27 Apr 2023
 | 27 Apr 2023
Status: this preprint is currently under review for the journal ANGEO.

Short Large-Amplitude Magnetic Structures (SLAMS) at Mercury observed by MESSENGER

Tomas Karlsson, Ferdinand Plaschke, Austin N. Glass, and Jim M. Raines

Abstract. We present the first observations of Short Large-Amplitude Magnetic Structures (SLAMS) at Mercury. We have investigated approximately four years of MESSENGER data to identify SLAMS in the Mercury foreshock. Defining SLAMS as magnetic field compressional structures, with an increase in magnetic field strength of at least twice the background magnetic field strength, when MESSENGER is located in the solar wind, we find 435 SLAMS. The SLAMS are found either in regions of a general ultra-low frequency (ULF) wave field, at the boundary of such a ULF wave field, or in a few cases isolated from the wave field. We present statistics on several properties of the SLAMS, such as temporal scale size, amplitude, and the presence of whistler-like wave emissions. We find that SLAMS are mostly found during periods of low interplanetary magnetic field strength, indicating that they are more common for higher solar wind Alfvénic Mach number (MA). We use the Tao solar wind model to estimate solar wind parameters to verify that MA is indeed larger during SLAMS observations than otherwise. Finally, we also investigate how SLAMS observations are related to foreshock geometry.

Tomas Karlsson et al.

Status: open (until 12 Jun 2023)

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Tomas Karlsson et al.

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Tomas Karlsson et al.


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Short summary
The solar wind interacts with the planets in the solar system, and creates a supersonic shock in front of them. The upstream region of this shock contains many complicated phenomena. One such phenomenon is small-scale structures of strong magnetic fields (SLAMS). These SLAMS have been observed at Earth, and are important in determining the properties of space around the planet. Until now SLAMS have not been observed at Mercury, but we here show for the first time that SLAMS exist also here.