Climate modelers understand how seasonal winds and ocean currents affect El Nio patterns in the eastern equatorial Pacific Ocean, impacting weather across the United States and sometimes around the world.
There is a cold tongue of surface waters stretching west along the equator from the coast of South America that has gone unrecognized.
The cold tongue influences the El Nio-Southern Oscillation, which affects weather in California and much of North America.
Earth's distance from the sun varies over the course of the year. Earth is 3 million miles closer to the sun than it is at its farthest point. The sun is more intense at perihelion.
The annual cycle of the cold tongue can be affected by a small yearly change in our distance from the sun. The effect of Earth's tilt on the seasons is understood to cause the cold tongue.
The period of the annual cycle arising from the tilt and distance effects are slightly different from one another.
Over a period of 11,000 years, the annual cycles from the distance effect and tilt go from being in phase to out of phase.
The distance effect is already incorporated into climate models, and his findings won't change predictions or climate projections. The 22,000-year phase cycle may have had effects for a long time. The timing of the ice ages is thought to have been affected by Earth's precession.
Other weather systems may be affected by the distance effect. The ENSO is likely affected because its workings are tied to the cold tongue season.
According to theory, the seasonal cycle of the cold tongue plays a key role in the development and cessation of ENSO events. Many of the key characteristics of ENSO are related to the seasonal cycle.
She said that ENSO events tend to peak during the Northern Hemisphere winters, and that they don't tend to persist beyond the spring. It is reasonable to think that the distance effect could have a big impact on ENSO.
Most people think that the cold tongue seasonal cycle is solved. There isn't anything interesting there. It is not solved according to this research. There is a mystery there. Our result raises the question of whether other regions on Earth have the same effect on the seasonal cycle.
The seasons are caused by the tilt of the Earth's axis according to co-author Anthony Broccoli. It's true and has been understood for a long time. The 'distance effect' may be a more important effect on climate than had been recognized before.
A group of people reported their findings in the journal Nature.
The Pacific cold tongue is affected by two different yearly cycles.
Seasonal change is the main driver of weather. The northern and southern hemispheres are illuminated differently because the equator is tilted. It's warmer in the north than it is in the south when the sun is overhead.
The Pacific equatorial trade winds, which blow from southeast to northwest across the south and equatorial Pacific and push surface waters west, cause upwelling of cold water along the equator that creates a tongue of cold surface water that spans from Ecuador across the Pacific
The strength of the trades is affected by the temperature of the cold tongue every year. This has a major influence on the ENSO, which peaks during the winter.
El Nio and La Nia affect whether California and the West Coast will have a wet or dry winter.
To understand if the El Nio/La Nia cycle has changed in the past, a lot of effort has been devoted to studying past climates. The annual cycle of ocean temperatures in the eastern Pacific cold tongue is what we focused on. The timing of perihelion, the point at which the earth is closest to the sun, has an influence on climate in the tropics.
Broccoli, co-director of the Rutgers Climate Institute, used a computer climate model to show that the distance changes caused by Earth's elliptical orbit dramatically changed the cold tongue yearly cycle. Climate modelers didn't pay much attention to the result.
The seasonal cycle was solved because our field is focused on El Nio. The result by Erb and Broccoli challenged the assumptions that were made.
The result of the simulations was confirmed by the group of people. The team showed how the effect works.
The world's'marine' and 'continental' hemispheres.
Changes in the sun's distance from Earth don't affect the Northern and Southern hemispheres in a different way. They warm the eastern hemisphere more than the western hemisphere because it is dominated by the Pacific Ocean.
The traditional way of thinking about monsoons is that the Northern Hemisphere warms up compared to the Southern Hemisphere, causing winds to blow onto land that causes monsoon rains. We're talking about east-west temperature differences that cause the winds here. The wind changes are coming from the east-west monsoon and the distance effect is the same.
The easterly trades in the west of the Pacific are affected by the differential heating of the marine and continental hemispheres.
The winds are strong when Earth is close to the sun. The winds become weak when the sun is farthest away. The annual cycle of the cold tongue can be traced back to the wind changes in the Eastern Pacific.
The distance effect on the cold tongue is one-third the strength of the tilt effect, and it leads to a strong annual cycle of the cold tongue. They canceled one another about 6,000 years ago. The distance effect on the cold tongue would have been larger in the past if Earth had been more elliptical.
The effect of such a cancellation could have had a worldwide effect on weather patterns.
The distance effect on climate can't be seen from observations because it's not comparable to the tilt effect.
The study is solely based on models. He said it's a prediction. A number of different models reproduce this behavior. In this study, we explained why this happens. We've found another annual cycle of the cold tongue that's driven by Earth's eccentricities.
The model-dependency of changes to ENSO is different from the robust changes to the cold tongue seasonal cycle.
While ENSO remains a challenge for climate models, we can look beyond climate model simulations to investigate the connection between changes in the annual cycle of the cold tongue and ENSO in the past. The paleoclimate records from the tropical Pacific have largely been interpreted in terms of past changes in ENSO, but our study underscores the need to separate changes in the cold tongue annual cycle from changes in ENSO.
The University of Wisconsin in Madison, the Massachusetts Institute of Technology, and William Roberts in the United Kingdom are all part of the group. The research was done while on sabbatical at the Research Institute for Environmental Changes of the Academia Sinica.
There are two annual cycles of the Pacific cold tongue under the influence of the sun. There is a DOI called 10.1038/s41586.
Journal information: Nature
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