GBDNA / TUTT Signatures

Guide to Baroclinic Disturbances | Mesoscale Cold Pools >
U N D E R   C O N S T R U C T I O N

Upper Level Cyclonic Systems
TUTT Signatures

Upper-level cyclones normally have convergence into their centers producing downward motion and clear skies. Divergence normally occurs along the periphery of the cyclone with rising motions causing cloudy skies and precipitation. Over land, however, convective activity is often present near the centers in the afternoon when enough instability is produced by a combination of daytime surface heating and the cold core of the upper-level low. The strongest convection normally occurs along the western periphery ahead of westward-moving cyclones (Source: NCEP).

TUTT signatures can serve to either shear apart nearby tropical features, or act to intensify the warm-core disturbance (if the center of the impulse drifts into the difluent upper right pocket of the TUTT). These baroclinic systems can also influence the steering of tropical waves and cyclones, depending on the vertical structure of the warmer feature. There are also cases of merger between the cold upper lows and the warmer counterparts, which may ultimately result in a larger circulation and a greater threat for hurricane formation. In a few scenarios, TUTT lows can give rise to subtropical or tropical cyclones (where the upper low warms and convection wraps around the diminished cold core, creating both vorticity and a surface circulation.

A TUTT can form at any time of the year. Greatest frequency of occurrence is in early and late summer, between 5°N and 35°N latitude in the Northern Hemisphere. The upper lows are easily discernible from concurrent warm-core disturbances, exhibiting a comma shape in satellite views with non-symmetry of radar echoes. Symptoms of apparent weather are heavy to severe thunderstorms in a mainly diurnal time frame.

"A Guide to Baroclinic Disturbances" is © 2007 by Larry Cosgrove.
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