Mid-latitude Cyclones Chapter 10 Mid-latitude Cyclones

Bergen school - Vilhelm Bjerknes: The Polar Front Theory was postulated in the early part of the twentieth century to describe the formation, development, and dissipation of mid-latitude cyclones. Mid-latitude cyclones are large systems that travel great distances and often bring precipitation and sometimes severe weather to wide areas. Lasting a week or more and covering large portions of a continent, they are familiar as the systems that bring abrupt changes in wind, temperature, and sky conditions.

divides the circulation of each hemisphere into three distinct cells: From Chapter 8 The three-cell model divides the circulation of each hemisphere into three distinct cells: the heat-driven Hadley cell that circulates air between the Tropics and subtropics, a Ferrel cell in the middle latitudes, and a polar cell.

As cyclogenesis begins, a “kink” develops along the boundary. Cyclogenesis is the formation of a mid-latitude cyclone. Initially, the polar front separates the cold easterlies and the warmer westerlies. As cyclogenesis begins, a “kink” develops along the boundary. The cold air north of the front begins to push southward behind the cold front, and air behind the warm front advances northward, creating a counterclockwise rotation around a weak low-pressure system.

Occlusion represents the end of the cyclone’s life cycle With further intensification, the low pressure deepens even further and distinct warm and cold fronts emerge from the original polar front. Convergence associated with the low pressure can lead to uplift and cloud formation, while linear bands of deeper cloud cover develop along the frontal boundaries. Occlusion represents the end of the cyclone’s life cycle and takes place as the center of the low pressure pulls back from the warm and cold fronts.

The figure depicts the typical structure of a mature cyclone and the processes causing uplift. Shaded areas represent the presence of cloud cover. The numbers represent an approximation of the precipitation probability.