Atmospheric and Oceanic Physics

[GordMay]

El Niño and La Niña

El Niño and La Niña are climate patterns, in the Pacific Ocean, that can affect weather worldwide.

El Niño has an impact on ocean temperatures, the speed and strength of ocean currents, the health of coastal fisheries, and local weather, from Australia to South America, and beyond.

Scientists use the Oceanic Nino Index [ONI], to measure deviations from normal sea-surface temperatures. El Niño events are indicated by sea surface temperature increases of more than 0.9° Fahrenheit, for at least five successive three-month seasons. The intensity of El Niño events varies from weak temperature increases (about 4–5° F), with only moderate local effects on weather and climate, to very strong increases (14–18° F) associated with worldwide climatic changes.

During normal conditions, in the Pacific ocean, trade winds blow west, along the equator, taking warm water from South America, towards Asia.
To replace that warm water, cold water rises from the depths [upwelling].

El Niño and La Niña are two opposing climate patterns, that break these normal conditions. Scientists call these phenomena the El Niño-Southern Oscillation [ENSO] cycle.

El Niño and La Niña can both have global impacts on weather, wildfires, ecosystems, and economies. Episodes of El Niño and La Niña typically last nine to 12 months, but can sometimes last for years. El Niño and La Niña events occur every two to seven years, on average, but they don’t occur on a regular schedule. Generally, El Niño occurs more frequently than La Niña.

El Niño

During El Niño, trade winds weaken. Warm water is pushed back east, toward the west coast of the Americas.

El Niño means ‘Little Boy’, in Spanish. South American fishermen first noticed periods of unusually warm water in the Pacific Ocean in the 1600s. The full name they used was “El Niño de Navidad”, because El Niño typically peaks around December.

El Niño can affect our weather significantly [1]. The warmer waters cause the Pacific jet stream to move south of its neutral position, and spread further east. With this shift, areas in the northern U.S. and Canada, are dryer and warmer than usual. But in the U.S. Gulf Coast and Southeast, these periods are wetter than usual, and have increased flooding.

El Niño also has a strong effect on marine life, off the U.S. Pacific coast. During normal conditions, upwelling brings water from the depths, to the surface; this water is cold and nutrient rich. During El Niño, upwelling weakens, or stops altogether. Without the nutrients from the deep, there are fewer phytoplankton off the coast. This affects fish that eat phytoplankton and, in turn, affects everything that eats fish. The warmer waters can also bring tropical species, like yellowtail and albacore tuna, into areas, that are normally too cold.

El Niño favors stronger hurricane activity, in the central and eastern Pacific basins, and suppresses it in the Atlantic basin [2].








La Niña

La Niña means ‘Little Girl’ in Spanish. La Niña is also sometimes called El Viejo, anti-El Niño, or simply "a cold event."

La Niña has the opposite effect of El Niño. During La Niña events, trade winds are even stronger than usual, pushing more warm water toward Asia. Off the west coast of the Americas, upwelling increases, bringing cold, nutrient-rich water to the surface.

These cold waters in the Pacific push the jet stream northward, and to weaken over the eastern Pacific. This tends to lead to drought in the southern U.S., and heavy rains and flooding in the Pacific Northwest, and Canada. During a La Niña year, winter temperatures are warmer than normal in the South, and cooler than normal in the North. La Niña can also lead to a more severe Atlantic hurricane season [2], and a less severe Pacific season.

During La Niña, waters off the Pacific coast are colder, and contain more nutrients than usual. This environment supports more marine life, and attracts more cold-water species, like squid and salmon, to places like the California coast.








[1] “United States El Niño Impacts” ➥ https://www.climate.gov/news-feature...%B1o-impacts-0

[2] “Impacts of El Niño and La Niña on the hurricane season”
➥ https://www.climate.gov/news-feature...rricane-season


Some Further reading:

[3] “What are La Niña and El Niño and why do they matter?”
➥ https://www.weather.gov/media/ajk/br...Winter1617.pdf

[4] “What are El Niño and La Niña, and how do they change the weather?”
➥ https://www.bbc.com/news/science-environment-64192508

[lestersails]

As an adolescent I aspired to lasting fame, I craved factual certainty, and I thirsted for a meaningful vision of human life - so I became a scientist. This is like becoming an archbishop so you can meet girls.
M. Cartmill

More seriously, this is an awesome thread. Pretty much everything is gray and/or probabilistic. Accepting and adapting to that without falling into the pit of nihilistic despair or using uncertainty to justify inaction is the key to being able to get along and get things done. Making good decisions in the face of uncertainty is an amazing and valuable skill.
Most people are certain they will arrive safely at their destination when they get on a plane. A minority really think they are going to die (identifiable by their white knuckles and beads of sweat). Only a few people think that there is a 1/8,000,000 chance they will die*, accept that risk, and go.

*https://news.mit.edu/2020/study-comm...afer-ever-0124

[dannc]

Originally Posted by lestersails

As an adolescent I aspired to lasting fame, I craved factual certainty, and I thirsted for a meaningful vision of human life - so I became a scientist. This is like becoming an archbishop so you can meet girls.
M. Cartmill...

That is an awesome quote. Very funny too. And so true.

Later,
Dan

[GordMay]

GLOBAL SCALE WEATHER AND FRONTOGENESIS:
➥ https://www.cruisersforum.com/galler...r&imageuser=79

[GordMay]

The JET STREAM(s)

Jet streams [the Jets] are relatively narrow bands of strong wind, in the tropopause, at the transition between the troposphere [where temperature decreases with height] and the stratosphere [where temperature increases with height],
typically occurring around ±30,000 feet, in elevation.

Within jet streams, the winds blow from west to east, but the band often shifts north and south, because jet streams follow the boundaries, between hot and cold air.

They form at the boundaries of adjacent air masses, with significant differences in temperature, such as the polar region, and the warmer air to the south.
They meander around the globe, dipping and rising in altitude/latitude, splitting at times, and forming eddies, and even disappearing altogether, to reappear somewhere else.

Jet streams also follow the Sun. As the Sun's elevation increases each day, in the spring, the average latitude of the jet stream shifts poleward.
By summer, in the Northern Hemisphere, the polar jet is typically found near the U.S. Canadian border.
As Autumn approaches, and the Sun's elevation decreases, the jet stream's average latitude moves toward the equator.

There are several different jet streams, around the globe.
The polar jet is located between the 50°-60° latitude lines, in both the Northern and Southern hemispheres.
On average, jet streams move at about 110 miles per hour. But dramatic temperature differences, between the warm and cool air masses, can cause jet streams to move at much higher speeds — 250 miles per hour, or faster. Speeds this high usually happen in polar jet streams in the winter time.
The subtropical jets [N & S] are located around the 30° latitude line.

The regions around 30° N/S, and 50°-60° N/S, are areas where changes in temperature, at any one point, are the greatest.
As the difference in temperature increases between the two locations, the strength of the wind increases.
Therefore, the regions around 30° N/S and 50°-60° N/S are also regions where the wind, in the upper atmosphere, is the strongest.

Jet streams are often depicted, on weather maps, by a line, indicating the location of the strongest wind. However, jet streams are wider, and not as distinct as a single line; they are regions where the wind speed increases toward a central core of greatest strength. Also, it does not reside at any one particular height, but can extend across hundreds of miles in width, and thousands of feet in height.

The fast-moving air currents in a jet stream can transport weather systems, from west to east, affecting temperature and precipitation. However, if a weather system is far away from a jet stream, it might stay in one place, causing heat waves or floods.

The jet directly impacts surface weather patterns.

Firstly , the jet acts to steer mid-latitude weather systems, so it can control which regions are storm-bound and, in the extreme, which can become dangerously dry.

Secondly , while the fastest winds of the jet core are far above the surface, weaker winds often extend all the way down to the surface. Many of us who live in the midlatitudes are acclimatized to prevailing westerly, and these winds are the very underbelly of the jet stream dragging along Earth’s surface.

Thirdly, the jet stream also acts as a sharp boundary, between contrasting air masses, with relatively warm, tropical air to the south, and much colder air on the northern, poleward side.
The location of the jet, and hence also the boundary, has a strong influence on temperatures, down at ground level.

The jet stream can also change the strength of an area of low pressure. It acts a bit like a vacuum cleaner, sucking air out of the top, and causing it to become more intense, lowering the pressure system. The lower the pressure within a system, generally the stronger the wind, and more stormy the result.

On the other hand, a slower, more buckled jet stream can cause areas of higher pressure to take charge, which typically brings less stormy weather, light winds, and dry skies.

Particularly on seasonal timescales, the jets can be nudged, or influenced, by other factors in the climate system, and ENSO is the prime example of this.

An El Niño event can affect the jets, in a couple of ways:
firstly, by warming the tropics and amplifying that crucial temperature contrast between latitudes,
and secondly by triggering regional patterns associated with Rossby waves .

[GordMay]

Oceanic and atmospheric Rossby waves [AKA: planetary waves] naturally occur, in rotating fluids [like air & water], largely due to the Earth's rotation. These waves affect the planet's weather and climate.

Atmospheric Rossby Waves
According to the National Weather Service, atmospheric Rossby waves form, primarily, as a result of the Earth's geography. Rossby waves help transfer heat, from the tropics, toward the poles, and cold air toward the tropics, in an attempt to return atmosphere to balance.
They also help locate the jet stream, and mark out the track of surface low pressure systems. The slow motion of these waves often results in fairly long, persistent weather patterns.

Rossby waves are a dominant component of the Ferrel circulation*. The tropical air carries heat poleward, and the polar air absorbs heat as it moves toward the Equator. The existence of these waves explains the low-pressure cells (cyclones) and high-pressure cells (anticyclones) that are important in producing the weather of the middle and higher latitudes.

* In the Ferrel cell, air flows poleward, and eastward, near the surface, and equatorward, and westward, at higher altitudes. This movement is the reverse, of the airflow, in the Hadley cell.

Oceanic Rossby Waves
Rossby waves, also known as planetary waves, naturally occur in rotating fluids. Within the Earth's ocean and atmosphere, these waves form, as a result of the rotation of the planet.
Waves at lower latitudes [closer to the equator] may take months, to a year to cross the ocean.
Waves that form farther away from the equator [at mid-latitudes] of the Pacific, may take closer to 10 to 20 years to make the journey.

The vertical motion of Rossby waves is small [±10cm], along the ocean's surface, and large [±91.4m] along the deeper thermocline [the transition area between the ocean's warm upper layer and colder depths].

Slow-moving oceanic Rossby waves are fundamentally different from ocean surface waves. Unlike waves that break along the shore, Rossby waves are huge, undulating movements of the ocean, that stretch, horizontally, across the planet, for hundreds of kilometers, in a westward direction.
They are so large and massive that they can change Earth's climate conditions. Along with rising sea levels, King Tides, and the effects of El Niño, oceanic Rossby waves contribute to high tides, and coastal flooding, in some regions of the world.

[GordMay]

Jet Streams play a critical role, in the location and severity, of weather events. Even a slight change, in the “waviness”, of the polar or the subtropical jet stream, can lead to dramatic weather changes, in mid-latitude regions.

Both peaks and valleys, of the Jet, have become more extreme, in recent decades.
This has led to changes in weather patterns.
Some places have grown wetter, and some drier, and there have also been more extended hot and cold spells, around the globe

Are these windy wanderings being caused by a warming planet, or vice versa? IDK!

One team of scientists say yes, and in a peer reviewed study [1], published in the journal Proceedings of the National Academy of Sciences [PNAS], they offer a theory to prove it.

A certain amount of waviness has always been a feature of jet streams. In the past 30 years, scientists have observed an intensification of the waves, coinciding with increased global warming. More waviness, in the jet stream, means that rain and wind remain in a region longer, than if the jet stream simply traveled due east, with no detours.

In the new study [1], the researchers developed a mathematical theory, that explains jet stream waviness, and then created a simulation of atmospheric circulation under warming conditions, to test their theory.

Because polar regions of the planet are warming faster than the mid-latitudes, the typical north-south temperature difference is lower. As this temperature difference decreases, it causes a slight drop in zonal winds, in the jet stream; which, in turn, leads to more meandering of the jet stream.
This means that the cyclones and anticyclones, associated with the meanders, are more stationary. There are weather systems ‘parked’ over some place on the planet. Thus, if a low-pressure system is sitting over one place, for a long time, moisture is just focused there, until the meanders start to move, and the weather system moves eastward. This can result in flooding.

However, another study [2], by Dr. Russell Blackport and Professor James Screen, shows that Arctic warming does not drive a more meandering jet stream. Their results strongly suggest that the observed, and simulated covariability, between waviness and temperature gradients, on interannual to decadal time scales, does not represent a forced response to Arctic amplification.

Instead, they believe any link is more likely to be a result of random fluctuations, in the jet stream, influencing Arctic temperatures, rather than the other way around.

[1] “Wavier jet streams driven by zonally asymmetric surface thermal forcing” ~ by Woosok Moon et al
Open Access ➥ https://www.pnas.org/doi/full/10.1073/pnas.2200890119

[2] "Insignificant effect of Arctic amplification on the amplitude of midlatitude atmospheric waves" ~ by Russell Blackport & James A. Screen
➥ https://www.science.org/doi/10.1126/sciadv.aay2880

[Pete7]

I enjoyed watching Sabrine and this YT film. She has a very dry sense of humour and lets slip every now and then. More to the point covers some interesting points.

https://www.youtube.com/watch?v=tnVW...neHossenfelder

[Chotu]

Adding to the resources, this article is one of the best written articles I have seen to help understand current weather trends from the top down.

The supporting graphics are incredible!

Gives you an excellent understanding of what’s to come and how El Niño and the jet stream will play together to create our (North American and European) weather patterns




https://www.severe-weather.eu/long-r...ada-europe-fa/