The Magnitude of IMF By Influences the Magnetotail Response to Solar Wind Forcing. Issue 11 (10th November 2021)

• Record Type: Journal Article
• Authors: Holappa, Lauri; Reistad, Jone Peter; Ohma, Anders; Gabrielse, Christine; Sur, Dibyendu
• Is Part Of: Journal of geophysical research. Volume 126:Issue 11(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-11-10
• Subjects: substorms -- solar wind; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2021JA029752
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: The dynamics of substorms are known to be dominated by the North‐South ( B z ) component of the Interplanetary Magnetic Field (IMF), which is the most important driver of the dayside reconnection. Even though the dawn‐dusk ( B y ) component is also known to play a role in substorm dynamics, its effects are not yet fully understood. In this paper we study how IMF B y modulates the onset latitude, strength and occurrence frequency of substorms as well as the isotropic boundary (IB) latitude of energetic protons. We show that the substorm onset latitude and the IB latitude are about one degree lower for large magnitude B y ( | B y | > 3 nT) than for small B y . In contrast, the substorm occurrence frequency is larger for small | B y | . We suggest that the magnetotail is more stable during large | B y |, requiring the magnetotail lobes (and hence the polar cap) to contain more flux to initiate a substorm compared to the situation when B y is small. Plain Language Summary: Substorms are global magnetic disturbances in which energy stored in the Earth's magnetic field is suddenly released, leading to intense aurorae and other space weather effects. Substorms are most frequent and strongest when the magnetic field incident to the Earth at the Sun‐Earth line has a strong southward component. In this paper we study how the occurrence and strength of substorms are affected by the east component of this magnetic field. We show that substorms are less frequent but stronger, with associated aurora extending to lower latitudes, when the east component is strongly positive or negative. These results help in developing more accurate space weather predictions in the future. Key Points: For similar solar wind forcing, increased IMF | B y | influence both substorm onset latitude and the proton isotropic boundary latitude Substorms are less frequent for large IMF | B y | for similar solar wind forcing The results indicate that the magnetotail response depends on the magnitude of the IMF B y component