Spatial coherence of interplanetary coronal mass ejection sheaths at 1 AU

Abstract

• Spatial coherence length of magnetic field in ICME sheaths is larger than in the solar wind and typically smaller than in ICME ejecta. • High frequency fluctuations are localized in ICME sheaths. • Large correlation length for B y is consistent with field line draping and shock deflection.

Transmission of an ICME Sheath Into the Earth's Magnetosheath and the Occurrence of Traveling Foreshocks

“…We highlight, together with the work by Ala‐Lahti et al. (2020) and by Blum et al. (2021), the importance that the fine structure of sheath fields have in this interplay.…”

“…We note our analysis is limited, for example, due to changes in spacecraft position and a relative large spacecraft separation that restrict the subsequent observations of short‐lived small‐scale fluctuations. However, larger‐scale fluctuations in ICME sheath exhibit less spatial variability (Ala‐Lahti et al., 2020) and the results presented in Figure 5 are an indicative of a trend. The figure shows that the probability of feature transmission increases significantly for frequencies below ∼0.01 Hz.…”

“…Similar to Ala‐Lahti et al. (2020), we compute the total Pearson correlation by applying the averaging estimator of correlation coefficients (Olkin & Pratt, 1958) for the individual Pearson correlation coefficients of the magnetic field magnitude and components. Pearson correlation coefficient measures the linear dependence of two random variables and is used to compare spacecraft measurements (e.g., Good et al., 2018; Lugaz et al., 2018).…”

“…Moreover, spatial variability of sheath fields in the longitudinal direction at 1 AU and its consequences for space weather has been addressed by Ala‐Lahti et al. (2020). The ICME sheath fields have a large‐scale structure being more coherently structured compared to the solar wind.…”

A Quarter Century ofWindSpacecraft Discoveries

“…Blue lines show and IMF with a 45° Parker spiral angle at the Earth's distance from the Sun. Scale lengths of the solar wind(Richardson & Paularena, 2001), ICME sheath(Ala-Mathi et al, 2020), and ICME ejecta(Lugaz et al, 2018) are illustrated in the y-direction with the color corresponding to the magnetic field component and magnitude as indicated for the sheath region. The correlation in light blue (σ tot ) illustrate the scale length associated with the overall Pearson correlation obtained by applying the averaging estimator of correlation coefficients for the Pearson correlation values of the magnitude and components (Adapted from Figure6inAla-Mathi et al, 2020).…”