Accumulated cyclone energy

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Accumulated cyclone energy (ACE) is a metric used to compare overall activity of tropical cyclones, utilizing the available records of windspeeds at six-hour intervals to synthesize storm duration and strength into a single index value. The ACE index may refer to a single storm or to groups of storms such as those within a particular month, a full season or combined seasons. It is calculated by summing the square of tropical cyclones' maximum sustained winds, as recorded every six hours, but only for windspeeds of at least tropical storm strength (≥ 34 kn; 63 km/h; 39 mph); the resulting figure is divided by 10,000 to place it on a more manageable scale. The calculation originated as the Hurricane Destruction Potential (HDP) index, which sums the squares of tropical cyclones' maximum sustained winds while at hurricane strength, at least 64 knots (≥ 119 km/h; 74 mph) at six-hour recorded intervals across an entire season. The HDP index was later modified to further include tropical storms...

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