Directed Network of Substorms Using SuperMAG Ground‐Based Magnetometer Data. Issue 12 (25th June 2019)

• Record Type: Journal Article
• Authors: Orr, L.; Chapman, S. C.; Gjerloev, J. W.
• Is Part Of: Geophysical research letters. Volume 46:Issue 12(2019)
• Page Start: 6268
• Page End: 6278
• Publication Date: 2019-06-25
• Subjects: substorms -- networks -- correlation -- ground magnetometers -- SuperMAG; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2019GL082824
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: We quantify the spatiotemporal evolution of the substorm ionospheric current system utilizing the SuperMAG 100+ magnetometers. We construct dynamical directed networks from this data for the first time. If the canonical cross‐correlation between vector magnetic field perturbations observed at two magnetometer stations exceeds a threshold, they form a network connection. The time lag at which canonical cross‐correlation is maximal determines the direction of propagation or expansion of the structure captured by the network connection. If spatial correlation reflects ionospheric current patterns, network properties can test different models for the evolving substorm current system. We select 86 isolated substorms based on nightside ground station coverage. We find, and obtain the timings for, a consistent picture in which the classic substorm current wedge forms. A current system is seen premidnight following the substorm current wedge westward expansion. Later, there is a weaker signal of eastward expansion. Finally, there is evidence of substorm‐enhanced convection. Plain Language Summary: Space weather makes beautiful auroral displays (the northern and southern lights), but with these come large‐scale electrical currents in the ionosphere, which generate disturbances of magnetic fields on the ground. These are observed by >100 magnetometer stations on the ground, and the challenge is to extract the important information from these many observations and present it as a few key parameters that indicate how severe the ground impact will be. Networks are now a common analysis tool in societal data, where people are linked based on various social relationships. Other examples of networks include the world wide web, where websites are connected via hyperlinks, or maps, where places are linked via roads. We have constructed networks from the magnetometer observations of space weather events (geomagnetic substorms), where magnetometers are linked if there is significant correlation between the observations. There has been considerable debate as to how the ionospheric pattern evolves during a geomagnetic substorm. We are able to use the networks to resolve some of these controversies. Key Points: The first dynamical network analysis of substorm current systems is directed, hence quantifying both formation and expansion Both the 100+ SuperMAG ground-based magnetometers and Polar VIS are utilized to obtain the full spatiotemporal pattern from isolated substorms We identified timings of a consistent sequence in which the classic substorm current wedge forms