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The general circulation of the atmosphere
By S. Tibaldi* and R
Mureau
* Current address: University of Bologna,
Department of Physics, Via Imerio 46, 40126 Bologna, Italy
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6 Summary and conclusions
The latitudinally dependent solar input establishes thermal gradients between poles and equator. Such gradients will result in pressure gradients and therefore in atmospheric motions. The atmosphere is rapidly rotating so that geostrophic balance will approximately establish. Together with hydrostatic balance, they will initially set up a Hadley-type symmetric circulation in thermal wind balance. This circulation, however, will never be observed in reality because it is baroclinically unstable and because mountains and land-sea contrasts will generate eddies. Such eddies make the pole-to-equator heat transport more efficient and decrease the thermal gradients. Eddies, however, transport momentum as well, both vertically and latitudinally. The spatial structure of the eddy/mean-flow interactions is such that regions of enhanced (or decreased) zonal flow are created due to either north-south or vertical convergence (or divergence) of eddy momentum flux. Such regions are the so-called jet streams. The subtle relationships between the eddies and the mean flow govern, therefore, the observed climate and are a crucial benchmark test for diagnosing systematic model deficiencies.
Figure 8 . The northward transport of energy (in units of petawatt = 1015 W) as a function of latitude. The outer curve is the net transport deduced from radiation measurements. The white area is the part transported by the atmosphere and the shaded area the part transported by the ocean. The lower curve denotes the part of the atmospheric transport due to transient eddies and is the mean of the monthly values from Oort (1971, Table 3). The horizontal scale is such that the spacing between latitudes is proportional to the area of the earth's surface between them, i.e. is linear in the sine of the latitude.
(a)
Figure 9 (a) Mean 500 hPa height field for the winter of 1985/86. (b) High-pass filtered variance of the 500 hPa height field for the same winter. (c) Low-pass filtered variance.
(b)
(c)
Figure 0 . Continued
Figure 10 . Probability density estimates for the detrended combined amplitude of the first five EOFs derived from two different subsamples: (a)1953-1968; (b)1969-1984.
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07.06.2002 |
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