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

Previous studies have established the importance of the increasing greenhouse gas (GHG) concentrations in causing trends in the thermosphere and ionosphere (T-I). Recent work indicates that the changing Earth's magnetic field is also important. We conduct whole atmosphere model simulations to examine T-I trends driven by these two drivers and their relative importance. We found that, (1) trends in the T-I, driven by either of the two drivers, exhibited significant latitudinal and longitudinal variability; (2) in the thermosphere, trends were predominantly driven by the GHG driver except that the magnetic field driver played a small role in the neutral temperature trend (∼25%) in some regions mainly in the longitude sector ∼120°W–20°E. The magnetic field driver played a more important role in the ionosphere in the longitude sector ∼120°W–20°E. In this longitude sector, the two drivers were comparable in driving the trends of hmF2, NmF2, and electron temperature; the relative importance of the two drivers to the ion temperature trend additionally depends on altitude, with the GHG driver being the dominant driver at lower altitudes (∼200–320 km), and the two drivers becoming comparable above; (3) although the magnetic field driver is important in the longitude sector ∼120°W–20°E, it drove both negative and positive trends in roughly equal amounts, consequently, its contributions to the global average trends in the T-I are negligible.