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Climatology of Pi2 Pulsations Deduced From the Wp Index.

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Title: Climatology of Pi2 Pulsations Deduced From the Wp Index.
Authors: Nakano, Shin'ya1,2 (AUTHOR) shiny@ism.ac.jp, Kataoka, Ryuho3 (AUTHOR), Nosé, Masahito4 (AUTHOR)
Source: Journal of Geophysical Research. Space Physics. Dec2025, Vol. 130 Issue 12, p1-10. 10p.
Subject Terms: *Geomagnetism, *Climatologists, Machine learning, Solar wind, Diurnal variations in meteorology, Seasonal physiological variations
Abstract: We examine the statistical properties of the Pi2 occurrence rate, especially the seasonal and universal‐time (UT) variations by analyzing the Wp index. The Wp index represents the wave power of Pi2 pulsations, and Pi2 events can be identified from the Wp index. We then examine the seasonal and UT variations of the Pi2 occurrence frequency. The results show that the Pi2 occurrence frequency is strongly dependent on the dipole tilt angle, which is equal to the geomagnetic latitude of the subsolar point. This means that the diurnal and annual variations of the Pi2 activity are mostly controlled by the so‐called equinoctial effect. We also evaluate the contribution of the Russell–McPherron effect and axial effect, both of which are attributed to the seasonal and UT variations of the solar wind observed around the Earth. We employ a machine‐learning‐based model trained to predict the Pi2 occurrence rate, and various synthetic data are fed into this model to discriminate the contribution of the solar wind variations from the equinoctial effect. It is found that the Russell–McPherron and axial effects hardly affect the Pi2 occurrence rate. Key Points: The seasonal and universal‐time (UT) variations of the Pi2 occurrence rate are examined by analyzing the Wp indexThe results show that the seasonal and UT variations of Pi2 pulsations are mostly controlled by the equinoctial effectAn analysis with a machine‐learning‐based model shows that the Russell‐McPherron and axial effects hardly affect the Pi2 occurrence rate [ABSTRACT FROM AUTHOR]
Copyright of Journal of Geophysical Research. Space Physics is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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  Data: Climatology of Pi2 Pulsations Deduced From the Wp Index.
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  Data: <searchLink fieldCode="AR" term="%22Nakano%2C+Shin'ya%22">Nakano, Shin'ya</searchLink><relatesTo>1,2</relatesTo> (AUTHOR)<i> shiny@ism.ac.jp</i><br /><searchLink fieldCode="AR" term="%22Kataoka%2C+Ryuho%22">Kataoka, Ryuho</searchLink><relatesTo>3</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Nosé%2C+Masahito%22">Nosé, Masahito</searchLink><relatesTo>4</relatesTo> (AUTHOR)
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  Data: <searchLink fieldCode="JN" term="%22Journal+of+Geophysical+Research%2E+Space+Physics%22">Journal of Geophysical Research. Space Physics</searchLink>. Dec2025, Vol. 130 Issue 12, p1-10. 10p.
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  Data: *<searchLink fieldCode="DE" term="%22Geomagnetism%22">Geomagnetism</searchLink><br />*<searchLink fieldCode="DE" term="%22Climatologists%22">Climatologists</searchLink><br /><searchLink fieldCode="DE" term="%22Machine+learning%22">Machine learning</searchLink><br /><searchLink fieldCode="DE" term="%22Solar+wind%22">Solar wind</searchLink><br /><searchLink fieldCode="DE" term="%22Diurnal+variations+in+meteorology%22">Diurnal variations in meteorology</searchLink><br /><searchLink fieldCode="DE" term="%22Seasonal+physiological+variations%22">Seasonal physiological variations</searchLink>
– Name: Abstract
  Label: Abstract
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  Data: We examine the statistical properties of the Pi2 occurrence rate, especially the seasonal and universal‐time (UT) variations by analyzing the Wp index. The Wp index represents the wave power of Pi2 pulsations, and Pi2 events can be identified from the Wp index. We then examine the seasonal and UT variations of the Pi2 occurrence frequency. The results show that the Pi2 occurrence frequency is strongly dependent on the dipole tilt angle, which is equal to the geomagnetic latitude of the subsolar point. This means that the diurnal and annual variations of the Pi2 activity are mostly controlled by the so‐called equinoctial effect. We also evaluate the contribution of the Russell–McPherron effect and axial effect, both of which are attributed to the seasonal and UT variations of the solar wind observed around the Earth. We employ a machine‐learning‐based model trained to predict the Pi2 occurrence rate, and various synthetic data are fed into this model to discriminate the contribution of the solar wind variations from the equinoctial effect. It is found that the Russell–McPherron and axial effects hardly affect the Pi2 occurrence rate. Key Points: The seasonal and universal‐time (UT) variations of the Pi2 occurrence rate are examined by analyzing the Wp indexThe results show that the seasonal and UT variations of Pi2 pulsations are mostly controlled by the equinoctial effectAn analysis with a machine‐learning‐based model shows that the Russell‐McPherron and axial effects hardly affect the Pi2 occurrence rate [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
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  Group: Ab
  Data: <i>Copyright of Journal of Geophysical Research. Space Physics is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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        Value: 10.1029/2025JA034345
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        Text: English
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      – SubjectFull: Machine learning
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      – SubjectFull: Solar wind
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      – SubjectFull: Diurnal variations in meteorology
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      – SubjectFull: Seasonal physiological variations
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      – TitleFull: Climatology of Pi2 Pulsations Deduced From the Wp Index.
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            NameFull: Nakano, Shin'ya
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            NameFull: Nosé, Masahito
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              M: 12
              Text: Dec2025
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