The vertical structure of the barotropically unstable wave in a tropical easterly current is studied by solving linearized quasi-geostrophic equations numerically. An easterly current with a sine-profile jet is assumed to exist in a belt between 5N and 25N with a maximum velocity of 10m sec-1. The vertical shear of the easterly current and surface friction are taken into account. It is found that the vertical structure in the lower troposphere represents some features of the easterly wave such as eastward tilt of the trough axis, upward motion located to the east of the trough and negative correlation between upward motion and temperature. While surface friction is an indispensable factor to these features, the vertical shear and the decreasing hori-zontal shear with respect to height in the lower troposphere act to suppress them. As suggested in a previous paper (Yamasaki and Wada, 1972), an extremum of frictional convergence is located to the east of the trough in a region where Z (meridional gradient of the absolute vorticity of an easterly current) around 900mb is negative, and another extremum is located slightly to the west of the trough in a region of positive Z.
The effect of parameterized convection on the barotropic unstable wave is also discussed.