A Case Study of an Easterly Jet Stream in the Tropics

An easterly current at 200 mb over the Southern Bahamas and Florida is identified as a jet stream which had originated in middle latitudes and had travelled along the eastern periphery of the dynamic anticyclone situated over the South Eastern United States. The properties of this current are studied and compared with those associated with middle latitudes jet streams. It is found that although this current is comparatively weak (core velocity about 70 kts), horizontal and vertical wind shears near its axis are comparable with those observed near the usually much stronger middle latitudes jet streams.

The mechanism responsible for the concentration of the kinetic energy in this narrow current is shown to be independent of any temperature contrast between two air masses in the lower and middle troposphere. The jet is further shown to be maintained by pressure heads and the continuous production and destruction of kinetic energy involved in its maintenance and motion occur as a result of accelerations in more or less laminar flow rather than by lateral or frictional stresses. Finally, the observed weather distribution is found to be influenced by the resonance and interference of the upper jet stream with waves in the lower easterlies.