HCRs) and cellular convection have been known for over 50 years. Yet our ability to predict whether HCRs, cellular convection, or no discernable organized (null) circulation will occur within a well-mixed convective boundary layer based upon easily observed environmental variables has been limited. Herein, a large database of 50 cases each of HCR, cellular convection, and null events is created that includes observations of mean boundary layer wind and wind shear, boundary layer depth; surface observations of wind, temperature, and relative humidity; and estimates of surface sensible heat flux. Results from a multiclass linear discriminant analysis applied to these data indicate that environmental conditions can be useful in predicting whether HCRs, cellular convection, or no circulation occurs, with the analysis identifying the correct circulation type on 72% of the case days. This result is slightly better than using a mean convective boundary layer (CBL) wind speed of 6 m s−1 to discriminate between HCRs and cells. However, the mean CBL wind speed has no ability to further separate out cases with no CBL circulation. The key environmental variables suggested by the discriminant analysis are mean sensible heat flux, friction velocity, and the Obukhov length.
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Nugent, Alison D., Ronald B. Smith, and Justin R. Minder. "Wind Speed Control of Tropical Orographic Convection." Journal of the Atmospheric Sciences 71, no. 7 (June 20, 2014): 2695–712. http://dx.doi.org/10.1175/jas-d-13-0399.1.
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Abstract This study compares observations from the Dominica Experiment (DOMEX) field campaign with 3D and 2D Weather Research and Forecasting Model (WRF) simulations to understand how ambient upstream wind speed controls the transition from thermally to mechanically forced moist orographic convection. The environment is a conditionally unstable, tropical atmosphere with shallow trade wind cumulus clouds. Three flow indices are defined to quantify the convective transition: horizontal divergence aloft, cloud location, and island surface temperature. As wind speed increases, horizontal airflow divergence from plume detrainment above the mountain changes to convergence associated with plunging flow, convective clouds relocate from the leeward to the windward side of the mountain as mechanically triggered convection takes over, and the daytime mountaintop temperature decreases because of increased ventilation and cloud shading. Possible mechanisms by which wind speed controls island precipitation are also discussed. The result is a clearer understanding of orographic convection in the tropics.
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Bengtsson, Lisa, Sander Tijm, Filip Váňa, and Gunilla Svensson. "Impact of Flow-Dependent Horizontal Diffusion on Resolved Convection in AROME." Journal of Applied Meteorology and Climatology 51, no. 1 (January 2012): 54–67. http://dx.doi.org/10.1175/jamc-d-11-032.1.
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AbstractHorizontal diffusion in numerical weather prediction models is, in general, applied to reduce numerical noise at the smallest atmospheric scales. In convection-permitting models, with horizontal grid spacing on the order of 1–3 km, horizontal diffusion can improve the model skill of physical parameters such as convective precipitation. For instance, studies using the convection-permitting Applications of Research to Operations at Mesoscale model (AROME) have shown an improvement in forecasts of large precipitation amounts when horizontal diffusion is applied to falling hydrometeors. The nonphysical nature of such a procedure is undesirable, however. Within the current AROME, horizontal diffusion is imposed using linear spectral horizontal diffusion on dynamical model fields. This spectral diffusion is complemented by nonlinear, flow-dependent, horizontal diffusion applied on turbulent kinetic energy, cloud water, cloud ice, rain, snow, and graupel. In this study, nonlinear flow-dependent diffusion is applied to the dynamical model fields rather than diffusing the already predicted falling hydrometeors. In particular, the characteristics of deep convection are investigated. Results indicate that, for the same amount of diffusive damping, the maximum convective updrafts remain strong for both the current and proposed methods of horizontal diffusion. Diffusing the falling hydrometeors is necessary to see a reduction in rain intensity, but a more physically justified solution can be obtained by increasing the amount of damping on the smallest atmospheric scales using the nonlinear, flow-dependent, diffusion scheme. In doing so, a reduction in vertical velocity was found, resulting in a reduction in maximum rain intensity.
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Thompson, W. B. "Convection in Horizontal Temperature Gradients." Geophysical Journal of the Royal Astronomical Society 14, no. 1-4 (January 26, 2010): 449. http://dx.doi.org/10.1111/j.1365-246x.1967.tb06261.x.
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PAPARELLA, F., and W. R. YOUNG. "Horizontal convection is non-turbulent." Journal of Fluid Mechanics 466 (September 10, 2002): 205–14. http://dx.doi.org/10.1017/s0022112002001313.
Повний текст джерелаАнотація:
Consider the problem of horizontal convection: a Boussinesq fluid, forced by applying a non-uniform temperature at its top surface, with all other boundaries insulating. We prove that if the viscosity, ν, and thermal diffusivity, κ, are lowered to zero, with σ ≡ ν/κ fixed, then the energy dissipation per unit mass, κ, also vanishes in this limit. Numerical solutions of the two-dimensional case show that despite this anti-turbulence theorem, horizontal convection exhibits a transition to eddying flow, provided that the Rayleigh number is sufficiently high, or the Prandtl number σ sufficiently small. We speculate that horizontal convection is an example of a flow with a large number of active modes which is nonetheless not ‘truly turbulent’ because ε→0 in the inviscid limit.
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Kuang, Zhiming. "Weakly Forced Mock Walker Cells." Journal of the Atmospheric Sciences 69, no. 9 (September 1, 2012): 2759–86. http://dx.doi.org/10.1175/jas-d-11-0307.1.
Повний текст джерелаАнотація:
Abstract Mock Walker cells driven by weak sea surface temperature (SST) forcing are studied using planetary-scale cloud system–resolving simulations and a simplified framework that represents convection with its linear response functions and parameterizes the large-scale flow based on the gravity wave equation. For sinusoidal SST forcings of the same amplitude, as the horizontal domain size increases, the mock Walker cells strengthen substantially and shorter vertical scales in the vertical velocity profile diminish. This is explained by the fact that temperature anomalies required to sustain a vertical velocity profile of given amplitude are stronger in cases of larger horizontal and smaller vertical scales. Such temperature anomalies become significant at planetary scales so that properly accounting for the horizontal momentum balance, including convective momentum transport (CMT), becomes necessary, while a weak temperature gradient approach that neglects horizontal momentum balance is no longer adequate. The downward advection component of the CMT in particular is important for capturing a number of features of the mock Walker cells. The extent of convective organization also affects the mock Walker cell through its effects on the sensitivities of convective heating and moistening to temperature and moisture anomalies. For strongly organized convection with deep inflows, these sensitivities are consistent with a layer mode of convective overturning, instead of the parcel mode as in unorganized convection, resulting in a weaker second baroclinic component in the mock Walker cells.
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Fedyushkin, A. I. "The effect of controlled vibrations on Rayleigh-Benard convection." Journal of Physics: Conference Series 2057, no. 1 (October 1, 2021): 012012. http://dx.doi.org/10.1088/1742-6596/2057/1/012012.
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Abstract The paper presents the results of a numerical study of convective heat transfer in a long horizontal layer heated from below with and without the vibration effect of the lower wall. The simulation was carried out on the basis of solving the Navier-Stokes 2D equations for an incompressible fluid in the Boussinesq approximation. It is shown that the influence of vibrations of the lower heated wall on the wave number of the convective flow roll structure, on the time and on the critical Rayleigh number of convection. The influence of controlled harmonic vibrations of wall on the structure of convective flow in the Rayleigh-Benard problem has been investigated. It is shown that the wave number of the periodic convective structure, the critical Rayleigh number, and the time of occurrence of Rayleigh-Benard convection under the vertical vibration effect on the horizontal layer from the lower wall are reduced.
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Fuhrer, Oliver, and Christoph Schär. "Dynamics of Orographically Triggered Banded Convection in Sheared Moist Orographic Flows." Journal of the Atmospheric Sciences 64, no. 10 (October 1, 2007): 3542–61. http://dx.doi.org/10.1175/jas4024.1.
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Abstract Shallow orographic convection embedded in an unstable cap cloud can organize into convective bands. Previous research has highlighted the important role of small-amplitude topographic variations in triggering and organizing banded convection. Here, the underlying dynamical mechanisms are systematically investigated by conducting three-dimensional simulations of moist flows past a two-dimensional mountain ridge using a cloud-resolving numerical model. Most simulations address a sheared environment to account for the observed wind profiles. Results confirm that small-amplitude topographic variations can enhance the development of embedded convection and anchor quasi-stationary convective bands to a fixed location in space. The resulting precipitation patterns exhibit tremendous spatial variability, since regions receiving heavy rainfall can be only kilometers away from regions receiving little or no rain. In addition, the presence of banded convection has important repercussions on the area-mean precipitation amounts. For the experimental setup here, the gravity wave response to small-amplitude topographic variations close to the upstream edge of the cap cloud (which is forced by the larger-scale topography) is found to be the dominant triggering mechanism. Small-scale variations in the underlying topography are found to force the location and spacing of convective bands over a wide range of scales. Further, a self-sufficient mode of unsteady banded convection is investigated that does not dependent on external perturbations and is able to propagate against the mean flow. Finally, the sensitivity of model simulations of banded convection with respect to horizontal computational resolution is investigated. Consistent with predictions from a linear stability analysis, convective bands of increasingly smaller scales are favored as the horizontal resolution is increased. However, small-amplitude topographic roughness is found to trigger banded convection and to control the spacing and location of the resulting bands. Thereby, the robustness of numerical simulations with respect to an increase in horizontal resolution is increased in the presence of topographic variations.
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Sumi, Yukari, and Hirohiko Masunaga. "A Moist Static Energy Budget Analysis of Quasi-2-Day Waves Using Satellite and Reanalysis Data." Journal of the Atmospheric Sciences 73, no. 2 (February 1, 2016): 743–59. http://dx.doi.org/10.1175/jas-d-15-0098.1.
Повний текст джерелаАнотація:
Abstract A moist static energy (MSE) budget analysis is applied to quasi-2-day waves to examine the effects of thermodynamic processes on the wave propagation mechanism. The 2-day waves are defined as westward inertia–gravity (WIG) modes identified with filtered geostationary infrared measurements, and the thermodynamic parameters and MSE budget variables computed from reanalysis data are composited with respect to the WIG peaks. The composite horizontal and vertical MSE structures are overall as theoretically expected from WIG wave dynamics. A prominent horizontal MSE advection is found to exist, although the wave dynamics is mainly regulated by vertical advection. The vertical advection decreases MSE around the times of the convective peak, plausibly resulting from the first baroclinic mode associated with deep convection. Normalized gross moist stability (NGMS) is used to examine the thermodynamic processes involving the large-scale dynamics and convective heating. NGMS gradually decreases to zero before deep convection and reaches a maximum after the convection peak, where low (high) NGMS leads (lags) deep convection. The decrease in NGMS toward zero before the occurrence of active convection suggests an increasingly efficient conversion from convective heating to large-scale dynamics as the wave comes in, while the increase afterward signifies that this linkage swiftly dies out after the peak.
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BURR, ULRICH, and ULRICH MÜLLER. "Rayleigh–Bénard convection in liquid metal layers under the influence of a horizontal magnetic field." Journal of Fluid Mechanics 453 (February 25, 2002): 345–69. http://dx.doi.org/10.1017/s002211200100698x.
Повний текст джерелаАнотація:
This article presents an analytical and experimental study of magnetohydrodynamic Rayleigh–Bénard convection in a large aspect ratio, 20[ratio ]10[ratio ]1, rectangular box. The test fluid is a eutectic sodium potassium Na22K78 alloy with a small Prandtl number of Pr≈0:02. The experimental setup covers Rayleigh numbers in the range 103< Ra<8×104 and Chandrasekhar numbers 0[les ]Q[les ]1.44×106 or Hartmann numbers 0[les ]M[les ]1200, respectively.When a horizontal magnetic field is imposed on a heated liquid metal layer, the electromagnetic forces give rise to a transition of the three-dimensional convective roll pattern into a quasi-two-dimensional flow pattern in such a way that convective rolls become more and more aligned with the magnetic field. A linear stability analysis based on two-dimensional model equations shows that the critical Rayleigh number for the onset of convection of quasi-two-dimensional flow is shifted to significantly higher values due to Hartmann braking at walls perpendicular to the magnetic field. This finding is experimentally confirmed by measured Nusselt numbers. Moreover, the experiments show that the convective heat transport at supercritical conditions is clearly diminished. Adjacent to the onset of convection there is a significant region of stationary convection with significant convective heat transfer before the flow proceeds to time-dependent convection. However, in spite of the Joule dissipation effect there is a certain range of magnetic field intensities where an enhanced heat transfer is observed. Estimates of the local isotropy properties of the flow by a four-element temperature probe demonstrate that the increase in convective heat transport is accompanied by the formation of strong non-isotropic time-dependent flow in the form of large-scale convective rolls aligned with the magnetic field which exhibit a simpler temporal structure compared to ordinary hydrodynamic flow and which are very effective for the convective heat transport.
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Shishkina, Olga. "Mean flow structure in horizontal convection." Journal of Fluid Mechanics 812 (January 5, 2017): 525–40. http://dx.doi.org/10.1017/jfm.2016.866.
Повний текст джерелаАнотація:
We analyse the global flow structures in horizontal convection systems, where the heat supply and removal takes place through separated parts of a lower horizontal surface of a fluid layer. The results are based on direct numerical simulations for the length-to-height aspect ratio of the convection cell $\unicode[STIX]{x1D6E4}=10$, Rayleigh number $\mathit{Ra}$ from $3\times 10^{8}$ to $3\times 10^{11}$ and Prandtl number $\mathit{Pr}$ from 0.05 to 50. The structure of the mean flows in horizontal convection is described in terms of time-averaged spatial distributions of the temperature, velocity, kinetic energy, thermal and kinetic dissipation rates. A possible scenario of transition to turbulent horizontal convection in the whole convection cell of a large aspect ratio is discussed.
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Lane, Todd P., and Mitchell W. Moncrieff. "Stratospheric Gravity Waves Generated by Multiscale Tropical Convection." Journal of the Atmospheric Sciences 65, no. 8 (August 1, 2008): 2598–614. http://dx.doi.org/10.1175/2007jas2601.1.
Повний текст джерелаАнотація:
Abstract The generation of gravity waves by multiscale cloud systems evolving in an initially motionless and thermodynamically uniform environment is explored using a two-dimensional cloud-system-resolving model. The simulated convection has similar depth and intensity to observed tropical oceanic systems. The convection self-organizes into preferred horizontal and temporal scales involving weakly organized propagating cloud clusters. The multiscale systems generate a broad spectrum of gravity waves with horizontal scales that range from the cloud-system scale up to the cloud-cluster scale. The gravity waves with the largest horizontal scale play an important role in modifying layered tropospheric inflow and outflow to the cloud systems, which in turn influence the multiscale convective organization. Slower-moving short-scale gravity waves make the strongest individual contribution to the vertical flux of horizontal momentum and cause a robust peak in the momentum flux spectrum that corresponds to the lifetime and spatial scale of the individual cloud systems.
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Riahi, D. N., and Albert T. Hsui. "Finite amplitude thermal convection with variable gravity." International Journal of Mathematics and Mathematical Sciences 25, no. 3 (2001): 153–65. http://dx.doi.org/10.1155/s0161171201004811.
Повний текст джерелаАнотація:
Finite amplitude thermal convection is studied in a horizontal layer of infinite Prandtl number fluid with a variable gravity. For the present study, gravity is restricted to vary quadratically with respect to the vertical variable. A perturbation technique based on a small parameter, which is a measure of the ratio of the vertical to horizontal dimensions of the convective cells, is employed to determine the finite amplitude steady solutions. These solutions are represented in terms of convective modes whose amplitudes can be either small or of order unity. Stability of these solutions is investigated with respect to three dimensional disturbances. A variable gravity function introduces two non-dimensional parameters. For certain range of values of these two parameters, double or triple cellular structure in the vertical direction can be realized. Hexagonal patterns are preferred for sufficiently small amplitude of convection, while square patterns can become dominant for larger values of the convective amplitude. Variable gravity can also affect significantly the wavelength of the cellular pattern and the onset condition of the convective motion.
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Tewari, S. S., and Y. Jaluria. "Mixed Convection Heat Transfer From Thermal Sources Mounted on Horizontal and Vertical Surfaces." Journal of Heat Transfer 112, no. 4 (November 1, 1990): 975–87. http://dx.doi.org/10.1115/1.2910509.
Повний текст джерелаАнотація:
An experimental study is carried out on the fundamental aspects of the conjugate, mixed convective heat transfer from two finite width heat sources, which are of negligible thickness, have a uniform heat flux input at the surface, and are located on a flat plate in the horizontal or the vertical orientation. The heat sources are wide in the transverse direction and, therefore, a two-dimensional flow circumstance is simulated. The mixed convection parameter is varied over a fairly wide range to include the buoyancy-dominated and the mixed convection regimes. The circumstances of pure natural convection are also investigated. The convective mechanisms have been studied in detail by measuring the surface temperatures and determining the heat transfer coefficients for the two heated strips, which represent isolated thermal sources. Experimental results indicate that a stronger upstream heat source causes an increase in the surface temperature of a relatively weaker heat source, located downstream, by reducing its convective heat transfer coefficient. The influence of the upstream source is found to be strongly dependent on the surface orientation, especially in the pure natural convection and the buoyancy dominated regimes. The two heat sources are found to be essentially independent of each other, in terms of thermal effects, at a separation distance of more than about three strip widths for both the orientations. The results obtained are relevant to many engineering applications, such as the cooling of electronic systems, positioning of heating elements in furnaces, and safety considerations in enclosure fires.
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Holloway, Christopher E., Steven J. Woolnough, and Grenville M. S. Lister. "The Effects of Explicit versus Parameterized Convection on the MJO in a Large-Domain High-Resolution Tropical Case Study. Part I: Characterization of Large-Scale Organization and Propagation*." Journal of the Atmospheric Sciences 70, no. 5 (April 23, 2013): 1342–69. http://dx.doi.org/10.1175/jas-d-12-0227.1.
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Abstract High-resolution simulations over a large tropical domain (~20°S–20°N, 42°E–180°) using both explicit and parameterized convection are analyzed and compared to observations during a 10-day case study of an active Madden–Julian oscillation (MJO) event. The parameterized convection model simulations at both 40- and 12-km grid spacing have a very weak MJO signal and little eastward propagation. A 4-km explicit convection simulation using Smagorinsky subgrid mixing in the vertical and horizontal dimensions exhibits the best MJO strength and propagation speed. Explicit convection simulations at 12 km also perform much better than the 12-km parameterized convection run, suggesting that the convection scheme, rather than horizontal resolution, is key for these MJO simulations. Interestingly, a 4-km explicit convection simulation using the conventional boundary layer scheme for vertical subgrid mixing (but still using Smagorinsky horizontal mixing) completely loses the large-scale MJO organization, showing that relatively high resolution with explicit convection does not guarantee a good MJO simulation. Models with a good MJO representation have a more realistic relationship between lower-free-tropospheric moisture and precipitation, supporting the idea that the moisture–convection feedback is a key process for MJO propagation. There is also increased generation of available potential energy and conversion of that energy into kinetic energy in models with a more realistic MJO, which is related to larger zonal variance in convective heating and vertical velocity, larger zonal temperature variance around 200 hPa, and larger correlations between temperature and ascent (and between temperature and diabatic heating) between 500 and 400 hPa.
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DIAZ, EMILIE, and LEONID BREVDO. "Absolute/convective instability dichotomy at the onset of convection in a porous layer with either horizontal or vertical solutal and inclined thermal gradients, and horizontal throughflow." Journal of Fluid Mechanics 681 (July 1, 2011): 567–96. http://dx.doi.org/10.1017/jfm.2011.220.
Повний текст джерелаАнотація:
By using the methods of the theory of two- and three-dimensional linear absolute and convective instabilities, we examine the nature of the instability at the onset of convection in a model of convection in an extended horizontal layer of a saturated porous medium with either horizontal or vertical salinity and inclined temperature gradients, and horizontal throughflow. First, normal modes are analysed and the critical values of the vertical thermal Rayleigh number,Rv, wavenumber vector, (k,l) and frequency, ω, are obtained for a variety of values of the horizontal thermal and salinity Rayleigh numbers,RhandSh, respectively, the vertical salinity Rayleigh numberSvand the horizontal Péclet number,Qh. In the computations, a high-precision pseudo-spectral Chebyshev-collocation method is used. In most of the cases of parameter combinations considered, the onset of convection occurs through a longitudinal mode. Most of the non-longitudinal critical modes are oscillatory. Further, it is revealed that there exists an absolute/convective instability dichotomy at the onset of three-dimensional convection in a set of the base states given by exact analytic solutions of the equations of motion in the model. This echoes the results of Brevdo (vol. 641, 2009, p. 475) for transverse modes in a model with inclined temperature gradient and vertical throughflow, but with no salinity. The dependence of the dichotomy on the inclined thermal gradient, and on the horizontal and the vertical salinity gradients is investigated, for the longitudinal modes treated both as two-dimensional as well as three-dimensional modes, and for the non-longitudinal modes. For a certain set of parameter cases, it was found that the destabilization through longitudinal modes treated as two-dimensional modes has the character of absolute instability whereas a three-dimensional analysis of these modes revealed that the instability is convective, with the group velocity vector of the emerging unstable wavepacket being parallel to the axis of the convection rolls. Since a similar effect was reported by Brevdo (vol. 641, 2009, p. 475) for a model with no salinity, we conclude that this effect is not a separate case. In most of the cases considered in which a marginally unstable base state is absolutely stable, but convectively unstable, the direction of propagation of the emerging unstable wavepacket is either parallel or perpendicular to the axis of the convection rolls. Only in the absolutely stable, but convectively unstable cases in which non-longitudinal modes are favourable, the angle, ϕ, between the group velocity vector of the unstable wavepacket and the axis of the rolls satisfies 0 < ϕ < 90°.
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Vreugdenhil, Catherine A., Ross W. Griffiths, and Bishakhdatta Gayen. "Geostrophic and chimney regimes in rotating horizontal convection with imposed heat flux." Journal of Fluid Mechanics 823 (June 15, 2017): 57–99. http://dx.doi.org/10.1017/jfm.2017.249.
Повний текст джерелаАнотація:
Convection in a rotating rectangular basin with differential thermal forcing at one horizontal boundary is examined using laboratory experiments. The experiments have an imposed heat flux boundary condition, are at large values of the flux Rayleigh number ($Ra_{F}\sim O(10^{13}{-}10^{14})$ based on the box length $L$), use water with Prandtl number $Pr\approx 4$ and have a small depth to length aspect ratio. The results show the conditions for transition from non-rotating horizontal convection governed by an inertial–buoyancy balance in the thermal boundary layer, to circulation governed by geostrophic flow in the boundary layer. The geostrophic balance constrains mean flow and reduces the heat transport as Nusselt number $Nu\sim (Ra_{F}Ro)^{1/6}$, where $Ro=B^{1/2}/f^{3/2}L$ is the convective Rossby number, $B$ is the imposed buoyancy flux and $f$ is the Coriolis parameter. Thus flow in the geostrophic boundary layer regime is governed by the relative roles of horizontal convective accelerations and Coriolis accelerations, or buoyancy and rotation, in the boundary layer. Experimental evidence suggests that for more rapid rotation there is another transition to a regime in which the momentum budget is dominated by fluctuating vertical accelerations in a region of vortical plumes, which we refer to as a ‘chimney’ following related discussion of regions of deep convection in the ocean. Coupling of the chimney convection in the region of destabilising boundary flux to the diffusive boundary layer of horizontal convection in the region of stabilising boundary flux gives heat transport independent of rotation in this ‘inertial chimney’ regime, and the new scaling $Nu\sim Ra_{F}^{1/4}$. Scaling analysis predicts the transition conditions observed in the experiments, as well as a further ‘geostrophic chimney’ regime in which the vertical plumes are controlled by local geostrophy. When $Ro<10^{-1}$, the convection is also observed to produce a set of large basin-scale gyres at all depths in the time-averaged flow.
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Yang, Gui-Ying, Brian Hoskins, and Julia Slingo. "Convectively Coupled Equatorial Waves. Part I: Horizontal and Vertical Structures." Journal of the Atmospheric Sciences 64, no. 10 (October 1, 2007): 3406–23. http://dx.doi.org/10.1175/jas4017.1.
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Abstract Multilevel 15-yr ECMWF Re-Analysis (ERA-15) and satellite-observed brightness temperature (Tb) data for the period May–October 1992 are used to examine the horizontal and vertical structures of convectively coupled equatorial waves. Dynamical waves are isolated using a methodology developed previously. Composite structures of convectively coupled equatorial waves are obtained using linear regression/correlation between convection (Tb) and dynamical structures. It is found that the relationship depends on the ambient flow and the nature of the convective coupling, and varies between off-equatorial- and equatorial-centered convection, different hemispheres, and seasons. The Kelvin wave structure in the Western Hemisphere is generally consistent with classic equatorial wave theory and has its convection located in the region of low-level convergence. In the Eastern Hemisphere the Kelvin wave tends to have convection in the region of enhanced lower-tropospheric westerlies and a tilted vertical structure. The Kelvin wave also tends to have a third peak in zonal wind amplitude at 500 hPa and exhibits upward propagation into the lower stratosphere. Lower-tropospheric westward-moving mixed Rossby–gravity (WMRG) and n = 1 Rossby (R1) wave structures and their relationship with convection are consistent with classic equatorial wave theory and the implied lower-tropospheric convergences. In the Eastern Hemisphere the WMRG and R1 waves have first baroclinic mode structures in the vertical. However, in the Western Hemisphere, the R1 wave has a barotropic structure. In the Eastern Hemisphere the R1 wave, like the Kelvin wave, tends to have equatorial convection in the region of enhanced lower-level westerlies, suggesting that enhanced surface energy fluxes associated with these waves may play an important organizing role for equatorial convection in this warm-water hemisphere. In the upper troposphere, eastward-moving Rossby–gravity (EMRG) and n = 1 gravity waves are found in the Eastern Hemisphere, and eastward-moving WMRG and R1 waves are found in the Western Hemisphere, suggestive of Doppler shifting of waves by the ambient flow.
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Panosetti, Davide, Steven Böing, Linda Schlemmer, and Jürg Schmidli. "Idealized Large-Eddy and Convection-Resolving Simulations of Moist Convection over Mountainous Terrain." Journal of the Atmospheric Sciences 73, no. 10 (September 21, 2016): 4021–41. http://dx.doi.org/10.1175/jas-d-15-0341.1.
Повний текст джерелаАнотація:
Abstract On summertime fair-weather days, thermally driven wind systems play an important role in determining the initiation of convection and the occurrence of localized precipitation episodes over mountainous terrain. This study compares the mechanisms of convection initiation and precipitation development within a thermally driven flow over an idealized double-ridge system in large-eddy (LESs) and convection-resolving (CRM) simulations. First, LES at a horizontal grid spacing of 200 m is employed to analyze the developing circulations and associated clouds and precipitation. Second, CRM simulations at horizontal grid length of 1 km are conducted to evaluate the performance of a kilometer-scale model in reproducing the discussed mechanisms. Mass convergence and a weaker inhibition over the two ridges flanking the valley combine with water vapor advection by upslope winds to initiate deep convection. In the CRM simulations, the spatial distribution of clouds and precipitation is generally well captured. However, if the mountains are high enough to force the thermally driven flow into an elevated mixed layer, the transition to deep convection occurs faster, precipitation is generated earlier, and surface rainfall rates are higher compared to the LES. Vertical turbulent fluxes remain largely unresolved in the CRM simulations and are underestimated by the model, leading to stronger upslope winds and increased horizontal moisture advection toward the mountain summits. The choice of the turbulence scheme and the employment of a shallow convection parameterization in the CRM simulations change the strength of the upslope winds, thereby influencing the simulated timing and intensity of convective precipitation.
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Engström, Maria, and Bo Nordell. "Seasonal groundwater turnover." Hydrology Research 37, no. 1 (February 1, 2006): 31–39. http://dx.doi.org/10.2166/nh.2006.0003.
Повний текст джерелаАнотація:
Seasonal air temperature variations and corresponding changes in groundwater temperature cause convective movements in groundwater similar to the seasonal turnover in lakes. Numerical simulations were performed to investigate the natural conditions for thermally driven groundwater convection to take place. Thermally driven convection could be triggered by a horizontal groundwater flow. Convection then starts at a considerably lower Rayleigh number (Ra) than the general critical Rayleigh number (Rac) assuming that 10°C groundwater is cooled to 4°C, i.e. heated from below convection in porous media. This study supports the hypothesis that seasonal temperature variations, under certain conditions, initiate and drive thermal convection.
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Homeyer, Cameron R., and Matthew R. Kumjian. "Microphysical Characteristics of Overshooting Convection from Polarimetric Radar Observations." Journal of the Atmospheric Sciences 72, no. 2 (February 1, 2015): 870–91. http://dx.doi.org/10.1175/jas-d-13-0388.1.
Повний текст джерелаАнотація:
Abstract The authors present observations of the microphysical characteristics of deep convection that overshoots the altitude of the extratropical tropopause from analysis of the polarimetric radar variables of radar reflectivity factor at horizontal polarization ZH, differential reflectivity ZDR, and specific differential phase KDP. Identified overshooting convective storms are separated by their organization and intensity into three classifications: organized convection, discrete ordinary convection, and discrete supercell convection. Composite analysis of identified storms for each classification reveals microphysical features similar to those found in previous studies of deep convection, with deep columns of highly positive ZDR and KDP representing lofting of liquid hydrometeors within the convective updraft and above the melting level. In addition, organized and discrete supercell classifications show distinct near-zero ZDR minima aligned horizontally with and at altitudes higher than the updraft column features, likely indicative of the frequent presence of large hail in each case. Composites for organized convective systems show a similar ZDR minimum throughout the portion of the convective core that is overshooting the tropopause, corresponding to ZH in the range of 15–30 dBZ and negative KDP observations, in agreement with the scattering properties of small hail and/or lump or conical graupel. Additional analyses of the evolution of overshooting storms reveals that the ZDR minima indicative of hail in the middle and upper troposphere and graupel in the overshooting top are associated with the mature and decaying stages of overshooting, respectively, supporting their inferred contributions to the observed polarimetric fields.
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Straneo, Fiammetta, Mitsuhiro Kawase, and Robert S. Pickart. "Effects of Wind on Convection in Strongly and Weakly Baroclinic Flows with Application to the Labrador Sea*." Journal of Physical Oceanography 32, no. 9 (September 1, 2002): 2603–18. http://dx.doi.org/10.1175/1520-0485-32.9.2603.
Повний текст джерелаАнотація:
Abstract Large buoyancy loss driving deep convection is often associated with a large wind stress that is typically omitted in simulations of convection. Here it is shown that this omission is not justified when overturning occurs in a horizontally inhomogeneous ocean. In strongly baroclinic flows, convective mixing is influenced both by the background horizontal density gradient and by the across-front advection of buoyancy due to wind. The former process—known as slantwise convection—results in deeper convection, while the effect of wind depends on the relative orientation of wind with respect to the baroclinic front. For the case of the Labrador Sea, wintertime winds act to destabilize the baroclinic Labrador Current causing a buoyancy removal roughly one-third as large as the air–sea buoyancy loss. Simulations using a nonhydrostatic numerical model, initialized and forced with observed fields from the Labrador Sea, show how the combination of wind and lateral gradients can result in significant convection within the current, in contrast with previous ideas. Though the advection of buoyancy due to wind in weakly baroclinic flows is negligible compared to the surface buoyancy removal typical of convective conditions, convective plumes are substantially deformed by wind. This deformation, and the associated across-front secondary circulation, are explained in terms of the vertical advection of wind-generated vorticity from the surface boundary layer to deeper depths. This mechanism generates vertical structure within the convective layer, contradicting the historical notion that properties become vertically homogenized during convection. For the interior Labrador Sea, this mechanism may be partly responsible for the vertical variability observed during convection, which modeling studies have until now failed to reproduce.
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Vreugdenhil, Catherine A., Bishakhdatta Gayen, and Ross W. Griffiths. "Transport by deep convection in basin-scale geostrophic circulation: turbulence-resolving simulations." Journal of Fluid Mechanics 865 (February 26, 2019): 681–719. http://dx.doi.org/10.1017/jfm.2019.64.
Повний текст джерелаАнотація:
Direct numerical simulations are used to investigate the nature of fully resolved small-scale convection and its role in large-scale circulation in a rotating $f$-plane rectangular basin with imposed surface temperature difference. The large-scale circulation has a horizontal geostrophic component and a deep vertical overturning. This paper focuses on convective circulation with no wind stress, and buoyancy forcing sufficiently strong to ensure turbulent convection within the thermal boundary layer (horizontal Rayleigh numbers $Ra\approx 10^{12}{-}10^{13}$). The dynamics are found to depend on the value of a convective Rossby number, $Ro_{\unicode[STIX]{x0394}T}$, which represents the strength of buoyancy forcing relative to Coriolis forces. Vertical convection shifts from a mean endwall plume under weak rotation ($Ro_{\unicode[STIX]{x0394}T}>10^{-1}$) to ‘open ocean’ chimney convection plus mean vertical plumes at the side boundaries under strong rotation ($Ro_{\unicode[STIX]{x0394}T}<10^{-1}$). The overall heat throughput, horizontal gyre transport and zonally integrated overturning transport are then consistent with scaling predictions for flow constrained by thermal wind balance in the thermal boundary layer coupled to vertical advection–diffusion balance in the boundary layer. For small Rossby numbers relevant to circulation in an ocean basin, vertical heat transport from the surface layer into the deep interior occurs mostly in ‘open ocean’ chimney convection while most vertical mass transport is against the side boundaries. Both heat throughput and the mean circulation (in geostrophic gyres, boundary currents and overturning) are reduced by geostrophic constraints.
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Zierep, Jürgen. "Rayleigh-Bénard convection with magnetic field." Theoretical and Applied Mechanics, no. 30 (2003): 29–40. http://dx.doi.org/10.2298/tam0301029z.
Повний текст джерелаАнотація:
We discuss the solution of the small perturbation equations for a horizontal fluid layer heated from below with an applied magnetic field either in vertical or in horizontal direction. The magnetic field stabilizes, due to the Lorentz force, more or less Rayleigh-B?nard convective cellular motion. The solution of the eigenvalue problem shows that the critical Rayleigh number increases with increasing Hartmann number while the corresponding wave length decreases. Interesting analogies to solar granulation and black spots phenomena are obvious. The influence of a horizontal field is stronger than that of a vertical field. It is easy to understand this by discussing the influence of the Lorentz force on the Rayleigh-B?nard convection. This result corrects earlier calculations in the literature.
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Nuissier, Olivier, Fanny Duffourg, Maxime Martinet, Véronique Ducrocq, and Christine Lac. "Hectometric-scale simulations of a Mediterranean heavy-precipitation event during the Hydrological cycle in the Mediterranean Experiment (HyMeX) first Special Observation Period (SOP1)." Atmospheric Chemistry and Physics 20, no. 23 (December 1, 2020): 14649–67. http://dx.doi.org/10.5194/acp-20-14649-2020.
Повний текст джерелаАнотація:
Abstract. Offshore convection occurred over the Mediterranean sea on 26 October 2012 and was well documented during the first Special Observation Period (SOP1) of the Hydrological cycle in the Mediterranean Experiment (HyMeX). This paper analyses the triggering and organizing factors involved in this convection case study, and examines how they are simulated and represented at hectometric resolutions. For that purpose, a large-eddy simulation (LES) of this real case study is carried out with a 150 m horizontal resolution over a large domain encompassing the convective systems and the low-level flow feeding convection over the sea. This LES is then compared to a reference simulation performed with a 450 m grid spacing in the heart of the so-called “grey zone” of turbulence modelling. An increase in horizontal resolution from 450 down to 150 m is unable, for this case study, to reduce significantly deficiencies of the simulation; this is more related to an issue of initial and lateral boundary conditions. Indeed, some of the triggering factors, such as a converging low-level flow driven by a surface low-pressure system, are simulated quite similarly for both simulations. However, differences for other mechanisms still exist since greater surface precipitation amounts are simulated at 450 m. It is found that the entrainment process, characterized by small eddies at the cloud edges, is strongly underestimated at 450 m horizontal resolution, missing the mixing with the environmental air. Therefore, too rapid a development of deep convection is simulated at this horizontal resolution, associated with fast-track microphysical processes and enhanced dynamics. By contrast, at 150 m horizontal resolution, the updraught cores are mainly resolved, as are the subsiding shell, while subgrid eddies, produced by dynamical processes, are localized at the cloud interior edges, better representing the entrainment process. Furthermore, this first LES of a real Mediterranean precipitating case study highlights a convective organization with very fine-scale features within the converging low-level flow, features that are definitively out of range of models with kilometric horizontal resolutions.
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Rivière, E. D., V. Marécal, N. Larsen, and S. Cautenet. "Modelling study of the impact of deep convection on the UTLS air composition – Part 2: Ozone budget in the TTL." Atmospheric Chemistry and Physics 6, no. 6 (May 18, 2006): 1585–98. http://dx.doi.org/10.5194/acp-6-1585-2006.
Повний текст джерелаАнотація:
Abstract. In this second part of a series of two papers which aim to study the local impact of deep convection on the chemical composition of the Upper Troposphere and Lower Stratosphere (UTLS), we focus on ozone simulation results using a mesoscale model that includes on-line chemistry. A severe convective system observed on 8 February 2001 at Bauru, Brazil, is studied. This unorganised convective system is composed of several convective cells that interact with each other. We show that there is an increase in the ozone concentration in the tropical transitional layer (TTL) in the model during this event, which is compatible with ozone sonde observations from Bauru during the 2004 convective season. The model horizontal variability of ozone in this layer is comparable with the variability of the ozone sonde observations in the same area. The calculation of the ozone budget in the TTL during a 24 h period in the area of the convective system shows that the ozone behaviour in this layer is mainly driven by dynamics. The horizontal flux at a specific time is the main contribution in the budget, since it drives the sign and the magnitude of the total ozone flux. However, when averaged over the 24 h period, the horizontal flux is smaller than the vertical fluxes, and leads to a net decrease of ozone molecule number of 23%. The upward motions at the bottom of the TTL, related to the convection activity is the main contributor to the budget over the 24h period since it can explain 70% of the total ozone increase in the TTL, while the chemical ozone production inside the TTL is estimated to be 29% of the ozone increase, if NOx production by lightning (LNOx) is taken into account. It is shown that downward motion at the tropopause induced by gravity waves generated by deep convection is non negligible in the TTL ozone budget, since it represents 24% of the ozone increase. The flux analysis shows the importance of the vertical contributions during the life time of the convective event (about 8 h). The TTL ozone is driven out of the domain horizontally by the convective outflow during this period, limiting the ozone increase in this layer.
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Mohd Kanafiah, Siti Farah Haryatie, Abdul Rahman Mohd Kasim, Syazwani Mohd Zokri, and Hussien Ali Muhammed Al Sharifi. "Mixed convection flow of Brinkman fluid with convective boundary condition at lower stagnation point of horizontal circular cylinder." Data Analytics and Applied Mathematics (DAAM) 2, no. 1 (June 29, 2021): 01–10. http://dx.doi.org/10.15282/daam.v2i1.6310.
Повний текст джерелаАнотація:
Convective heat transfer occurs when heat is transferred from one level to another upon the motion of fluid. Understanding on the characteristics of fluid flow is essential since it will produce the desired output of the product. therefore, this paper examines the mixed convection flow at lower stagnation point of horizontal circular cylinder on Brinkman fluid saturated in porous region with convective boundary condition. The influence of Brinkman, mixed convection and conjugate parameter on the flow field are studied. To reduce the complexity of the equations, a suitable similarity transformation is used. The numerical results of governing equations are obtained via bvp4c tools in Matlab. The effect of mixed convection, Brinkman and conjugate parameter on the temperature and velocity profile, skin friction coefficient together with Nusselt number are analysed and portrayed in graph and table form. The velocity profile increased with improving mixed convection and conjugate value, but decreased with increasing Brinkman factor. It is also discovered that the temperature decrease when the mixed convection parameter increase. This theoretical results will benefit the researchers, particularly in the manufacturing industry, in validating experimental study data.
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SAID, Abdessadek AIT HAJ, Mahfoud ELFAGRICH, and Omar ABOUNACHIT. "Numerical investigation of free convection through a horizontal open-ended axisymmetric cavity." Indian Journal of Science and Technology 14, no. 13 (April 9, 2021): 1081–96. http://dx.doi.org/10.17485/ijst/v14i13.2259.
Повний текст джерелаАнотація:
Objectives: The purposes of this work are to investigate the free convective heat transfer in an axis-symmetric open-ended cavity heated from below and to propose useful correlations of Nusselt number. Methods: The governing equations that model the fluid flow and the temperature field are solved using a control volume-based finite differences method. Under steady state condition, the natural convective flow is considered to be laminar, incompressible and axisymmetric. The Boussinesq approximation with constant thermophysical properties is adopted. Numerical experimentations are performed to deduce the optimum sizes of the calculation domain and the mesh grid. Findings: the obtained results indicate that when Rayleigh number (Ra) and aspect ratio (A) are low the heat transfer is weak and mainly conductive. The increase of Ra and A enhances the convective heat transfer mode thereby the heat transfer is ameliorated. Unlike the Rayleigh Bénard convection, the transition from conduction to convection produces at critical value of Rayleigh number (Rac) that is variable dependent on A. Novelty: To the best of authors knowledge, the formula of (Rac) elaborated in this work for the studied cavity is the first attempt. As well, correlation of Nusselt numbers (Nu) for the cold upper plate in terms of Ra and A is performed. Comparisons between Nu at the lower plate given in previous work and Nusselt number at the upper plate is conducted. Keywords: free convection; circular plates; Nusselt number correlations; open ended cavity; critical Rayleigh number
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Murphy, J. O., and J. M. Lopez. "Evolution of a Horizontal Scale for Magnetoconvection." Publications of the Astronomical Society of Australia 7, no. 2 (1987): 112–16. http://dx.doi.org/10.1017/s1323358000022025.
Повний текст джерелаАнотація:
AbstractThe non-linear modal equations governing magnetoconvection in a fluid layer have been integrated forward in time incorporating a discrete spectrum of horizontal wave numbers, distributed within the range supporting convection. By progressively deleting some of the decaying modes and introducting additional modes within the range of growth it is possible to establish the evolution, or otherwise, of a preferred horizontal scale, which determines the horizontal cell size of the convective motions. Further, the influence of the magnetic field strength on cell extent can also be determined.
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Wirth, A., and B. Barnier. "Mean Circulation and Structures of Tilted Ocean Deep Convection." Journal of Physical Oceanography 38, no. 4 (April 1, 2008): 803–16. http://dx.doi.org/10.1175/2007jpo3756.1.
Повний текст джерелаАнотація:
Abstract Convection in a homogeneous ocean is investigated by numerically integrating the three-dimensional Boussinesq equations in a tilted, rotating frame ( f–F plane) subject to a negative buoyancy flux (cooling) at the surface. The study focuses on determining the influence of the angle (tilt) between the axis of rotation and gravity on the convection process. To this end the following two essential parameters are varied: (i) the magnitude of the surface heat flux, and (ii) the angle (tilt) between the axis of rotation and gravity. The range of the parameters investigated is a subset of typical open-ocean deep convection events. It is demonstrated that when gravity and rotation vector are tilted with respect to each other (i) the Taylor–Proudman–Poincaré theorem leaves an imprint in the convective structures, (ii) a horizontal mean circulation is established, and (iii) the second-order moments involving horizontal velocity components are considerably increased. Tilted rotation thus leaves a substantial imprint in the dynamics of ocean convection.
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Cessi, Paola, and W. R. Young. "Fixed-flux convection in a tilted slot." Journal of Fluid Mechanics 237 (April 1992): 57–71. http://dx.doi.org/10.1017/s0022112092003355.
Повний текст джерелаАнотація:
We study fixed-flux convection in a long, narrow slot which is inclined to the horizontal. (Gravity is in the vertical direction, and horizontal is perpendicular to this.) Because of the fixed-flux boundary conditions the convective modes have much larger lengthscales in the along-slot direction than in the transverse direction. In the case of a horizontal slot this disparity in scales has been previously exploited to obtain an amplitude equation for the single mode which first becomes unstable as the Rayleigh number is increased above critical. When the slot is tilted we show that there is a distinguished limit in which there are two active modes in the slightly supercritical regime. This new limit is when the horizontal wavenumber, the supercriticality, and the tilt of the slot away from vertical, are all small. A modification of the well-known expansion for fixed flux convection in a horizontal slot leads to a coupled system of partial differential equations for the amplitudes of the two modes.Numerical solution of this system suggests that all initial conditions eventually evolve into one of the two states, both of which consist of a single, steady roll in the cavity. The states are distinguished by the direction of circulation of the roll, and by the buoyancy fields, which are quite different in the two cases.
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GRAMBERG, H. J. J., P. D. HOWELL, and J. R. OCKENDON. "Convection by a horizontal thermal gradient." Journal of Fluid Mechanics 586 (August 14, 2007): 41–57. http://dx.doi.org/10.1017/s0022112007006635.
Повний текст джерелаАнотація:
This paper considers a paradigm large-Prandtl-number, large-Rayleigh-number forced convection problem suggested by the batch melting process in the glass industry. Although the fluid is heated from above, non-uniform heating in the horizontal direction induces thermal boundary layers in which colder liquid is driven over hotter liquid. This leads to an interesting selection problem in the boundary layer analysis, whose resolution is suggested by a combination of analytical and numerical evidence.
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Sanmiguel Vila, Carlos, Stefano Discetti, Giovanni Maria Carlomagno, Tommaso Astarita, and Andrea Ianiro. "On the onset of horizontal convection." International Journal of Thermal Sciences 110 (December 2016): 96–108. http://dx.doi.org/10.1016/j.ijthermalsci.2016.06.019.
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de Malmazet, Erik, and Georges Berthoud. "Convection film boiling on horizontal cylinders." International Journal of Heat and Mass Transfer 52, no. 21-22 (October 2009): 4731–47. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2009.03.065.
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