Rapid Cyclogenesis
Rapid Cyclogenesis describes a very fast and intensive development of an Occlusion cloud spiral from a low level cloud head. Upper air processes are driving factors in such a development.
Rapid Cyclogenesis (RaCy) describes the development of a cloud head located on the pole ward side of a frontal zone into a cyclonic cloud spiral. The life cycle of this mechanism ranges from 6 to 48 hours. While classical cyclogenesis through Wave development is often slow and the Wave bulge dissolves after some time or produces a spiral after some days, Rapid Cyclogenesis usually leads to a fast development of a cloud spiral. Comparing again Wave development and Rapid Cyclogenesis, a main difference can be found in the orientation of the relative stream forming the cloud head, or cloud bulge. It is similar to a Warm Conveyor Belt in the case of the Wave turning to east/north-eastern direction, but quite opposite in the case of Rapid Cyclogenesis turning to west/south-western directions. While in the case of Wave development stratospheric air (if present at all) does not reach down to levels lower than 300 hPa, in the case of Rapid Cyclogenesis stratospheric air is a key feature and protrudes much further downward (down to approximately 500 hPa or even lower).