the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Investigation of the occurrence of significant deviations in the magnetopause location: Solar wind and foreshock effects
Abstract. The dynamic motion of the magnetopause, the boundary between the Earth's magnetic field and the interplanetary magnetic field, is mainly driven by pressure variations and changes in the interplanetary magnetic field. Common magnetopause models can predict the location of the magnetopause in response to upstream conditions from different sets of input parameters, including pressure and the interplanetary magnetic field. However, recent studies have shown that some effects of upstream conditions may still be poorly understood, as deviations between model and in situ observations beyond the expected scatter due to constant magnetopause motion are quite common. Using data from the three most recent multi-spacecraft missions to near Earth space (Cluster, THEMIS and MMS), we investigate the occurrence of these large deviations in observed magnetopause crossings from common empirical models. By comparing the results from different models, we find that the occurrence of these events appears to be model independent, suggesting that some physical processes may be missing from the models. To find these processes, we test whether the deviant magnetopause crossings are statistically associated with foreshocks and/or different solar wind types and show that in at least 50 % of cases the foreshock can be responsible for the large deviations in the magnetopause's location. In the case where the foreshock is unlikely to be responsible, two distinct classes of solar wind are found to occur most frequently in association with the occurrence of magnetopause deviations: the "fast" solar wind and the solar wind plasma associated with transients such as interplanetary coronal mass ejections. Therefore, the plasma conditions associated with these solar wind classes could be responsible for the occurrence of deviant magnetopause observations. Our results may help to develop new and more accurate models of the magnetopause, which will be needed, for example, to accurately interpret the results of the upcoming SMILE mission.
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Status: open (until 19 Nov 2024)
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RC1: 'Comment on egusphere-2024-2956', Anonymous Referee #1, 06 Nov 2024
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The manuscript “Investigation of the occurrence of significant deviations in the magnetopause location: Solar wind and foreshock effects” by Niklas Grimmich et al. contains a huge statistical analysis for the magnetopause location. It combines two empirical models of the magnetopause (Shue et al. (1988), Nguyen et al. (2022)) and data from three different spacecraft missions, CLUSTER, THEMIS and MMS. He tries to study the deviations between the models and the data using different solar wind conditions, different θBn angles and different regions of the magnetosphere. He concludes that foreshock is in some cases responsible for these deviations. From my point of view, this is a work that includes a lot of information and tries to cover all the aspects and possibilities of the deviation issue between the real and the model location of the MP. However, I believe that there are some problems that are not addressed or they are not addressed properly. In this respect, the material presented in this research is valuable and appropriate for publication after a few important points are discussed.
More comments are to be found in the supplementary file.
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RC2: 'Comment on egusphere-2024-2956', Anonymous Referee #2, 06 Nov 2024
reply
This study investigates possible sources of the scatter (deviations) of observed magnetopause locations about parameterized models of the average magnetopause shape and position. The deviations of the observed magnetopause position from that of the models is investigated as a function of the IMF orientation (i.e., defining the foreshock, leading to convected oscillations), and for different ‘types’ of solar wind. The cause(s) of deviations of the observed magnetopause location from that expected from statistical models is of interest, and has been examined by several investigators (though not appropriately referenced nor discussed here). Aside from an exploration of different ‘types’ of solar wind, it is not clear how this investigation improves upon these earlier efforts. There are also many questions about the methodologies employed within this study that need to be answered and comments to be addressed before this study can be considered for publication in Annales Geophysicae.
More and specific comments are to be found in the supplementary file.
Data sets
Database: Cluster Magnetopause Crossings between 2001 and 2020 Niklas Grimmich et al. https://doi.org/10.17605/OSF.IO/PXCTG
Database: THEMIS magnetopause crossings between 2007 and mid-2022 Niklas Grimmich et al. https://doi.org/10.17605/OSF.IO/B6KUX
8 years of dayside magnetospheric multiscale (MMS) unsupervised clustering plasma regions classifications Vicki Toy-Edens et al. https://doi.org/10.5281/zenodo.10491877
OMNI dataset J. King and N. Papitashvili https://spdf.gsfc.nasa.gov/pub/data/omni/omni_cdaweb/
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