A dipole mode in the tropical Indian Ocean

Abstract

For the tropical Pacific and Atlantic oceans, internal modes of variability that lead to climatic oscillations have been recognized, but in the Indian Ocean region a similar ocean-atmosphere interaction causing interannual climate variability has not yet been found. Here we report an analysis of observational data over the past 40 years, showing a dipole mode in the Indian Ocean: a pattern of internal variability with anomalously low sea surface temperatures off Sumatra and high sea surface temperatures in the western Indian Ocean, with accompanying wind and precipitation anomalies. The spatio-temporal links between sea surface temperatures and winds reveal a strong coupling through the precipitation field and ocean dynamics. This air-sea interaction process is unique and inherent in the Indian Ocean, and is shown to be independent of the El Niño/Southern Oscillation. The discovery of this dipole mode that accounts for about 12% of the sea surface temperature variability in the Indian Ocean--and, in its active years, also causes severe rainfall in eastern Africa and droughts in Indonesia--brightens the prospects for a long-term forecast of rainfall anomalies in the affected countries.

Perspectives on CMIP5 model performance in the Nile River headwaters regions

“…For teleconnections analysis, we examine linear correlations between seasonal precipitation and four indices that are commonly associated with precipitation variability in the Nile basin (Camberlin, 1997, 2009; Anyah and Semazzi, 2006; Block and Rajagopalan, 2007; Segele et al , 2009; Kundzewicz and Stakhiv, 2010; Diro et al , 2011; Berhane et al , 2014): (1) an ENSO index computed from the 3‐month running means of SST anomalies between 10°S–10°N and 120°E–80°W, (2) Global SST anomaly (GSST), as an indicator of global‐scale climate variability and change (in this study SST between 60°N–60°S are considered), (3) a dynamically based Indian Summer Monsoon Index (ISM; http://apdrc.soest.hawaii.edu/projects/monsoon) calculated as the difference of zonal wind at 850 mbar between region 1 (5°–15°N and 40°–80°E) and region 2 (20°–30°N and 70°–90°E) for the JJAS season (Wang and Fan, 1999), and (4) an Indian Ocean Dipole (IOD) index calculated as the difference between the tropical western Indian Ocean (50°–70°E, 10°S–10°N) and the tropical south‐eastern Indian Ocean (90°–110°E, 10°S–0°N) (Saji et al , 1999). All anomalies are calculated from the 1950–1995 climatology.…”

Synchronicity of historical dry spells in the Southern Hemisphere

“…-Indian Ocean Dipole (IOD; Saji et al, 1999;Ashok et al, 2003;Verdon and Franks, 2005), which in this study is represented by the Dipole Model Index (DMI) developed by Saji et al (1999), defined as the difference in sea surface temperature anomaly between the tropical western Indian Ocean (50-70 • E, 10 • S-10 • N) and the tropical southeastern Indian Ocean (90-110 • E, 10 • SEquator).…”

The response of African land surface phenology to large scale climate oscillations

“…The Indian Ocean Dipole (IOD) is an interannual (year-to-year) climate pattern across the tropical Indian Ocean first identified in 1999 (Saji et al, 1999). In the positive phase of the IOD, trade winds are stronger than usual and cooler-than-average sea surface temperatures are prevalent across the eastern tropical Indian Ocean, near Indonesia and Australia.…”