Near‐Earth Solar Wind: Plasma Characteristics From ARTEMIS Measurements

Abstract

The interaction between the solar wind and Earth's magnetosphere is the main driver of magnetosphere dynamics because many important processes in Earth's inner and outer magnetosphere can be considered as responses to solar wind parameter variations. Therefore, accurate measurements of these parameters (density, velocity, ion, and electron temperature) in the near‐Earth solar wind is critical for understanding and forecasting magnetosphere dynamics. Moreover, the solar wind is a natural laboratory for investigation of plasma turbulence, including the configuration and dynamics of coherent plasma structures (such as large‐amplitude waves, discontinuities, and interplanetary shocks). A major solar wind parameter database, the OMNI database, consists of solar wind proton characteristics and magnetic field parameters but does not provide electron characteristics. We consider a supplementary solar wind data set compiled by observations of the two Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) probes. We compare characteristics available in both the ARTEMIS and OMNI data sets. We also describe characteristics of solar wind electron components measured by ARTEMIS (density, temperature, and anisotropy). Finally, we discuss opportunities for investigation of the near‐Earth solar wind provided by the ARTEMIS data set.

Statistical Study of Whistler Waves in the Solar Wind at 1 au

“…Panels (a) and (b) present distributions of all events and whistler wave events in (q e /q 0 , T e⊥ /T e|| ) parameter plane. In accordance with previous statistical studies (e.g., Štverák et al 2008;Artemyev et al 2018) solar wind electrons at 1 AU most often exhibit parallel temperature anisotropy, T e⊥ /T e|| < 1. Panels (a) and (b) are combined to compute the occurrence probability in (q e /q 0 , T e⊥ /T e|| ) parameter plane.…”

“…The growth rate is almost independent of the proton to core electron temperature ratio, because in realistic conditions protons do not resonate with whistler waves produced by the WHFI . In what follows we keep T p /T c = 1 which is a reasonable assumption at 1 AU (e.g., Newbury et al 1998;Artemyev et al 2018). To evaluate the maximum and minimum frequencies of whistler waves that can be generated by the WHFI instability, we fix β e and vary n c /n 0 , T h /T c and ∆v c /v A in the ranges typical for the solar wind at 1 AU (Table 1).…”

Solar Wind Proton Deceleration in Front of the Terrestrial Bow Shock

“…This deceleration is not seen in SWM, probably because SWM was switched on at larger distances from the BS. The results of our analysis complement a study of Artemyev et al (2018) that is dealing with a comparison of the ARTEMIS temperature and density with those from the OMNI database. They found that these parameters agree within a factor of 2 and concluded that the ARTEMIS data can be used for investigations of the near-Earth SW.…”

On the Kinetic Nature of Solar Wind Discontinuities

“…The scattering rate in RDs exponentially depends on the ratio of electron gyroradius (in B n ) and discontinuity thickness: this ratio varies between 10 2 (no scattering; for B n ∼ 10% of B l magnitude and the RD thickness ∼ 1,000 km) and 10 0 (strong scattering; for B n < 1% of B l magnitude magnitude and the RD thickness ∼ 100 km). For each discontinuity we calculate Δv l and Δv A (note that for our data set we do not have accurate measurements of ion temperature and anisotropy in the solar wind; see details in Artemyev, Angelopoulos, & McTiernan, 2018; and thus only the electron temperature anisotropy is included in the calculations; see equation (1)) and plot them in Figure 4a. According to Figures 2 and 3, the observed discontinuities share properties of both RDs and TDs.…”

“…But do RDs and TDs in the entire data set share these properties? For each discontinuity we calculate Δv l and Δv A (note that for our data set we do not have accurate measurements of ion temperature and anisotropy in the solar wind; see details in Artemyev, Angelopoulos, & McTiernan, 2018; and thus only the electron temperature anisotropy is included in the calculations; see equation (1)) and plot them in Figure 4a. There is a clear correlation between Δv l and Δv A (except for discontinuities with |Δv l | insufficiently large to be defined), but instead of |Δv A | ∼ |Δv l | we observe |Δv A | ∼ 2|Δv l |.…”