(Abbreviated MCC.) A subset of mesoscale convective systems (MCS) that exhibit a large, circular (as observed by satellite), long-lived, cold cloud shield. The cold cloud shield must exhibit the following physical characteristics. Size: A - Cloud shield with continuously low infrared (IR) temperature ≤ -32°C must have an area ≥ 105 km2; and B - Interior cold cloud region with temperature ≤ -52°C must have an area ≥ 0.5 X 105 km2. Initiate: Size definitions A and B are first satisfied Duration: Size definitions A and B must be met for a period ≥ 6 h. Maximum extent: Contiguous cold cloud shield (IR temperature ≤ -33°C) reaches maximum size. Shape: Eccentricity (minor axis/major axis) ≥ 0.7 at time of maximum extent. Terminate: Size definitions A and B no longer satisfied. Alternatively, a dynamical definition of an MCC requires that the system have a Rossby number of order 1 and exhibit a horizontal scale comparable to the Rossby radius of deformation. In midlatitude MCS environments, the Rossby radius of deformation is about 300 km.
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