Is the positive phase of the Indian Ocean Dipole developing? During the last 30 days the western equatorial Indian Ocean has warmed dramatically while waters northwest of Australia have cooled. The Bureau of Meteorology/Australia forecasts the IOD and show a short-term weak positive phase followed by neutral phase for AU wintertime. However, if the current trend continues many dramatic influences will follow for MAR/APR/MAY and especially JUN/JUL/AUG.
Fig. 1: Bureau of Meteorology/Australia depiction of the processes involved with the positive phase of the Indian Ocean Dipole.
Fig. 2: The Indian Ocean SSTA analysis reveals warm/cool zones on opposite ends of the basin.
Fig. 3: The 30-day SSTA changes across the Indian Ocean SSTA.
According to the Bureau of Meteorology/Australia onset of climate on Australia during +IOD occurs during spring and peaks in summer when a dry regime emerges over central and southeast continent (Fig. 4). The dryness tends to be harsh and drought certain. Drought conditions are already present across Eastern Australia (Fig. 5).
Fig. 4: Historical relationship of anomalous rainfall across Australia during +IOD regimes.
Fig. 5: As of February 1, 2018 the soil moisture anomalies across Australia.
The sudden rapid change in the SSTA pattern across the tropical Indian Ocean is likely due to a robust Madden Julian oscillation episode most intense across Indonesia and the West Pacific equatorial region during early-to-middle February. Low level wind speeds increased in the eastern equatorial Indian Ocean forcing up-welling cooler water to the surface. During the emerging +IOD of the past 30 days northeast and southeast Argentina have trended drier worsening drought.
Summary: Likely due to a robust Madden Julian oscillation located in equatorial Indonesia to the West Pacific for early-to-middle February low level wind speeds increased over the eastern equatorial Indian Ocean to up-well deep water and cause rapid cooling. In-turn trade winds slowed down allowing piling of warm water in the western equatorial Indian Ocean. The pattern indicated represents evolution of a positive phase Indian Ocean Dipole. If this trend continues and +IOD fully develops Australia drought would expand from eastern sections to central sections in middle 2018. The Bureau of Meteorology/Australia is not forecasting +IOD. However, these sudden changes in the tropical Indian Ocean SSTA pattern imply a +IOD forecast adjustment may be ahead.
