Jet stream in upper troposphere and cyclone formation

In this report, cases of relatively straight westerly flow aloft are investigated in an attempt to find criteria that indicate under what circumstances cyclone formation will take place along low‐tropospheric disturbances in such instances. It is found that pronounced cyclogenesis will occur mainly if the westerly current aloft is very strong and concentrated in a narrow latitudinal band, constituting a “jet stream.” The structure of the jet stream is discussed with particular emphasis on the tropopause region. Finally the suggested relation between jet stream and cyclone formation is illustrated with the period January 27 to 29, 1947.