Stable stratification

FIGURE 2-8 Density versus temperature curve for water. Maximum density occurs at 4°C thus, stratification in a lake can occur in winter with bottom waters near 4°C and less dense surface waters closer to 0°C. In summer, if stratification occurs, the warmer water will be at the surface. Note that a given spread in water temperature conveys a larger density contrast between the waters (and hence a more stable stratification) at higher temperatures than at lower temperatures. The density of ice is much less than the density of liquid water (note the broken scale for ice density). 

This type of stable stratification can also occur when warmer and thereby lighter air masses move over cold ground air. The heavier and often exhause gas polluted air can no longer exchange with the lighter air above it. This type... 

Turbulent flow in canopies on complex topography and the effects of stable stratification... 

The vertical structure of the ocean features a decrease of temperature with increasing depth and a correspondingly stable stratification. A shallow surface layer of 50-100 m thickness is vertically well mixed due to agitation by wind force. This portion represents only a small subvolume, but it is of crucial importance to the exchange of C02 with the atmosphere. Compared with the bulk of the ocean, the mixed layer responds quickly to changes in the atmosphere and it must be treated as a separate reservoir. The depth of the mixed layer is variable. We adopt the recommendation of Bolin et al. (1981) and use a value of 75 m. This is a seasonal average obtained by Bathen (1972) from measurements in the Pacific Ocean. 

In turbulent flow, stable stratification significantly damps turbulence and reduces heat transfer in the vertical direction. 

The accidental release of gaseous hydrogen or die spillage of liquid hydrogen leads to the evolution and dispersion of a gas cloud whose shape is influenced by the type and rate of release and by the atmospheric conditions as well as by topography. Liquid hydrogen at 20 K which immediately starts to vaporize upon release, behaves like a heavier-than-air gas in the very first phase ( cold sink effect ). This short phase of negative buoyancy with a reduced heat and mass transfer due to the stable stratification effects is replaced by an enhanced positive buoyancy as soon as, due to continuous air entrainment from outside into the gas cloud, the cloud temperature has been raised to > 22 K. The dilution... 

Planck hold that when R, < 0, stratified fluid is unstable stratification when R, = 0, sstratified fluid is homogeneous fluid when R, > 0, sstratified fluid is stable stratification when R,. > 2, turbulence is inhibited. In 1931, Taylor, after further analysis that the upper limit of stability of stratified fluid R(>1. 

From the direct numerical simulation of mixing layers with the code FLOW-SB, detailed flow and temperature information in space and time can be obtained. A iarge number of simulations was performed (at relatively low Reynolds number) in a wide Prandtl number (Pr) range (from 0.00535 for liquid sodium, to 6.9 for water), where the Richardson number (Ri) varies from 0.0 (no stratification) to 0.2 (close to critical, stable stratification). 

Stable 0 < Ri < 0.25 Mechanical turbulence weakened by stable stratification... 

The model applies a Gaussian plume model up to a specified transition distance, which is dependent on atmospheric stability 200 m for unstable, 500 m for neutral, and 1000 m for stable stratification, respectively. Outside this nearby zone, the gradient-transfer approach is used for computing the diffusion in the vertical direction. 

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