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Geomagnetic Field Model Indicates Shrinking Northern Auroral Oval
Author(s) -
Zossi Bruno,
Fagre Mariano,
Amit Hagay,
Elias Ana G.
Publication year - 2020
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1029/2019ja027434
Subject(s) - earth's magnetic field , polar , magnetosphere , dipole , geology , flux (metallurgy) , geophysics , atmospheric sciences , interplanetary magnetic field , geodesy , physics , solar wind , magnetic field , astronomy , materials science , quantum mechanics , metallurgy
Polar cap and auroral oval areas are presented for the period 1900–2015 using a model of the magnetosphere and the International Geomagnetic Reference Field Version 12 (IGRF‐12) model for the geomagnetic field. The effect of the main field long‐term changes is addressed considering steady interplanetary conditions. Until ~1940 both northern and southern polar cap areas increased with time, consistent with the geomagnetic dipole moment decrease during this period. Thereafter, while the southern polar cap area continued to increase steadily, the northern polar cap area has been decreasing rapidly. This hemispherical dichotomy is related to asymmetry in the core field and its secular variation. In the southern polar region the surface field intensity has been decreasing throughout the entire period, whereas in the northern polar region an intensity decrease turned to an increase from 1940 to present day. This recent surface intensity increase stems from intensification of the flux patch below Siberia and cessation of weakening of the flux patch below North America, both on the core‐mantle boundary. The surprising temporal decrease in the area of the northern polar cap has important implications for space weather and communication systems. While the decreasing dipole intensity allows more particles to penetrate the atmosphere, a shrinking northern auroral oval implies an increase in particle precipitation density, resulting in more severe damage to airplanes and ships positioning systems, spacecraft electronic systems and airline passengers when passing above this region. Further study is needed to observationally establish that the northern auroral oval, as defined by optical occurrences of aurora, is indeed shrinking.