Dear Tom,

What is the highest temperature ever recorded in the Earth’s atmosphere? I have read that a reading of higher than 3,500 degrees is possible in the upper atmosphere.

Kenneth Jacobs, Wilmette

Dear Kenneth,

What you have read is correct. In fact, readings of 4,000 degrees exist in portions of the upper atmosphere, in the ionosphere — a layer extending from about 30 to 600 miles above the Earth’s surface. It forms the boundary between the lower atmosphere, where we live and breathe, and the almost complete vacuum of outer space.

That high temperature of the ionosphere is not a “temperature” in the sense that we perceive it. It is based on the kinetic energy of gas molecules and free electrons and ions that are “heated” to rapid movement by bombardment from high-energy particles arriving from space and by short-wave energy from the sun. So few molecules and other particles exist at that great height that the total amount of energy there is minimal compared to what exists at the Earth’s surface. In an atmosphere so rarefied that is in near vacuum, the concepts of heat and temperature are meaningless.