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.

Ionospheric Trend Over Wuhan During 1947–2017: Comparison Between Simulation and Observation

“…Our simulation shows that the overall geomagnetic effect on h m F 2 trend is comparable with that of Journal of Geophysical Research: Space Physics 10.1002/2017JA024675 CO 2 effect, while for f o F 2 trend, the geomagnetic effect is much stronger than CO 2 effect. This is in good agreement with the main conclusion of Cnossen (2014).…”

“…In comparison with other simulation studies, all the results show overall negative trend over Wuhan in both f o F 2 and h m F 2 , which accords well with the current simulation (Cnossen, ; Cnossen et al, ; Elias, ; Qian et al, ). Of those simulations, Cnossen et al () has similar configurations as the current study but assuming a 25% reduction of the dipole moment.…”

Ionospheric Trend Over Wuhan During 1947–2017: Comparison Between Simulation and Observation

“…Our simulation shows that the overall geomagnetic effect on h m F 2 trend is comparable with that of Journal of Geophysical Research: Space Physics 10.1002/2017JA024675 CO 2 effect, while for f o F 2 trend, the geomagnetic effect is much stronger than CO 2 effect. This is in good agreement with the main conclusion of Cnossen (2014).…”

“…In comparison with other simulation studies, all the results show overall negative trend over Wuhan in both f o F 2 and h m F 2 , which accords well with the current simulation (Cnossen, ; Cnossen et al, ; Elias, ; Qian et al, ). Of those simulations, Cnossen et al () has similar configurations as the current study but assuming a 25% reduction of the dipole moment.…”

Climate Changes in the Upper Atmosphere: Contributions by the Changing Greenhouse Gas Concentrations and Earth's Magnetic Field From the 1960s to 2010s

“…Our results are qualitatively consistent with Cnossen (2014), which evaluated the relative importance of the trends of the magnetic field and GHG concentrations to the trends of the neutral and ion temperatures near the F2 peak (∼300 km) at 12 LT, under the solar minimum and geomagnetically quiet condition from March 1 to May 1, 2008, in the following aspects: (1) the impact of the trend of the magnetic field is mainly in the longitude sector of ∼120°W–20°E. Our simulations additionally show that this is true for nighttime as well; (2) the neutral temperature trend is predominantly driven by the trends of the GHG concentrations; (3) the ion temperature trend is driven comparably by the two trend drivers.…”

Analysis and Attribution of Climate Change in the Upper Atmosphere From 1950 to 2015 Simulated by WACCM‐X

“…The spatial patterns of trends in h m F 2 , N m F 2 , and TEC (the latter similar to the pattern in N m F 2 ) clearly point to a superposition of CO 2 and main magnetic field effects, with the latter dominating the trends in the region of ∼50 • S to 20 • N, ∼60 • W to 20 • E, in good agreement with previous studies (Cnossen, 2014; 10.1029/2020JA028623 Cnossen & Richmond, 2013). While trends associated with main magnetic field changes can be either positive or negative, depending on the location, patches of negative trends are considerably stronger and larger in size than patches of positive trends.…”

Ionospheric Trend Over Wuhan During 1947–2017: Comparison Between Simulation and Observation

“…Our simulation shows that the overall geomagnetic effect on h m F 2 trend is comparable with that of Journal of Geophysical Research: Space Physics 10.1002/2017JA024675 CO 2 effect, while for f o F 2 trend, the geomagnetic effect is much stronger than CO 2 effect. This is in good agreement with the main conclusion of Cnossen (2014).…”

“…In comparison with other simulation studies, all the results show overall negative trend over Wuhan in both f o F 2 and h m F 2 , which accords well with the current simulation (Cnossen, ; Cnossen et al, ; Elias, ; Qian et al, ). Of those simulations, Cnossen et al () has similar configurations as the current study but assuming a 25% reduction of the dipole moment.…”

Climate Changes in the Upper Atmosphere: Contributions by the Changing Greenhouse Gas Concentrations and Earth's Magnetic Field From the 1960s to 2010s

“…Our results are qualitatively consistent with Cnossen (2014), which evaluated the relative importance of the trends of the magnetic field and GHG concentrations to the trends of the neutral and ion temperatures near the F2 peak (∼300 km) at 12 LT, under the solar minimum and geomagnetically quiet condition from March 1 to May 1, 2008, in the following aspects: (1) the impact of the trend of the magnetic field is mainly in the longitude sector of ∼120°W–20°E. Our simulations additionally show that this is true for nighttime as well; (2) the neutral temperature trend is predominantly driven by the trends of the GHG concentrations; (3) the ion temperature trend is driven comparably by the two trend drivers.…”

Analysis and Attribution of Climate Change in the Upper Atmosphere From 1950 to 2015 Simulated by WACCM‐X

“…The spatial patterns of trends in h m F 2 , N m F 2 , and TEC (the latter similar to the pattern in N m F 2 ) clearly point to a superposition of CO 2 and main magnetic field effects, with the latter dominating the trends in the region of ∼50 • S to 20 • N, ∼60 • W to 20 • E, in good agreement with previous studies (Cnossen, 2014; 10.1029/2020JA028623 Cnossen & Richmond, 2013). While trends associated with main magnetic field changes can be either positive or negative, depending on the location, patches of negative trends are considerably stronger and larger in size than patches of positive trends.…”

Ionospheric Trend Over Wuhan During 1947–2017: Comparison Between Simulation and Observation

“…Our simulation shows that the overall geomagnetic effect on h m F 2 trend is comparable with that of Journal of Geophysical Research: Space Physics 10.1002/2017JA024675 CO 2 effect, while for f o F 2 trend, the geomagnetic effect is much stronger than CO 2 effect. This is in good agreement with the main conclusion of Cnossen (2014).…”

“…In comparison with other simulation studies, all the results show overall negative trend over Wuhan in both f o F 2 and h m F 2 , which accords well with the current simulation (Cnossen, ; Cnossen et al, ; Elias, ; Qian et al, ). Of those simulations, Cnossen et al () has similar configurations as the current study but assuming a 25% reduction of the dipole moment.…”

Climate Changes in the Upper Atmosphere: Contributions by the Changing Greenhouse Gas Concentrations and Earth's Magnetic Field From the 1960s to 2010s

“…Our results are qualitatively consistent with Cnossen (2014), which evaluated the relative importance of the trends of the magnetic field and GHG concentrations to the trends of the neutral and ion temperatures near the F2 peak (∼300 km) at 12 LT, under the solar minimum and geomagnetically quiet condition from March 1 to May 1, 2008, in the following aspects: (1) the impact of the trend of the magnetic field is mainly in the longitude sector of ∼120°W–20°E. Our simulations additionally show that this is true for nighttime as well; (2) the neutral temperature trend is predominantly driven by the trends of the GHG concentrations; (3) the ion temperature trend is driven comparably by the two trend drivers.…”

Analysis and Attribution of Climate Change in the Upper Atmosphere From 1950 to 2015 Simulated by WACCM‐X

“…The spatial patterns of trends in h m F 2 , N m F 2 , and TEC (the latter similar to the pattern in N m F 2 ) clearly point to a superposition of CO 2 and main magnetic field effects, with the latter dominating the trends in the region of ∼50 • S to 20 • N, ∼60 • W to 20 • E, in good agreement with previous studies (Cnossen, 2014; 10.1029/2020JA028623 Cnossen & Richmond, 2013). While trends associated with main magnetic field changes can be either positive or negative, depending on the location, patches of negative trends are considerably stronger and larger in size than patches of positive trends.…”