JAMSTEC News
[Column] An extreme negative Indian Ocean Dipole is expected in early boreal summer.
May 23, 2022
Application Laboratory (APL)
The whole tropical Indian Ocean is now warmer-than-normal. However, the SINTEX-F coupled model of APL (※1) predicts occurrence of an extreme negative Indian Ocean Dipole in early boreal summer. It also predicts the present La Niña-like state in tropical Pacific to persist until boreal mid-autumn, and then decay in late boreal autumn. Therefore, Indonesia and Australia (East Africa) may experience extremely wetter (drier) than normal conditions in the coming seasons, owing to the expected co-occurrence of an extreme negative Indian Ocean Dipole and a La Niña-like state.
What is a negative event of the Indian Ocean Dipole?
The Indian Ocean Dipole (IOD) is a coupled ocean-atmosphere phenomenon in the Indian Ocean. A negative IOD is normally characterized by anomalous warming of sea surface temperature (SST) in the southeastern equatorial Indian Ocean and anomalous cooling of SST in the western equatorial Indian Ocean (Fig. 1). It brings heavy rainfall over the Indonesian region and severe droughts/forest fires over East Africa. Therefore, successful prediction of the IOD is crucial for societal applications.
- Figure 1
- SST anomalies are shaded (red color is for warm anomalies and blue is for cold). White patches indicate increased convective activities and arrows indicate anomalous wind directions during negative IOD events.
Is the Indian Ocean Dipole predictable?
A few studies have already assessed seasonal predictability of the IOD by dynamical and statistical prediction systems. Although some potential sources of the predictability were found (e.g. the subsurface Indian Ocean, the tropical Pacific conditions), IOD prediction is still challenging. Nevertheless, the SINTEX-F has demonstrated high performance in predicting IOD in recent years (e. g. 2019 extreme positive IOD event, press release (https://www.jamstec.go.jp/e/about/press_release/20200406/).
An extreme negative Indian Ocean Dipole is predicted for early boreal summer
The SINTEX-F predicts that an extreme negative Indian Ocean Dipole will occur in early boreal summer (Fig. 2). It will mature in boreal mid-autumn, and then start to decay in late boreal autumn. As regards to the seasonally averaged rainfall in September－November 2022 (Fig. 3), East Africa may experience extremely drier than normal conditions, owing to the extreme negative IOD, as similar to the 2021 drought seen in the region (column, https://www.jamstec.go.jp/e/jamstec_news/20211208/). The persisting drought in East Africa would be very damaging to the local socio-economic conditions. Besides, Indonesia and Australia may experience extremely wetter than normal conditions owing to the expected co-occurrence of the extreme negative Indian Ocean Dipole and the La Niña-like state.
We should be careful about those extreme climate events. The quasi real-time forecasts by the SINTEX-F are updated every month and made publicly available (see https://www.jamstec.go.jp/aplinfo/sintexf/e/seasonal/outlook.html).
- Figure 2
- Monthly Indian Ocean Dipole Index (DMI, in °C) from May 2021 to April 2023 from the observational data of NOAA OISSTv2 (black) and the predictions issued on May 1, 2022 by the several versions of the SINTEX-F2 system; the 12-ensemble by the F2, the 12-ensemble by the F2-3DVAR, and the 12-ensemble by the F2si. The details are available at the SINTEX-F2 website (https://www.jamstec.go.jp/aplinfo/sintexf/e/seasonal/overview2.html). DMI is defined as the SST anomaly difference between the western pole off East Africa (50°E–70°E, 10°S–10°N) and the eastern pole off Sumatra (90°E–110°E, 10°S–Eq.).
- Figure 3
- Prediction of precipitation anomaly averaged in September–November 2022 (mm day-1) issued on May 1, 2022 by the SINTEX-F2 (36-members ensemble mean).
※1: For seasonal climate predictions, APL has developed the SINTEX-F ocean-atmosphere coupled general circulation model under the EU-Japan research collaboration. Using the system, we have achieved great successes and it has become one of the leading models of the world for predicting the tropical climate variations in particular IOD, El Niño/La Niña, and the El Niño/La Niña Modoki. The details are available at the SINTEX-F2 website (https://www.jamstec.go.jp/aplinfo/sintexf/e/seasonal/overview2.html).