Universal properties of mirror mode turbulence in the Earth's magnetosheath

Abstract

We use more than 7 years of Time History of Events and Macroscale Interactions during Substorms observations to quantify the non‐Gaussian properties associated with mirror mode turbulence in the Earth's magnetosheath. We find that non‐Gaussian statistics of mirror modes lead to the parabolic collapse of kurtosis as the square of the skewness (K = aS2+B with a ∼ 1.3 and b ∼− 1). The parabolic scaling is a global constraint for the magnetosheath and is dictated by kinetic processes. This parabolic scaling is qualitatively independent of the distance to the magnetopause or bow shock, which implies that, even though the bow shock is driving the mirror mode instability, the dynamical evolution of mirror structures is independent of the source region and due to local processes. The parabolic relationship and coefficients between kurtosis and skewness for mirror modes in the Earth's magnetosheath are also similar to those found in a wide range of geophysical and laboratory turbulent environments, providing further evidence that turbulent systems dominated by non‐Gaussian fluctuations hold universal statistical properties.

Statistical analysis of mirror mode waves in sheath regions driven by interplanetary coronal mass ejection

“…Absolute amplitudes, however, are clearly higher for MMs found in the Earth's magnetosheath. Dimmock et al (2015) and Osmane et al (2015) reported MMs in the magnetosheath of the Earth with absolute amplitudes approximately between 10 and 20 nT. Although some MMs in our study had ampli- tudes up to 10 nT, the average absolute amplitude was only about 3 nT.…”

“…ICMEdriven sheaths are of great interest for solar-terrestrial studies as they are strong drivers of geomagnetic activity (e.g., Tsurutani et al, 1988;Huttunen et al, 2002;Huttunen and Koskinen, 2004;Siscoe et al, 2007;Kilpua et al, 2017, see also Echer et al, 2011;Oliveira and Raeder, 2014;Lugaz et al, 2016), and their shocks have a key role in the acceleration of solar energetic particles (e.g., Reames, 1999;Manchester et al, 2005). Similarly to planetary magnetosheaths (e.g., Soucek et al, 2008;Osmane et al, 2015), MM waves may have large-scale effects on ICME sheaths.…”

“…Previous studies have mostly utilized linear polarization and compression of MM waves when identifying these structures (e.g., Tátrallyay and Erdős, 2005;Soucek et al, 2008;Dimmock et al, 2015;Osmane et al, 2015). In practice, these studies have computed both the maximum variance direction of the magnetic field vector (B m ; Sonnerup and Cahill, 1967) and its direction with respect to the average magnetic field direction b 0 = [B 1 ,B 2 ,B 3 ]/|B 1 ,B 2 ,B 3 |, where the subscripts 1, 2 and 3 denote the components of the magnetic field vector, by applying the minimum variance analysis (MVA).…”

“…Because the magnetic field data have 3 s time resolution, two successive intervals may overlap by 57 s with each other. Similarly to Soucek et al (2008), Dimmock et al (2015) and Osmane et al (2015), we use the MVA to calculate the eigenvalues of the maximum (λ max ), intermediate (λ int ) and minimum (λ min ) variance directions and the angle (θ bm ) between B m and b 0 . We also require that λ max /λ int > 1.5, λ min /λ int > 0.3 and θ bm < 30 • for an interval to pass the MVA test.…”

“…Skewness describes the asymmetry of a distribution and is positive for intervals with peaks and negative for intervals with dips (see e.g., Osmane et al, 2015).…”