Lack of relationship between geoeffectiveness and orientations of magnetic clouds with bipolar B<inf>z</inf> and unipolar southward B<inf>z</inf>

Teh Wai Leong, Mardina Abdullah, Alina Marie Hasbi

Research output: Contribution to journalArticle

Abstract

Abstract In this study, 38 magnetic clouds (MCs) that caused significant geomagnetic storms (the minimum SYM-H, SH<inf>min</inf>, ≤-50 nT) are examined, in which 17 MCs were unipolar B<inf>z</inf> in south (S-type) and 21 MCs were bipolar B<inf>z</inf> (north-to-south, NS-type, or south-to-north, SN-type). For S-type MC, inclination angle of the axis of the MC, |θ|, is ≥45°, while |θ|<45° for bipolar MC. This paper aims to address a question: is the intensity of a MC-driven storm correlated with the orientations of bipolar and S-type MCs? Our results demonstrate that there is no direct and significant relationship between geoeffectiveness and orientations of bipolar and S-type MCs. In other words, there is no MC preference (bipolar or S-type MC) to regulate the SH<inf>min</inf> of the storm. On the whole, the SH<inf>min</inf> is found to strongly correlate with southward field B<inf>z</inf> (cc=0.96) and with the y component of the solar wind convective electric field (cc=-0.91) but to weakly correlate with solar wind speed (cc=-0.65). This result is consistent with previous studies by Wu and Lepping (2002), J. Geophys. Res. 107 (A10), 1314. doi:10.1029/2001JA000161. By separating MC-driven storms by size into moderate (-100 nT<SH<inf>min</inf>≤-50 nT), intense (-200 nT<SH<inf>min</inf>≤-100 nT), and super-intense (SH<inf>min</inf>≤-200 nT) categories, we find that (1) there was a high-speed stream at the trailing of NS-type MCs for moderate and intense storms, and (2) for super-intense storms driven by bipolar or S-type MCs, both solar wind speed and dynamic pressure had a significant jump at the same time before the onset of the storm, as compared to the other two categories. These jumps are the signatures of a shock. We conclude that the SH<inf>min</inf> of a MC-driven storm is regulated by the cloud's southward field B<inf>z</inf> and the y component of the electric field, regardless of whether the MC is bipolar or S-type. Also, the ambient solar wind structure (e.g., shock) ahead of MC may play a role in regulating the storm's intensity.

Original languageEnglish
Article number3860
Pages (from-to)27-34
Number of pages8
JournalPlanetary and Space Science
Volume115
DOIs
Publication statusPublished - 1 Sep 2015

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magnetic clouds
solar wind
electric field
wind velocity
geomagnetic storm
shock
electric fields
dynamic pressure
magnetic storms
inclination
signatures
high speed

Keywords

  • Geomagnetic storms
  • Interplanetary magnetic fields
  • Magnetic clouds

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

@article{2903d495ae1544b88286d969a9a06706,
title = "Lack of relationship between geoeffectiveness and orientations of magnetic clouds with bipolar Bz and unipolar southward Bz",
abstract = "Abstract In this study, 38 magnetic clouds (MCs) that caused significant geomagnetic storms (the minimum SYM-H, SHmin, ≤-50 nT) are examined, in which 17 MCs were unipolar Bz in south (S-type) and 21 MCs were bipolar Bz (north-to-south, NS-type, or south-to-north, SN-type). For S-type MC, inclination angle of the axis of the MC, |θ|, is ≥45°, while |θ|<45° for bipolar MC. This paper aims to address a question: is the intensity of a MC-driven storm correlated with the orientations of bipolar and S-type MCs? Our results demonstrate that there is no direct and significant relationship between geoeffectiveness and orientations of bipolar and S-type MCs. In other words, there is no MC preference (bipolar or S-type MC) to regulate the SHmin of the storm. On the whole, the SHmin is found to strongly correlate with southward field Bz (cc=0.96) and with the y component of the solar wind convective electric field (cc=-0.91) but to weakly correlate with solar wind speed (cc=-0.65). This result is consistent with previous studies by Wu and Lepping (2002), J. Geophys. Res. 107 (A10), 1314. doi:10.1029/2001JA000161. By separating MC-driven storms by size into moderate (-100 nT<SHmin≤-50 nT), intense (-200 nT<SHmin≤-100 nT), and super-intense (SHmin≤-200 nT) categories, we find that (1) there was a high-speed stream at the trailing of NS-type MCs for moderate and intense storms, and (2) for super-intense storms driven by bipolar or S-type MCs, both solar wind speed and dynamic pressure had a significant jump at the same time before the onset of the storm, as compared to the other two categories. These jumps are the signatures of a shock. We conclude that the SHmin of a MC-driven storm is regulated by the cloud's southward field Bz and the y component of the electric field, regardless of whether the MC is bipolar or S-type. Also, the ambient solar wind structure (e.g., shock) ahead of MC may play a role in regulating the storm's intensity.",
keywords = "Geomagnetic storms, Interplanetary magnetic fields, Magnetic clouds",
author = "{Wai Leong}, Teh and Mardina Abdullah and Hasbi, {Alina Marie}",
year = "2015",
month = "9",
day = "1",
doi = "10.1016/j.pss.2014.11.021",
language = "English",
volume = "115",
pages = "27--34",
journal = "Planetary and Space Science",
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}

TY - JOUR

T1 - Lack of relationship between geoeffectiveness and orientations of magnetic clouds with bipolar Bz and unipolar southward Bz

AU - Wai Leong, Teh

AU - Abdullah, Mardina

AU - Hasbi, Alina Marie

PY - 2015/9/1

Y1 - 2015/9/1

N2 - Abstract In this study, 38 magnetic clouds (MCs) that caused significant geomagnetic storms (the minimum SYM-H, SHmin, ≤-50 nT) are examined, in which 17 MCs were unipolar Bz in south (S-type) and 21 MCs were bipolar Bz (north-to-south, NS-type, or south-to-north, SN-type). For S-type MC, inclination angle of the axis of the MC, |θ|, is ≥45°, while |θ|<45° for bipolar MC. This paper aims to address a question: is the intensity of a MC-driven storm correlated with the orientations of bipolar and S-type MCs? Our results demonstrate that there is no direct and significant relationship between geoeffectiveness and orientations of bipolar and S-type MCs. In other words, there is no MC preference (bipolar or S-type MC) to regulate the SHmin of the storm. On the whole, the SHmin is found to strongly correlate with southward field Bz (cc=0.96) and with the y component of the solar wind convective electric field (cc=-0.91) but to weakly correlate with solar wind speed (cc=-0.65). This result is consistent with previous studies by Wu and Lepping (2002), J. Geophys. Res. 107 (A10), 1314. doi:10.1029/2001JA000161. By separating MC-driven storms by size into moderate (-100 nT<SHmin≤-50 nT), intense (-200 nT<SHmin≤-100 nT), and super-intense (SHmin≤-200 nT) categories, we find that (1) there was a high-speed stream at the trailing of NS-type MCs for moderate and intense storms, and (2) for super-intense storms driven by bipolar or S-type MCs, both solar wind speed and dynamic pressure had a significant jump at the same time before the onset of the storm, as compared to the other two categories. These jumps are the signatures of a shock. We conclude that the SHmin of a MC-driven storm is regulated by the cloud's southward field Bz and the y component of the electric field, regardless of whether the MC is bipolar or S-type. Also, the ambient solar wind structure (e.g., shock) ahead of MC may play a role in regulating the storm's intensity.

AB - Abstract In this study, 38 magnetic clouds (MCs) that caused significant geomagnetic storms (the minimum SYM-H, SHmin, ≤-50 nT) are examined, in which 17 MCs were unipolar Bz in south (S-type) and 21 MCs were bipolar Bz (north-to-south, NS-type, or south-to-north, SN-type). For S-type MC, inclination angle of the axis of the MC, |θ|, is ≥45°, while |θ|<45° for bipolar MC. This paper aims to address a question: is the intensity of a MC-driven storm correlated with the orientations of bipolar and S-type MCs? Our results demonstrate that there is no direct and significant relationship between geoeffectiveness and orientations of bipolar and S-type MCs. In other words, there is no MC preference (bipolar or S-type MC) to regulate the SHmin of the storm. On the whole, the SHmin is found to strongly correlate with southward field Bz (cc=0.96) and with the y component of the solar wind convective electric field (cc=-0.91) but to weakly correlate with solar wind speed (cc=-0.65). This result is consistent with previous studies by Wu and Lepping (2002), J. Geophys. Res. 107 (A10), 1314. doi:10.1029/2001JA000161. By separating MC-driven storms by size into moderate (-100 nT<SHmin≤-50 nT), intense (-200 nT<SHmin≤-100 nT), and super-intense (SHmin≤-200 nT) categories, we find that (1) there was a high-speed stream at the trailing of NS-type MCs for moderate and intense storms, and (2) for super-intense storms driven by bipolar or S-type MCs, both solar wind speed and dynamic pressure had a significant jump at the same time before the onset of the storm, as compared to the other two categories. These jumps are the signatures of a shock. We conclude that the SHmin of a MC-driven storm is regulated by the cloud's southward field Bz and the y component of the electric field, regardless of whether the MC is bipolar or S-type. Also, the ambient solar wind structure (e.g., shock) ahead of MC may play a role in regulating the storm's intensity.

KW - Geomagnetic storms

KW - Interplanetary magnetic fields

KW - Magnetic clouds

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