Upward Heat Transport Research Articles

The impact of an intense summer cyclone on 2012 Arctic sea ice retreat

AbstractThis model study examines the impact of an intense early August cyclone on the 2012 record low Arctic sea ice extent. The cyclone passed when Arctic sea ice was thin and the simulated Arctic ice volume had already declined ~40% from the 2007–2011 mean. The thin sea ice pack and the presence of ocean heat in the near surface temperature maximum layer created conditions that made the ice particularly vulnerable to storms. During the storm, ice volume decreased about twice as fast as usual, owing largely to a quadrupling in bottom melt caused by increased upward ocean heat transport. This increased ocean heat flux was due to enhanced mixing in the oceanic boundary layer, driven by strong winds and rapid ice movement. A comparison with a sensitivity simulation driven by reduced wind speeds during the cyclone indicates that cyclone‐enhanced bottom melt strongly reduces ice extent for about 2 weeks, with a declining effect afterward. The simulated Arctic sea ice extent minimum in 2012 is reduced by the cyclone but only by 0.15 × 106 km2 (4.4%). Thus, without the storm, 2012 would still have produced a record minimum.

Nature of orogenesis and volcanism in the Caucasus region based on results of regional tomography

Abstract. In the paper, we discuss the problem of continental collision and related volcanism in the Caucasus and surrounding areas based on the analysis of the upper mantle seismic structure in a recently derived model by Koulakov (2011). This model, which includes P and S-velocity anomalies down to 1000 km depth, was obtained from tomographic inversion of worldwide travel time data from the catalogue of the International Seismological Center. It can be seen that the Caucasus region is squeezed between two continental plates, Arabian to the south and European to the north, which are displayed in the tomographic model as high-velocity bodies down to about 200–250 km depth. On the contrary, a very bright low-velocity anomaly beneath the collision area implies that the lithosphere in this zone is very thin, which is also supported by strong horizontal deformations and crustal thickening indicating weak properties of the lithosphere. In the contact between stable continental and collision zones, we observe a rather complex alternation of seismic anomalies having the shapes of sinking drops. We propose that the convergence process causes crustal thickening and transformation of the lower crust material into the dense eclogite. When achieving a critical mass, the dense eclogitic drops trigger detachment of the mantle lithosphere and its delamination. The observed high-velocity bodies in the upper mantle may indicate the parts of the descending mantle lithosphere which were detached from the edges of the continental lithosphere plates. Very thin, or even absent, mantle parts of the lithosphere leads to the presence of hot asthenosphere just below the crust. The crustal shortening and eclogitisation of the lower crustal layer leads to the dominantly felsic composition of the crust which is favourable for the upward heat transport from the mantle. This, and also the factors of frictional heating and the radioactivity of felsic rocks, may be the origin of volcanic centres in the Caucasus and surrounding collisional areas.

Correction of Excessive Precipitation over Steep and High Mountains in a GCM

Abstract Excessive precipitation over steep and high mountains (EPSM) is a well-known problem in GCMs and mesoscale models. This problem impairs simulation and data assimilation products. Among the possible causes investigated in this study, it was found that the most important one, by far, is a missing upward transport of heat out of the boundary layer due to the vertical circulations forced by the daytime upslope winds, which are forced by heated boundary layer on the subgrid-scale slopes. These upslope winds are associated with large subgrid-scale topographic variation, which is found over steep and high mountains. Without such subgrid-scale heat ventilation, the resolvable-scale upslope flow in the boundary layer generated by surface sensible heat flux along the mountain slopes is excessive. Such an excessive resolvable-scale upslope flow combined with the high moisture content in the boundary layer results in excessive moisture transport toward mountaintops, which in turn gives rise to EPSM. Other possible causes investigated include 1) a poorly designed horizontal moisture flux in the terrain-following coordinates, 2) the conditions for cumulus convection being too easily satisfied at mountaintops, 3) conditional instability of the computational kind, and 4) the absence of blocked flow drag. They are all minor or inconsequential. The ventilation effects of the subgrid-scale heated-slope-induced vertical circulation (SHVC) have been parameterized by removing heat from the boundary layer and depositing it in the layers higher up when topographic variance exceeds a critical value. Test results using the NASA Goddard Earth Observing System GCM version 5 (GEOS-5) have shown that the EPSM problem is largely solved.

Rayleigh–Bénard convection: Improved bounds on the Nusselt number

We consider Rayleigh–Bénard convection as modelled by the Boussinesq equations in the infinite-Prandtl-number limit. We are interested in the scaling of the average upward heat transport, the Nusselt number Nu, in terms of the non-dimensionalized temperature forcing, the Rayleigh number Ra. Experiments, asymptotics and heuristics suggest that Nu ∼ Ra1/3. This work is mostly inspired by two earlier rigorous work on upper bounds of Nu in terms of Ra. (1) The work of Constantin and Doering establishing Nu ≲ Ra1/3ln 2/3Ra with help of a (logarithmically failing) maximal regularity estimate in L∞ on the level of the Stokes equation. (2) The work of Doering, Reznikoff and the first author establishing Nu ≲ Ra1/3ln 1/3Ra with help of the background field method. The paper contains two results. (1) The background field method can be slightly modified to yield Nu ≲ Ra1/3ln 1/15Ra. (2) The estimates behind the background field method can be combined with the maximal regularity in L∞ to yield Nu ≲ Ra1/3ln 1/3ln Ra — an estimate that is only a double logarithm away from the supposedly optimal scaling.

The Effect of the Sea Ice Freshwater Flux on Southern Ocean Temperatures in CCSM3: Deep-Ocean Warming and Delayed Surface Warming

Abstract This study explores the role of sea ice freshwater and salt fluxes in modulating twenty-first-century surface warming in the Southern Ocean via analysis of sensitivity experiments in the Community Climate System Model, version 3 (CCSM3). In particular, the role of a change in these fluxes in causing surface cooling, expanding sea ice, and increasing deep oceanic storage of heat in the Southern Ocean is investigated. The results indicate that in response to the doubling of CO2 concentrations in the atmosphere in CCSM3, net freshwater input from sea ice to the ocean increases south of 58°S (owing to less growth) and decreases from 48° to 58°S (owing to less melt). The freshwater source from changing precipitation in the model is considerably less than from sea ice south of 58°S, but it serves to compensate for the reduction in sea ice melt near the ice edge, leaving almost no net freshwater flux change between about 48° and 58°S. As a result, freshwater input principally from sea ice reduces ocean convection, which in turns reduces the entrainment of heat into the mixed layer and reduces the upward heat transport along isopycnals below about 1000 m. The reduced upward heat transport (from all sources) causes deep-ocean heating south of 60°S and below 500-m depth, with a corresponding surface cooling in large parts of the Southern Ocean in the model. These results indicate that changing sea ice freshwater and salt fluxes are a major component of the twenty-first-century delay in surface warming of the Southern Ocean and weak reduction in Antarctic sea ice in model projections.

Accelerated warming of the Southern Ocean and its impacts on the hydrological cycle and sea ice

The observed sea surface temperature in the Southern Ocean shows a substantial warming trend for the second half of the 20th century. Associated with the warming, there has been an enhanced atmospheric hydrological cycle in the Southern Ocean that results in an increase of the Antarctic sea ice for the past three decades through the reduced upward ocean heat transport and increased snowfall. The simulated sea surface temperature variability from two global coupled climate models for the second half of the 20th century is dominated by natural internal variability associated with the Antarctic Oscillation, suggesting that the models' internal variability is too strong, leading to a response to anthropogenic forcing that is too weak. With increased loading of greenhouse gases in the atmosphere through the 21st century, the models show an accelerated warming in the Southern Ocean, and indicate that anthropogenic forcing exceeds natural internal variability. The increased heating from below (ocean) and above (atmosphere) and increased liquid precipitation associated with the enhanced hydrological cycle results in a projected decline of the Antarctic sea ice.

Crustal noble gases in deep brines as natural tracers of vertical transport processes in the Michigan Basin

Noble gas concentrations and isotopic ratios are presented for 38 deep (∼0.5–3.6 km) brine samples in the Michigan Basin. These brine samples clearly show the presence of an important crustal component of 4He, 21Ne, 40Ar, and 136Xe. Both 40Arcrust and 136Xecrust display the presence of a strong vertical gradient along the sedimentary strata of the basin. We show that the in situ production for these two gases within the sedimentary strata is insufficient to account for the observed crustal component in the Michigan brines. These point to the presence of a deep, external source for crustal noble gases, likely the Precambrian crystalline basement beneath the Michigan Basin. Furthermore, observed elemental ratios of crustal noble gases (4He/40Ar, 21Ne/40Ar, 4He/136Xe, and 21Ne/136Xe) in these brines vary over several orders of magnitude with respect to the expected production ratios from the crystalline basement rocks and display a systematic pattern within the basin. Specifically, samples above the Salina Group (shallow formations) are relatively enriched in 4Hecrust and 21Necrust with respect to 40Arcrust and 136Xecrust, as opposed to those below the massive Salina evaporite layer (deeper formations) which exhibit complementary patterns. We show that such a general trend is best explained by a Rayleigh‐type elemental fractionation model involving upward transport of crustal noble gases and associated elemental fractionation processes, controlled by both diffusion‐ and solubility‐related mechanisms. As previously indicated by the mantle and atmospheric noble gas signatures in these same Michigan brine samples, release of deep crustal noble gases into the basin is yet another independent indicator pointing to the occurrence of a past thermal event in the basin. We suggest that recent reactivation of the ancient midcontinent rift system underneath the Michigan Basin is likely responsible for the upward transport of heat and loss of the atmospheric noble gas component, as well as release of crustal (still ongoing) and mantle noble gases into the basin via deep‐seated faults and fracture zones. Such a model also supports an internal heat source hypothesis as being largely responsible for the existence of past high temperatures in the basin without involvement of large‐scale brine migration from peripheral forming orogenic fold belts.

Increasing Antarctic Sea Ice under Warming Atmospheric and Oceanic Conditions

Abstract Estimates of sea ice extent based on satellite observations show an increasing Antarctic sea ice cover from 1979 to 2004 even though in situ observations show a prevailing warming trend in both the atmosphere and the ocean. This riddle is explored here using a global multicategory thickness and enthalpy distribution sea ice model coupled to an ocean model. Forced by the NCEP–NCAR reanalysis data, the model simulates an increase of 0.20 × 1012 m3 yr−1 (1.0% yr−1) in total Antarctic sea ice volume and 0.084 × 1012 m2 yr−1 (0.6% yr−1) in sea ice extent from 1979 to 2004 when the satellite observations show an increase of 0.027 × 1012 m2 yr−1 (0.2% yr−1) in sea ice extent during the same period. The model shows that an increase in surface air temperature and downward longwave radiation results in an increase in the upper-ocean temperature and a decrease in sea ice growth, leading to a decrease in salt rejection from ice, in the upper-ocean salinity, and in the upper-ocean density. The reduced salt rejection and upper-ocean density and the enhanced thermohaline stratification tend to suppress convective overturning, leading to a decrease in the upward ocean heat transport and the ocean heat flux available to melt sea ice. The ice melting from ocean heat flux decreases faster than the ice growth does in the weakly stratified Southern Ocean, leading to an increase in the net ice production and hence an increase in ice mass. This mechanism is the main reason why the Antarctic sea ice has increased in spite of warming conditions both above and below during the period 1979–2004 and the extended period 1948–2004.

A simple diagnostic calculation of marine stratocumulus cloud cover for use in general circulation models

An improved diagnostic calculation for determining the marine stratocumulus (SCu) cloud cover has been implemented for atmospheric and coupled general circulation models (GCMs). The approach aims to improve the simulated climatological features of the lower troposphere and to reduce warm sea surface temperature (SST) biases that develop along western continental coasts in the subtropical regions of coupled GCMs. In the new diagnostic calculation introduced in the present study, the SCu cloud cover was linearly regressed to atmospheric stability, and the temporal and spatial distributions of the regression coefficients were estimated beforehand using observational data sets. The upward transport of heat, moisture and momentum in subcloud layers accompanying the SCu was also simulated by controlling the vertical diffusion coefficients. Using the new calculation, the SCu cloud cover in an atmospheric GCM become more representative in both spatial and seasonal variations. In addition, the simulation of related atmospheric structures in the lower troposphere is considerably improved. Furthermore, when the new calculation is applied to a coupled GCM, SST values to the west of continents in subtropical areas display weakened warm biases and more realistic seasonal cycles resulting from the modification of the downward shortwave radiation flux at the sea surface. The new calculation introduces both local and large‐scale improvements in model climatology over low‐latitude and midlatitude regions. In the eastern Pacific, for example, a shallow meridional circulation across the equator is excited, and the strength and location of the intertropical convergence zone and the seasonal cycle of equatorial SST become more realistic.

Thermobaric deep convection, baroclinic instability, and their roles in vertical heat transport around Maud Rise in the Weddell Sea

Numerical experiments with two‐ and three‐dimensional nonhydrostatic models in a rotating frame have been executed to investigate thermobaric deep convection, subsequent baroclinic instability, and their roles in vertical heat transport, using hydrographic data around Maud Rise in the Weddell Sea, Antarctica. Overturning of the water column due to thermobaric convection is apt to occur on the southern and northern flanks of the rise, and induces upward heat transport. The depth of overturning is two times larger on the northern flank (∼1.5 km) than on the southern flank (∼0.7 km). To the contrary, no overturning occurs over the top of the rise in 90 days. Baroclinic instability develops at a density front formed between the overturned and unoverturned regions since a density contrast at the front is enhanced by thermobaricity. Heat transport due to baroclinic instability is similarly upward, and at peak becomes comparable to that due to the overturning. Applicability of the results to the cooling events previously reported is also discussed.

Plume fluxes from seismic tomography

We use mantle plume images from finite frequency tomography and the Stokes equation to obtain a quantitative estimate of the heat and volume flux across several well resolved plume sections in mid-mantle. Although not a perfect barrier, widening of plumes just below 670 km depth indicates that the phase transition from ringwoodite to perovskite plus magnesowüstite and possibly iron enrichment of the lower mantle resists plume passage into the upper mantle. Estimated heat- and volume flux for individual plumes at mid-mantle depths is greater than predicted by surface observations of buoyancy flux, even for very high viscosity. Although uncertainties are large, the high flux observed in plumes at mid-mantle depth is compatible with the view that plumes are responsible for all upward advective heat transport in the lower mantle that eventually breaks through into the upper mantle.

Hawaiian mantle xenoliths and magmas: Composition and thermal character of the lithosphere

Recent seismological investigations into the Hawaiian mantle and geophysical studies of the Hawaiian Swell have led to divergent models regarding the thermal structure and role of the lithosphere in Hawaiian magmatism. Whereas some models require that the Hawaiian plume erodes the lower lithosphere and replaces it with plume-derived residues and cumulates, others do not require any thinning of the lithosphere. In this paper, we develop a model for the physical and thermal characteristics of the oceanic lithosphere beneath Oahu, Hawaii, from the mantle xenoliths included in the rejuvenated stage lavas (Honolulu Volcanics, HV) that erupted through the Salt Lake Crater (SLC) and Kaau-Pali-Kalihi (KPK) vents. Three main xenolith suites are found at Oahu: spinel peridotite, garnet pyroxenite, and dunite. Dunites are generally shallow cumulates, whereas the peridotite and pyroxenite xenoliths are from the mantle. Plagioclase peridotite (harzburgite) is rare, and represents a ~15 km thick lithospheric layer below the ~15 km thick crust (MOR-generated oceanic crust + thickened crust formed by Koolau shield volcano activity). The harzburgite layer is underlain by a spinel peridotite layer. Spinel peridotites from SLC and KPK differ in chemical and isotopic composition. SLC spinel peridotites have unusually enriched 176 Hf/ 177 Hf but highly nonradiogenic 187 Os/ 188 Os isotopic compositions, likely indicating that they are metasomatized, recycled (previously subducted) oceanic lithospheric fragments. On the other hand, KPK spinel peridotites exhibit compositional characteristics of the 90 m.y. old lithosphere beneath Oahu that has been variably metasomatized by passing HV magmas. We suggest that the lower lithosphere beneath SLC and KPK are very different in their petrologic composition. The lower lithosphere (60–90 km) beneath SLC is extensively veined and fragmented by garnet clinopyroxenite intrusives and mixed with spinel peridotite blobs that are recycled subducted lithospheric fragments. For the KPK lithosphere, we favor a model in which the lower part is peridotitic. The thickness of our model lithosphere beneath Oahu is ~90 km. The seismic low-velocity zone beneath Oahu is likely due to the presence of small amounts of hydrous-alkalic and carbonatitic (+kimberlitic) melts. The isotopic data suggest little or no interaction between the basal lithosphere and Koolau shield magmas (mostly plume-derived, particularly those with near bulk-earth Nd- and Sr-isotope ratios), suggesting that during shield-stage volcanism, magmas used well-insulated (i.e., a reaction zone of 60 km) xenoliths are isotopically depleted and lack the typical Koolau-like signature. Therefore, the lower lithosphere was not significantly eroded by Koolau magmatism. KPK spinel peridotites give temperatures of 900–1040 °C for the intermediate lithosphere, which is about 200–400 °C hotter than what would be expected of a normal 90 Ma lithosphere. We suggest that such an anomalously high temperature is due to heating of the wall rocks (lithosphere) by ascending HV magmas and not due to simple basal heating of the lithosphere by the hot spot/plume followed by gradual (conductive) upward transport of heat. Thermobarometry of garnet-bearing xenoliths suggests that these rocks equilibrated at ~2–3 GPa and 1200–1350 °C. This temperature range is 50–200° less than that predicted by a recent model (Ribe and Christensen 1999). The plume that generated the Koolau shield magmas was a complex mixture composed predominantly of Koolau source materials at its center and blocks of old recycled lithosphere in its outer fringes that were later rafted into the lithosphere beneath SLC.

Passively Cooled Railway Embankments for Use in Permafrost Areas

Permafrost (permanently frozen ground) underlies approximately 25% of the world’s land surface. Construction of surface facilities in these regions presents unique engineering challenges due to the alteration of the thermal regime at the ground surface. Even moderate disturbance of the preexisting ground surface energy balance can induce permafrost thawing with consequent settlement and damage to roadway or railway embankments. Railway embankments are particularly susceptible to thaw settlement damage because of the need to maintain the alignment and even grade of the rails. The present work examines the heat transfer and thermal characteristics of railway embankments constructed of unconventional, highly porous materials. It is possible to produce a passive cooling effect with such embankments because of the unstable density stratification and resulting natural convection that can occur during winter months. The convection enhances the upward transport of heat out of the embankment during winter, thus cooling the lower portions of the embankment and underlying foundation soil. Numerical results have been obtained with an unsteady two-dimensional finite-element model that is capable of solving the coupled governing equations of pore air flow and energy transport. The numerical results are obtained for conditions typical of those found in railway configurations which allow open exchange of air between the embankment structure and the surrounding ambient air mass.

移動する熱源に対するゆっくり回転している大気の非線形応答 : 金星大気に関連した数値実験

The three-dimensional response of a slowly-rotating atmosphere to mobile heating is investigated by using a multi-layer primitive equation model on the sphere. The velocity of planetary rotation and that of solar heating are fixed at the values of Venus. The global circulation is assumed to be induced only by the solar radiation absorbed by the ground. The global circulation induced in this way can produce an atmospheric stability by the upward heat transport. In order to examine this nonlinear effect, the model is numerically integrated from a state of neutral stratification. It is found that the direct circulation between the day and night sides predominates always for standard parameter values. The temperature maximum point on the equator is deviated from the subsolar point by 60°. The horizontal temperature contrast between the day and night sides is very small (0.16 K in the lowest layer). The atmospheric stratification produced by the global circulation is also too weak even in the night side. In the experiments with one solar day assumed to be 1/2 or 1/4 of Venus' solar day (117 days), the zonally uniform meridional circulation appears in place of the direct circulation.

Structure of the Atmosphere of Jupiter: Galileo Probe Measurements

Temperatures and pressures measured by the Galileo probe during parachute descent into Jupiter's atmosphere essentially followed the dry adiabat between 0.41 and 24 bars, consistent with the absence of a deep water cloud and with the low water content found by the mass spectrometer. From 5 to 15 bars, lapse rates were slightly stable relative to the adiabat calculated for the observed H2/He ratio, which suggests that upward heat transport in that range is not attributable to simple radial convection. In the upper atmosphere, temperatures of >1000 kelvin at the 0.01-microbar level confirmed the hot exosphere that had been inferred from Voyager occultations. The thermal gradient increased sharply to 5 kelvin per kilometer at a reconstructed altitude of 350 kilometers, as was recently predicted. Densities at 1000 kilometers were 100 times those in the pre-encounter engineering model.

Winter-time convection in open-graded embankments

Winter-time natural convection in open-graded gravel embankments is studied using a numerical representation of the unsteady two-dimensional momentum and energy equations. The analysis examines the ability of these embankments to maintain the structural integrity of thaw-unstable permafrost that often underlies roadway or airport embankments in northern climates. As a result of low ambient temperatures acting on the embankment surface during winter months, an unstable density stratification develops in the embankment. Buoyancy-driven convection of the pore air occurs in reaction to the density gradient. The convection enhances the upward transport of heat out of the embankment during winter months, thus cooling the lower portions of the embankment and underlying foundation soil. During summer months the density stratification is stable and convection does not occur. Consequently, summer-time heat transfer is dominated by thermal conduction which transports heat less effectively. The results of the present study show that the winter-time convection can lower foundation soil temperatures beneath open-graded embankments by as much as 5°C on an annual average basis compared to stan0ard sand and gravel embankments. Time varying temperatures and pore air velocites are calculated for different embankmenkt permeabilities and the results are visualized in the form of isotherm and velocity vector plots for different times of the year.

Evaluation of turbulent fluxes over Maitri, Antarctica

Turbulent fluxes have been evaluated for clear sunny days over the Indian Antarctic station, Maitri, using the basic meteorological data recorded at four levels of a 28 m tower. The data are supplemented with radiation data. The surface layer over Maitri remains thermally stratified during the hours of minimum solar insolation, the so-called nighttime period. The surface winds during this period are generally very strong resulting in high momentum fluxes. In particular, for high winds (>12 m s−1), the temperature gradient is found to be less positive than for moderate winds (4 to 7 m s−1). Solar insolation provided the daytime heating necessary for the diurnal variation of atmospheric stability, and hence, for the turbulent fluxes. Thus, on clear days daytime conditions are marked by upward transport of heat with reduced momentum flux, while stable nighttime conditions are marked by a downward heat flux with increased momentum fluxes.

Large-eddy simulations of the effects of hilly terrain on the convective boundary layer

Large-eddy simulations of the convective boundary layer are compared over hilly versus flat surfaces. Moderate values for the height and horizontal spacing of the hills were selected. Thermally-direct hill-valley circulations are induced by the uneven terrain, accounting for a significant fraction of the resolved energy in the boundary-layer eddies. The probability of upward eddy motion reaches up to 70% over the hilltops and down to 15% over the valleys. Above-average values of both subgrid scale turbulent kinetic energy and upward eddy heat transport are found above the higher terrain. Horizontal spectra of vertical motion are strongly biased toward the horizontal scales of the terrain. Vertical profiles of atmospheric variables obtained by horizontal averaging, however, exhibit no significant differences between hilly and flat terrain simulations.

Turbulent transport of scalar quantities within and above a paddy field

An experiment was conducted to study turbulent transport processes of scalar quantities within and above a rice plant canopy. A sonic anemometer-thermometer and a Lyman-α humidiometer were used to measure the turbulent fluxes of sensible and latent heat and related turbulence statistics within a paddy field. The sensible and latent heat fluxes measured at two heights within and above the plant canopy showed that the upper layer of this plant canopy was an active source region and that the source strength of sensible and latent heat depended on the solar radiation and physiology of rice plants. Analysis of joint probability distributions of w and T and of w and q within this plant canopy showed that downdrafts were remarkably efficient for upward transport of sensible and latent heat in the daytime. The vertical fluxes of temperature and humidity variance were also divergent from the upper layer of plant canopies. The power spectra of temperature and humidity within the plant canopy decreased rapidly in the high frequency range, compared with the - 2/3 law relationship of nS(n) vs log n observed above plant canopies.

Natural Convection of a Heat Generating Fluid in a Closed Cavity

Thermal convection of a heat generating fluid in a rectangular enclosure, cooled at the side walls, is investigated in the boundary-layer regime at large internal Rayleigh numbers. A boundary-layer analysis is employed to derive a system of equations valid near the vertical walls and a corresponding system valid in the core of the enclosure. The boundary-layer equations were solved using a modified Oseen linearization method. It was found that the primary convective flow consists of a bicellular circulation in which the cold, descending boundary layers at the lateral walls generate a nearly uniform, upward flow in the core. In addition, a strong, stable, vertical temperature gradient is established in the core by the process of upward transport of heat. The side-wall heat flux distribution shows that most of the heat generated within the cavity is removed along the upper one-half of each vertical wall. It is expected that the results of this work can be applied in studies of the containment of heat generating radioactive materials and in analyses of convection driven by electrical currents or exothermic chemical reactions.