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Topic: Convection cell

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In the News (Wed 22 May 19)

 Educator's Guide to Convection
The convection that students are most likely to have observed is in cumulonimbus clouds or "thunderheads." These towering vertical clouds can be seen to evolve over a few minutes.
The bright center of each cell is the top of a rising column of hot gas.
Convection acts as described in the examples above where gravity's effects are present (so that warm, low density fluids can rise and cool, high density fluids can fall).
www.solarviews.com /eng/edu/convect.htm   (567 words)

 Foster John : Storm Time Plasma Transport at Middle and High Latitudes
Associated with the large-scale enhancement of the ionospheric convection electric field during disturbed geomagnetic conditions, solar-produced F region plasma is transported to and through the noontime cleft from a source region at middle and low latitudes in the afternoon sector.
They found that the prenoon convection cell, bringing plasma sunward from the predawn darkness, was associated with low F region densities, while the postnoon convection cell was clearly marked by the higher densities of the lower-latitude afternoon sector F region.
As the Earth rotates under the convection pattern, the region of sunward convection extends to an increasingly equatorward geographic latitude as time progresses from 12 UT to 24 UT. During the subsequent 12-hour period, the reverse is true, and the extent of the convection pattern retreats poleward in geographic coordinates.
www.haystack.edu /~jcf/papers/tongue.htm   (7461 words)

 The horizontal cell sizes of mantle convection induced by the effect of continental plates   (Site not responding. Last check: 2007-10-22)
Further, the velocity amplitude of the convection induced by the horizontal temperature difference is evaluated as a function of the Rayleigh number and the horizontal scale of the convection cell.
By comparing this velocity amplitude with that of intrinsic thermal convection induced by the vertical temperature difference, the maximum horizontal size of the convection cell is obtained as a function of the Rayleigh number.
These values suggest that an upwelling of the convection cell extending over the margin of a supercontinent can be generated beneath the center of the continent in the case of whole mantle convection, however, in the case of upper mantle convection, an upwelling appears beneath its margin.
www.nagare.or.jp /mm/99/matsumoto/index.htm   (402 words)

 [No title]
Cells cannot act as heat engines, for they have no means of permitting heat to flow from a warmer to a cooler body.
An example of a convection cell, of interest for the origin of life, is the water circulating in a volcanic hot spring.
Convection has been related to the origin of life by many authors but only in very general terms.
geocities.com /ResearchTriangle/Node/5345/html_files/introduction.html   (2502 words)

 [No title]
It is generally accepted that HCRs form in environments with some amount of convective instability (vertical heat flux at the surface) and wind shear (in the boundary layer).
For example, open and closed cell convection tend to occur in environments that are convectively unstable and have weak wind shear.
Hence L is indirectly a measure of the convective instability generated by the vertical heat flux through the surface layer.
apollo.lsc.vsc.edu /classes/met455/notes/section9/1.html   (1028 words)

 Tomi Haramina: Current Research   (Site not responding. Last check: 2007-10-22)
Convective thermal turbulence is interesting both for its obvious engineering and geophysical applications and as a model system for turbulence study.
This state of convective thermal turbulence is characterized by a large-scale mean circulating flow that spans the entire system, an exponential probability distribution function of the temperature fluctuation at the center of the convection cell, and scaling laws for the heat flux and other measured quantities.
Thermistors can be lowered into the cell through holes in the middle and at a corner of the cell using translation table with accuracy of 3µm.
www.uni-geophys.gwdg.de /~tharamin/research.html   (711 words)

 searched for: convection current cycle in the atmosphere   (Site not responding. Last check: 2007-10-22)
Convection Modified from Convection: A current event from the Lawrence Hall of Science, Great...
of air with a rising and falling current is called a convection cell.
circulation patterns known as convection currents in the atmosphere, in water, and in the mantle of Earth.
www.love2dance.org.uk /convection_current_cycle_in_the_atmosphere.html   (270 words)

 Zhang Lab
A nearly parallel light beam is used to form a shadowgraph of the cell, which shows the position of the floater as well as the flow pattern.
A time series of the oscillation in the convection cell, with Ra ~ 10^8, Pt ~ 6, Re ~ 50: (1) About 10 minutes after the floater came to the left side of the cell, a hot raising structure is visible under the floater.
The aspect ratio is 3.3 and the floater covers 36% of the free surface of the convection cell.
www.physics.nyu.edu /~jz11/freeboundary.html   (525 words)

 CONVECTION CELL   (Site not responding. Last check: 2007-10-22)
In tectonics, a pattern of mass movements of mantle material in which the central area is uprising and the outer area is down flowing, due to heat variations.
In a well-organized process of convection, a given mass of air in which there is a systematic pattern of internal motion and little or no mixing with neighbouring masses.
cellula di convezione (convection loop, convective cell), cellula convettiva (convective cell), cella di convezione (convection loop, convective cell).
www.websters-online-dictionary.org /co/convection+cell.html   (277 words)

 Rayleigh-Benard Convection   (Site not responding. Last check: 2007-10-22)
Rayleigh-Benard convection is the instability of a fluid layer which is confined between two thermally conducting plates, and is heated from below to produce a fixed temperature difference.
In order for convection to occur, a small plume of hot fluid which begins to rise toward the top of the cell must grow in strength, rather than fizzle out.
This competition of forces is parameterized by the Rayleigh number, which is the temperature difference, but appropriately normalized to take into account the geometry of the convection cell and the physical properties of the fluid.
physics.ucsd.edu /was-daedalus/convection/rb.html   (625 words)

 Plasma convection [Oulu]   (Site not responding. Last check: 2007-10-22)
This creates the two cell pattern relating to the convection electrojets in the highly conducting auroral region (see, e.g., Clauer and Kamide, 1985; also term ionospheric DP 2 or "disturbance polar of the second type" current system has been used).
It is usually thought that the high latitude cells (that are on open field lines all the time) are due to reconnection, and the low latitude cells are formed due to viscous interaction (Axford and Hines, 1961).
Observations of just the ionospheric convection signature cannot distinguish between viscous and reconnection based convections, but the measured high cross-polar cap potentials and the dependence of the convection geometry on IMF By suggest that the merging process dominates over viscous interaction when the IMF has a southward component.
www.oulu.fi /~spaceweb/textbook/convect.html   (478 words)

 El Niño explained   (Site not responding. Last check: 2007-10-22)
A convection cell is driven by heat at the ocean surface.
During an El Niño, the convection cell moves east, altering the entire pattern of wet-and-dry weather in the Pacific.
The water that blows westward across the ocean is replaced by deep, cold, nutrient-laden water that rises to the surface near South America, feeding a vibrant fishery along Peru and Ecuador and cooling the sea surface.
whyfiles.org /050el_nino/2.html   (589 words)

 FuelCellStore.com,Demonstrational Fuel Cell System Index,educational fuel cell system,demonstration fuel cell ...   (Site not responding. Last check: 2007-10-22)
3 W Convection fuel cell stack is a 4 cell stack that does not require external humidification or pressurization.
10 W Convection fuel cell stack is a 4 cell stack that does not require external humidification or pressurization.
Multi Combines an electrolyser, fuel cell and direct methanol fuel cell into one unit that is mounted on a clear base plate for use with an overhead projector.
www.fuelcellstore.com /products/index/demonstration_fuelcell_index.html   (827 words)

 The 3-cell theory
The three cells of general circulation of the Northern Hemisphere are similar to those of the Southern Hemisphere.
The air which comprises this cell circulates poleward at the surface and equator-ward aloft with rising currents at 60° (polar front) and descending currents at 30° (high-pressure belt).
This air converges with the poleward flow from the mid-latitude cell and is deflected upward with a portion circulating poleward again and the remainder equatorward.
www.tpub.com /weather2/3-5.htm   (459 words)

 Spin-Up of a Convection Cell   (Site not responding. Last check: 2007-10-22)
A cylindrical Rayleigh-Bénard convection cell, initially in a state of turbulent convection, is subjected to impulsive spin-up about its vertical axis.
The final state of the cell is that of rotating turbulent convection at a constant rotation rate.
Water filling the cell is seeded with thermochromic liquid crystals that change their color with temperature.
me.unm.edu /~kalmoth/fluids/biftree.html   (218 words)

Note that the flow defines a convection cell (actually two cells) in which upward flow above the flame (caused by heating of the fluid which causes expansion and a reduction in density) causes horizontal flow near the surface of the liquid.
Convection in the Earth:  Thermal convection is inferred to exist on a large scale in at least two regions in the Earth.
  Convective flow within the outer core not only brings heat to the core-mantle boundary where some of it is transferred into the mantle, but also causes the Earth's magnetic field by motions of the electrically conductive inner core material.
www.eas.purdue.edu /~braile/edumod/convect/convect.htm   (2865 words)

 Session AG - Convection.
Temperature measurements were carried out at the center of a convection cell with rough upper and lower surfaces.
The vertical heat flux in the rough cells is found to be increased by \sim 25% when compared with that in the smooth cells.
A thermal convection in a vertical slot with infinite extent is investigated in the presence of a horizontal magnetic field which is perpendicular to the side-walls.
flux.aps.org /meetings/BAPSDFD96/abs/S160.html   (1558 words)

 II.2.d. APPLICATIONS. GAFD Turbulence: PPM Simulations of Intensely Turbulent Compressible Convection
This region was wide enough only for a single convection cell in the lower portion of the unstable layer, where the local pressure scale height was largest.
Therefore the region of the simulation was set to contain only a single convection cell so that all possible grid resolution permitted by the size and speed of the computing resources available could be concentrated on this single convection cell in order to give an accurate representation of these interactions.
This PPM convection code on the T3D began at a performance level of about 7.3 Gflop/s on 512 processors, and through heroic and bizarre modifications to the code which should have been made by the compiler, David Porter managed to increase this performance to 9.7 Gflop/s.
www.colorado.edu /engineering/Aerospace/CAS/CF.d/NSF.finalrep.d/finalrep.II.2.d.html   (795 words)

 Convection Cell (thymol blue cell)   (Site not responding. Last check: 2007-10-22)
The convection cell is made from two sheets of 0.5cm plexiglass (front clear, rear translucent), separated by a 0.5cm gap for the liquid, the indicator thymol blue.
To see the convection effect, thymol blue, which is ordinarily yellow, turns blue when ionized.
Fill the cell with the aid of a funnel and stand it in a shallow dish (with all the silicon rubber sealant, it still tends to leak) You will need a lab clamp to hold it upright.
www.fas.harvard.edu /~scdiroff/lds/ThermalPhysics/ConvectionCellThymolBlue/ConvectionCellThymolBlue.html   (321 words)

 The Mechanism Causing Plate Tectonic Movements
Finally, convection cell flow rates are driven by the amount of heat that is present, so that also would make the Core convective cells and the Mantle convective cells much more active and much more dynamically unstable than today.
This instability is very logical, since at the bottom of the kettle, as a particular convection cell develops, it acts to remove heat from that specific location on the bottom, but tends NOT to do so for adjacent areas.
Very quickly, the one area is cooled (because of the effectiveness of the convection cell) and the adjacent areas get hotter (because they do NOT have an effective way of releasing their heat).
mb-soft.com /public/tecto3.html   (4453 words)

 Turbulent Thermal Convection
High Rayleigh number turbulent thermal convection is simulated to determine the effects of Rayleigh number, aspect ratio, mean shear, rotation and boundary conditions on heat transfer and flow characteristics.
Detailed understanding of the spatial structure and dynamics of the convective rolls and coherent thermal plumes is important in evaluating the overall heat-transfer process and scaling laws which distinguish soft and hard turbulence.
These are results from Rayleigh Benard convection simulations at a Rayleigh number of 6.5x10**6 and 3.5x10**7 at a Prandtl number of 0.72.
www.enseeiht.fr /hmf/travaux/CD9598/travaux/optmfn/BES_PHOENICS/96-97/Caini-Gelene/RB_convectio_tur.html   (960 words)

 The ramblings of A.H.E.Retic
Next consider that if two cells start up under a continental plate and create two parallel rifts then unless a subduction zone also starts up within the continental plate between the rifts or at the edge of one of the rifts then the centres of the rifts must move apart (pl3.gif).
This means that if the energy supply to each ridge is to be maintained then the convection cells will have to go along with the centres of the rifts and move apart in exact lock step with the rifts.
Im sure that Arthur would agree that it is the ridge that is in control and it is dragging this meek and mild convection cell across the face of the earth like a naughty child being pulled by the ear.
www.geo.ucalgary.ca /~duckwrth/tmpretic.html   (3974 words)

 Lobe cell convection and polar cap precipitation
The characteristic electric and magnetic field signature of lobe cells as observed by the low-altitude FAST satellite in 55 dawn-dusk passes are compared with Polar ultraviolet images of polar cap auroral activity.
Initial results from 34 events of UV image coverage suggest that there is an intimate coupling between the sunward convection flow of the lobe cell and transpolar auroral arcs or diffuse polar cap precipitation in ∼62% of these cases.
Moreover, the presence of lobe cells coincide with UV data intensifications in the premidnight 2000–2400 MLT sector and/or the postnoon 1500 MLT region in ∼59% of all cases with UVI coverage.
www.agu.org /pubs/crossref/2003/2002JA009725.shtml   (396 words)

 Explaining Earth's Magnetic Field and Oceanic Magnetic Banding
This could be due to the overall dimensions of the cell, the velocities of the flow rate, the proportion of ionized Iron present in the cell flow, or any of a number of other possible differences.
If either of the two source convection cells has a slight change of heat intake from the central heat source, or if ANY of a large number of parameters slightly changed, the magnetic field produced by that cell could change fairly quickly (in days, hours, minutes) by an amount of one part in ten thousand.
Since only a moderate variation of amount of ionized Iron being transported in that cell, or localized heat input to that cell, or the cell movement path is involved, such a change COULD occur during a very short period of time.
mb-soft.com /public/tecto2.html   (6880 words)

 [4.03] Sunspots and Giant-Cell Convection   (Site not responding. Last check: 2007-10-22)
Analogous to the superposition of the granular convection on the supergranular convection, the ~ 30,000 km diameter supergranules are superposed on these still larger giant cells.
Because the giant cells make up the large-scale end of a continuous power spectrum that peaks at the size scale of supergranules, it appears that the giant cells are made by the same mode of convection as the supergranules.
This, along with the long lives (weeks) of large sunspots, suggests that large sunspots sit in long-lived, deep downflows at the corners of giant cells, and that the distance from leader to follower sunspots in large bipolar groups is the distance from one giant-cell corner to the next.
www.aas.org /publications/baas/v32n2/spd2000/6.htm   (324 words)

 Some unanswered questions [This Dynamic Earth, USGS]
While convective flow can be observed easily in a pot of boiling soup, the idea of such a process stirring up the Earth's interior is much more difficult to grasp.
Cold, denser material convects downward and hotter, lighter material rises because of gravity; this movement of material is an essential part of convection.
In addition to the convective forces, some geologists argue that the intrusion of magma into the spreading ridge provides an additional force (called "ridge push") to propel and maintain plate movement.
pubs.usgs.gov /publications/text/unanswered.html   (1495 words)

 Newton's Apple: Teacher's Guides
The energy is removed as heat by conduction, convection, and radiation.
Convection is the transfer of heat in fluids.
convection cell a circulatory flow of energy set in motion by unequal heating of a fluid
www.ktca.org /newtons/11/fire.html   (1148 words)

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