On the Angular Momentum Balance in the Equatorial Trough Zone of the Eastern Hemisphere

A study has been made of the conditions for seasonal balance of zonal angular momentum, during Southern summer, in the troposphere overlying the equatorial (monsoonal) Westerlies. The observational data are not adequate to determine the finer details of balance. It is shown that by and large it can be accounted for by zonal pressure gradients and meridional transport of Earth’s angular or Ω-momentum (a Coriolis effect). Zonal and meridional stresses due to advective and eddy transports of relative zonal or ū-momentum as well as the surface frictional stresses are of considerably smaller magnitude. This confirms for a monsoonal region the conclusions of Palmer (1958), from observations in the North Pacific in June, that quasi-geostrophic equilibrium occurs down to very low latitudes above the planetary friction layer.

The high-level easterly jet stream is shown to play an important part in two aspects of balance.