Secondary Low Centres in Occlusion Cloud Bands
Secondary Low Centres are small scale cloud vortices which develop within already mature Occlusion cloud bands.
Secondary Lows appear as a cloud vortex within the frontal cloud band. A Secondary Low often forms within a Neutral Occlusion, that is, the Occlusion is neither warm nor cold. In this type a strong jet runs over the Occlusion point. The low forms usually between the Occlusion point and the midpoint of the occluded Front. Nearly all Secondary Lows form in systems over the sea during the winter season. This follows from the fact that the basic westerly flow is stronger during the winter, and the deepening of a low is easier over the relatively warm water. Although the secondary lows are associated with strong jets, there seems to be no obvious connection to the conceptual model FI by Jet. The processes in the left exit region are involved in less than half of the cases. But if the left exit region is favourably situated in the vicinity of the occluded front, it can enhance the development. In the process of the secondary low development there is temporarily a back bent part in the occluded Front. However the situation differs to the common Back Bent Occlusion.