Regional And Mesoscale Meteorology Team
Daily Satellite Discussion
Friday July 18, 1997
07:15 UTC
07:15 UTC
The first requirement is that the cloud shield has a 100,000 square km area of IR temperatures below or equal to -32 degrees C, and that an interior cold cloud region at or below -52 degrees C must cover 50,000 square km. The first image (left) is from 0715 this morning, near the time of maximum extent. The red enhanced pixels have IR temperatures between -31.2 and -33.2 degrees C. The yellow ellipse represents points 320 km from the center. Note: in the satellite projection, points equidistant from a single point are ellipses, not circles. The storm is also displayed in a polar stereographic projection for comparison (right). The area covered by a circle of radius 320 km is 321,700 sq. km. The blue pixels have IR temperatures between -51.2 and -53.2 degrees C. Here the black ellipse represents points 230 km from the center. Such a circle covers 166,190 sq km. The first two conditions are satisfied.
There is also a time requirement. To be classified an MCC, the time period over which the first two conditions exist must be met for six hours or more. Further, the time period from when these two conditions are first met until the time they are no longer met defines the lifetime of the MCC. This loop shows the system every two hours from 0015 Z to 1615 Z. I only checked the first two conditions near the time of maximum extent, but the storm is around the size of North Dakota from 0415 Z to 1215 Z. North Dakota is 178695 sq. km.
The shape of the systems is also defined. At the time of maximum extent, as defined by the area of the -32 or below IR temperature, minor axis/major axis is greater than or equal to 0.7. Because the ellipse on the satellite projection is actually a circle, the quantity minor axis/major axis is close to one in this case.
For further reading please see
Maddox, R.A., 1980:Mesoscale convective complexes. Bull. Amer. Meteor. Soc., 61, 1374-1378.
Jack Dostalek