|
|
|
|
Monitoring of the tropical Pacific and Indian Ocean:
We monitor the evolution of three phenomena in tropical Indo-Pacific region, namely, the Indian Ocean Dipole Mode, canonical Rasmusson and Carpenter type of ENSO, and the recently identified ENSO Modoki phenomenon.
For monitoring the current status of the El Nino and Southern Oscillation (ENSO), the Niño 1+2, Niño 3, Niño 3.4, and Niño 4 indices are used, which represent the area-averaged SST anomalies in the eastern tropical Pacific, off the coasts of Peru and Chile (10°S-0°N, 90°-80°W), the eastern equatorial Pacific (5°S-5°N, 150°-90°W), the central equatorial Pacific (5°S-5°N, 170°-120°W), and the western equatorial Pacific (5°S-5°N, 160°-150°W), respectively.
The Indian Ocean Dipole mode (IOD) is a pattern of internal variability with anomalously low sea surface temperatures off Sumatra and high sea surface temperature in the western Indian Ocean. This dipole mode causes severe rainfall in eastern Africa and droughts in Indonesia in its active years (Saji et al., 1999). The Dipole Mode Index (DMI) defines the difference in SST anomaly between tropical western Indian Ocean (60°E-80°E, 10°S-10°N) and tropical south-eastern Indian Ocean (90°E-110°E, 10°S-Equator) ) (Saji and Yamagata, 2003).
The warming events in the central equatorial Pacific associated with a horseshoe pattern are flanked by a colder sea surface temperature anomaly (SSTA) on both sides along the equator. The phenomenon is named as El Nino Modoki (pseudo-El Nino) (Ashok et al., 2007). The El Nino Modoki Index (EMI) is defined as the [SSTA]A-0.5*[SSTA]B-0.5*[SSTA]C, where SSTA is the anomalous SST. The brackets represent the area averaging over each of the region A(165°E-140°W, 10°S-10°N), B(110°W-70°W, 15°S-5°N), and C(125°E-145°E, 10°S -20°N), respectively.
|
|
 |
Data Source:
The monthly mean OI-SST (NOAA Optimum Interpolation (OI) Sea Surface Temperature) (http://www.cdc.noaa.gov/cdc/data.noaa.oisst.v2.html) anomalies are used to monitor the current condition of ENSO and IOD. It covers from December 1981 to the latest. Base period for climatology is 1982~2007.
References:
Ashok, K., S. K. Behera, S. A. Rao, H. Weng and T. Yamagata, 2007. El Nino Modoki and its possible teleconnection. J. Geophys. Res., 112, C11007, doi:10.1029/2006JC003798.
Saji, N. H., B. N. Goswami, P. N. Vinayachandran and T. Yamagata, 1999. A Dipole Mode in the tropical Indian Ocean. Nature, 401 (23): 360363.
Saji, N. H., and Yamagata, T., 2003. Possible impacts of Indian Ocean dipole mode events on global climate. Climate Research, 25, 151-169.
|
|
