Three-Year Global Survey of Coronal Null Points from Potential-Field-Source-Surface (PFSS) Modeling and Solar Dynamics Observatory (SDO) Observations

TL;DR

This study combines PFSS modeling and SDO/AIA observations over three years to analyze the distribution and observability of coronal null points, revealing hemispheric activity effects and the proportion of observable nulls.

Contribution

It provides the first comprehensive survey of coronal null points combining modeling and observations over an extended period, highlighting observability factors and distribution patterns.

Findings

Approximately 31% of predicted nulls were observed in SDO/AIA images.

Null observability is influenced by hemispheric activity asymmetry.

No significant effect of eigenvalues or spine orientation on null observability.

Abstract

This article compiles and examines a comprehensive coronal magnetic-null-point survey created by potential-field-source-surface (PFSS) modeling and Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) observations. The locations of 582 potential magnetic null points in the corona were predicted from the PFSS model between Carrington Rotations (CR) 2098 (June 2010) and 2139 (July 2013). These locations were manually inspected, using contrast-enhanced SDO/AIA images in 171 angstroms at the east and west solar limb, for structures associated with nulls. A Kolmogorov--Smirnov (K--S) test showed a statistically significant difference between observed and predicted latitudinal distributions of null points. This finding is explored further to show that the observability of null points could be affected by the Sun's asymmetric hemisphere activity. Additional K--S tests show no effect on observability related to eigenvalues associated with the fan and spine structure surrounding null points or to the orientation of spine. We find that approximately 31% of nulls obtained from the PFSS model were observed in SDO/AIA images at one of the solar limbs. An observed null on the east solar limb had a 51.6% chance of being observed on the west solar limb. Predicted null points going back to CR 1893 (March 1995) were also used for comparing radial and latitudinal distributions of nulls to previous work and to test for correlation of solar activity to the number of predicted nulls.