Statsraad Lehmkuhl is on a date with La Niña
May 22, the students on board Statsraad Lehmkuhl finally got to take a swim, jumping into the Pacific Ocean from the ship. The water was 25 ℃, nice and warm, but still several degrees cooler than normal. The La Niña phenomenon is the cause.
Our planet has many cycles. Everyone are familiar with night and day, and the seasons, but there are more - both in the warm interior of our earth, in the sea and in the atmosphere.
Right now, in the middle of the Pacific Ocean, the Statsraad Lehmkuhl is sailing surrounded by a phenomenon called La Niña, the little girl in Spanish. She is the sister of El Niño, the little boy. The siblings are the two phases of a cycle called ENSO.
El Niño is hot and La Niña cold.
The last six months, the surface water in the east of the Pacific Ocean has been 3-4-5 degrees colder than normal. The reason is that the trade wind, normally blowing steady from east to west, is unusually strong, and pushes the water on the surface west towards Indonesia.
The water must be replaced, and this is done by water streaming up from the depths off the coast of South America. This water is cold, and in the satellite image below we see how it spreads westwards like a blue belt.
The temperature in the sea affects the atmosphere above. The warm water that now accumulates in the west of the Pacific Ocean heats the air above. Pockets of warm air tend to rise upwards, like a hot-air balloon. Hot air can hold a lot of water vapor that is transported upwards with the rising air.
High in the atmosphere, the temperature drops, the air cools down, and can no longer hold on to the water vapor. Clouds form and it starts to rain. So, La Niña makes it rain more than normal over Indonesia, the Philippines and Malaysia. Australia and the southern part of Africa also receive more precipitation than normal.
But the phenomenon also affects the weather further away. Northeastern Africa is dryer in La Niña years, and so is western South America. Brazil further north is getting wetter.
Canada and the northern United States also receive more rainfall than normal, especially in winter. In the southern United States it is getting drier.
The effect of La Niña is so powerful, and affects such large areas, that the years the phenomenon occurs normally have been the coolest when we look at the temperature of the entire globe as a whole.
La Niña lasts only a few months, before the temperature in the sea returns to normal.
El Niño is the other phase of the ENSO cycle, and is in many ways the opposite of La Niña.
The phenomenon occurs when the trade winds are unusually weak, or even turn and blow to the east instead of to the west. This causes the surface water to lie still, no cold water is streaming up along the coast of Chile, and the Pacific becomes warmer and warmer.
The deep-water is rich in nutrients. Without new supply, the surface water not only becomes warmer, but also more and more nutrient-poor. The usually rich fishing off Chile can completely collapse in the El Niño years, and birds, sea lions, seals and whales struggle to find enough food.
If the humid and warm El Niño wind blows in towards the Andes, it is lifted up by the mountains and cooled down. This causes huge amounts of precipitation in the desert areas of Chile, Peru and Ecuador, with floods and landslides as a result.
On the west side of the Pacific Ocean, El Niño makes the air drier, and the monsoon rain on which then agriculture in Southeast Asia is so dependent can fail.
The El Niño years have been the warmest years recorded on our planet, but as the figure above shows, global warming makes even La Niña years now warmer than the El Niño years were just 20 years ago.