Wind speed gradient

As a consequence of the very rough surface of a coniferous canopy (which in no way approaches a plane structure) thermal fluxes from these surfaces are relatively small ie. forest canopy surfaces are relatively cooler than the surfaces of farm crops (18). The spire like structure of the crown result in daytime temperature gradients immediately above the canopy surface which are small and wind speed gradients which are relatively large. It should he anticipated that buoyant (free convective) eddies generated by vertical temperature gradients will be relatively unimportant and that wind speed gradients will provide the major source of eddy currents. 

Finally, applying sitrface-layer similarity, the wind speed gradient of (5) can be generalized into... 

Fig. 17-13. Balance of forces resulting in gradient wind around high pressure. Note that the wind speed is greater for a given pressure gradient force than that around low pressure.

Fig. 3.8. The pattern of a cloud is decided by the temperature and its gradient, T() > Tx > T2. the wind speed, and gravity.

The Monin-Obukhov length L is not a parameter that is routinely measured. Colder (1972), however, established a relation between the stability classes of Pasquill, the roughness height zo (see Section VII,B), and L. The results of his investigation are shown in Fig. 4. Alternatively, the local wind speed and cloud cover measurements are used to estimate the Pasquill stability class (Table IV). In addition, Colder developed a nonogram for relating the gradient Richardson number R-, to the more easily determined bulk Richardson number / (, ... 

Velocity and temperature gradients are confined to the surface layer defined by z < I-. Above L the wind velocity and potential temperature are virtually uniform with height. Venkatram (1978) has presented a method to estimate the value of the convective velocity scale w,. On the basis of this method, he showed that convective conditions in the planetary boundary layer are a common occurrence (Venkatram, 1980). In particular, the planetary boundary layer is convective during the daytime hours for a substantial fraction of each year ( 7 months). For example, for a wind speed of 5 m sec , a kinematic heat flux Qo as small as O.PC sec can drive the planetary boundary layer into a convective state. 

Gradient diffusion was assumed in the species-mass-conservation model of Shir and Shieh. Integration was carried out in the space between the ground and the mixing height with zero fluxes assumed at each boundary. A first-order decay of sulfur dioxide was the only chemical reaction, and it was suggested that this reaction is important only under low wind speed. Finite-difference numerical solutions for sulfur dioxide in the St. Louis, Missouri, area were obtained with a second-order central finite-difference scheme for horizontal terms and the Crank-Nicolson technique for the vertical-diffusion terms. The three-dimensional grid had 16,800 points on a 30 x 40 x 14 mesh. 

Air-sea exchange processes are consequently dependent upon the concentration gradient and the transfer velocity. The transfer velocity is not a constant, but rather depends upon several physical parameters, such as temperature, wind speed and wave state. The exchange can also be attenuated by the presence of a surface film or slick. Alternatively, the exchange can be facilitated by bubble formation. The concentration... 

Fig. 13.1 Observations black) and model forecasts of NO2, wind speed, 2 m temperature and wind direction left), and forecast error for NO2, wind speed and 2 m temperature right) at observation site Valle Hovin. Forecasts dotted) and observations solid) of vertical temperature gradient 2-25 m bottom right) (from 0degaard et al. 2004)...

Under the range of wind speeds and temperature gradients available in Florida, we compared, side by side, our gustiness meter with the British bivane in the Bushnell meadows and forest. Also we made these comparisons at Rosamond Dry Lake. At all of these sites and with large scatter of points, we found that standard vertical width of the bivane record multiplied by the numerical factor of 0.23 was equal to our measured vertical gustiness ... 

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