Zonal circulation

Rossby C.-G. (1939). Relation between variations in the intensity of the zonal circulation of the atmosphere and the displacements of the semi-permanent centers of action. J. Marine Research, 2, 38-55. 

The results showed that the decrease in frequency and intensity of MBls since the mid-1970s and the complete absence of such events between February 1983 and January 1993 can probably be attributed to increased zonal circulation, resulting in both intensified precipitation in the Baltic region and increased river runoff (cf. also Schinke and Matthaus, 1998). These results were confirmed by model simulations carried out by Meier and Kauker (2003). 

Fig. 1-6. Mean zonal circulation in the northern hemisphere, 0-20 km. Distribution of wind velocities (in units of m/s) was taken from Labitzke (1980). W, Mean winds from the west E, mean winds from the east the heavy lines indicate the approximate location of the polar front, the broken lines the tropopause. The maximum wind speed coincides approximately with the subtropical jet stream. The location of the polar jet fluctuates considerably and does not show up in the average. The center is to illustrate wind directions near the earth surface (trade winds and westerlies) cyclones (C) and anticyclones (A) imbedded in the westerlies are only sketched the frontal systems associated with cyclones cannot be shown in this extremely simplified diagram.

Evidence for the second viewpoint comes from measurements of longer-lived radionucleides within the radium decay sequence, specifically bismuth-210 and lead-210. The major routes for nuclei conversion within the radium decay scheme are shown in Fig. 7-27. The direct decay product of radium-226, an alpha-emitter, is radon-222, which escapes the Earth surface. Only the continents are a source the contribution from the oceans is negligible. Since the half-life time of radon-222 is only 3.8 days, its distribution in the troposphere is rather uneven. Over the continents the mixing ratio declines with increasing altitude (see Fig. 1-9). Over the oceans, the vertical gradient is reversed, as the oceans act as a sink and the zonal circulation keeps supplying material from the middle and upper troposphere. The immediate... 

A zonal circulation of the atmosphere confined to equatorial regions and driven principally by the oceanic temperature gradient. In the Pacific, air flows westward from the colder, eastern area to the warm, western ocean, where it acquires warmth and moisture and subsequently rises. A return flow aloft and subsidence over the eastern ocean complete the cell, water stress effect... 

Because at higher latitudes the coriolis force deflects wind to a greater extent than in the tropics, winds become much more zonal (flow parallel to lines of latitude). Also in contrast to the persistent circulation of the tropics, the mid-latitude circulations are quite transient. There are large temperature contrasts, and temperature may vary abruptly over relatively short distances (frontal zones). In these regions of large temperature contrast, potential energy is frequently released and converted into kinetic energy as wind. Near the surface there are many closed pressure sys-... 

There is a zonal atmospheric circulation system associated with this normal ocean condition called the Walker Cell (Eig. 10-7). Evaporation rates are high over the warm pool and warm moist air ascends to great heights (deep convection) producing extensive cloud systems and rain. The Walker Cell is closed by westerly winds aloft and subsidence in the high-pressure zone of the eastern Pacific. 

In winter (December), a zonal (western) circulation prevails in the stratosphere at moderate latitudes. In January and February, the circulation in the stratosphere is unstable, and the meridianal transference prevails over the zonal one (Stolypina, 1981). This is, because the circumpolar cyclonic whirlwind shifts to the south, the Pacific maximum shifts to the north, and both of them become immobile. An inerease in the height of SA maximum location and in the maximum optieal thiekness is observed (Chen and Lelevkin, 2000). 

It is important to note that the diabatic circulation can be estimated from the thermodynamic and continuity equations only if the temperature distribution is known a priori. However, a fully self-consistent mean meridional circulation can be obtained when the momentum budget is considered together with the thermodynamic and continuity equations. When transformations (3.64a, b) are applied to the zonal mean equations (3.53-3.60), the solution of the following momentum, continuity, and thermodynamic equations defines the transformed Eulerian mean (TEM) or residual circulation (here expressed in log-pressure coordinates) ... 

Equations (3.67) to (3.69) show that, in a hypothetical case where the effects of wave transience and dissipation are ignored (Gu and G = 0) in both the thermodynamic and momentum equations and steady state is assumed, the atmosphere would eventually reach a radiative equilibrium, corresponding to a temperature distribution similar to that displayed in Figure 3.31. In this case, the residual circulation (v, w ) would vanish and the temperatures would be quite different from those observed, particularly at the tropical tropopause and in the mesosphere. At the same time, zonal winds would be considerably faster than are observed with a particularly strong polar vortex during winter. 

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