The intensity and evolution of the extreme storms in January 1938. (arXiv:2010.15762v1 [astro-ph.SR])

The intensity and evolution of the extreme storms in January 1938. (arXiv:2010.15762v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Hayakawa_H/0/1/0/all/0/1">Hisashi Hayakawa</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hattori_K/0/1/0/all/0/1">Kentaro Hattori</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pevtsov_A/0/1/0/all/0/1">Alexei A. Pevtsov</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ebihara_Y/0/1/0/all/0/1">Yusuke Ebihara</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Shea_M/0/1/0/all/0/1">Margaret A. Shea</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+McCracken_K/0/1/0/all/0/1">Ken G. McCracken</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Daglis_I/0/1/0/all/0/1">Ioannis A. Daglis</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bhaskar_A/0/1/0/all/0/1">Ankush Bhaskar</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ribeiro_P/0/1/0/all/0/1">Paulo Ribeiro</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Knipp_D/0/1/0/all/0/1">Delores J. Knipp</a>

Major solar eruptions occasionally direct interplanetary coronal mass
ejections (ICMEs) to Earth and cause significant geomagnetic storms and
low-latitude aurorae. While single extreme storms are of significant threats to
the modern civilization, storms occasionally appear in sequence and, acting
synergistically, cause ‘perfect storms’ at Earth. The stormy interval in
January 1938 was one of such cases. Here, we analyze the contemporary records
to reveal its time series on their source active regions, solar eruptions,
ICMEs, geomagnetic storms, low-latitude aurorae, and cosmic-ray (CR)
variations. Geomagnetic records show that three storms occurred successively on
17/18 January (Dcx ~ -171 nT) on 21/22 January (Dcx ~ -328 nT) and on 25/26
January (Dcx ~ -336 nT). The amplitudes of the cosmic-ray variations and sudden
storm commencements show the impact of the first ICME as the largest (~ 6%
decrease in CR and 72 nT in SSC) and the ICME associated with the storms that
followed as more moderate (~ 3% decrease in CR and 63 nT in SSC; ~ 2% decrease
in CR and 63 nT in SSC). Interestingly, a significant solar proton event
occurred on 16/17 January and the Cheltenham ionization chamber showed a
possible ground level enhancement. During the first storm, aurorae were less
visible at mid-latitudes, whereas during the second and third storms, the
equatorward boundaries of the auroral oval were extended down to 40.3{deg} and
40.0{deg} in invariant latitude. This contrast shows that the initial ICME was
probably faster, with a higher total magnitude but a smaller southward
component.

Major solar eruptions occasionally direct interplanetary coronal mass
ejections (ICMEs) to Earth and cause significant geomagnetic storms and
low-latitude aurorae. While single extreme storms are of significant threats to
the modern civilization, storms occasionally appear in sequence and, acting
synergistically, cause ‘perfect storms’ at Earth. The stormy interval in
January 1938 was one of such cases. Here, we analyze the contemporary records
to reveal its time series on their source active regions, solar eruptions,
ICMEs, geomagnetic storms, low-latitude aurorae, and cosmic-ray (CR)
variations. Geomagnetic records show that three storms occurred successively on
17/18 January (Dcx ~ -171 nT) on 21/22 January (Dcx ~ -328 nT) and on 25/26
January (Dcx ~ -336 nT). The amplitudes of the cosmic-ray variations and sudden
storm commencements show the impact of the first ICME as the largest (~ 6%
decrease in CR and 72 nT in SSC) and the ICME associated with the storms that
followed as more moderate (~ 3% decrease in CR and 63 nT in SSC; ~ 2% decrease
in CR and 63 nT in SSC). Interestingly, a significant solar proton event
occurred on 16/17 January and the Cheltenham ionization chamber showed a
possible ground level enhancement. During the first storm, aurorae were less
visible at mid-latitudes, whereas during the second and third storms, the
equatorward boundaries of the auroral oval were extended down to 40.3{deg} and
40.0{deg} in invariant latitude. This contrast shows that the initial ICME was
probably faster, with a higher total magnitude but a smaller southward
component.

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