Abstract
AbstractAn important location for future space weather monitoring is the Lagrange point 5 (L5) of the Sun‐Earth system. We test the performance of L5 for space weather monitoring using STEREO B observations of an Earth‐directed coronal mass ejection (CME), seen as a partial halo by SOHO at L1. STEREO B (located close to L5) continuously tracked the CME. By using these data in combination with methods to calculate the CME arrival time at the Earth (extrapolation, drag‐based model, and a magnetohydrodynamic model), we demonstrate that the estimation of the CME arrival time can be drastically improved by adding L5 data. Based on the L1 data alone, one could predict that the CME would arrive at the Earth. Using only the L5 data, one would not expect an arrival, as the estimations of the CME 3‐D configuration is uncertain. The combination of L1 and L5 data leads to an ambiguous prediction of the CME arrival due to low CME brightness in L1 data. To obtain an unambiguous prediction, one needs its 3‐D configuration, from observing the CME material close to the plane of the sky from at least two viewpoints (in this case L5 and, coincidentally, L4). This event demonstrates that L1 observations may be better to determine CME arrival, but L5 observations are superior for constraining arrival time. In this work, the advantages and caveats of using data from a space weather monitor at L5 for predicting interplanetary propagation of CMEs are discussed and demonstrated in a direct case study.
Highlights
Coronal mass ejections (CMEs) are huge eruptive events observed in the solar corona, in which magnetized solar plasma is expelled into interplanetary space
Less satisfactory than predictions based on the J‐map tracking technique, this result highlights how even the single Lagrange point 5 (L5) viewpoint allows to perform a significantly better estimate of the arrival time of Earth‐directed CMEs compared to a view limited to L1
We have analyzed the coronal and heliospheric propagation of a CME observed when the STEREO B spacecraft was located at the L5 Lagrangian point of the Sun‐Earth system
Summary
Coronal mass ejections (CMEs) are huge eruptive events observed in the solar corona, in which magnetized solar plasma is expelled into interplanetary space. As the ejected material traverses interplanetary space, CMEs become known as interplanetary CMEs (ICMEs) When they arrive at the Earth with a favorable orientation of their magnetic field (i.e., a strong and long‐lasting southward component), they may produce geomagnetic storms (e.g., Bothmer & Zhukov, 2007; Schwenn, 2006). The early determination of the direction of propagation of halo CMEs (toward or away from the Earth) is of vital importance for providing prompt warnings of possible geoeffectiveness. Another issue is that the speeds of halo CMEs measured by LASCO are plane‐of‐the‐sky projected speeds and do not always provide a good estimate of their radial speeds (e.g., Schwenn et al, 2005). The placement of a spacecraft away from the Sun‐Earth line can provide the crucial viewpoint needed for an early characterization of Earth‐directed CMEs, in particular the CME propagation direction, measurement of the CME speed, and tracking of the CME propagation in the heliosphere
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