Simulated Trends in Ionosphere-Thermosphere Climate Due to Predicted Main Magnetic Field Changes From 2015 to 2065

Abstract

The strength and structure of the Earth's magnetic field is gradually changing. During the next 50 years the dipole moment is predicted to decrease by $\sim$ 3.5%, with the South Atlantic Anomaly expanding, deepening, and continuing to move westward, while the magnetic dip poles move northwestward. We used simulations with the Thermosphere-Ionosphere-Electrodynamics General Circulation Model to study how predicted changes in the magnetic field will affect the climate of the thermosphere-ionosphere system from 2015 to 2065. The global mean neutral density in the thermosphere is expected to increase slightly, by up to 1% on average or up to 2% during geomagnetically disturbed conditions ( $K_p\ge 4$ ). This is due to an increase in Joule heating power, mainly in the Southern Hemisphere. Global mean changes in total electron content (TEC) range from $-$ 3% to +4%, depending on season and UT. However, regional changes can be much larger, up to about $\pm$ 35% in the region of $\sim$ 45°S to 45°N and 110°W to 0°W during daytime. Changes in the vertical $\overrightarrow{E}\times \overrightarrow{B}$ drift are the most important driver of changes in TEC, although other plasma transport processes also play a role. A reduction in the low-latitude upward $\overrightarrow{E}\times \overrightarrow{B}$ drift weakens the equatorial ionization anomaly in the longitude sector of $\sim$ 105-60°W, manifesting itself as a local increase in electron density over Jicamarca (12.0°S, 76.9°W). The predicted increase in neutral density associated with main magnetic field changes is very small compared to observed trends and other trend drivers, but the predicted changes in TEC could make a significant contribution to observationally detectable trends.

Keywords: ionosphere; long‐term trend; magnetic field; prediction; secular variation; thermosphere.

Figure 1

Magnetic field intensity (nT) in 2015 (left) and the difference between 2065 and 2015 (right) based on the IGRF (2015) and the Aubert (2015) prediction (2065). The white (gray) line marks the magnetic equator in 2015 (2065), and white dots (gray squares) mark the positions of the magnetic dip poles in 2015 (2065). The black triangle marks the location of Jicamarca, which we examine in section 3.3.

Figure 2

Difference (mf2065‐mf2015) in global mean (solid lines), NH (dashed lines), and SH (dotted lines) neutral density (%) versus height for the full year (black), for high geomagnetic activity conditions ( $K_p\ge 4$; red), and for low geomagnetic activity conditions ( $K_p\le 2$; blue). Differences that are statistically significant at the 95% level are plotted with thick lines, while thin lines show nonsignificant differences.

Figure 3

Difference in global mean TEC as a function of month and UT in TECU (left) and % (right).

Figure 4

TEC (TECU) in 2015 (left) and the difference between 2065 and 2015 (right) at 6 UT (top) and 18 UT (bottom) averaged over all days of the year. The black triangle marks the location of Jicamarca.

Figure 5

TEC (TECU) in 2015 (left) and the difference between 2065 and 2015 (right) at 18 UT plotted in magnetic latitude and geographic longitude averaged over all days of the year.

Figure 6

The vertical component of the $\overrightarrow{E}\times \overrightarrow{B}$ drift (top), the vertical component of the neutral wind projected onto the magnetic field ( $(\overrightarrow{U}·\overrightarrow{b})·(\overrightarrow{b}·\overrightarrow{k})$ (middle), and the vertical component of the field‐aligned diffusion (bottom) for mf2015 (left) and the mf2065‐mf2015 difference (right) at 18 UT averaged over all days of the year. Note that the color scale for the vertical $\overrightarrow{E}\times \overrightarrow{B}$ drift is fixed to $\pm$80 m/s (mf2015; left) and $\pm$20 m/s (mf2065‐mf2015; right) to allow for direct comparisons with the other velocity components and better visualization of the response at low to middle latitudes, while actual values at high latitudes are higher.

Figure 7

Annual mean electron density profile at Jicamarca for mf2015 (black) and mf2065 (red) averaged over all UTs. The 95% confidence interval is marked with thin lines.

Figure 8

Annual mean $N_m{F}_2$ and vertical $\overrightarrow{E}\times \overrightarrow{B}$ drift at Jicamarca as a function of LT for mf2015 (black) and mf2065 (red). The 95% confidence interval is marked with thin lines.

Figure 9

Annual mean $N_m{F}_2$ at 77.5°W and 18 UT (13 LT) as a function of latitude for mf2015 (black) and mf2065 (red). The 95% confidence interval is marked with thin lines. The black dotted line marks the latitude of Jicamarca.