Atmosphere spatial scales

Interferometry in astronomy is used to surpass the limitations on angular resolution set by the Earth s atmosphere (i. e., speckle interferometry), or by the diffraction of the aperture of a single telescope. We will focus in this lecture on interferometry with multiple telescope arrays with which it is possible to obtain information on spatial scales of the source beyond the diffraction limit of its member telescopes. 

Budgets and cycles can be considered on very different spatial scales. In this book we concentrate on global, hemispheric and regional scales. The choice of a suitable scale (i.e. the size of the reservoirs), is determined by the goals of the analysis as well as by the homogeneity of the spatial distribution. For example, in carbon cycle models it is reasonable to consider the atmosphere as one reservoir (the concentration of CO2 in the atmosphere is fairly uniform). On the other hand, oceanic carbon content and carbon exchange processes exhibit large spatial variations and it is reasonable to separate the... 

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

The motions on the largest spatial scales amount to the aggregate of the world s synoptic weather systems, often called the general circulation. Both with respect to substances that have atmospheric lifetimes of a day or more and with regard to the advection of water, it is useful to depict the nature of this general circulation. The mean circulation is described to some extent in terms of the Hadley and Ferrell cells shown in Fig. 7-4. They describe a coupled circulation... 

Mountain chains such as the European Alps constitute an important factor in atmospheric circulation [1]. They trigger a variety of climatic and meteorological effects and cover a wide range of the spatial scale [2]. For example, they are manifested in the modification of the inner-continental climate zones or in the small-scale distribution of precipitation. Both can be important for the hydrology of alpine catchments. 

In addition, the processes discussed in Sect. 2.2.1 are specifically modified in mountainous regions, where the influence of the relief on atmospheric circulation can be thermal, mechanical or a combination of the two [9]. [10] has broken down these effects using the spatial scale (Fig. 3). 

Fig. 3 Influences of mountains on atmospheric circulation - broken down according to spatial scale [10]...

Clearly, direct techniques for measuring OH are needed that provide concentrations either at a point or over relatively restricted spatial scales. Two (absorption and laser-induced fluorescence) are direct, spectroscopic methods and two others (mass spectrometry and a radiocarbon method) rely on conversion of OH to another species that is measured. Each of these approaches and some of the intercomparisons that have been carried out are discussed briefly in the following sections. A good overview of these methods is found in a review by Eisele and Bradshaw (1993) and articles by Crosley (1994, 1995a, 1995b) and papers in a special issue of the Journal of the Atmospheric Sciences [52 (19), October 1, 1995]. 

The relation between length and time scales of diffusion, calculated from the Einstein-Smoluchowski law (Eq. 18-8), are shown in Fig. 18.11 for diffusivities between 10 10 cm2s 1 (helium in solid KC1) and 108 cm2s (horizontal turbulent diffusion in the atmosphere). Note that the relevant time scales extend from less than a millisecond to more than a million years while the spatial scales vary between 1 micrometer and a hundred kilometers. The fact that all these situations can be described by the same gradient-flux law (Eq. 18-6) demonstrates the great power of this concept. 

While molecular diffusivity is commonly independent of direction (isotropic, to use the correct expression), turbulent diffusivity in the horizontal direction is usually much larger than vertical diffusion. One reason is the involved spatial scales. In the troposphere (the lower part of the atmosphere) and in surface waters, the vertical distances that are available for the development of turbulent structures, that is, of eddies, are generally smaller than the horizontal distances. Thus, for pure geometrical reasons the eddies are like flat pancakes. Needless to say, they are more effective in turbulent mixing along their larger axes than along their smaller vertical extension. 

Variability may be defined as reflecting fluctuations in the atmosphere, of natural origin, with both temporal and spatial scales examples are diurnal, seasonal, solar activity-related variations impulsive events such as volcano eruptions and solar proton events fluctuations linked to some peculiar meteorological conditions, for example, intense cyclonic activities and jet streams. Variability by itself is a whole program to be conducted ideally on a four-dimensional basis (latitude, longitude, altitude, and time) by space vehicles, for example, satellites or from the space shuttle. This area of research is certainly the most urgent one to be de-... 

Emissions of biogenic sulfur compounds to the atmosphere result from an imbalance between metabolic formation processes and biological or physicochemical consumption processes, determined on the spatial scale of the available methods for measuring emission fluxes. Variability in emissions... 

The critical need to achieve high signal-to-noise ratios for spatially resolved measurement of several free radicals has spawned a number of research efforts aimed at improving our ability to observe such radicals as OH, HO2, NO, NO2, etc., with orders of magnitude better sensitivity than was previously available. A major impetus behind this research has been the realization that atmospheric variability on the spatial scale of a hundred meters in the vertical drives fluctuations in several of the key reactiye species, which provide ample concentration variation to carry out covariance studies to establish cause and effect within subsets of free radical reaction sets. 

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