Climatology of Mediterranean cyclones: defining intensity of a cyclone
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The intensity of a cyclone can be measured by its total surface circulation, which is the geostrophic vorticity integral over the cyclone domain. The cyclone domain can be defined as the area inside the zero vorticity line (the area with positive vorticity).
According to this criterion, a large cyclone with high vorticity would be an intense cyclone. A large cyclone with small vorticity would not be an intense cyclone, neither would be if vorticity is high but not the cyclone area is small.
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EXERCISE: Taken into account this definition of cyclone intensity, guess what would be the intensity of a cyclone, 1000000 square kilometres large (twice the size of Spain). Suposse that the mean geostrophic vorticity over its domain is 0.5f, being f the Coriolis parameter at 45 degrees latitude.
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Right!, if we consider a unit of total circulation as
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| our cyclone would be a 5 units intense one.
We can subjetively define WEAK CYCLONES, as those with less than 4 units of total circulation. Those with 7 or more units of total circulation would be considered as INTENSE CYCLONES. In between these limits an intermediate, moderate cyclones class would fall. According to this, our cyclone would be a moderate one. |
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EXERCISE: Suppose that for the cyclone on the picture above, the zero geostrophic vorticity line matches the 1010 mb isobar, so as we can assume its size being about 1 million square kilometers. Suppose that its mean geostrophic relative vorticity is 0.8f, (where f is the Coriolis parameter at 45 degrees latitude). According to the definitions on the prior slide, which type of cyclone would be this one?
Sorry but this is not correct, check your figures and try another choice.
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| Right!, considering the question figures, our cyclone would have an intensity of 8 total circulation units, so it can be classified as an intense one. Actually, the maximum total circulation of this cyclone, when doing a more accurate calculation, was found to be 12.8 units. |
