Abstract
The interaction between Earth's magnetic field and the solar wind results in the formation of a collisionless bow shock 60,000–100,000 km upstream of our planet, as long as the solar wind fast magnetosonic Mach (hereafter Mach) number exceeds unity. Here, we present one of those extremely rare instances, when the solar wind Mach number reached steady values <1 for several hours on 17 January 2013. Simultaneous measurements by more than ten spacecraft in the near-Earth environment reveal the evanescence of the bow shock, the sunward motion of the magnetopause and the extremely rapid and intense loss of electrons in the outer radiation belt. This study allows us to directly observe the state of the inner magnetosphere, including the radiation belts during a type of solar wind-magnetosphere coupling which is unusual for planets in our solar system but may be common for close-in extrasolar planets.
Highlights
The interaction between Earth’s magnetic field and the solar wind results in the formation of a collisionless bow shock 60,000–100,000 km upstream of our planet, as long as the solar wind fast magnetosonic Mach number exceeds unity
Sub-fast solar wind conditions represent the most extreme and unusual regime which occurs at Earth
A perturbation characteristic of the in situ counterpart of a coronal mass ejections (CMEs) can be identified around 00:00 universal time (UT) on 17 January 2013, and is characterized, first, by elevated and highly variable pressures for 16 h, with rapid changes occurring at field and flow discontinuities
Summary
The interaction between Earth’s magnetic field and the solar wind results in the formation of a collisionless bow shock 60,000–100,000 km upstream of our planet, as long as the solar wind fast magnetosonic Mach (hereafter Mach) number exceeds unity. During this period of sub-Alfvenic and sub-fast solar wind, more than 10 spacecraft made measurements in the dayside magnetosphere and in Earth’s radiation belt.
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