Definitions of Downburst, Microburst, and Burst Swaths
Fig. 1 Graphical Illustrations of a Downburst, a number of Microburst embedded within a Downburst, and a number of Burst Swaths embedded within a Microburst. Note the divergent characteristics with each of these wind phenomena (Courtesy Fujita and Wakimoto 1981). (Click on image for a larger image).
Definition of a Downburst: A strong downdraft which induces an outburst of damaging winds on or near the surface. A family of downburst is called a "downburst cluster" or collection of downburst having overall lengths of over 50 to 60 n miles. The overall size of an individual downburst can vary from 4 to 6 n miles. The damage pattern at the surface is 'highly divergent.' Several microburst can be identified within an individual downburst. We have seen and documented this damging wind pattern in a number of cases. During his studies in the mid 1970s most downburst winds (47%) fell into the category of F0 (traditional Fujita scale) which means that estimated wind speeds varied from 40 to 72 mph. About (32%) of the downburst reached F1 category with wind speeds varying from 73 to 112 mph. About 20% of the downburst cases reached or exceeded F2 intensity. Below are some examples we have documented over the years.
Definition of a Microburst: A strong downdraft which induces an outburst of damaging winds over an area from 1/2 to 1 statue mile. The life time of a microburst is less than 20 minutes. Several microbursts can occur within a downburst as shown in the middle figure above.
Definition of Burst Swath: is defined as extreme wind occurring within a microburst. A long narrow burst swath can often resemble a path of a tornado, however the corn or tree pattern within a burst swath is highly divergent. Burst swaths can range to 50 to 150 yards long. During the damage assessment of May 8, 2009 we uncovered several microburst and burst swaths south and east of Fredrickstown MO in east-central Madison County MO in which nearly complete deforestation.
We will be showing examples below: