Processes Contributing to the Rapid Development of Extratropical Cyclones

The study of extratropical cyclones has provided the basis for vigorous scientific debates within the meteorological community for at least the past 150 years. In her monograph entitled The Thermal Theory of Cyclones: A History of Meteorological Thought in the Nineteenth Century, Kutzbach (1979) documents the interest of the leading European and American meteorologists of the 19th and early 20th centuries in providing a description of the weather and airflow associated with cyclones and identifying the physical processes that contribute to their development. In the 19th century, the emergence of the so-called “thermal theory of cyclones” (see Fig. 6.1) was based, to a large degree, on the work of Espy, who believed that the decrease of surface pressure in storms is related primarily to the release of latent heat in the ascending air near the storm center. By the early 20th century, the theoretical work of Margules and V. Bjerknes and the observational studies by Dines (which indicated extratropical cyclones were cold core systems) led to a more dynamically based perspective on cyclogenesis. The energy conversions and low-level convergence associated with instabilities in regions marked by significant temperature gradients (especially in the lower troposphere) were recognized as important contributing factors in the development of extra tropical storms.