9/16/2023 0 Comments Rain in laChanges in the winds also allow cool water to rise up from the deep ocean in the east. Westerly winds weaken along the equator allowing warm water to shift towards Africa. Temperatures are close to normal across the tropical Indian Ocean, and hence the neutral IOD results in little change to Australia's climate. Air rises above this area and falls over the western half of the Indian Ocean basin, blowing westerly winds along the equator. Water from the Pacific flows between the islands of Indonesia, keeping seas to Australia's northwest warm. Sustained positive values are indicative of La Niña conditions, and sustained negative values indicative of El Niño conditions. Positive SOI values are shown in blue, with negative in orange. The following figure demonstrates the typical fluctuations in SOI over a period of 11 years. The SOI is calculated using the pressure differences between Tahiti and Darwin. The Southern Oscillation Index, or SOI, gives an indication of the development and intensity of El Niño or La Niña events in the Pacific Ocean. Cloudiness and rainfall north of Australia are supressed, typically leading to below average winter–spring rainfall for eastern parts of the country, and a drier start to the northern wet season. Trade winds weaken (or reverse) and warmer surface water builds up in the central Pacific. Cloudiness and rainfall north of Australia are enhanced, typically leading to above average winter–spring rainfall for eastern and central parts of the country, and a wetter start to the northern wet season. Trade winds strengthen, increasing the temperature of the warm water north of Australia. The warmest waters in the equatorial Pacific build up to the north of Australia and that area become the focus for cloudiness and rainfall. Trade winds push warm surface water to the west and help draw up deeper, cooler water in the east. This change in ocean temperature sees a shift in cloudiness and rainfall from the western to the central tropical Pacific Ocean. However, during El Niño years, the trade winds weaken and the central and eastern tropical Pacific warms up. This warmer area of ocean is a source for convection and is associated with cloudiness and rainfall. The ocean surface north and northeast of Australia is typically 28 to 30☌ or warmer, near South America the Pacific This means that under "normal" conditions the western tropical Pacific is 8 to 10☌ warmer than the eastern tropical Pacific. Hence waters in the western equatorial Pacific are able to warm more effectively under the influence of the tropical sun. However in the far western Pacific there is no cool current, and weaker Trades mean that this "upwelling" effect is reduced. Furthermore, along the equator, strong east to southeasterly Trade winds cause the ocean currents in the eastern Pacific to draw water from the deeper ocean towards the surface, helping to keep the surface cool. In the eastern Pacific, the northward flowing Humbolt current brings cooler water from the Southern Ocean to the tropics. El Niño Southern Oscillation(ENSO) is the term used to describe the oscillation between the El Niño phase and the La Niña, or opposite, phase. This occurs every three to eight years and is associated with a weaker Walker Circulation (see diagram below) and drier conditions in eastern Australia. Refers to the extensive warming of the central and eastern tropical Pacific Ocean which leads to a major shift in weather patterns across the Pacific. This climate influence is related to: El Niño La Niña The Australian Monsoon What is it? ENSO is the oscillation between El Niño and La Niña conditions.
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