A statistical study of magnetic field fluctuations in the dayside magnetosheath and their dependence on upstream solar wind conditions

Abstract

The magnetosheath functions as a natural interface connecting the interplanetary and magnetospheric plasma. Since the magnetosheath houses the shocked solar wind, it is populated with abundant magnetic field turbulence which are generated both locally and externally. Although the steady state magnetosheath is to date relatively well understood, the same cannot be said of transient magnetic perturbations due to their kinetic nature and often complex and numerous generation mechanisms. The current manuscript presents a statistical study of magnetic field fluctuations in the dayside magnetosheath as a function of upstream solar wind conditions. We concentrate on the ambient higher‐frequency fluctuations in the range of 0.1 Hz → 2 Hz. We show evidence that the dawn (quasi‐parallel) flank is visibly prone to higher‐amplitude magnetic perturbations compared to the dusk (quasi‐perpendicular) region. Our statistical data also suggest that the magnitude of turbulence can be visibly enhanced close to the magnetopause during periods of southward interplanetary magnetic field orientations. Faster (> 400 km s−1) solar wind velocities also appear to drive higher‐amplitude perturbations compared to slower speeds. The spatial distribution also suggests some dependence on the magnetic pileup region at the subsolar magnetopause.

A statistical study into the spatial distribution and dawn‐dusk asymmetry of dayside magnetosheath ion temperatures as a function of upstream solar wind conditions

“…The standard error in this case is between 2 eV and 4 eV and varies little from this range. The reduction in error could be explained by the decrease in the amplitude of magnetic turbulence during SSW speeds [ Dimmock et al , ].…”

The dawn–dusk asymmetry of ion density in the dayside magnetosheath and its annual variability measured by THEMIS

“…To compile our data sets, we extracted magnetosheath observations from the complete THEMIS catalogue using our magnetospheric data analysis tool (see Dimmock and Nykyri (2013); Dimmock et al (2014Dimmock et al ( , 2015a). We quantitatively showed the asymmetry during typical solar wind conditions (Fig.…”

“…To summarise these asymmetries: magnetic field strength, plasma velocity, temperature anisotropy and mirror mode occurrence favour the dusk-flank and magnetic field turbulence, ion total temperature and ion number density are stronger on the dawn-side (Paularena et al, 2001;Němeček et al, 2003;Longmore et al, 2005;Walsh et al, 2012;Dimmock and Nykyri, 2013;Dimmock et al, 2014Dimmock et al, , 2015a. Remaining issues are the following: (1) what are their underlying physical mechanisms, and (2) what role do they play in driving magnetospheric plasma properties such as the formation of the cold dense plasma sheet.…”

“…We utilised our existing data analysis tool developed over the past 3 years (see Dimmock and Nykyri, 2013;Dimmock et al, 2014Dimmock et al, , 2015a to compile annual data sets of magnetosheath ion density measurements between 2008 through 2014. We also investigate the solar wind parameter dependence for each year separately to shed further light on the physical driver.…”

“…The physical processes leading to magnetosheath dawn-dusk asymmetries (Paularena et al, 2001;Longmore et al, 2005;Walsh et al, 2012;Dimmock and Nykyri, 2013;Dimmock et al, 2014Dimmock et al, , 2015a, are fundamental in solar wind-magnetosphere coupling as they can directly impact plasma transport processes at the magnetopause. Our results imply that the role they play is time dependent and this needs to be taken into consideration in the analysis of long duration data sets of both magnetosheath and magnetospheric measurements.…”