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The Magnitude of IMF By Influences the Magnetotail Response to Solar Wind Forcing

First Published : October 21, 2021

Written by Lauri Holappa, Jone Peter Reistad, Anders Ohma, Christine Gabrielse, Dibyendu Sur

DOI : 10.1029/2021JA029752

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The dynamics of substorms are known to be dominated by the North-South (urn:x-wiley:21699380:media:jgra56834:jgra56834-math-0003) component of the Interplanetary Magnetic Field (IMF), which is the most important driver of the dayside reconnection. Even though the dawn-dusk (urn:x-wiley:21699380:media:jgra56834:jgra56834-math-0004) 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 urn:x-wiley:21699380:media:jgra56834:jgra56834-math-0005 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 urn:x-wiley:21699380:media:jgra56834:jgra56834-math-0006 (urn:x-wiley:21699380:media:jgra56834:jgra56834-math-0007 nT) than for small urn:x-wiley:21699380:media:jgra56834:jgra56834-math-0008. In contrast, the substorm occurrence frequency is larger for small urn:x-wiley:21699380:media:jgra56834:jgra56834-math-0009. We suggest that the magnetotail is more stable during large urn:x-wiley:21699380:media:jgra56834:jgra56834-math-0010, requiring the magnetotail lobes (and hence the polar cap) to contain more flux to initiate a substorm compared to the situation when urn:x-wiley:21699380:media:jgra56834:jgra56834-math-0011 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.

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