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JOSEPH SELA
and
A. WIIN-NIELSEN

Abstract

A two level quasi-geostrophic model for zonally averaged conditions has been integrated for a period of a few years. The model is forced by Newtonian heating and has internal and surface friction. The interaction between the zonal flow and the eddies is simulated through the use of exchange coefficients for the transports of quasi-geostrophic potential vorticity and sensible heat.

The results of the integrations show that the model predicts a qualitatively correct annual variation of the zonal winds and the zonal temperature, although the predicted annual cycle has a too large amplitude compared with observations. The times of the maximum amounts of available potential and kinetic energy are well predicted as well as the typical time lag between the two quantities. The same statement holds for the generation of zonal available potential energy and the dissipation of zonal kinetic energy. The energy diagram obtained as an average for 1 yr of integration compares well with the corresponding diagram based on observations.

The major weakness of the model (i.e., the large annual variation of most quantities) is probably related to the simplicity of the thermal forcing.

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JACQUES DEROME
and
A. WIIN-NIELSEN

Abstract

The middle-latitude standing wave problem is investigated by means of a quasi-geostrophic, linear, steady-state model in which the zonal current is perturbed by the lower boundary topography and by a distribution of heat sources and sinks. All the perturbations are assumed to have a single meridional wavelength and the dissipation is considered to take place in the surface boundary layer using, as a first approach, a horizontally uniform drag coefficient.

After investigating some basic properties of the model atmosphere, some computations are made to determine its response to the combined forcing by topography and by diabatic heating for January 1962. The resulting perturbations are found to be in rather good agreement with the observed standing waves. The results also indicate that the standing waves forced by the topography are in about the same position as those forced by the diabatic heating and that the former have somewhat larger amplitudes than the latter.

The effect of allowing the drag coefficient to have one constant value over the continents and a smaller constant value over the oceans is examined and found to be quite important when the ratio of the two values is 6, but small (yet such as to bring the computed and observed eddies into closer agreement than in the case of a uniform drag coefficient) for a ratio of 2.

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A. WIIN-NIELSEN
and
MARGARET DRAKE

Abstract

The energy conversion between the vertical shear flow and the vertical mean flow has been computed using atmospheric data from the isobaric surfaces: 850, 700,500, 300, and 200 mb. In comparison with earlier calculations based on a smaller vertical resolution (2 levels) and a smaller sample, it is found that the new calculations give larger numerical values in better agreement with the results of numerical experiments concerning the general circulation of the atmosphere. The energy transformation has been computed in the wave number regime, and it is found that the medium-scale waves are responsible for the major portion of the transformation.

The amounts of energy in the baroclinic component (the vertical shear flow) and the barotropic component (the vertical mean flow) have been computed as a function of wave number. It is found that the kinetic energy in the barotropic component is about 2.6 times the kinetic energy in the baroclinic component. The partitioning of the kinetic energy between the zonal flow and the eddies is such that the eddies contain more energy than the zonal flow. This result applies for the vertical shear flow as well as the vertical mean flow and is in contrast to the results obtained from numerical experiments regarding the general circulation.

The present computations include only the energy calculations which would be present in a quasi-non-divergent model. Later calculations will provide estimates of the remaining term of the energy conversion.

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A. WIIN-NIELSEN
and
MARGARET DRAKE

Abstract

The contribution from the divergent part of the horizontal wind to the energy conversion between the vertical shear flow and the vertical mean flow has been computed using atmospheric data from the isobaric surfaces: 850, 700, 500, 300, and 200 mb. The new calculations supplement earlier computations giving the energy conversion based on an assumption that the horizontal winds are non-divergent.

It is found that the contribution from the divergent part of the horizontal wind normally is very small compared with the contribution from the non-divergent part. The former energy conversion is as a matter of fact generally not significantly different from zero.

The abnormal winter 1962–63 has been investigated separately. It is found that energy conversion by the divergent wind component during this period was much larger and constituted a larger fraction of the total conversion than during any other period.

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A. WIIN-NIELSEN
and
MARGARET DRAKE

Abstract

The total kinetic energy in the atmosphere has been subdivided into four energy reservoirs. The partition of the kinetic energy is accomplished by dividing the total flow into the vertical mean flow (the barotropic con ponent) and the vertical shear flow (the baroclinic component). Each of these components is subdivided into the zonal components and the eddy components.

The complete energy exchange diagram is derived by dividing a given energy conversion into the contribution from the quasi-non-divergent flow and the contribution from the divergent flow. Such a subdivision of the energy conversion is advantageous because the calculations are based on geopotential data.

Calculations have been carried out for five months (January, April, July, October 1962 and January 1963) based on five isobaric surfaces (20, 30, 50, 70, and 85 cb.). The complete energy diagrams are presented for each month together with an averaged diagram representing the annual mean. The results obtained for the four months in 1962 are in good agreement with each other showing not only the same directions of the energy conversions but also a marked annual variation for the major, non-divergent conversions generally with a minimum during the summer season.

The annual mean diagram is compared with the mean diagram obtained in a numerical simulation of the atmospheric general circulation. Good agreement is found in most energy conversions with two major exceptions. The results in the observational study which depend entirely on the mean meridional circulation suffer from the fact that the present data can not give a true picture of the Hadley circulation in the low latitudes. The energy conversion which depends entirely on the eddies is larger in the observational study than in the experimental study. The reason for this discrepancy is ascribed to the lower intensity of the eddies in the experimental study and, in particular, to the lack of energy on the planetary scale in the general circulation experiment.

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