El Nino - What is it?
Met Office - UK Weather
https://www.youtube.com/watch?v=WPA-KpldDVc

Transkript (automatisch erstellt)

0:04 Every few years the El Niño phenomenon kicks into life in the Pacific Ocean around the equator. It can affect weather around the world
0:13 changing the odds of floods, drought, heatwaves and cold seasons for different regions even raising global temperatures.
0:21 But what is El Niño and how does it happen? Firstly we need to know what's normally happening in the tropical Pacific.
0:29 This vast stretch of ocean sees consistent winds called 'trade winds' that blow from east to west.
0:36 These winds push warm water near the surface in their direction of travel, so the warm water piles
0:43 up on the western side of the ocean around Asia and Australasia On the other side of the ocean around South and Central America
0:51 as the warmer water gets pushed away from the coast it's replaced by cold water which is pulled up from deeper down in the ocean
1:00 a process called upwelling. This creates a temperature difference across the tropical Pacific with warmer water piled up in the West
1:09 and cooler water in the east. Warmer water adds extra heat to the air which causes the air to rise with more vigor
1:17 and its this rising air that creates an area of more unsettled weather with more cloud in rainfall
1:24 That rising air in the West sets up atmospheric circulation across this part of the world
1:31 with warm moist air rising on one side of the Ocean and cooler dryer air descending on the other
1:38 This circulation reinforces the easterly winds so this part of the world sits in a self-perpetuating state
1:46 until El Niño begins. If conditions are right tropical Pacific weather systems or slow changes in the ocean around the equator
1:56 can set off a chain of events which weaken or even reverse the usual trade winds With weakened trade winds there's less push
2:05 of warm surface water to the western side of the ocean and less upwelling of cold water
2:11 on the eastern side. This allows the usually colder parts of the ocean to warm canceling out the normal temperature difference.
2:20 Because the area of warmest water moves so does the associated wet and unsettled weather.
2:26 This changes rainfall patterns over the equatorial Pacific as well as the large-scale wind
2:34 patterns. It's this change in winds which has a knock-on effect changing temperature and rainfall in locations
2:41 around the world. The main impacts are around the tropics where you see an increase in the risk of floods
2:48 in Peru and droughts in Indonesia, India and parts of Brazil. But virtually wherever you are in the world
2:56 El Niño has the potential to affect you directly via the weather or indirectly via socio-economic impacts
3:04 There's another impact from El Niño which happens because of all the extra heat at the surface of the tropical Pacific.
3:11 This releases vast amounts of energy into the atmosphere which can temporarily push up global temperatures.
3:19 This is why El Niño years often feature among the warmest on record. Each El Niño event
3:26 is different so the global impacts can change. You can find out more about the different impacts of El Niño
3:33 on our website. El Niño peaks around Christmas-time and last for several months. It can dive back to neutral conditions
3:41 but sometimes reverses into La Niña. This is the flip side of the oscillation which sees
3:50 a strengthening of the normal trade winds. This pushes the warmest water to the far western part of the tropical Pacific
3:58 and increases the upwelling of cold water in the east. This cooler water
4:04 extends out from the coast of the Americas towards the central part of the ocean La Niña also impacts global weather
4:12 and tends to have opposite effects to El Niño. You can also see more about La Niña and its impacts
4:19 on our website.