Tropical forcing of atmospheric motions in a numerical model

Abstract

AbstractThe effects of tropical forcing on the atmosphere have been isolated in two general‐circulation models – one hemispheric, one global – by eliminating other zonally asymmetric forcing such as mountains and extratropical ocean/land thermal contrasts. Tropical surface temperatures were found to force upper tropospheric geopotentials in the tropics and geopotentials throughout the troposphere in middle and high latitudes with little scale dependence up to about wavenumber 5. In the hemispheric experiment the tropical forcing generated Rossby–Haurwitz waves similar to tesseral harmonics with 3 or 5 nodes between the poles; the associated phase agreement between tropical forcing and the tropical and extratropical response was also a dominant feature of the global experiment despite the more complicated structure of the forcing field. Some aspects of the results are explicable by wave propagation theory including a strong dependence on wavenumber of the geopotential response in the tropical lower troposphere.