米蘭科維奇循環（Milankovitch cycles）是地球氣候變化的重要理論基礎之一，描述了地球軌道參數變化對氣候變化的影響。這些循環是由塞爾維亞天文學家米盧廷·米蘭科維奇（Milutin Milankovi?）在20世紀早期提出的，并在20世紀后半葉得到廣泛接受和進一步發展。
米蘭科維奇循環主要包括以下三種周期變化：偏心率（Eccentricity）變化、軌道傾角（Obliquity）變化、進動（Precession）變化。
這些循環的變化會導致地球接收到太陽輻射的分布和強度發生變化，從而影響到地球的氣候。例如，當地球軌道的偏心率較大時，地球距離太陽的距離變化較大，氣候可能更加寒冷；當軌道傾角較大時，季節的變化會更加明顯；而進動變化則會影響季節的持續時間和強度。米蘭科維奇循環理論為解釋地球氣候變化提供了重要的框架，被廣泛應用于地質學、氣候學和古氣候研究中，對于理解過去氣候變化和預測未來氣候變化具有重要意義。
運行軌道的三個變化
為一個約九萬六千年的周期。其間地球的軌道皆在圓形與橢圓形之間變化
。軌道離心率越小（越接近圓形）時，四季變化相對較不明顯，也不易有冰期的發生。反之，離心率越接
近1（但不等于）的軌道，四季明顯，也較易產生冰期。
2.地球自轉軸傾斜角度的變化
地球自轉軸的傾斜角度介于21.5度到24.5度之間，以四萬一千年為周期。
角度越大，高緯度地區因接受輻射的時間差異較大，易形成冰期。現今地球自轉軸傾斜角度為23.44度，
且有減少的跡象。
3.地球的歲差
因地球自轉軸的進動，造成一個大約兩萬六千年的周期。在遠日點時，若北半球傾向太陽
，冬天溫度將會相對較高；若因進動而導致南半球在遠日點時傾向太陽，北半球的冬天將較為酷寒。又
因北半球陸地多，比熱小，溫度容易下降，而較容易形稱冰期。
但，米蘭科維奇循環并未完全解釋氣候的變化，特別是冰期的產生，因為冰期的發生顯然小于十萬年這
個周期。
上述三種因素會集合影響地球的氣溫變化，例：當地球在遠日點且繞日運行的軌道離心率趨近于1，地球
自轉軸傾斜角度為最大的24.5度，且南半球傾向太陽，將可能發生極低溫的情形。此三個因素隔行掃描影響
著地球氣溫，每個因素不同的表現也讓地球的氣溫更加不可預測。
Earth’s movements
Milankovitch cycles are the collective effect of changes in the Earth's movements upon its climate, named after Serbian civil engineer and mathematician Milutin Milankovi?. The eccentricity, axial tilt, and 歲差 of the Earth's orbit vary in several patterns, resulting in 100,000-year ice age cycles of the Quaternary glaciation over the last few million years. The 地球's axis completes one full cycle of precession approximately every 26,000 years. At the same 時間, the elliptical orbit rotates, more slowly, leading to a 21,000-year cycle between the seasons and the orbit. In addition, the angle between Earth's rotational axis and the normal to the plane of its orbit moves from 22.1 degrees to 24.5 degrees and back again on a 41,000-year cycle. Currently, this angle is 23.44 degrees and is decreasing.
As the 地球 spins around its axis and orbits around the Sun, several quasi-periodic variations occur. Although the curves have a large number of sinusoidal components, a few components are dominant. Milankovitch studied changes in the eccentricity, obliquity, and precession of 地球's movements. Such changes in movement and orientation change the amount and location of solar radiation reaching the Earth. This is known as solar forcing (an example of radiative forcing). Changes near the north polar 面積 are considered important due to the large amount of land, which reacts to such changes more quickly than the oceans do.
軌道科學公司 shape (eccentricity) 軌道形狀(偏心率)
The 地球's orbit is an ellipse. The eccentricity is a measure of the departure of this ellipse from circularity. The shape of the Earth's orbit varies from being nearly circular (low eccentricity of 0.005) to being mildly elliptical (high eccentricity of 0.058) and has a mean eccentricity of 0.028. The major component of these variations occurs on a period of 413,000 years (eccentricity variation of ±0.012). A number of other terms vary between 95,000 and 136,000 years, and loosely combine into a 100,000-year cycle (variation of ?0.03 to +0.02). The present eccentricity is 0.017.
If the 地球 were the only planet orbiting our Sun, the eccentricity of its orbit would not vary in time. The Earth's eccentricity varies primarily due to interactions with the gravitational fields of Jupiter and Saturn. As the eccentricity of the orbit evolves, the semi-major axis of the 軌道科學公司 ellipse remains unchanged. From the 透視 of the perturbation theory used in celestial mechanics to compute the evolution of the orbit, the semi-major axis is an adiabatic invariant. According to Kepler's third law the period of the orbit is determined by the semi-major axis. It follows that the 地球's orbital period, the length of a sidereal year, also remains unchanged as the orbit evolves.
Currently the difference between closest approach to the Sun (perihelion) and furthest distance (aphelion) is only 3.4% (5.1 million km). This difference is equivalent to about a 6.8% change in incoming solar radiation. Perihelion presently occurs around January 3, while aphelion is around July 4. When the orbit is at its most elliptical, the amount of solar radiation at perihelion is about 23% greater than at aphelion. This difference is roughly 4 times the value of the eccentricity.
Season (Northern Hemisphere) Durations
Year Date: GMT Season Duration
2005 Winter Solstice 12/21/2005 18:35 88.99 days
2006 Spring Equinox 3/20/2006 18:26 92.75 days
2006 Summer Solstice 6/21/2006 12:26 93.65 days
2006 Autumn Equinox 9/23/2006 4:03 89.85 days
2006 Winter Solstice 12/22/2006 0:22 88.99 days
2007 Spring Equinox 3/21/2007 0:07 沒被記錄
本資料來自http://aa.usno.海軍mil
Orbital mechanics require that the length of the seasons be 正比例 to the areas of the seasonal quadrants, so when the eccentricity is extreme, the seasons on the far side of the orbit can be substantially longer in duration. When autumn and winter occur at closest approach, as is the case currently in the northern hemisphere, the 地球 is moving at its maximum velocity and therefore autumn and winter are slightly shorter than spring and summer. Thus, summer in the northern hemisphere is 4.66 days longer than winter and spring is 2.9 days longer than autumn.
Axial tilt (obliquity)
The angle of the 地球's axial tilt (obliquity) varies with 尊重 to the plane of the Earth's orbit. These slow 2.4° obliquity variations are roughly periodic, taking approximately 41,000 years to shift between a tilt of 22.1° and 24.5° and back again. When the obliquity increases, the amplitude of the seasonal cycle in insolation (INcident SOLar radiATION) increases, with summers in both hemispheres receiving more radiative 熔劑 from the Sun, and the winters less radiative flux. As a result, it is assumed that the winters become colder and summers warmer.
But these changes of opposite sign in the summer and winter are not of the same 星等 The annual mean insolation increases in high latitudes with increasing obliquity, while lower latitudes experience a 還原 in insolation. Cooler summers are suspected of encouraging the start of an ice age by melting less of the previous winter's ice and snow. So it can be argued that lower obliquity favors ice ages both because of the mean insolation reduction in high latitudes as well as the additional 還原 in summer insolation.
Currently the 地球 is tilted at 23.44 degrees from its orbital plane, roughly half way between its extreme values. The tilt is in the decreasing phase of its cycle, and will reach its minimum value around the year 10,000 AD.
Precession (wobble)
Precession is the change in the direction of the 地球's axis of rotation relative to the fixed stars, with a period of roughly 26,000 years. This gyroscopic motion is due to the tidal forces exerted by the sun and the moon on the 固體 Earth, associated with the fact that the 地球 is not a perfect sphere but has an equatorial bulge. The sun and moon contribute roughly equally to this effect. In addition, the orbital ellipse itself precesses in Space樂隊 (anomalistic precession), primarily as a result of interactions with Jupiter and Saturn. This orbital precession is in the opposite sense to the gyroscopic motion of the axis of rotation, shortening the period of the precession of the equinoxes with respect to the perihelion from 26,000 to 21,000 years.
When the axis is aligned so it points toward the Sun during perihelion, one polar hemisphere will have a greater difference between the seasons while the other hemisphere will have milder seasons. The hemisphere which is in summer at perihelion will receive much of the corresponding increase in solar radiation, but that same hemisphere will be in winter at aphelion and have a colder winter. The other hemisphere will have a relatively warmer winter and cooler summer.
When the Earth's axis is aligned such that aphelion and perihelion occur near the equinoxes, the Northern and Southern Hemispheres will have similar contrasts in the seasons.
At present, perihelion occurs during the Southern Hemisphere's summer, and aphelion is reached during the southern winter. Thus the Southern Hemisphere seasons are somewhat more extreme than the Northern Hemisphere seasons, when other factors are 相等
參考資料 >
米蘭科維奇循環.geologyscience.2024-04-08
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《地球科學》發表文章:從40萬年長偏心率周期看米蘭科維奇理論.新華網.2024-04-08