@article{0ac27179ed61465cbec4923515febb48,
title = "Diagnosing the Time‐Dependent Nature of Magnetosphere‐Ionosphere Coupling via ULF Waves at Substorm Onset",
abstract = "Azimuthal structuring is usually observed within the brightening auroral substorm onset arc; such structure has been linked to the exponential growth of electromagnetic ultralow‐frequency (ULF) waves. We present a case study investigating the timing and frequency dependence of such ULF waves on the ground and in the near‐Earth magnetotail. In the magnetotail, we observe an increase in broadband wave power across the 10‐ to 100‐s period range. On the ground, the arrival times spread from an epicenter. The onset of longer period waves occurs first and propagates fastest in latitude and longitude, while shorter periods appear to be more confined to the onset arc. The travel time from the spacecraft to the ground is inferred to be approximately 1–2 min for ULF wave periods between 15 and 60 s, with transit times of 60 s or less for longer period waves. This difference might be attributed to preferential damping of the shorter period waves, as their amplitude would take longer to rise above background levels. These results have important consequences for constraining the physics of substorm onset processes in the near‐Earth magnetotail and their communication to the ground.",
keywords = "ULF epicenter, ULF waves, auroral beads, substorm onset, timing, wavelet",
author = "Smith, {A. W.} and Rae, {I. J.} and C. Forsyth and Watt, {C. E. J.} and Murphy, {K. R.} and Mann, {I. R.}",
note = "Funding Information: We acknowledge NASA contract NAS5‐02099 and thank V. Angelopoulos for use of data from the THEMIS Mission. Specifically, we also acknowledge U. Auster and W. Baumjohann for the use of FGM data provided under the lead of the Technical University of Braunschweig and with financial support through the German Ministry for Economy and Technology and the German Center for Aviation and Space (DLR) under contract 50 OC 0302; S. Mende and E. Donovan for use of the ASI data, the CSA for logistical support in fielding and data retrieval from the GBO stations, and NSF for support of GIMNAST through grant AGS‐1004736; and S. Mende and C. T. Russell for use of the GMAG data and NSF for support through grant AGS‐1004814; I.R. Mann, D.K. Milling, and the rest of the CARISMA team for use of GMAG data. CARISMA is operated by the University of Alberta, funded by the Canadian Space Agency ( http://www.carisma.ca/carisma‐data‐repository ). AWS and IJR were supported by STFC Consolidated grant ST/S000240/1 and NERC grant NE/P017150/1. CF was supported by the NERC Independent Research Fellowship NE/N014480/1 and STFC Consolidated grant ST/S000240/1. CEJW was supported by STFC Consolidated grant ST/R000921/1 and NERC grant NE/P017274/1. KRM is support by the NSF grant number 1602403, NASA ROSES Guest Investigator 18‐HGIO18/2‐0122, and Space Weather Operations to Research 18‐HSWO2R18‐0010. The analysis in this paper was performed using Python, including the Pandas (McKinney, 2010 ), Numpy (van der Walt et al., 2011 ), Scikit‐learn (Pedregosa et al., 2011 ), Scipy (Virtanen et al., 2020 ), and Matplotlib (Hunter, 2007 ) libraries",
year = "2020",
month = nov,
language = "English",
volume = "125",
journal = "Journal of Geophysical Research: Space Physics",
issn = "2169-9380",
publisher = "American Geophysical Union",
number = "11",
}