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tokens: well as the narrow range of scales involved, we are only able to claim qualitative similarity with the Mallet et al. ( 2017 ) prediction. Figure 2. Spectral index of the dissipation range binned in the (, β e ) plane. The black square marks the region with the steepest spectral indices in the range of 0.1 ≲ β e ≲ 1 and . To resolve the ambiguous results obtained with Figures 1 (d) and (e), we repeat our analysis with the subset of the data within the black square in Figure 2 , which encloses 41% of the total data and is bounded by 0.1 ≲ β e ≲ 1 and . The spectral indices are significantly steeper in this region, and if this is caused by reconnection, then may have significantly better scaling with in the marked region than with ρ c . In Figure 3 (a), the slope of the power-law fit for as a function of closely agrees with the one based on the full distribution. In contrast, in Figure 3 (b), the slope of the power-law fit for as a function of is remarkably close to 0. Based on this, we suggest that at least at low β e magnetic reconnection may control the ion-scale break of the solar wind turbulence. The intercept of the power-law fit is , implying C D = 4.7 (see Equation ( 1 )). Figure 3. (a) and (b) are identical to Figures 1 (e) and (d); however, they present the subset of measurements, which are within the black square in Figure 2 corresponding to 41% of the overall data points. Both and were close to normally distributed in our data, thus we use an F -test to investigate whether they have equal variance. The ratio of the sample variances is with 95% confidence intervals of [0.8328; 0.8468]. Thus we reject the null hypothesis and conclude that predicts the break with smaller spread than ρ c . Finally, the scaling of as a function of β i , while significant over the whole range of β i present in the data, is not particularly strong. With reference to the results of Chen et al. ( 2014 ), Mallet et al. ( 2017 ) pointed out that correlations between and β i could cause the scaling behavior of d i to mimic that of . Neglecting a nearly constant factor ,and so if were anticorrelated with β i , the ratio would scale less strongly with β i than otherwise expected. Figure 4 shows that empirically, such an anticorrelation does in fact exist in the solar wind (at least at low β i ). Assuming that the break scale (as does appear to be the case: see Figures 1 (d) and 3 (b)), this contributes to the rather shallow scaling of in Figure 1 (b). Similar consideration could contribute to the shallow scaling of with . Figure 4. 2D histogram showing the distribution of the measurements in the () plane. The least-square fit is indicated with a black line and the average and standard deviation of each 5% of the data are marked in white. 4. Conclusion In this Letter, we have presented a statistical study of the break scale between the inertial and dissipation ranges of the solar wind turbulence spectrum, and to what extent agrees with the fundamental ion length