Publication: JGR; HAO Author: Liying Qian; Authors as listed in article: Liying Qian, Joseph M. McInerney, Stan S. Solomon, Hanli Liu, and Alan G. Burns
Previous studies have established the importance of the increasing greenhouse gas 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.
Simulated thermosphere and ionosphere temperatures at 300 km in the 1960s, thermosphere mass density at 400 km in the 1960s, and their changes from the 1960s to 2010s, at 17UT, due to the change of greenhouse gas concentrations, and the change of the Earth’s magnetic field, respectively, under solar minimum and geomagnetically quiet conditions. (a), (a1), (a2): Neutral temperature and its changes; (b), (b1), (b2): ion temperature and its changes; (c), (c1, (c2): electron temperature and its changes; (d), (d1), d(2): mass density and its changes.
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 greenhouse gas 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 ~ 120oW – 20oE. The magnetic field driver played a more important role in the ionosphere in the longitude sector ~ 120oW – 20oE. 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 greenhouse gas driver being the dominant driver at lower altitudes (~ 200 km – 320 km), and the two drivers becoming comparable above; (3) although the magnetic field driver is important in the longitude sector ~ 120oW – 20oE, 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.