Impact angle control of interplanetary shock geoeffectiveness: A statistical study

We present a survey of interplanetary (IP) shocks using Wind and ACE satellite data from January 1995 to December 2013 to study how IP shock geoeffectiveness is controlled by IP shock impact angles. A shock list covering one and a half solar cycle is compiled. The yearly number of IP shocks is found...

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Bibliographic Details
Published in:Journal of geophysical research. Space physics 2015-06, Vol.120 (6), p.4313-4323
Main Authors: Oliveira, Denny M., Raeder, Joachim
Format: Article
Language:English
Subjects:
Advanced Composition Explorer
Auroral substorms
Correlation
Correlation coefficient
Correlation coefficients
Earth magnetosphere
Geomagnetic stations
Geomagnetism
Geophysics
Ground-based observation
Impact angle
interplanetary shocks
Low speed
Magnetic fields
Magnetometers
Magnetotails
Satellite data
Solar cycle
Solar cycles
Statistical analysis
substorms
Sunspot numbers
Sunspots
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Summary:We present a survey of interplanetary (IP) shocks using Wind and ACE satellite data from January 1995 to December 2013 to study how IP shock geoeffectiveness is controlled by IP shock impact angles. A shock list covering one and a half solar cycle is compiled. The yearly number of IP shocks is found to correlate well with the monthly sunspot number. We use data from SuperMAG, a large chain with more than 300 geomagnetic stations, to study geoeffectiveness triggered by IP shocks. The SuperMAG SML index, an enhanced version of the familiar AL index, is used in our statistical analysis. The jumps of the SML index triggered by IP shock impacts on the Earth's magnetosphere are investigated in terms of IP shock orientation and speed. We find that, in general, strong (high speed) and almost frontal (small impact angle) shocks are more geoeffective than inclined shocks with low speed. The strongest correlation (correlation coefficient R = 0.78) occurs for fixed IP shock speed and for varied IP shock impact angle. We attribute this result, predicted previously with simulations, to the fact that frontal shocks compress the magnetosphere symmetrically from all sides, which is a favorable condition for the release of magnetic energy stored in the magnetotail, which in turn can produce moderate to strong auroral substorms, which are then observed by ground‐based magnetometers. Key Points Interplanetary shocks and solar cycle Statistical analysis of interplanetary shock properties Geomagnetic activity triggered by interplanetary shocks
ISSN:2169-9380
2169-9402
DOI:10.1002/2015JA021147