Possible record-breaking cooling in the thermosphere

One of the most important ways the solar cycle affects our planet is by cooling off the thermosphere during solar minimum. The thermosphere is the part of the earth’s atmosphere that begins at about 50 miles (80 kilometers) above the earth’s surface, extends to outer space, and is characterized by steadily increasing temperature with height. New data from NASA’s SABER instrument on board NASA’s TIMED satellite confirms the notion that our atmosphere is losing heat energy near the edge of space as we approach solar minimum. In fact, if current trends continue, it could soon set a Space Age record for cold according to NASA. There is good news and bad news in all of this. The good news is that when the thermosphere cools, it actually shrinks, thereby reducing drag on satellites in low Earth orbit which can increase the life of a satellite. The bad news is that this cooling aloft tends to delay the natural decay of space junk resulting in a more cluttered environment around Earth.

Thermosphere Climate Index (TCI)

The SABER instrument has been in orbit for only 17 years and it monitors infrared radiation from carbon dioxide (CO2) and nitric oxide (NO), two substances that play a vital role in the energy output of our thermosphere, the very top level of our atmosphere. By measuring the infrared glow of these molecules, SABER can assess the thermal state of gas at the very top of the atmosphere in the thermosphere. NASA has actually created an index called the Thermosphere Climate Index (TCI) to measure how much NO is dumped from the thermosphere into outer space. During the solar maximum phase, TCI is very high and it is low at the time of solar minimum.

According to NASA, the TCI is currently very low indeed as SABER is measuring 33 billion watts of infrared power from NO which is ten times smaller than what is seen during more active phases of a solar cycle. In fact, TCI numbers are very close to setting a record and that could very well happen sometime during the next several months (source). Although SABER has been in orbit for only 17 years, NASA has calculated the TCI going all the way back to the 1940s. According to NASA, “SABER taught us to do this by revealing how TCI depends on other variables such as geomagnetic activity and the sun’s UV output–things that have been measured for decades”.