Accumulated cyclone energy (ACE) is a metric used by various agencies to express the energy released by a tropical cyclone during its lifetime. It is calculating by summing the square of a tropical cyclone's maximum sustained winds, measured every six hours. The resulting total can be divided by 10,000 to make it more manageable, or added to other totals in order to work out a total for a particular group of storms. The calculation was originally created by William Gray and his associates at Colorado State University as the Hurricane Destruction Potential index, which took the square of each hurricane's maximum sustained winds above every six hours. This index was adjusted by the United States National Oceanic and Atmospheric Administration in 2000 to include all tropical cyclones, with winds above and renamed accumulated cyclone energy. The index has since been used by various other agencies to calculate a storm's accumulated cyclone energy, including the Australian Bureau of Meteorology as well as the India Meteorological Department. The highest ACE calculated for a single storm is 82, for Hurricane/Typhoon Ioke in 2006. History The accumulated cyclone energy index was originally created by William Gray and his associates at Colorado State University, as the Hurricane Destruction Potential index (HDP). They argued that the destruction of a hurricane's wind and storm surge was better related to the square of the maximum wind speed (Vmax2) than simply to the maximum wind speed. The index was calculated by squaring the estimated maximum sustained wind speed by themselves, for all tropical cyclones with windspeeds of above every six hours over the entire season. This scale was subsequently adjusted by the United States National Oceanic and Atmospheric Administration (NOAA) to include all tropical cyclones, with winds above . NOAA also renamed it the accumulated cyclone energy index. Since the scale was adjusted by NOAA, the storm totals have been used in a number of different ways, by various agencies and researchers, including the Australian Bureau of Meteorology and the India Meteorological Department. These purposes include to categorize how active a tropical cyclone season was as well as to identify possible long-term trends in a certain area such as the Lesser Antilles. Calculation The accumulated cyclone energy of a season is calculated by summing the squares of the estimated maximum sustained velocity of every tropical cyclone that has wind speeds of or higher, at six-hour intervals. The numbers are