Upper Tropospheric Cyclonic Vortex - Characteristics

Characteristics

The tropical upper tropospheric cyclone has a cold core, meaning it is stronger aloft than at the Earth's surface, or stronger in areas of the troposphere with lower pressures. This is explained by the thermal wind relationship. It also means that a pool of cold air aloft is associated with the feature. If both an upper tropospheric cold-core low and lower tropospheric easterly wave trough are in-phase, with the easterly wave near or to the east of the upper level cyclone, thunderstorm development (also known as moist convection) is enhanced. If they are out-of-phase, with the tropical wave west of the upper level circulation, convection is suppressed due to convergence aloft leading to downward motion over the tropical wave or surface trough in the easterlies. Upper level cyclones also interact with troughs in the subtropical westerlies, such as cold fronts and stationary fronts. When the subtropical disturbances in the Northern Hemisphere actively move southward, or dig, the area between the upper tropospheric anticyclone to its west and cold-core low to its east generally have strong northeasterly winds in addition to a rapid development of active thunderstorm activity. Cloud bands associated with upper tropospheric cyclonic vortices are aligned with the vertical wind shear. Animated satellite cloud imagery is a better tool for their early detection and tracking. The low-level convergence caused by the cut-off low can trigger squall lines and rough seas, and the low-level spiral cloud bands caused by the upper level circulation are parallel to the low-level wind direction. This has also been witnessed with upper level lows which occur at higher latitudes. For example, in areas where small-scale snow bands develop within the cold sector of extratropical cyclones.