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Extract from the Sacramento Peak Observatory page on the World Wide Web
This is the solar atmosphere between the photosphere and the corona.
(i) height about 2500 kilometers
(ii) temperature increases rapidly from the 4300 Kelvin to 1 million Kelvin
(iii) density is 8 x 10
(1/80,000) to 1 x 10
less dense than water
(iv) pressure - not much
The chromosphere's temperature gradient is increasing with height, so spectral lines are in emission and explains the color just prior or after a total solar eclipse. Because the temperature is increasing and elements are ionizing, the spectral lines are different than the photosphere.
The heating is due to the density decrease and mechanical heating. The density decrease allows for higher particle velocities which translates to higher energy. Mechanical energy is added to the
chromosphere from the convection zone. The granulation overshoots hundreds of kilometers. The effect in the chromosphere with the lower density is akin to popping a whip. Other oscillations below the chromosphere contribute to the mechanical heating, too.
Organized magnetic fields are common in the chromosphere because the density is not sufficient to mix the magnetic fields as the photosphere does. Supergranules have horizontal flows over a large distance, and the weak magnetic fields are pushed to the boundaries. Also present at the supergranule boundaries
are gas jets, called spicules. They are typically thousands of kilometers high with a 10,000 kilometer maximum height.
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