Upper Level Low
Cut off low in upper levels without corresponding surface low, accompanied by cloud bands at the boundaries and convective cloud in the low center.
Upper Level Lows are closed cyclonically circulating eddies. As these lows are only upper and mid-tropospheric features, they do not have a corresponding low within the lower levels of the troposphere, at least in the beginning. The development of an Upper Level Low depends on the existence of unstable waves within the general flow in the upper levels of the troposphere. These unstable waves are caused by a phase shift between the temperature wave and the potential wave which can lead to further developments. The temperature wave being situated behind the potential wave. Therefore CA can be found within the area of the upper level trough. During this stage of development the field of the absolute topography is characterized by an increase of the amplitude of the potential wave and sometimes also by a decrease of the wavelength. The same development takes place for the temperature wave. In the northern hemisphere a southward deviation of the isohypses and isotherms of the upper level trough can be observed leading to a deepening of the trough. Finally the trough will start to detach from the meridional stream and the formation of a cut of low (Upper Level Low) can be observed.