Thermosphere Climate Index (TCI)

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Climatologists now know that the Sun is entering one of its deepest minima of the space era, with all the consequences it entails for the dangerousness of human missions subject to a very sensitive increase in cosmic rays, indeed a solar minimum means less protection. But how does the atmosphere respond to these solar cycles? A new parameter seems to open up new avenues of investigation.

Our atmosphere, especially the higher one, must respond in some way to the variation of solar activity. In particular, the study of the thermosphere (over 100 km high) has proven to be fundamental, which shows a very strong link with the solar cycle. In simple terms, it has been found that the temperature of the thermosphere increases significantly during solar maxima and decreases during minima. This effect depends on the thermal energy loss of our atmosphere as a whole.

These results are obtained through the SABER instrumentation inserted in NASA's TIMED satellite, which analyzes the infrared emissions of CO2 and nitric oxide (NO), two substances that regulate the energy balance between 100 and 300 km in height. The analysis of the data and their detailed study recently led NASA to create a new parameter, the Thermosphere Climate Index (TCI), a number expressed in watts that day by day measures the amount of NO discharged from the thermosphere towards outer space and the thermal energy that molecules discharge into space. The TCI is very high (HOT) during solar maxima, and very low (COLD) during solar minima.

As already mentioned, the thermosphere plays a fundamental role in the response of the atmosphere to solar activity and, therefore, this new parameter has become equally fundamental for any climate model also related to lower layers (nothing can be considered separate and independent in the atmosphere).

Although SABER has only been in orbit for 17 years, it has been possible to calculate the TCI value up to the 1940s, since other connections with parameters already well known for several decades have been highlighted.

In the attached graph (M. G. Mlynczak et al., NASA Langley Research Center, Hampton, Virginia), the trend of the TCI starting from 1950 is reported, and its perfect correspondence with diagrams related to solar spots is more than evident.

At present, the TCI is worth 46 GW (GigaWatt) of infrared energy from NO, which is equivalent to a value ten times lower than that of the solar maximum of 1957-58, therefore, the upper part of the Earth's atmosphere is ten times colder than back then. The TCI values are very close to the record of cold (minimum of 2009) that could also be surpassed in the coming months, towards the end of the year.

To conclude that this new relationship cannot be of great help in future climate models would be a real insult to reason.

I hope to be able to publish a further analysis tomorrow.