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Notes on Sunlight

October 8, 2015

For the plate tectonics simulation, users can input an earth tilt as well as a rotation direction when the create the simulation. Tilt affects where the sunlight is strongest. You’ll notice that the highest amount of sunlight radiation falls on and under the equator, as our earth is tilted 23.5 degrees.

ceres_net_radiation_200809

Radiation is strongest around the equator and the sunlight equator

This tilt has numerous effects on the climate, as more sunlight beneath the equator produces more fluctuations in temperature meaning generally higher precipitation. The rotational direction effects which direction the current flows. Mountains cast shadows of dryness on their western faces.

If Earth had a east to west rotation, Africa would be lush and all of the Americas and China would be barren desert.

globalrainmap

Precipitation keeps up as you approach the equator, and mountains and continents leave shadows of dryness

It’s also worth noting the clines of skin color adapted to combat the higher sunlight radiation. The tilt explains Central African skin color, though I cannot answer as to why South Africans or Indonesians don’t have Congo level pigment. Perhaps the modern day populations who migrated there have yet to adapt to the sunlight, as it takes several generations to adapt fully. A colleague noted that diet also plays a major role in skin pigmentation, however it is out of scope for this simulation. Fully exploring this topic will come when the human element is introduced to the simulation.

global_distribution_of_skin_color

Clines of human skin color

One thing I’m noticing is that the people on the same longitude as the Congo don’t have skin as dark as the Congolese. Could this be due to the Earth’s tilt? Would the highest sunlight be somewhere to the south of the Indian Ocean

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