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George P. Cressman
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George P. Cressman
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George P. Cressman
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president's page

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George P. Cressman
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George P. Cressman
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George P. Cressman

The development and motion of typhoon “Doris,” which was observed during the first two weeks of May, 1950, are studied. The development of the storm is examined with respect to previously published theories of storm formation. The original deepening occurred in the low latitude portion of an extended trough, after the fracture of the trough. This is in agreement with a model proposed by Riehl. The motion of the deepening storm relative to the high-level flow patterns differed from previously studied examples in that the deepening occurred as the low-level cyclone moved from under the west side of an upper anticyclone toward a position under an upper cyclone. The storm developed as two cyclonic vortices, which gradually merged into one, in agreement with a principle of Fujiwhara.

The motion of the storm northward, as it broke through the subtropical ridge line, is shown. After examination of several possibilities, this motion is attributed to the resultant of all the Coriolis forces acting on the storm, as discussed by Rossby. The suggestion is made that this resultant force becomes prominent in determining the motion of the storm due to changes in the radial velocity profile and the increasing geographical extent of the storm.

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Karl R. Johannessen
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George P. Cressman

A formula for the propagation of trough and ridge lines was tested on synoptic maps. It was found that it works best on the 500-mb chart. At this level the systematic error was found to be small for troughs (< 1 long.° per day) but considerable for ridges (+ 3 to +5 long. ° per day). However, the error scatter was about the same for troughs and ridges. It was found that computations of ridges over elevated terrain such as the Rocky Mountains region have a larger positive systematic error than ridges over flat country. This was not found to be the case for troughs. It is concluded that better results can be expected the closer the actual streamline pattern resembles the model for which the formula was derived.

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