Atmosphere horizontal motion

In the real atmosphere horizontal motions along latitude and longitude must also be taken into consideration. Thus, the ozone concentration profile should show a significant derivation near the tropopause due to the downward transport of 03 from the expected profile without vertical eddy diffusion. 

So far in discussing motion in the atmosphere, we have been emphasizing only horizontal motions. Although of much smaller magnitude than horizontal motions, vertical motions are important both to daily weather formation and to the transport and dispersion of pollutants. 

The horizontal motion of the atmosphere (or wind) is characterized by four spatial scales. These, with their conventional names, are ... 

Horizontal motion of the atmosphere, or wind, is a response of the air to the forces that are present. These include the force due to the pressure gradient, the Coriolis force associated with the rotation of the Earth, and frictional forces acting to retard any motion. If the acceleration of the air mass and frictional effects are small, the horizontal velocity is described by the following expression ... 

Table 1-8. Time Constants for Horizontal and Vertical Transport by Atmospheric Mean Motions and Eddy Diffusion11... 

The system of equations of horizontal motion [Eqs. (9) and (10)], hydrostatic equilibrium [Eq. (16)], mass continuity [Eq. (12)], thermodynamics [Eq. (8)], and the ideal gas law [Eq. (7)] is called the hydrostatic prediction model, or primitive equations. The hydrostatic assumption modifies the basic atmospheric prediction system in such a way as to eliminate the vertical propagation of sound waves. 

Wind speed has velocity components in all directions so that there are vertical motions as well as horizontal ones. These random motions of widely different scales and periods are essentially responsible for the movement and diffusion of pollutants about the mean downwind path. These motions can be considered atmospheric turbulence. If the scale of a turbulent motion (i.e., the size of an eddy) is larger than the size of the pollutant plume in its vicinity, the eddy will move that portion of the plume. If an eddy is smaller than the plume, its effect will be to difhise or spread out the plume. This diffusion caused by eddy motion is widely variable in the atmosphere, blit even when the effect of this diffusion is least, it is in the vicinity of three orders of magnitude greater than diffusion by molecular action alone. 

The atmosphere is nearly always in motion. The scales and magnitude of these motions extend over a wide range. Although vertical motions certainly occur in the atmosphere and are important to both weather processes and the movement of pollutants, it is convenient to consider wind as only the horizontal component of velocity. 

The vertical motion of the plume to the height where it becomes horizontal is known as the plume rise, (refer back to Figure 1). The plume rise is assumed to be a function primarily of the emission conditions of release, (i.e. velocity and temperature characteristics). A velocity in the vertical plane gives the gases an upward momentum causing the plume to rise until atmospheric turbulence disrupts the integrity of the plume. At this point the plume ceases to rise. This... 

In natural systems (lakes, oceans, atmosphere) turbulent diffusion is usually anisotropic (i.e., much larger in the horizontal than vertical direction). There are two main reasons for that observation (1) the extension of natural systems in the horizontal is usually much larger than in the vertical. Thus, the turbulent structures (often called eddies) that correspond to the mean free paths of random motions often look like pancakes that is, they are flat along the vertical axis and mainly extended along the horizontal axes. (2) Often the atmosphere or the water body in a lake or ocean is density stratified (i.e., the density increases with depth). This compresses the eddies even further in the vertical. Gravitational forces keep the water parcels from moving too far away from the depth where they are neutrally buoyant, that is, where they have the same density as their environment. Thus, the anisotropic shape of the eddies results in turbulent diffusivities which differ in size along different spatial directions. 

As Brenguier (2003) noted, a contributing factor to the uncertainty is drizzle in clouds that form in the atmospheric boundary layer (ABL). In particular, this circumstance illustrates the importance of the adequate retrieval of cloud cover dynamics in the ABL. Another problem is connected with consideration (parameterization) of small-scale processes in the ABL and their non-linearity. For instance, aerosols acting as cloud concentration nuclei (CCN) can be determined from upward motions at the cloud bottom which should be reproduced at a spatial resolution (in the horizontal) of the order of 100 m. The present parameterization schemes still do not meet these requirements. 

The second stage realizes a two-step procedure that re-calculates the ozone concentration over the whole space S = (tp, A, z) (, A)e l 0atmospheric boundary layer (zH 70 km), whose consideration is important in estimating the state of the regional ozonosphere. These two steps correspond to the vertical and horizontal constituents of atmospheric motion. This division is made for convenience, so that the user of the expert system can choose a synoptic scenario. According to the available estimates (Karol, 2000 Kraabol et al., 2000 Meijer and Velthoven, 1997), the processes involved in vertical mixing prevail in the dynamics of ozone concentration. It is here that, due to uncertain estimates of Dz, there are serious errors in model calculations. Therefore the units CCAB, MFDO, and MPTO (see Table 4.9) provide the user with the principal possibility to choose various approximations of the vertical profile of the eddy diffusion coefficient (Dz). 

As an example, let us now examine the specific case of particle motion at 25°C and atmosphere pressure. The related physical properties are dp = 0.001 m, pp = 1000 kg-nf p, = 1.145 kg-in. and pg = 1.798 Pa s. The calculated values for the terminal velocity and the operational condition ranges are given in Table 2.2. An important conclusion that can be drawn from the data listed in the fourth column of Table 2.2 is that the Stokes regime cannot exist in co-axial horizontal impinging streams while other regimes are applicable in this kind of impinging stream. 

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... 

On a large scale, particles (as well as gases) are moved through the atmosphere by advection and turbulence, i.e., horizontal and vertical winds (Wexler et al. 1994 Seinfeld and Pandis 1998). Simultaneous with these large-scale motions are the smaller-scale processes that can transport particles across surface boundary layers (e.g., at the Earth s surface) and thus remove them. As discussed earlier, diffusion is the dominant removal mechanism for small particles because of their high diffusion coefficients and low gravitational settling velocities. Because of their very small sizes, nanoparticles can slip... 

The atmospheric boundary layer (ABL) is that portion of the atmosphere where surface drag due to the motion of the air relative to the ground modifies synoptic-scale motions caused by horizontal pressure gradients, Coriolis forces, and buoyancy. The depth of the ABL is highly variable (50 to 2000 m), but it generally increases with proximity to the equator, with wind speed, and as the earth surface roughness, but it decreases... 

Figure 3 shows the typical shape of a smoke-plume in a stable atmosphere. In this case, there is a vertical temperature gradient such that the air aloft is hotter and less dense then the air near the ground - a so-called temperature inversion - and the resulting absence of ambient vertical motion causes the plume to fan out under the influence of the prevailing horizontal airflow. In comparison with its profile for neutral stability, the flattened cone of the stable-atmosphere plume may be supposed to retain a... 

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