Monitoring the Solar Wind Before It Reaches L1

Abstract

Space weather predictions of the solar wind impacting Earth are usually first based on remote-sensing observations of the solar disc and corona, and eventually validated and/or refined with in-situ measurements taken at the Sun$-$Earth Lagrange L1 point, where real-time monitoring probes are located. However, this pipeline provides, on average, only a few tens of minutes of lead time, which decreases to $\sim$30 minutes or less for large solar wind speeds of $\sim$800 km/s and above. The G5 geomagnetic storm of 2024 May provided an opportunity to test predictions generated employing real-time data from the STEREO-A spacecraft, placed 13° west of Earth and 0.04 au closer to the Sun than L1 at the time of the event, as shown recently by Weiler et al. (2025). In this Commentary, we contextualise these results to reflect upon the advantages of measuring the solar wind in situ upstream of L1, leading to improvements in both fundamental research of interplanetary physics and space weather predictions of the near-Earth environment.

Commentary accepted for publication in Space Weather, 11 pages, 2 figures

References in corpus (7)

• Strong coronal channelling and interplanetary evolution of a solar storm up to Earth and Mars
• Self-Similarity of ICME Flux Ropes: Observations by Radially Aligned Spacecraft in the Inner Heliosphere
• Quantifying errors in 3D CME parameters derived from synthetic data using white-light reconstruction techniques
• Collection, Collation, and Comparison of 3D Coronal CME Reconstructions
• Using Solar Orbiter as an upstream solar wind monitor for real time space weather predictions
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• A coronal mass ejection encountered by four spacecraft within 1 au from the Sun: Ensemble modelling of propagation and magnetic structure

Cited by in corpus (1)

• Investigating potential benefits of future sub-L1 missions with STEREO-A