General background on the oscillation itself, for context alongside the live reading above.

What

An irregular oscillation in the sea-surface temperature difference between the western and eastern tropical Indian Ocean, measured by the Dipole Mode Index (DMI).

Ocean

Tropical Indian Ocean.

Most effective

The SST gradient between the western Indian Ocean (off the Horn of Africa) and the southeastern Indian Ocean (off Sumatra), which in turn modulates rainfall across South and Southeast Asia.

• Positive IOD Warmer water in the west, cooler in the east; tends to enhance monsoon rainfall over India and South Asia, while favoring drought over Indonesia and eastern Australia.
• Negative IOD Cooler water in the west, warmer in the east; tends to suppress South Asian monsoon rainfall, and can reinforce El Niño's drying effect when the two coincide.
• Neutral No strong east-west SST gradient; minimal IOD-driven influence on regional rainfall.

How this chart is measured, for context alongside the line above.

Source

NOAA PSL, HadISST1.1 sea-surface temperature analysis. The dashed "DMI (BOM fill)" segment instead uses the Bureau of Meteorology's real-time weekly IOD index (GAMSSA-based) for months since HadISST1.1 stopped publishing.

Spatial span

Two boxes: a western pole, 10°S–10°N, 50°E–70°E (off the Horn of Africa), and an eastern pole, 10°S–0°, 90°E–110°E (off Sumatra). See the map below.

Method

Mean SST anomaly in the western box minus the mean SST anomaly in the eastern box. The threshold for a positive or negative phase is ±0.4°C. Unlike ENSO, there is no official persistence rule for IOD -- a single month past threshold is enough to classify the phase.

General background on the oscillation itself, for context alongside the live reading above.

What

An eastward-moving pulse of enhanced and suppressed tropical rainfall and convection that circles the globe roughly every 30–60 days. Unlike ENSO or the IOD, it is intraseasonal (weeks, not years).

Ocean

Originates over the Indian Ocean and propagates eastward across the Indian and Pacific Oceans along the equator.

Most effective

The Indian Ocean and Maritime Continent/western Pacific, where its convective center most strongly modulates the South Asian monsoon.

• Indian Ocean phase (RMM phases 2–3, active) Convection centered over the Indian Ocean; tends to trigger active, wet monsoon spells over South Asia.
• Maritime Continent phase (RMM phases 6–7, active) Convection centered over the Maritime Continent/western Pacific; tends to trigger monsoon break, dry spells over South Asia.
• Other-active (RMM phases 1, 4, 5, 8) Convective center elsewhere (western Hemisphere/Africa or western Pacific); mixed, indirect effect on South Asian rainfall.
• Inactive (amplitude below 1) Convective signal too weak to read reliably; little effect on the monsoon either way.

How this chart is measured, for context alongside the line above.

Source

The Bureau of Meteorology's Real-time Multivariate MJO (RMM) index, built from combined empirical orthogonal functions of near-equatorial outgoing longwave radiation and 850/200-hPa zonal wind, averaged around the full tropical belt rather than a single fixed box. The dashed "MJO amplitude (ROMI fill)" segment instead uses NOAA/PSL's OLR-only ROMI index, converted to an RMM-equivalent amplitude, for any month RMM has no value for (kept as a fallback; RMM itself has been current since this site switched to BOM's live feed URL in August 2026).

Spatial span

Not a fixed lat/lon box like the IOD or the ENSO-tab indices -- RMM is a single combined index computed across the full near-equatorial belt, so there's no box to map here.

Method

Each day's amplitude is √(RMM1² + RMM2²), BOM's standard Wheeler-Hendon measure of overall intraseasonal activity; this chart plots the mean of that daily value across each calendar month. A value of 1 or higher is considered dynamically active.