Warm water and converging winds near Australia contribute to convection, and hence rainfall for eastern Australia. Indeed, the sea level near Australia can be one metre higher than at South America. Winds over the tropical Pacific, known as the trade winds, blow from east to west piling the warm top layer water against the east coast of Australia and Indonesia. Between these two water masses there is a sharp temperature change known as the thermocline. Underneath, the ocean is colder and far more static. The top layer of the tropical Pacific Ocean (about the first 200 metres) is warm, with water temperatures between 20C and 30C. These events are associated with widespread changes in the climate system that last several months, and can lead to significant human impacts affecting things such as infrastructure, agriculture, health and energy sectors.The simplest way to understand El Niño and La Niña is through the sloshing around of warm water in the ocean. We now better understand these impacts and reproduce many of them in our climate models. For example, El Niño years are one factor that can increase the risk of colder winters in the UK.Įl Niño is also thought to limit development of tropical storms in the North Atlantic, likewise La Niña can enhance development. Our research helped show that the El Niño and La Niña cycle has impacts all over the world. While the global climate system contains many processes, ENSO is by far the dominant feature of climate variability on inter-annual timescales. The name 'ENSO' is a reminder that close interaction between the atmosphere and ocean is an essential part of the process. 'ENSO' stands for 'El Niño Southern Oscillation', where 'Southern Oscillation' is the term for atmospheric pressure changes between the east and west tropical Pacific that accompany both El Niño and La Niña episodes in the ocean. These episodes alternate in an irregular inter-annual cycle called the ENSO cycle. Video: What is El Niño?ĮNSO - an interaction with the atmosphere and the ocean Approximately half of all years are described as neutral. These may be within a period of warming or cooling in the cycle. There are also neutral phases of the cycle when conditions are closer to the long-term average (within +/- 0.5 ☌). Cooler, drier than average weather is experienced in the tropical eastern Pacific. The conditions for declaring 'La Niña' differ between different agencies, but during an event sea temperatures can often fall 3-5 ☌ below average. 'La Niña' or "the girl" is the term adopted for the opposite side of the fluctuation, which sees episodes of cooler than average sea surface temperature in the equatorial Pacific. The effects of El Niño often peak during December it's name "the boy" is thought to have originated as "El Niño de Navidad " centuries ago when Peruvian fishermen named the weather phenomenon after the newborn Christ. El Niño is felt strongly in the tropical eastern Pacific with warmer than average weather. The name 'El Niño' is widely used to describe the warming of sea surface temperature that occurs every few years, typically concentrated in the central-east equatorial Pacific.Īn El Niño is declared when sea temperatures in the tropical eastern Pacific rise 0.5 ☌ above the long-term average.
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