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

I Cnossen,A Maute

doi:10.1029/2019ja027738

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 ∼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 ( Kp≥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 ±35% in the region of ∼45°S to 45°N and 110°W to 0°W during daytime. Changes in the vertical E→×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 E→×B→ drift weakens the equatorial ionization anomaly in the longitude sector of ∼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.

Highlights

The strength and structure of the Earth's magnetic field is continually changing: Over the past ∼180 years, the magnetic dipole moment has decreased by about 10%, while the magnetic dip poles have been moving northwestward in both hemispheres (Jackson et al, 2000; Thébault et al, 2015)
There are small differences in the contributions from the Northern Hemisphere (NH) and Southern Hemisphere (SH): The neutral density difference is consistently larger in the SH than in the NH in the lower thermosphere, up to ∼250- to 300-km altitude, while the reverse is true in the upper thermosphere, up to ∼500-km altitude
The weakening of the equatorial ionization anomaly (EIA) structure is fully consistent with the reduction in the upward E⃗ × B⃗ drift we find at Jicamarca, as the EIA itself is driven by the low-latitude vertical E⃗ × B⃗ drift (e.g., Anderson, 1981)

Summary

Introduction

The strength and structure of the Earth's magnetic field is continually changing: Over the past ∼180 years, the magnetic dipole moment has decreased by about 10%, while the magnetic dip poles have been moving northwestward in both hemispheres (Jackson et al, 2000; Thébault et al, 2015). A recent prediction of the Earth's magnetic field by Aubert (2015) showed that these trends are expected to continue during the coming century. The method used by Aubert (2015) combines geomagnetic data with a geodynamo model in a data assimilation framework to predict the geomagnetic field up to 100 years into the future. The ensemble spread gives an estimate of the prediction error. The dipole moment decreases by about 3.5%, from 7.78 × 1022 Am2 in 2015 to 7.51 × 1022 Am2 in 2065

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Results

Discussion

Conclusion