On the origins and timescales of geoeffective IMF

Lockwood, Mike, Owens, Mathew J., Barnard, Luke A., Bentley, Sarah, Scott, Chris J. and Watt, Clare (2016) On the origins and timescales of geoeffective IMF. Space Weather, 14 (6). pp. 406-432. ISSN 1542-7390

2016SW001375.pdf - Published Version
Available under License Creative Commons Attribution 4.0.

Download (2MB) | Preview
Official URL: https://doi.org/10.1002/2016SW001375


Southward interplanetary magnetic field (IMF) in the geocentric solar magnetospheric (GSM) reference frame is the key element that controls the level of space weather disturbance in Earth's magnetosphere, ionosphere, and thermosphere. We discuss the relation of this geoeffective IMF component to the IMF in the geocentric solar ecliptic (GSE) frame, and using the almost continuous interplanetary data for 1996–2015 (inclusive), we show that large geomagnetic storms are always associated with strong southward, out‐of‐ecliptic field in the GSE frame: Dipole tilt effects, which cause the difference between the southward field in the GSM and GSE frames, generally make only a minor contribution to these strongest storms. The time‐of‐day/time‐of‐year response patterns of geomagnetic indices and the optimum solar wind coupling function are both influenced by the timescale of the index response. We also study the occurrence spectrum of large out‐of‐ecliptic field and show that for 1 h averages it is, surprisingly, almost identical in ICMEs (interplanetary coronal mass ejections), around CIRs/SIRs (corotating and stream interaction regions) and in the “quiet” solar wind (which is shown to be consistent with the effect of weak SIRs). However, differences emerge when the timescale over which the field remains southward is considered: for longer averaging timescales the spectrum is broader inside ICMEs, showing that these events generate longer intervals of strongly southward average IMF and consequently stronger geomagnetic storms. The behavior of out‐of‐ecliptic field with timescale is shown to be very similar to that of deviations from the predicted Parker spiral orientation, suggesting the two share common origins.

Item Type: Article
Subjects: F300 Physics
F500 Astronomy
F800 Physical and Terrestrial Geographical and Environmental Sciences
F900 Others in Physical Sciences
Department: Faculties > Engineering and Environment > Mathematics, Physics and Electrical Engineering
Depositing User: Rachel Branson
Date Deposited: 04 Aug 2020 09:01
Last Modified: 31 Jul 2021 12:04
URI: http://nrl.northumbria.ac.uk/id/eprint/43963

Actions (login required)

View Item View Item


Downloads per month over past year

View more statistics