Origin and Structure of High-Level Cyclones South of the Maximum Westerlies

This study deals with a special type of cyclones formed in the belt of the upper westerlies. The development begins as wave-like deformation of the upper flow and this deformation increases in amplitude until the cold air in the southern part of the trough becomes separated from the cold air in the north. The process of separation may be described as a cutting-off of a cold vortex. The process is described in some detail for a special case. High-level cyclones formed in this manner are not rare: on the contrary, such upper air disturbances are of great importance for the weather phenomena in certain regions, especially at latitudes between 30°-50° N. They can also be regarded as an important link in the large-scale quasi-horizontal ineridional exchange of air masses.