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The vertical motion field in the thermosphere is calculated from the continuity equation. This calculation is based on a field of horizontal winds and an intermediate model of the thermospheric temperature field consistent with the density structure inferred from satellite drag data. The vertical motion consists of a component due to rise and fall of constant pressure surfaces and a component due to horizontal maas divergences, both components being of the order of 1 m. sec.−1 Only the latter component is of importance for thermodynamic considerations. The adiabatic warming associated with the diurnally variable part of the vertical motion due to mass divergence gives a second heat source which is of magnitude comparable to the heating by solar radiation. The time-averaged meridional circulation also implies large adiabatic warming and cooling. This computed mean meridional circulation cannot be reconciled with the heat balance of the thermosphere. The thermospheric temperature field at low levels in high latitudes can be changed so as to reverse the direction of the mean meridional pressure gradient and thus to give a mean meridional circulation consistent with heat balance considerations. Existing global thermospheric models could be improved by adjustment of the temperature field at low levels in such a way that vertical motions computed from horizontal winds give a plausible adiabatic heating field.

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Julio Buchmann
Jan Paegle
Lawrence Buja
, and
R. E. Dickinson


A series of experiments using real-data general circulation model integrations is performed to study the impact of remote tropical Pacific heating modifications upon the rainfall over the Amazon Basin. In one set of experiments, a heating term is added to the thermodynamic equation in the western tropical Pacific Ocean, and in the second set, the sea surface temperatures are cooled in the eastern Pacific Ocean. The rainfall of northern sections of South America decreases in the first set of experiments and increases in the second set of experiments. Examination of the circulation changes for the second set of experiments suggests that the remote links occur through equatorially trapped flow modifications, perhaps related to the east-west Walker cells, rather than through midlatitude teleconnections via Hadley cells. The time evolution of these patterns suggests them to be clearly relevant for medium range weather prediction in the tropics.

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