Alternate Definitions for transition region

That region of the solar atmosphere lying between the chromosphere and the corona where the temperature rises from 104K to 106K. The transition region is only a few thousand kilometers thick.

Above the solar chromosphere and solar corona there is a transition region. The temperature here rises from 20000 to ~ 1-2 millions of K. Below the transition region, gravity dominates the shape of most features, so that the Sun may be described in terms of layers and horizontal features (like sunspots); above the transition region, dynamic forces dominate the shape of most features, so that the transition region itself is not a well- defined layer at a particular altitude.