Localised Angular Structure in Faraday Rotation Scaling

In a preceding study, large-scale coherence in Faraday rotation measure (RM) statistics was demonstrated using structure-function diagnostics. In this follow-up, we investigate whether that global coherence contains intrinsic local structure at smaller angular scales.

Using localized estimates of structure-function slopes, angular correlation analysis, shuffle-based null tests, and latitude-split control samples, we identify a robust and invariant meso-scale angular coherence length of approximately 2.6 degrees, within bin-resolution uncertainty. Here, “meso-scale” refers to angular organization intermediate between individual source separations and the global RM coherence envelope.

This meso-scale is clearly distinct from the larger coherence envelope, previously identified at angular scales of approximately 10–15 degrees (Doumbouya 2026a). The 2.6-degree scale persists under detrending, normalization, and sky partitioning, indicating genuine hierarchical magnetic organization rather than survey geometry or latitude-dependent artefacts.

This work builds directly on the control-diagnostic framework developed in Doumbouya (2026a,b), which established the presence of large-scale magnetic organization in RM data without invoking parity breaking. The present analysis extends that framework by resolving a previously unreported, localized angular coherence scale embedded within the broader RM coherence structure.