A numerical investigation of the connexion between two-dimensional momentum transfer and jetstream formation

Summary

When studying the problem of jetstream formation, the question should be investigated to what extent two-dimensional barotropic momentum transfer might be able to produce jetstream-like currents. Therefore we have performed numerical integrations of the shallow water equations on the sphere with Rossby-Haurwitz wave initial conditions given by ψ=a ²[−A ₀sin ϕ+Acos^mϕ sin ϕ cosmλ], i.e. a superrotation of the atmosphere with a superposed perturbation. The divergence in our model will produce perturbations about the neutral solution, moreover we have varied systematically the strength of the basic flow, represented byA ₀, so as to obtain insight into the flow pattern developing from the initial field under such interaction conditions.

Summing up the main results, we found that for relatively small initial zonal kinetic energy 0≤(A ₀/A)²<0.3 the development of the flow pattern is characterized by a northward transport of angular momentum; the convergence of this transport achieves the formation of jetstream-like currents within 2.5–4 days at 32°N, whereby most of the eddy kinetic energy is converted into zonal kinetic energy. If 0.3<(A ₀/A)²≤1, a southward transport of angular momentum is observed, the westwind maximum now located at 9°N; the energy conversion$\bar K_E \to \bar K_z$ is retarded, being completed after 5–6 days.