The importance of geomagnetic field changes versus rising CO₂levels for long-term change in the upper atmosphere

Abstract

The Earth's upper atmosphere has shown signs of cooling and contraction over the past decades. This is generally attributed to the increasing level of atmospheric CO 2 , a coolant in the upper atmosphere. However, especially the charged part of the upper atmosphere, the ionosphere, also responds to the Earth's magnetic field, which has been weakening considerably over the past century, as well as changing in structure. The relative importance of the changing geomagnetic field compared to enhanced CO 2 levels for long-term change in the upper atmosphere is still a matter of debate. Here we present a quantitative comparison of the effects of the increase in CO 2 concentration and changes in the magnetic field from 1908 to 2008, based on simulations with the ThermosphereIonosphere-Electrodynamics General Circulation Model (TIE-GCM). This demonstrates that magnetic field changes contribute at least as much as the increase in CO 2 concentration to changes in the height of the maximum electron density in the ionosphere, and much more to changes in the maximum electron density itself and to low-/mid-latitude ionospheric currents. Changes in the magnetic field even contribute to cooling of the thermosphere at~300 km altitude, although the increase in CO 2 concentration is still the dominant factor here. Both processes are roughly equally important for long-term changes in ion temperature.

Long-term variations of the upper atmosphere parameters on Rome ionosonde observations and their interpretation

“…An average daytime h m F 2 is ∼300 km then an h m F 2 decrease is ∼3 km. This is close to the result of model (TIE-GCM) simulations by Cnossen (2014) for a ∼28% increase in CO 2 concentration which gave a fairly uniform decrease in h m F 2 of about 5 km. Assuming that CO 2 increase has started 30-40 years ago one may expect a trend in h m F 2 of 1 km/decade.…”

“…The same result follows from TIE-GCM model simulations by Cnossen (2014) which show "very clearly how little influence the increase in CO 2 concentration has had on f o F 2 ". Therefore, negative f o F 2 and f o F 1 trends ( Fig.…”

Geomagnetic control of the midlatitude foF1 and foF2 long‐term variations: Recent observations in Europe

“…It should be stressed that there are no direct experimental confirmations that a 20% CO 2 increase in the Earth's atmosphere [ Houghton et al ., ] can explain the observed ionospheric trends. Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIE‐GCM) simulations by Cnossen [] have shown “very clearly how little influence the increase in CO 2 concentration has had on f o F 2 ” and this agrees with theoretical and previous model predictions by Rishbeth [] and Rishbeth and Roble []. The first TIE‐GCM simulations by Rishbeth and Roble [] with doubled CO 2 mixing ratio gave a small f o F 2 decrease, mostly less than 0.5 MHz.…”

Long-term variation in the upper atmosphere as seen in the geomagnetic solar quiet daily variation

“…This enhancement in the foE due to the greenhouse effect may lead to a positive trend in the Sq amplitude. The effect of enhanced greenhouse gases on the Sq amplitude was recently simulated by Cnossen (2014), who showed that changes in the ambient magnetic field contribute much more to the long-term trends in the Sq amplitude than enhanced greenhouse gases.…”