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The Indian Ocean Dipole (IOD), also known as the Indian Niño, is an irregular oscillation of sea-surface temperatures in which the western Indian Ocean becomes alternately warmer and then colder than the eastern part of the ocean. ==The phenomenon== The IOD involves an aperiodic oscillation of sea-surface temperatures, between "positive", "neutral" and "negative" phases. A positive phase sees greater-than-average sea-surface temperatures and greater precipitation in the western Indian Ocean region, with a corresponding cooling of waters in the eastern Indian Ocean—which tends to cause droughts in adjacent land areas of Indonesia and Australia. The negative phase of the IOD brings about the opposite conditions, with warmer water and greater precipitation in the eastern Indian Ocean, and cooler and drier conditions in the west. The IOD also affects the strength of monsoons over the Indian subcontinent. A significant positive IOD occurred in 1997–8, with another in 2006. The IOD is one aspect of the general cycle of global climate, interacting with similar phenomena like the El Niño-Southern Oscillation (ENSO) in the Pacific Ocean. The IOD phenomenon was first identified by climate researchers in 1999. Yet evidence from fossil coral reefs demonstrates that the IOD has functioned since at least the middle of the Holocene period, 6500 years ago. An average of four each positive/negative IOD events occur during each 30-year period with each event lasting around six months. However, there have been 12 positive IODs since 1980 and no negative events from 1992 until a strong negative event in late 2010. The occurrence of consecutive positive IOD events are extremely rare with only two such events recorded, 1913–1914 and the three consecutive events from 2006–2008 which preceded the Black Saturday bushfires. Modelling suggests that consecutive positive events could be expected to occur twice over a 1,000 year period. The positive IOD in 2007 evolved together with La Niña which is a very rare phenomenon that has happened only once in the available historical records (in 1967). A strong negative IOD developed in October 2010, which, coupled with a strong and concurrent La Niña, caused the 2010–2011 Queensland floods and the 2011 Victorian floods. In 2008, Dr Nerilie Abram used coral records from the eastern and western Indian Ocean to construct a coral Dipole Mode Index extending back to 1846AD.〔(【引用サイトリンク】title=Coral Dipole Mode Index, World Data Center for Paleoclimatology )〕 This extended perspective on IOD behaviour suggested that positive IOD events increased in strength and frequency during the 20th century.〔(【引用サイトリンク】title=Coral Dipole Mode Index, Abram et al. 2008, Nature Geoscience )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Indian Ocean Dipole」の詳細全文を読む スポンサード リンク
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