Vertical mixing, atmosphere

From the viewpoint of air pollution, both stable surface layers and low-level inversions are undesirable because they minimize the rate of dilution of contaminants in the atmosphere. Even though the surface layer may be unstable, a low-level inversion will act as abarrier to vertical mixing, and contaminants will accumulate in the surface layer below the inversion. Stable atmospheric conditions tend to be more frequent and longest in persistence in the autumn, but inversions and stable lapse rates are prevalent at all seasons of the year. 

The resultant O3 layer is critically important to life on Earth as a shield against LTV radiation. It also is responsible for the thermal structure of the upper atmosphere and controls the lifetime of materials in the stratosphere. Many substances that are short-lived in the troposphere (e.g. aerosol particles) have lifetimes of a year or more in the stratosphere due to the near-zero removal by precipitation and the presence of the permanent thermal inversion and lack of vertical mixing that it causes. 

Atmospheric C02 equilibrates instantaneously with dissolved oceanic carbonates. Actually, Broecker and Peng (1982) show that the rate-limiting step for this process is vertical mixing in the ocean which takes place in approximately 1600 years. 

When the turbulence in the atmospheric boundary layer is maintained largely by buoyant production, the boundary layer is said to be in a convective state. The source of buoyancy is the upward heat flux originating from the ground heated by solar radiation. Convective turbulence is relatively vigorous and causes rapid vertical mixing in the atmospheric boundary layer. 

The atmosphere is complicated in other ways. The emission of primary pollutants occurs throughout the day and night (varying with time and location), adding to some of the previous day s well-aged pollutants. As the sun rises, the light intensity increases in a nonlinear fashion. The movement of air is important—vertical mixing and lateral transport from one community to another. With today s computers, it is now practical to construct a model that includes the detailed chemistry and all these variables. 

Wingenter, O. W M. K. Kubo, N. J. Blake, T. W. Smith, D. R. Blake, and F. S. Rowland, Hydrocarbon and Halocarbon Measurements as Photochemical and Dynamical Indicators of Atmospheric Hydroxyl, Atomic Chlorine, and Vertical Mixing Obtained during Lagrangian Flights, . /. Geophys. Res., 101, 4331-4340... 

Radioactive or stable isotopes of noble gases are also used to determine vertical turbulent diffusion in natural water bodies. For instance, the decay of tritium (3H)— either produced by cosmic rays in the atmosphere or introduced into the hydrosphere by anthropogenic sources—causes the natural stable isotope ratio of helium, 3He/ 4He, to increase. Only if water contacts the atmosphere can the helium ratio be set back to its atmospheric equilibrium value. Thus the combined measurement of the 3H-concentration and the 3He/4He ratio yields information on the so-called water age, that is, the time since the analyzed water was last exposed to the atmosphere (Aeschbach-Hertig et al., 1996). The vertical distribution of water age in lakes and oceans allows us to quantify vertical mixing. 

Fig. VIII-4. Nomenclature of the earth s atmosphere based on a temperature classification. The stratosphere is the region of temperature inversion, that is, the temperature increases with height and is stable against vertical mixing since dense cold air is at the bottom of the layer.

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). 

No simple correlation between chlorophyll a and DMS concentration exists in oceanic surface waters. However, average surface water DMS concentrations show relatively small variations over large extents of the oceans. The variations that are observed may be attributted to factors such as phytoplankton variability, seasonal changes in water masses, differences in vertical mixing in the water column, and ventilation of DMS to the atmosphere. 

The movement of atmospheric constituents within a region and between regions is a key process in atmospheric chemistry. For example, the transport of chemicals from the troposphere to the stratosphere sets off the depletion of ozone. Conversely, the downward transport from the stratosphere increases ozone in the troposphere. The phenomenon that most distinguishes the troposphere from the stratosphere is the rate of vertical mixing. The time scale for the vertical transport of air and other chemical species in the troposphere can be of a few hours, whereas vertical transport in the stratosphere can last months or years. 

Atreya S. K., Wong M. H., Owen T. C., Mahaffy P. R., Niemann H. B., de Pater I., Drossart P., and Encrenaz Th. (1999b) A comparison of the atmospheres of Jupiter and Saturn deep atmospheric composition, cloud structure, vertical mixing, and origin. Planet. Space Sci. 47, 1243-1262. 

Wingenter O. W., Kubo M. K., Blake N. 1., Smith T. W., Ir., Blake D. R., and Rowland F. S. (1996) Hydrocarbon and halocarbon measurements as photochemical and dynamical indicators of atmospheric hydroxyl, atomic chlorine, and vertical mixing obtained during Lagrangian flights. J. Geophys. Res. 101, 4331-4340. 

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