Earth's changing orbit over the last 100Ky. The orientation is
such that spring equinox (indicated by a vertical bar) is directly to
the front with the sun behind it. Northern Hemisphere summer is to
our right, and Northern Hemisphere winter is to the left. The apsidal
(dashed) line connects perihelion (Earth's closest approach to the
sun) to aphelion (the point when Earth is furthest from the sun). The
rotation of the apsidal line occurs because of the precession of the
equinoxes and has a roughly twenty-two thousand year period. The
semi-circle around the Earth indicates the location of the equator and
the straight line is the polar axis. Obliquity is defined as the
angle between the orbital and equatorial planes. The variations in
Earth's obliquity and the eccentricity of Earth's orbit have both been
increased in magnitude by a factor of ten. Also, the Earth's angular
velocity has been decreased by a factor of five thousand. Note that
Earth's angular velocity is slowest at aphelion and fastest at
perihelion.
Similar to the above but where the perspective is initially one of looking
down upon Earth's orbital plane and is then rotated such that spring equinox is
in the foreground with the sun behind it.
Orbitally induced changes in insolation. Changes in insolation intensity at
the top of Earth's atmosphere over the last 400Ky. Shading indicates the
diurnally averaged insolation in Watts per meter squared as a function of
latitude and day of the year. The black triangle at bottom indicates the
location of perihelion. At left is the anomaly in annual average insolation,
which varies with changes in Earth's obliquity.
To depict spatial (latitude and longitude) and temporal (annual and
>18KY) variability, insolation is zonally averaged and projected onto a sphere.
Each degree of longitude roughly corresponds to a day of the year, and both the
dominant seasonal cycle and long term orbital changes are evident. For the
equatorial view, the perspective rotates to make all the seasons
observable.
Similar to the above but with an equatorial view and a perspective that
rotates to make all seasons observable.
Plots
Summer energy defined as the sum of the diurnal average insolation on days
exceeding a specified threshold. Plots of summer energy are provided for the
last 500 ky for various thresholds at various latitudes: 85S, 75S,
65S, 55S, 45S,
35S, 25S, 15S,
5S, 5N, 15N, 25N,
35N, 45N, 55N,
65N, 75N, 85N.
The seasonal cycle depicted under various orbital configurations. Each
figure has five sub-panels where the top panel shows the seasonal cycle when
Earth's obliquity is 23.3 (the average value) and Earth's closest approach to
the sun (perihelion) occurs variously during northern hemisphere summer, fall
equinox, winter, and spring equinox. The low four panels show the seasonal
cycle for each orientation of perihelion with respect to the seasons but for an
obliquity of 22.3, 23.3, and 24.3 degrees. A relatively large eccentricity of
0.05 is used for all insolation figures: 85S, 75S, 65S, 55S, 45S, 35S, 25S, 15S, 5S,
5N, 15N, 25N, 35N, 45N, 55N, 65N, 75N, 85N.