Using rotated principal component analysis, 200mb wind data from the First GARP Global Experiment are analyzed in the East Asia winter monsoon region. It is found that there exist slowly eastward-moving disturbances with a wind-speed maximum embedded in the jet stream (jet streak). The implied vertical circulation that is transverse to the jet streak is thermally direct in the entrance region of jet streak and thermally indirect in the exit region. The Lagrangian momentum equation for transient part of the flow indicates that the magnitude of westerly acceleration of an air parcel moving through the jet streak is related to the Coriolis acceleration of the transient ageostrophic flow, the advection of mean momentum by transient flow and momentum conversion between mean and transient flow due to transient eddies. Estimates of terms in this equation in the entrance region of jet streak suggest that the increase of westerly momentum due to the Coriolis acceleration of the ageostrophic flow is mostly balanced by the decrease due to the mean easterly momentum advection by the transient jet-streak flow. Thus, the confluence theory of Namias and Clapp (1949) appears to be valid for the slowly moving jet streaks in the East Asia jet stream. / Graduation date: 1989