Accumulated Cyclone Energy

The Accumulated Cyclone Energy (ACE ) is one of the National Oceanic and Atmospheric Administration ( NOAA) measure used to express the activity of Atlantic hurricane seasons. It uses an estimation of the energy converting system for a tower of its activity, and is calculated every six hours. The ACE of a season is the sum of all the ACEs of the individual storms and includes the number, intensity and duration of all tropical cyclones of the season.


The ACE is calculated as the sum of the squares of the estimated sustained maximum speed of each active tropical storm (wind speeds of 35 knots or more ) in six-hour intervals. The numbers are usually divided by 10,000 in order to manage them more easily. The unit of ACE is 104 kn2 and for use as an index, this unit is assumed. If a storm of a season continues through the date of December 31 of the year addition, the ACE is one of the storm for the previous year.

With vmax than estimated, sustained wind speed in knots.

The kinetic energy is proportional to the square of the velocity and by summing the energy with a time interval, one comes to the Accumulated Energy. As long as the duration of a tower increases, more and more value is added and the ACE of growing, so that prolonged storms stronger than a higher ACE accumulate storms of shorter duration. Although ACE is a value proportional to the converted energy of a storm, there is no direct calculation of the energy.

A related quantity is the Hurricane Destruction Potential ( HDP), which is identical to the ACE, except that it is calculated only for the time periods in which the storm is a hurricane.


Over the period 1950-2000 the NOAA calculated for the Atlantic basin:

  • Median of the annual index to 87.5
  • Average of the annual index to 93.2

The ACE of a season is used to classify the hurricane seasons after their activity. The classification system divides it into the NOAA:

  • Above-average season: An ACE value above 103 ( 117% of the median), there are at least two of the following three terms provided in addition to the long-term average: number of tropical storms (10) hurricane (6) and Big Hurricane ( 2)
  • Near- average season: neither over nor below the average
  • Below-average season: An ACE value below 66 (75% of the median)

Individual storms

The highest ever for a storm adopted ACE is 73.6 for the San Ciriaco Hurricane of 1899. This single storm had a higher ACE than some entire season.

Other storms with high ACEs are of Hurricane Ivan in 2004 with an ACE of 70.4 and Hurricane Donna of 1960 with an ACE of 64.6

Atlantic hurricane seasons from 1950 to 2007 by ACE

The designation is based on another hyperactive weighting algorithm that puts more emphasis on Big Hurricane, but is indicative of an ACE of about 153 ( 175% of the median).

The 2005 season met on September 5, all of the criteria above-average season, faster than any previous season. The data at this time were ACE = 103, TS = 13, HR = 6, MH = 3 On September 11, she qualified as a hyperactive season - only in 1950, this was achieved faster.

For the definitions of the terms " about", " almost" or " below" the average the Section climatology above.

East Pacific ACE

The Accumulated Cyclone Energy is also used in the eastern and central Pacific Ocean. Data of the ACE are starting backed up with the Pacific hurricane season 1971 reliable. The season with the highest ACE since 1971 is the season of 1992. The 1977 season had the lowest ACE. The current, above-average season is the season of 1997, the current almost - average season, the 2002 season and the current below-average season is the season of 2007.

Western Pacific ACE

The ACE is also used in the Western Pacific. 2004 had an ACE of 464 104 kt2 for the Pacific Northwest. This was the third highest since 1965, after 1992 and 1997., The 40 -year norm ( 1965-2004 ) is 305 / -99 104 kt2.