Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userCharacteristics of the Flank Magnetopause: THEMIS Observations
84
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The terrestrial magnetopause is the boundary that shields the Earths magnetosphere on one side from the shocked solar wind and its embedded interplanetary magnetic field on the other side. In this paper, we show observations from two of the Time History of Events and Macroscales Interactions during Substorms (THEMIS) satellites, comparing dayside magnetopause crossings with flank crossings near the terminator. Macroscopic properties such as current sheet thickness, motion, and current density are examined for a large number of magnetopause crossings. The results show that the flank magnetopause is typically thicker than the dayside magnetopause and has a lower current density. Consistent with earlier results from Cluster observations, we also find a persistent dawn-dusk asymmetry with a thicker and more dynamic magnetopause at dawn than at dusk.
rate research
Read More
We consider the one-dimensional equilibrium problem of a shear-flow boundary layer within an extended Hall-MHD (eHMHD) model of plasma that retains first-order finite Larmor radius (FLR) corrections to the ion dynamics. We provide a generalized version of the analytic expressions for the equilibrium configuration given in Cerri et al. (2013) [Cerri et al., Phys. Plasmas 20, 112112 (2013)], highlighting their intrinsic asymmetry due to the relative orientation of the magnetic field $mathbf{b}=mathbf{B}/|mathbf{B}|$ and the fluid vorticity $mathbf{omega}=mathbf{ abla}timesmathbf{u}$ ($mathbf{omega b}$ asymmetry). Finally, we show that FLR effects can modify the Chapman--Ferraro current layer at the flank magnetopause in a way that is consistent with the observed structure reported by Haaland et al. (2014) [Haaland et al., J. Geophys. Res. Space Phys. 119, 9019-9037 (2014)]. In particular, we are able to qualitatively reproduce the following key features: (i) the dusk-dawn asymmetry of the current layer, (ii) a double-peak feature in the current profiles, and (iii) adjacent current sheets having thicknesses of several ion Larmor radii and with different current directions.
We report THEMIS and Geotail observations of prolonged magnetopause (MP) expansions during long-lasting intervals of quasi-radial interplanetary magnetic field (IMF) and nearly constant solar wind dynamic pressure. The expansions were global: the magnetopause was located more than 3 RE and ~7 RE outside its nominal dayside and magnetotail locations, respectively. The expanded states persisted several hours, just as long as the quasi-radial IMF conditions, indicating steady-state situations. For an observed solar wind pressure of ~1.1-1.3 nPa, the new equilibrium subsolar MP position lay at ~14.5 RE, far beyond its expected location. The equilibrium position was affected by geomagnetic activity. The magnetopause expansions result from significant decreases in the total pressure of the high-beta magnetosheath, which we term the low-pressure magnetosheath (LPM) mode. A prominent LPM mode was observed for upstream conditions characterized by IMF cone angles less than 20 ~ 25 grad, high Mach numbers and proton plasma beta<1.3. The minimum value for the total pressure observed by THEMIS in the magnetosheath adjacent to the magnetopause was 0.16 nPa and the fraction of the solar wind pressure applied to the magnetopause was therefore 0.2, extremely small. The equilibrium location of the magnetopause was modulated by a nearly continuous wavy motion over a wide range of time and space scales.
The magnetopause is a current sheet forming the boundary between the geomagnetic field on one side and the shocked solar wind on the other side. This paper discusses properties of the low-latitude dawn and dusk flanks of the magnetopause. The reported results are based on a large number of measurements obtained by the Cluster satellites during magnetopause traversals. Using a combination of single-spacecraft and multispacecraft techniques, we calculated macroscopic features such as thickness, location, and motion of the magnetopause. The results show that the typical flank magnetopause is significantly thicker than the dayside magnetopause and also possesses a pronounced and persistent dawn-dusk asymmetry. Thicknesses vary from 150 to 5000 km, with an median thickness of around 1400 km at dawn and around 1150 km at dusk. Current densities are on average higher on dusk, suggesting that the total current at dawn and dusk are similar. Solar wind conditions and the interplanetary magnetic field cannot fully explain the observed dawn-dusk asymmetry. For a number of crossings we were also able to derive detailed current density profiles. The profiles show that the magnetopause often consists of two or more adjacent current sheets, each current sheet typically several ion gyroradii thick and often with different current direction. This demonstrates that the flank magnetopause has a structure that is more complex than the thin, one-dimensional current sheet described by a Chapman-Ferraro layer.
The first computation of the compressible energy transfer rate from $sim$ 0.2 AU up to $sim$ 1.7 AU is obtained using PSP, THEMIS and MAVEN observations. The compressible energy cascade rate $varepsilon_C$ is computed for hundred of events at different heliocentric distances, for time intervals when the spacecraft were in the pristine solar wind. The observational results show moderate increases of $varepsilon_C$ with respect to the incompressible cascade rate $varepsilon_I$. Depending on the level of compressibility in the plasma, which reach up to 25 $%$ in the PSP perihelion, the different terms in the compressible exact relation are shown to have different impact in the total cascade rate $varepsilon_C$. Finally, the observational results are connected with the local ion temperature and the solar wind heating problem.
The Earths magnetosphere represents a natural plasma laboratory that allows us to study the behavior of particle distribution functions in the absence of Coulomb collisions, typically described by the Kappa distributions. We have investigated the properties of these functions for ions and electrons in different magnetospheric regions, thereby making it possible to reveal the $kappa$-parameters for a wide range of plasma beta ($beta$) values (from $10^{-3}$ to $10^{2}$). This was done using simultaneous ion and electron measurements from the five Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft spanning the years 2008 to 2018. It was found that for a fixed plasma $beta$, the $kappa$-index and core energy ($E_c$) of the distribution can be modeled by the power-law $kappa=AE_c^gamma$ for both species, and the relation between $beta$, $kappa$, and $E_c$ is much more complex than earlier reported: both $A$ and $gamma$ exhibit systematic dependencies with $beta$. Our results indicate that $beta sim 0.1-0.3$ is a range where the plasma is more dynamic since it is influenced by both the magnetic field and temperature fluctuations, which suggests that the transition between magnetically dominated plasmas to kinetically dominated plasmas occurs at these values of $beta$. For $beta > 1 $, both $A$ and $gamma$ take nearly constant values, a feature that is especially notable for the electrons and might be related to their demagnetization. The relation between $beta$, $kappa$, and $E_c$ that we present is an important result that can be used by theoretical models in the future.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
