tokens: (b) Group 1 (red line) and Group 2 (blue line) events; (c) Group 3 (red line) and Group 4 (blue line) events. To reveal the reason for this difference, the intermittent structures are grouped according to the intensity and direction changes of magnetic field. The intensity changes are determined by a normalized parameter , where and B 0 is the average of the magnetic field strength of the whole sheath. The directional changes are also divided into two groups: Δ θ > 45° and Δ θ ≤ 45°, as current sheets with Δ θ > 45° are categorized to strong currents in Borovsky Denton ( 2011 ). Thus, the intermittent structures are grouped into the following four categories: (1) and Δ θ > 45°; (2) and Δ θ ≤ 45°; (3) and Δ θ > 45°; (4) and Δ θ ≤ 45°. Figure 2 (b) shows the associated proton temperature of intermittent structures with significant magnetic field intensity changes (). A substantial enhancement (10%) of the normalized proton temperature can be found regardless of the value of Δ θ , revealing that local heating is prominent near these coherent structures. Near the intermittent structures without large changes in magnetic field magnitude (), local enhancement is still prominent (nearly 8%) near current sheets with large shear angles (Δ θ > 45°), but is not significant near current sheets with small shear angles (Δ θ ≤ 45°), as shown in Figure 2 (c). However, 10,831 of the total 12,426 intermittent structures identified fall into Group 4, so the average enhancement of normalized proton temperature is only 3%, as shown in Figure 2 (a). As shown in Figures 2 (b) and (c), the normalized proton temperature suffers a significant enhancement near current sheets with Δ θ > 45° (red lines). We then analyze the association between the temperature enhancement and the scale of such current sheets. The superposed-epoch analysis is performed for strong current sheets identified under four different time lags. Figure 3 shows that the temperature enhancement becomes more prominent as the spatial scale (≈ τ · V sh ) of the current sheets decreases. Meanwhile, the heating effect is more localized near thinner current sheets. When the time lag is 3 s, the normalized proton temperature has already dropped 7% at a distance of 10 5 km, but it almost remains the same at this distance when the time lag increases to 120 s. This result suggests that the intermittent heating mainly occurs at thin current sheets instead of large-scale ones. Figure 3. Averages of normalized proton temperature conditioned on the distance from strong current sheets (Δ θ > 45°) at different timescales. 4. Summary and Discussion A total of 12,426 PVI events have been identified in the sheaths of 71 MC events observed by the WIND spacecraft, with the criterion of PVI ≥ 3. Superposed-epoch analysis of normalized proton temperature associated with the PVI peaks identified shows that the averaged temperature enhancement is not prominent near the current sheets in the MC sheath, which is different
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