Horizontal winds

Brookhaven Gustiness Classes (Based on Variations of Horizontal Wind Direction over 1 Hr at the Height of Release)... 

Intensity of turbulence These factors, represented by the standard deviations of the horizontal wind direction, Og, the standard deviation of the vertical wind component, a, and the gustiness as measured by the standard deviation of the wind speed, all have significant bearing on the dispersion of emissions from a stack. 

It is known that the vertical distribution of diffusing particles from an elevated point source is a function of the standard deviation of the vertical wind direction at the release point. The standard deviations of the vertical and horizontal wind directions are related to the standard deviations of particle concentrations in the vertical and horizontal directions within the plume itself. This is equivalent to saying that fluctuations in stack top conditions control the distribution of pollutant in the plume. Furthermore, it is known that the plume pollutant distributions follow a familiar Gaussian diffusion equation. 

Even though upward motion causes cooling of a parcel of air, the condensation of water vapor can maintain the temperature of a parcel of air above that of the surrounding air. When this happens, the parcel is buoyant and may accelerate further upwards. Indeed, this is an unstable situation which can result in violent updrafts at velocities of meters per second. Cumulus clouds are produced in this fashion, with other phenomena such as lightning, heavy precipitation and locally strong horizontal winds below the cloud (which provide the air needed to support the vertical motion). 

In Fig. 14.1 (top panel) the impact from the initialization on the horizontal winds is illustrated. The modifications are generally less than 0.1 m/s and over large areas less than 0.02 m/s, both for hydrostatic and non-hydrostatic data. The corrections are thus small and could not be expected to violate the general flow pattern. Note that the corrections seem to be very small in relation to the corresponding errors in Fig. 14.1 (middle and bottom panels), which is a bit misleading as the latter results from integrated errors. 

The horizontal wind components, potential temperature and specific humidity are used in METRAS as forcing fields. Changes in the scalar quantities temperature and humidity are mainly induced by advection and diffusion, i.e. processes that depend on the wind. Therefore, we define the conditions for writing the model results only in dependence of changes in the horizontal wind components. The model results were alternatively written at regular intervals (3 h, 6 h), if the... 

Success of the Reel Down approach hinges on the stability of the system under stratospheric conditions (characterized by low pressures, but potentially large horizontal wind fields). Oscillatory motion developed in any axis of the suspended experiment cluster can compromise experimental control and thus the quality of the observations. A prototype system was constructed to test the feasibility of such a system in the stratosphere. Technical details are described in detail elsewhere [19]. 

Since horizontal transport across the boundaries of the column is neglected and since it moves with the average ground-level horizontal wind velocity, the column may be mathematically represented as a horizontally uniform but vertically non-uniform column with a time-varying source of pollutants at the base. Thus, the only independent variables are time t and vertical distance z. The concentration of species i at time t and height z in the column Ci z,t) (From this point on we use Ci to denote , the mean concentration of species i.) is determined by integration of the abridged form of (7),... 

The map preparation is a tedious, time consuming process. It is more convenient to calculate the horizontal wind components at a point interpolating field wind data. Wayne et al. (22), Wendell (76), and McCracken et al. (36) have adopted formulas of the form... 

Depending on its explosive yield, a nuclear test may introduce radioactive materials to various heights in the atmosphere. The lowest level of the atmosphere is the troposphere, in which turbulent air movements occur. In addition to prevailing horizontal winds, there is also considerable vertical motion as evidenced by clouds, rain and... 

Several peculiarities of real droplet layer media should be accounted for in the models. The most important feature is the ability of droplets to be drifted by the horizontal wind, while they fall vertically under the action of the gravitation force. It has been accounted for in the first model. 

Emeis, S., and Frandsen, S. (1993) Reduction of horizontal wind speed in a boundary layer with obstacles, Bound.-Layer Meteorol. v. 64,297-305. 

On the other hand, the effect of the wet removal can be practically neglected here.3 It is thus understandable that the residence time of trace constituents is greater in the stratosphere than in the troposphere. Above the tropopause the horizontal wind speed first decreases then increases with height. Consequently, a secondary maximum in the wind speed can be observed in this atmospheric layer. The increase of the temperature ends approximately at an altitude of SO km (stratopause), where the temperature is around 0 °C (see Fig. 1). Above this level, in the mesosphere, the temperature again decreases (third layer in the homosphere). For this reason the stratopause can be considered as an active heat-supplying surface similar to the Earth s surface. In this atmospheric region the distribution of the temperature makes possible the convection which, in favourable cases, results in a formation of so-called noctilucent clouds at an altitude of about 80 km (mesopause) where the temperature is only around — 80 °C. This is the coldest level of our atmosphere. 

One of the most important atmospheric dynamical quantities is the zonal wind (wind speed in the longitudinal direction). Wind velocities are conventionally positive for eastward winds (also called westerlies) and negative for westward winds (easterlies). They are mostly derived from the observed thermal structure of the atmosphere, although local values can be provided by radiosonde and radar measurements. To date, very few attempts have been made to directly measure the atmospheric wind components from space. The High Resolution Doppler Imager (HRDI) on board the Upper Atmosphere Research Satellite (UARS) has provided information on horizontal winds in the mesosphere/lower thermosphere (50-115 km) and in the stratosphere (10-40 km) by observing the Doppler shifts in the emission lines of an O2 atmospheric... 

Figure 3-4 Horizontal wind field at 25 km altitude measured by the UARS/HRDI instrument on 8 March 1994. From Ortland et al. (1996).

Boundary layer conditions are called labile when convection predominates in the vertical air exchange stable when the vertical air motions are dampened, such as by a temperature inversion and indifferent or neutral when the vertical turbulence is induced solely by the horizontal wind field. In the last case, the horizontal wind speed is generally found to increase with height in accordance with a logarithmic function... 

Tiefenau, H. K., and P. Fabian (1972). The specific ozone destruction at the ocean surface and its dependence on horizontal wind velocity from profile measurements. Arch. Meteorol. Geophys. Bioklimatol. Ser. A 21, 399-412. 

We have seen that the horizontal wind components in the atmosphere obey the geostrophic equations ... 

Rjj = horizontal wind reaction, or shear, at the base of the tower, lbs. 

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