Dayside Polar Cap Density Enhancements Formed During Substorms
Name
JGR Space Physics - 2020 - Goodwin - Dayside Polar Cap Density Enhancements Formed During Substorms.pdf
Description
Published version
Size
7.5 MB
Format
Adobe PDF
Checksum (MD5)
055ad65348da35343632a4bc3ce98950
Author(s)
Goodwin, LV
Nishimura, Y
Coster, AJ
Zhang, S
Nishitani, N
Ruohoniemi, JM
Anderson, BJ
Zhang, Q‐H
Date Issued
October 9, 2020
Journal
Journal of Geophysical Research: Space Physics
Publisher
American Geophysical Union
Citation
Goodwin, L. V., Nishimura, Y., Coster, A. J., Zhang, S., Nishitani, N., Ruohoniemi, J. M., et al. (2020). Dayside polar cap density enhancements formed during substorms. Journal of Geophysical Research: Space Physics, 125, e2020JA028101.
Version
Final published version
Abstract
The formation of polar cap density enhancements, such as tongues‐of‐ionization (TOIs), are often attributed to enhanced dayside reconnection and convection due to solar wind changes. However, ionospheric poleward moving density enhancements can also form in the absence of changes in the solar wind. This study examines how TOI and patch events that are not triggered by solar wind changes relate to magnetospheric processes, specifically substorms. Based on total electron content and Super Dual Auroral Radar Network (SuperDARN) observations, we find substorms that occur at the same time as TOIs are associated with sudden enhancements in dayside poleward flows during the substorm expansion phase. Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) observations also show enhanced field‐aligned currents (FACs) that extend into the dayside ionosphere during this period. We suggest that the global enhancement of FACs and convection during these substorms are the drivers of these TOIs by enhancing dayside convection and transporting high‐density lower‐latitude plasma into the polar cap. However, we also find that not all substorms are coincident with polar cap density enhancements. A superposed epoch study showed that the AL index for TOIs during substorms is not particularly stronger than substorms without TOIs, but epoch studies of AMPERE observations do show events with TOIs to have a higher total FAC on both the dayside and nightside. Our results show the importance of TOI formation during substorms when solar wind drivers are absent, and the importance of considering substorms in the global current system. This work also shows the need to incorporate substorms into models of high‐latitude global convection and currents.
MIT Department
Haystack Observatory
Terms of Use
Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use.
Persistent DSpace Link
DOI of Published Version
https://doi.org/10.1029/2020ja028101
