Causal Analysis of Influence of the Solar Cycle and Latitudinal Solar-Wind Structure on Co-Rotation Forecasts

Nachiketa Chakraborty, Harriet Turner, Mathew Owens, Matthew Lang

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Abstract

Studying solar-wind conditions is central to forecasting the impact of space weather on Earth. Under the assumption that the structure of this wind is constant in time and co-rotates with the Sun, solar-wind and thereby space-weather forecasts have been made quite effectively. Such co-rotation forecasts are well studied with decades of observations from STEREO and near-Earth spacecraft. Forecast accuracy is primarily determined by three factors: i) the longitudinal separation of spacecraft from Earth determines the corotation time (and hence forecast lead time) [δ t] over which the solar wind must be assumed to be constant, ii) the latitudinal separation (or offset) between Earth and spacecraft [δθ]] determines the degree to which the same solar wind is being encountered at both locations, and iii) the solar cycle, via the sunspot number (SSN), acts as a proxy for both how fast the solar-wind structure is evolving and how much it varies in latitude. However, the precise dependencies factoring in uncertainties are a mixture of influences from each of these factors. Furthermore, for high-precision forecasts, it is important to understand what drives the forecast accuracy and its uncertainty. Here we present a causal inference approach based on information-theoretic measures to do this. Our framework can compute not only the direct (linear and nonlinear) dependencies of the forecast mean absolute error (MAE) on SSN, Δ θ , and Δ t , but also how these individual variables combine to enhance or diminish the MAE. We provide an initial assessment of this with the potential of aiding data assimilation in the future.

Original languageEnglish
Article number142
Number of pages20
JournalSolar Physics
Volume298
Issue number12
DOIs
Publication statusPublished - 13 Dec 2023

Bibliographical note

This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

Funder

We have benefited from sunspot data provided by the Royal Observatory of Belgium SILSO, RGO/SOON sunspot-latitude and -area data collated by David Hathaway and Lisa Upton, and OMNI data provided by NASA/SPDF. We benefited from useful discussions as part of the International Space Science Institute (ISSI, Bern) team “Magnetic open flux and solar-wind structuring in interplanetary space” (2019 – 2021) led by Manuela Temmer.

Funding Information:
This work was part-funded by Science and Technology Facilities Council (STFC) grant number ST/V000497/1.

Publisher Copyright:
© 2023, The Author(s).

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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