This article is more than 10 months old

This article is more than 10 months old

Twenty years ago in 1999 a new weather pattern was described for the first time. Now it has shifted up a gear and is causing devastation across east Africa.

The Indian Ocean dipole, sometimes called the Indian El Niño, is an irregular oscillation in which the surface temperature of the sea is alternatively greater in the ocean’s west and its east. The positive phase, when it is warmer in the west, sees more rain in the west and greater chance of drought in the east. These are reversed in a negative phase.

According to Australia’s Bureau of Meteorology, the current positive dipole is the strongest since measurements began in 2001, although there may have been a similar pattern in 1997. The latest dipole may have contributed to record-breaking monsoon rainfall in India.

The warm ocean around east Africa is bringing torrential rain. Flooding has displaced hundreds of thousands of people in Somalia and submerged towns in South Sudan, while flash floods have caused landslides in Kenya, Ethiopia and Tanzania.

The dipole is also suspected of having produced hot weather and drought in south-eastern Australia, a region previously thought to be influenced mainly by the Pacific El Niño.

The current dipole is expected to peak later in November, with extreme weather continuing until it passes.