Earth-sun distance dramatically alters seasons in the equatorial Pacific in a 22,000-year cycle

Posted: November 13, 2022 by oldbrew in climate, Cycles, ENSO, modelling, research, weather
Tags: ,

Apogee = position furthest away from Earth. Earth. Perihelion = position closest to the sun. Moon. Perigee = position closest to Earth. Sun. Aphelion = position furthest away from the sun. (Eccentricities greatly exaggerated!)

Planetary cycles affecting climate. The study title: ‘Two annual cycles of the Pacific cold tongue under orbital precession’. Some real climate change theory to ponder.
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Weather and climate modelers understand pretty well how seasonal winds and ocean currents affect El Niño patterns in the eastern equatorial Pacific Ocean, impacting weather across the United States and sometimes worldwide, says Robert Sanders, University of California – Berkeley (via

But new computer simulations show that one driver of annual weather cycles in that region—in particular, a cold tongue of surface waters stretching westward along the equator from the coast of South America—has gone unrecognized: the changing distance between Earth and the sun.

The cold tongue, in turn, influences the El Niño-Southern Oscillation (ENSO), which impacts weather in California, much of North America, and often globally.

The Earth-sun distance slowly varies over the course of the year because Earth’s orbit is slightly elliptical. Currently, at its closest approach—perihelion—Earth is about 3 million miles closer to the sun than at its farthest point, or aphelion. As a result, sunlight is about 7% more intense at perihelion than at aphelion.

Research led by the University of California, Berkeley, demonstrates that the slight yearly change in our distance from the sun can have a large effect on the annual cycle of the cold tongue. This is distinct from the effect of Earth’s axial tilt on the seasons, which is currently understood to cause the annual cycle of the cold tongue.

Because the period of the annual cycle arising from the tilt and distance effects are slightly different, their combined effects vary over time, said lead researcher John Chiang, UC Berkeley professor of geography.

“The curious thing is that the annual cycle from the distance effect is slightly longer than that for tilt—around 25 minutes, currently—so over a span of about 11,000 years, the two annual cycles go from being in phase to out of phase, and the net seasonality undergoes a remarkable change, as a result,” Chiang said.

Chiang noted that the distance effect is already incorporated into climate models—though its effect on the equatorial Pacific was not recognized until now—and his findings will not alter weather predictions or climate projections.

But the 22,000-year phase cycle may have had long-term, historical effects. Earth’s orbital precession is known to have affected the timing of the ice ages, for example.

The distance effect—and its 22,000-year variation—also may affect other weather systems on Earth. The ENSO, which also originates in the equatorial Pacific, is likely affected because its workings are closely tied to the seasonal cycle of the cold tongue.

“Theory tells us that the seasonal cycle of the cold tongue plays a key role in the development and termination of ENSO events,” said Alyssa Atwood, a former UC Berkeley postdoctoral fellow who is now an assistant professor at Florida State University in Tallahassee.

“Because of this, many of ENSO’s key characteristics are synced to the seasonal cycle.”

Full article here.
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Study: Two annual cycles of the Pacific cold tongue under orbital precession (Nov. 2022)

  1. […] Earth-sun distance dramatically alters seasons in the equatorial Pacific in a 22,000-year cycle — … […]

  2. oldbrew says:

    From the Berkeley website…

    Caption: The monthly sea surface temperature in the eastern Pacific Ocean in normal, El Niño and El Niña years. The strength of the Pacific cold tongue, most evident in the top image, is linked to the El Niño-Southern Oscillation (ENSO). (Image credit: NOAA)

    Source —
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    Also — A Tale of two Annual Cycles: The Remarkable Change in Pacific Cold Tongue Seasonality Under Orbital Precession
    Event Type: Webinar [April 2022]

    Speaker: John Chiang, University of California – Berkeley


    I will argue that the surface temperature of the Pacific cold tongue possesses not one, but two distinct annual cycles. One originates from the Earth’s axial tilt (“tilt effect”), and in accord with current understanding of how the cold tongue annual cycle arises. The other annual cycle is driven by the variation in Earth-Sun distance (‘distance effect’) from orbital eccentricity. As the two annual cycles possess slightly different periodicities, over a precession cycle the two annual cycles interfere resulting in a complex evolution of net cold tongue seasonality. The annual cycle amplitude from the distance effect increases linearly with eccentricity, and is comparable to the amplitude from the tilt effect at the largest eccentricity values over the past half million years. Mechanistically, the distance effect on the cold tongue arises through a seasonal longitudinal shift in the Walker circulation and subsequent wind forcing on the tropical Pacific ocean-atmosphere system. Implications of this finding for paleoclimate, and for our understanding of seasonality, will be discussed.

  3. oldbrew says:

    Precession modulation of the South Pacific westerly wind belt over the past million years [2019]
    Frank Lamy , John C. H. Chiang, Gema Martínez-Méndez, +6, and Jan-Berend Stuut
    . . .

    The southern westerly wind belt interacts with the Antarctic Circumpolar Current and strongly impacts the Southern Ocean carbon budget, and Antarctic ice-sheet dynamics across glacial–interglacial cycles. We investigated precipitation-driven sediment input changes to the Pacific off Chile over the past one million years, revealing strong precession (19/23-ka) cycles. Our model simulations indicate that the observed cycles are linked to meridional shifts in water vapor transport from the tropical Pacific toward Chile, ultimately forced by variations of the subtropical jet. The wintertime strengthening of the jet is unique to the South Pacific realm and affects winter-controlled atmosphere–ocean processes at mid- and high southern latitudes, with implications for the global overturning circulation and the oceanic storage of atmospheric CO2. [bold added]
    – – –
    The ~112 kyr perihelion precession is the beat period of the 19 and 23 kyr. cycles – see Orbital Resonance post…

  4. P.A.Semi says:

    Perihelium distance in January also affects European February temperature:

    Blue line is temperature anomaly, difference from long-time average, in a rectangle roughly over Europe, averaged during whole February, with +1 -1 °C range marked, in NOAA/NCEP re-analysis, the black line is EMB (Earth-Moon barycenter) Perihelium distance (upward near Sun, downward more far from Sun) from JPL ephemerides…

    The perihelium distance is different each year, beside slowly progressing toward more circular orbit, ie. more distant in northern winter, toward multiple thousands years from now…

    From this can be expected, that there is a decade of colder winters in Northern hemisphere ahead, if there were no other impulses like El Nino/La Nina etc…
    (Actually, multiple different signals may add to produce final answer…)

    From longer perspective – there is some cycle pulsing between more circular and more elliptical (when more elliptical, the perihelium is closer to Sun) and the perihelium shifts in the year (by cca 1 month in 2000 years? – now it softens Northern winters and summers, but in cca 10000 years it will make both harsher), while the Earth axis precession also influences date shifting somehow (I’m not sure about period)…


  5. Paul Vaughan says:

    excerpt from the modelling article:

    “Earth’s ‘marine’ and ‘continental’ hemispheres […] warm the eastern “continental hemisphere” dominated by the North and South American and African and Eurasian landmasses, more than it warms the Western Hemisphere […] east-west monsoon […] winds generated by […] differential heating of the marine and continental hemispheres […] wind changes are then propagated”

    The top mode of observed (minus seasonal) variability is east-west for all the major variables.

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