Decomposition of Geomagnetic Secular Acceleration Into Traveling Waves Using Complex Empirical Orthogonal Functions

• Published in: Geophysical research letters Vol. 47; no. 17
• Main Authors: Chi‐Durán, Rodrigo, Avery, Margaret S., Knezek, Nicholas, Buffett, Bruce A.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 16.09.2020
• Subjects: Acceleration; Angular velocity; Chaos; Decomposition; Empirical orthogonal functions; Equator; Equatorial regions; Geomagnetic field; Geomagnetism; Orthogonal functions; Phase velocity; Satellite observation; Short pulses; Standing waves; Stratification; Traveling waves; Wave number
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2020GL087940

Satellite observations reveal short pulses in the second time derivative of the geomagnetic field. We seek to interpret these signals using complex empirical orthogonal functions (CEOFs). This methodology decomposes the signal into traveling waves, permitting estimates for the period, angular wave number, and phase velocity. We recover CEOFs from the CHAOS‐6 model, focusing on three geographic regions with strong secular acceleration. Two regions are confined to the equator, while the third is located under Alaska. We find evidence for both eastward and westward traveling waves with periods between 7 and 20 years. There is also evidence for weaker standing waves with complex spatial patterns. Two of the three regions have waves that are compatible with predictions for waves in a stratified fluid. Our results yield estimates for the structure of fluid stratification at the top of the core. Key Points Complex empirical orthogonal functions are computed from models of geomagnetic acceleration Eastward and westward traveling waves are detected in equatorial and high‐latitude regions Phase velocities and wavenumbers are compatible with waves in a stratified layer