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General Discussion >> Hurricane Ask/Tell

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Reged: Tue
Posts: 9
Loc: Lake Buena Vista, FL
Questions Regarding ACE
      #89211 - Mon Aug 30 2010 03:37 PM

I am curious how the ACE stacks up now that Danielle has been churning for a while (and was a major) and with Earl a major and 97L about to do something. It seems I saw something posted that the ACE was around 25 and my question is what impact do these big storms, if they stick around for a while, even if out to sea, have on total ACE? As the number gets bigger, are the chances for big storms diminished? Is the ACE (accumulated cyclone energy) computed when the storm forms, or does its longevity add to the number? And finally, is there a limit to how much ACE can be expended? Or is the number/amount infinite? It seems improbable (but not impossible) that we could have hurricane after hurricane lining up. Seems there must be some balance or equilibrium point.

(Post moved to the appropriate Forum. Since I deal with storm totals rather than energy totals - I'll leave this one to somebody else.)

Edited by Ed Dunham (Mon Aug 30 2010 04:11 PM)

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Reged: Wed
Posts: 1710
Loc: 45.95N 84.55W
Re: Questions Regarding ACE [Re: ChrisS]
      #89384 - Fri Sep 03 2010 04:09 AM

ACE is computed starting when a storm becomes a tropical storm and ends when it is no longer a tropical storm (weakening/dissipation, extratropical transition, and so on). Longer-lived and stronger storms have higher ACE values, since it is a sum over all times of the wind speed squared.

It is a measure of what activity has already occurred and has little to no predictive value in terms of future activity. It is not a quantity that is 'expended' -- and, in fact, is not really an 'energy' at all. It's just a way of quantifying tropical activity by weighting longer-lived and more intense storms greater than shorter-lived and/or weaker storms.

Tropical systems contribute in a small way to the global energy budget, but we do not as of yet know why there are only about 90 worldwide per year. It quite likely has absolutely nothing to do with ACE, however. Controls on hurricane activity may arise out of other, truer energy considerations -- such as upper ocean heat content -- but again, this has nothing to do with ACE.

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(or view them on the main page for any active Atlantic storms!)

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