The HadISST (Hadley Centre Sea Ice and Sea Surface Temperature) dataset is used to define the years of El Niño, El Niño Modoki, and La Niña events and to find out the impacts of these events on typhoon activity. The results show that the formation positions of typhoon are farther eastward moving in El Niño years than in La Niña years and much further eastward in El Niño Modoki years. The lifetime and the distance of movement are longer, and the intensity of typhoons is stronger in El Niño and in El Niño Modoki years than in La Niña years. The Accumulated Cyclone Energy of typhoon is highly correlated with the Oceanic Niño Index with a correlation coefficient of 0.79. We also find that the typhoons anomalously decrease during El Niño years but increase during El Niño Modoki years. Besides, there are two types of El Niño Modoki, I and II. The intensity of typhoon in El Niño Modoki I years is stronger than in El Niño Modoki II years. Furthermore, the centroid position of the Western Pacific Warm Pool is strongly related to the area of typhoon formation with a correlation coefficient of 0.95.
Recent studies have found that there are two types of El Niño in the tropical Pacific, namely: Eastern-Pacific El Niño (EP-El Niño) and Central-Pacific El Niño (CP-El Niño) [
The Oceanic Niño Index (ONI) provided by the Climate Prediction Center in the National Oceanic and Atmospheric Administration (NOAA) is used to define El Niño and La Niña events. The anomalous ONI value of five consecutive months at or above
The area and sea surface temperature (SST) of WPWP might be affected by El Niño, El Niño Modoki, and La Niña events. To find out the changes of WPWP with typhoon characteristics during these events, the study area is limited to 40.5°N–30.5°S and 120.5°E–119.5°W. The area within the 28°C isotherm of SST is defined as the area of WPWP. It can be calculated by [
Typhoon data is obtained from JMA and JTWC. The contents of both datasets include longitude, latitude, lifetime, minimum pressure and maximum wind, length of movement, average moving speed, and range of movement of a typhoon. Typhoon grading intensity standards with reference to the JMA are according to the definition of National Hurricane Center. The Accumulated Cyclone Energy (ACE) formula is used to identify the intensity of a typhoon and is defined as [
The years of El Niño and La Niña in the period of 1950–2012 are defined by ONI. We have identified 19 El Niño events and 21 La Niña events during the data span. In the El Niño years, warm water moves from west to east with Kelvin waves in the tropical Pacific and replaces the cold surface water of the Humboldt Current. Extensive Pacific warming and the reduction in easterly trade winds limit upwelling of cold water in the equatorial eastern Pacific. The La Niña year is the opposite of the El Niño year; SST across the eastern and central equatorial Pacific is lower than normal. The El Niño Modoki has its warm SST anomaly in the 10°S
SST anomaly of (a) 2009-2010, (b) 2002-2003, (c) 1992-1993, and (d) 2010-2011 as examples for El Niño, El Niño Modoki I, El Niño Modoki II, and La Niña events, respectively.
Previous study [
The years of El Niño, El Niño Modoki I, El Niño Modoki II, and La Niña events from 1950 to 2012.
Event | Year (from July to June of next year) |
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El Niño | 1951-52, 1957-58, 1963-64, 1965-66, 1968-69, 1969-70, 1972-73, 1976-77, 1982-83, 1987-88, 1997-98, 2006-07, 2009-10 |
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El Niño Modoki I | 1977-78, 1986-87, 1991-92, 1994-95, 2002-03, 2004-05 |
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El Niño Modoki II | 1990-91, 1992-93 |
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La Niña | 1950-51, 1954–57, 1962-63, 1964-65, 1967-68, 1970–72, 1973–76, 1984-85, 1988-89, 1995-96, 1998–01, 2007-08, 2010–12 |
The best track data of typhoon provided by JMA are used in this study. There are 1594 typhoons found from 1951 to 2011, 492 in El Niño years, 512 in La Niña years, and 590 in normal years. The average of formation position of typhoons is at 15.2°N, 140.6°E in El Niño years, at 17.2°N, 135°E in La Niña years, and at 16.2°N, 136.5°E in normal years. Comparing El Niño and El Niño Modoki years in the period of 1977 to 2011, typhoon began its extended lifecycle at 14.8°N, 140.2°E in El Niño years, at 15.6°N, 141.4°E in El Niño Modoki I years, and at 15.4°N, 141.7°E in El Niño Modoki II years (Figure
The average formation area of typhoon in El Niño years (Red), El Niño Modoki I years (Magenta), El Niño Modoki II years (Green), La Niña years (Blue), and normal years (Black). The semimajor and semiminor axes of an ellipse are the standard deviation of formation positions of typhoons in longitude and latitude, respectively.
Statistical results of formation position, ACE, number, maximum wind speed, lifetime, distance of movement, minimum pressure, moving speed, and moving range of typhoon are summarized in Table
The statistic results of typhoon in Niño years, El Niño Modoki I years, El Niño Modoki II years, normal years, and La Niña years from 1977 to 2011.
1977~2011 | Formation position of latitude (°N) | Formation position of longitude (°E) | ACE (104 kt2) | Number | Maximum wind speed (kt) | Lifetime (hour) | Distance of movement (km) | Minimum pressure (hPa) | Moving speed (km/hour) | Moving range of longitude (°) | Moving range of latitude (°) |
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El Niño |
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El Niño Modoki I |
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El Niño Modoki II |
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Normal |
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La Niña |
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We use ACE to measure overall activity of typhoon during a year. The calculation of average ACE (Unit:
The mean of ACE of a year in the five events. The bar represents one standard deviation.
Relationship between ACE and ONI (
The definition of maximum wind speed of typhoons provided by JMA (10 min mean) is different from that of JTWC (1 min mean). Therefore, the occurrence percentage of typhoon strength from both datasets may be different. A comparison of both datasets from 1977 to 2011 is shown in Table
Percentage of different typhoon categories of each event for JMA and JTWC from 1977 to 2011.
Event/data | JMA | JTWC | ||||
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Tropical storm | Category 1 + 2 | Category 3 + 4 + 5 | Tropical storm | Category 1 + 2 | Category 3 + 4 + 5 | |
El Niño | 33.9% | 38.0% | 28.1% | 25.8% | 28.3% | 45.8% |
El Niño Modoki I | 41.8% | 44.1% | 14.1% | 32.7% | 29.6% | 37.7% |
El Niño Modoki II | 41.7% | 45.0% | 13.3% | 25.9% | 39.7% | 34.5% |
Normal | 44.5% | 44.5% | 11.0% | 35.4% | 33.3% | 31.2% |
La Niña | 54.7% | 36.8% | 8.5% | 41.5% | 27.7% | 30.8% |
Figure
The distribution of average SST in (a) El Niño, (b) El Niño Modoki I, (c) El Niño Modoki II, (d) La Niña, and (e) normal years.
The average WPWP area in the five events. The bar represents one standard deviation.
The average location of the centroid of WPWP in different events. El Niño (Red), El Niño Modoki I (Magenta), El Niño Modoki II (Green), La Niña (Blue), and the normal (Black), respectively.
The centroid of WPWP (Blue) and the formation position of typhoon (Red) in five events.
This is a preliminary study on the impacts of El Niño, El Niño Modoki, and La Niña events on the typhoon activity. We identify 19 El Niño events and 21 La Niña events during the period of 1950–2012. We also find that there are two types of El Niño Modoki, I and II. The statistical results show that the lifetime, length of movement, and range of movement of typhoons are larger in El Niño years than those in La Niña years. The intensity in El Niño years is relatively strong, but the moving speed is almost the same as that in La Niña years. The average intensity of typhoon in El Niño Modoki I years is stronger than that in El Niño Modoki II years. The formation positions of typhoon are moved further eastward in El Niño years than that in La Niña years and much further eastward in El Niño Modoki years. ACE and ONI is corrected with a correlation coefficient of 0.79. The WPWP area is larger in El Niño and El Niño Modoki years than that in La Niña years. The centroid of the WPWP and the position of the typhoon formation are highly correlated with a correlation coefficient of 0.95.
The authors appreciate the Met Office Hadley Centre for Climate Change for providing the HadISST data, as well as the Japan Meteorological Agency and the Joint Typhoon Warning Center for providing typhoon data. Two anonymous reviewers providing useful comments and suggestions are also grateful. This work was supported by the National Science Council of Taiwan through Grants NSC 98-2611-M-019-017-MY3 and NSC 102-2611-M-019-011.