Accumulated Cyclone Energy
The Accumulated Cyclone Energy (ACE) is a measure used by the National Oceanic and Atmospheric Administration (NOAA) to express the activity of Atlantic hurricane seasons. It uses an estimate of the energy that a storm system will dissipate during its activity, and is calculated every six hours. The ACE of a season is the sum of all ACEs of the individual storms and includes the number, strength and duration of all tropical cyclones in the season.
Formulas
The ACE is calculated as the sum of the squares of the estimated maximum sustained speed of each active tropical storm (wind speeds of 35 knots or more) at six hour intervals. The numbers are usually divided by 10,000 to make them easier to work with. The unit of the ACE is 10 4 kn 2 and this unit is assumed for use as an index. If a season storm continues beyond December 31 of any year, the storm's ACE counts for the previous year.
with v max as the estimated sustained wind speed in knots.
The kinetic energy is proportional to the square of the speed and by adding the energy with a time interval, one comes to the accumulated energy. As the duration of a storm increases, more and more values are added and the ACE increases, so that longer lasting storms accumulate a higher ACE than more powerful storms of shorter duration. Although the ACE is a value proportional to the energy converted by a storm, it is not a direct calculation of the energy.
A related quantity is the Hurricane Destruction Potential (HDP) , which is identical to the ACE, except that it is only calculated for the time periods in which the storm is a hurricane.
climatology
For the period 1950 to 2000, NOAA calculated for the Atlantic basin:
- Median of the annual index at 87.5
- Average of the annual index at 93.2
A season's ACE is used to classify the hurricane seasons according to their activity. The NOAA classification system divides them into:
- Above-average season : An ACE value above 103 (117% of the median), at least two of the following three terms are required in addition to the long-term average : number of tropical storms (10), hurricanes (6) and large hurricanes (2)
- Near-average season : neither above nor below average
- Below average season : An ACE value below 66 (75% of median)
Single storms
The highest ACE ever assumed for a storm is 73.6 for the San Ciriaco hurricane of 1899 . This single storm had a higher ACE than some entire seasons.
Other storms with high ACEs are Hurricane Ivan of 2004 with an ACE of 70.4 and Hurricane Donna of 1960 with an ACE of 64.6
Atlantic hurricane seasons since 1950 according to ACE
The term hyperactive is based on a different weighting algorithm that puts more weight on large hurricanes, but is indicative of an ACE of around 153 (175% of the median).
The 2005 season fulfilled all the criteria for an above-average season on September 5 , faster than any previous season. The data at this point in time were ACE = 103, TS = 13, HR = 6, MH = 3. On September 11th, it qualified as a hyperactive season - only in 1950 this was achieved faster.
key • ACE Accumulated Cyclone Energy • TS Number of tropical storms • MR Number of hurricanes ( SS categories 1–5) • MH Number of major hurricanes (categories 3–5) (Fields with record numbers are bold )
For definitions of the terms "above", "almost" or "below" the average, see the Climatology section above.
| season | ACE | TS | MR | MH | classification |
|---|---|---|---|---|---|
| Atlantic hurricane season 2005 | 248 | 27 | 15th | 7th | above average ( hyperactive ) |
| Atlantic hurricane season 1950 | 243 | 13 | 11 | 8th | above average ( hyperactive ) |
| Atlantic hurricane season 1995 | 228 | 19th | 11 | 5 | above average ( hyperactive ) |
| 2004 Atlantic hurricane season | 225 | 14th | 9 | 6th | above average ( hyperactive ) |
| Atlantic hurricane season 1961 | 205 | 11 | 8th | 7th | above average ( hyperactive ) |
| 1955 Atlantic hurricane season | 199 | 12 | 9 | 6th | above average ( hyperactive ) |
| 1998 Atlantic hurricane season | 182 | 14th | 10 | 3 | above average ( hyperactive ) |
| Atlantic hurricane season 1999 | 177 | 12 | 8th | 5 | above average ( hyperactive ) |
| Atlantic hurricane season 2003 | 175 | 16 | 7th | 3 | above average ( hyperactive ) |
| Atlantic hurricane season 1964 | 170 | 12 | 6th | 6th | above average ( hyperactive ) |
| Atlantic hurricane season 1996 | 166 | 13 | 9 | 6th | above average ( hyperactive ) |
| Atlantic hurricane season 1969 | 158 | 17th | 12 | 5 | above average ( hyperactive ) |
| 1980 Atlantic hurricane season | 147 | 11 | 9 | 2 | above average |
| Atlantic hurricane season 1966 | 145 | 11 | 7th | 3 | above average |
| 1951 Atlantic hurricane season | 137 | 10 | 8th | 5 | above average |
| 1989 Atlantic hurricane season | 135 | 11 | 7th | 2 | above average |
| 2008 Atlantic hurricane season | 123 | 16 | 8th | 5 | above average |
| 1967 Atlantic hurricane season | 122 | 8th | 6th | 1 | almost average |
| 1958 Atlantic hurricane season | 121 | 10 | 7th | 5 | above average |
| Atlantic hurricane season 1963 | 118 | 9 | 7th | 2 | almost average |
| Atlantic hurricane season 2000 | 116 | 14th | 8th | 3 | above average |
| 1954 Atlantic hurricane season | 113 | 11 | 8th | 2 | above average |
| 2001 Atlantic hurricane season | 106 | 15th | 9 | 4th | above average |
| 1953 Atlantic hurricane season | 104 | 14th | 6th | 4th | above average |
| 1988 Atlantic hurricane season | 103 | 12 | 5 | 3 | above average |
| 1971 Atlantic hurricane season | 97 | 13 | 6th | 1 | almost average |
| 1981 Atlantic hurricane season | 93 | 11 | 7th | 3 | almost average |
| Atlantic hurricane season 1979 | 91 | 8th | 5 | 2 | almost average |
| Atlantic hurricane season 1990 | 91 | 14th | 8th | 1 | almost average |
| 1960 Atlantic hurricane season | 88 | 7th | 4th | 2 | almost average |
| 1985 Atlantic hurricane season | 88 | 11 | 7th | 3 | almost average |
| --- (median = 87.5) --- | |||||
| 1952 Atlantic hurricane season | 87 | 7th | 6th | 3 | almost average |
| Atlantic hurricane season 1965 | 85 | 6th | 4th | 1 | almost average |
| 1957 Atlantic hurricane season | 84 | 8th | 3 | 2 | almost average |
| Atlantic hurricane season 1992 | 82 | 6th | 4th | 1 | almost average |
| 1976 Atlantic hurricane season | 81 | 8th | 6th | 2 | almost average |
| 2006 Atlantic hurricane season | 79 | 10 | 5 | 2 | almost average |
| 1959 Atlantic hurricane season | 78 | 11 | 7th | 2 | almost average |
| Atlantic hurricane season 1975 | 73 | 8th | 6th | 3 | almost average |
| 2007 Atlantic hurricane season | 72 | 15th | 6th | 2 | almost average |
| 1984 Atlantic hurricane season | 71 | 12 | 5 | 1 | almost average |
| 2002 Atlantic hurricane season | 66 | 12 | 4th | 2 | below average |
| Atlantic hurricane season 1978 | 62 | 11 | 5 | 2 | below average |
| 1974 Atlantic hurricane season | 61 | 7th | 4th | 2 | below average |
| 1956 Atlantic hurricane season | 54 | 8th | 4th | 2 | below average |
| 1973 Atlantic hurricane season | 43 | 7th | 4th | 1 | below average |
| 1997 Atlantic hurricane season | 40 | 7th | 3 | 1 | below average |
| 1993 Atlantic hurricane season | 39 | 8th | 4th | 1 | below average |
| Atlantic hurricane season 1962 | 36 | 5 | 3 | 1 | below average |
| 1986 Atlantic hurricane season | 36 | 6th | 4th | 0 | below average |
| 1968 Atlantic hurricane season | 35 | 7th | 4th | 0 | below average |
| 1970 Atlantic hurricane season | 34 | 10 | 5 | 2 | below average |
| 1987 Atlantic hurricane season | 34 | 7th | 3 | 1 | below average |
| Atlantic hurricane season 1991 | 34 | 8th | 4th | 2 | below average |
| 1994 Atlantic hurricane season | 32 | 7th | 3 | 0 | below average |
| Atlantic hurricane season 1982 | 29 | 5 | 2 | 1 | below average |
| 1972 Atlantic hurricane season | 28 | 4th | 3 | 0 | below average |
| Atlantic hurricane season 1977 | 25th | 6th | 5 | 1 | below average |
| 1983 Atlantic hurricane season | 17th | 4th | 3 | 1 | below average |
East Pacific ACE
The Accumulated Cyclone Energy is also used in the eastern and central Pacific Ocean. ACE data is backed up reliably starting with the 1971 Pacific hurricane season . The season with the highest ACE since 1971 is the 1992 season . The 1977 season had the lowest ACE. The current above-average season is 1997 , the current almost-average season is 2002 and the current below-average season is 2007 .
West Pacific ACE
The ACE is also used in the western Pacific. 2004 had an ACE of 464 10 4 kt 2 for the Northwest Pacific. That was the third highest since 1965, after 1992 and 1997. The 40-year norm (1965–2004) is (305 ± 99) 10 4 kt 2 .
See also
Web links
- Climate Prediction Center - Background Information: The North Atlantic Hurricane Season
- NOAA ACE by year from 1851
- National Climatic Data Center - Atlantic Basin 2004 Accumulated Cyclone Energy (ACE) Index
- National Climatic Data Center - Atlantic Basin 2005 Accumulated Cyclone Energy (ACE) Index
- 2004 Pacific NW Typhoon Season ACE pdf (96 kB)