The Sheath and Duration of Coronal Mass Ejections: Multi-Spacecraft Studies
ROSES ID: NNH23ZDA001N-LWS Selection Year: 2023
Program Element: Focused Science Topic
Principal Investigator: Noe Lugaz
Affiliation(s): University of New Hampshire
Project Member(s):
Zhuang, Bin Co-I - University of New Hampshire
Al-Haddad, Nada Co-I - University of New Hampshire
Summary:
We propose to investigate the development of the sheath regions of coronal mass ejections (CMEs) during their interplanetary propagation, and the resulting properties of the sheath regions as well as the duration/size of CMEs, especially that of the magnetic ejecta part which may have enhanced and steady magnetic fields driving geomagnetic storms. About 80% of magnetic ejecta measured at 1 AU are preceded by a dense sheath, and for ~55% of all events, there is a fast-forward shock ahead of the sheath. The sheath region carries the majority of the CME mass, and is the region with the highest dynamic pressure of the entire CME structure. Investigating CME sheath regions is therefore critical to understand the solar wind-magnetosphere coupling during CME times, with sheaths resulting in large compression of Earth's magnetosphere and impacts on Earth's radiation belts. In addition, sheath regions can be directly imaged by coronagraphs and heliospheric imagers, which makes it possible to forecast the sheath region of CMEs before impact at L1. Similarly, the duration of a CME can be quantified from remote observations and is a key parameter to determine how long Earth's magnetosphere will be under disturbed solar wind conditions and to forecast the magnitude of the magnetic field strength inside CME at 1 AU. Our key science objective is to understand how the CME propagation affects the presence and properties of the sheath region at 1 AU and the duration of the CME, and their variability on moderate scales. To do so, we address the following science questions:
1- How can the presence/absence, size and properties (density, magnetic field, temperature and velocity of the plasma within the sheath) of the sheath region near 1 AU be understood in terms of the CME propagation from the Sun to the in-situ spacecraft?
2- How do CME properties, especially duration/size and sheath properties, vary on moderate scales (0.3-10° or ~0.005- 0.17 AU in arc length) and/or in the last few hours before impacting Earth and how does this limit our forecasting capability?
3- Can the duration of a CME at 1 AU be forecasted from remote observations or measurements closer to the Sun than L1?
Methodology:
In order to answer the science questions, we primarily rely on (a) remote heliospheric observations by STEREO/SECCHI, SolOHI (when available) and PSP/WISPR (when available), and (b) in-situ measurements close to the Sun by PSP and SolO, especially during conjunction with assets at L1 or near 1 AU (STEREO-A). To investigate the variations of the CME and sheath properties on moderate scales, we also propose to study all events measured by STEREO-A and L1 as STEREO-A approaches the Sun-Earth line including all of 2022 (and magnetic field measurements at least to June 2023), as well as measurements of CMEs during time periods when spacecraft at L1 (Wind, ACE, DSCOVR) are separated by at least 0.005 AU.
Relevance to FST:
The proposed work is directly relevant to FST#3. It combines remote and in-situ data to understand CME propagation and the resulting structure. In particular, it focuses on "understanding the evolution of CMEs and their substructures" and "integrat[e] new combinations of observations to extract additional physical information about the evolution of CMEs and their substructures.' This project also advances NASA LWS program goal "Understand how and in what ways dynamic space environments affect human and robotic exploration activities".
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