Active-time bowl-shaped dependence of proton IB spatial distribution

Determine whether, during geomagnetically active intervals, the proton isotropy boundary (IBp) dispersion region’s minimum and maximum IGRF L-shell and magnetic latitude distributions exhibit a bowl-shaped dependence across magnetic local time, and ascertain whether the inward shift and peak near 20–21 MLT continue across adjacent MLT sectors.

Background

The paper analyzes the spatial distribution of proton isotropy boundaries (IBp) across magnetic local time (MLT), L-shell, and magnetic latitude (MLAT), and compares quiet versus active geomagnetic intervals. A bowl-shaped (U-shape) distribution in L-shell/MLAT is evident at quiet times, but active-time behavior appears to shift pre-midnight and move radially inward.

Because of low sample size in certain MLT sectors at active times, the authors state they cannot establish whether the active-time trend continues or retains a bowl shape. Clarifying this behavior would refine understanding of IB morphology and its dependence on geomagnetic activity and local time.

References

At active times the distribution shifts to pre-midnight and moves radially inward by 1-2 L-shells, peaking at 20-21 MLT, although the low sample size of events in the vicinity makes it impossible to determine whether the trend continues, and whether it is bowl-shaped.

— Statistical Characteristics of the Proton Isotropy Boundary  (2409.04488 - Wilkins et al., 2024) in Section 4 (Results), discussion of Figure 5