Moderate Nesting and Cross-Equatorial Asymmetry of Active Regions in Solar Cycle 24

TL;DR

This study analyzes sunspot emergence patterns during Solar Cycle 24, revealing moderate nesting behavior with hemispheric asymmetry and specific rotational velocities associated with active region nests.

Contribution

It provides the first detailed quantification of sunspot nesting behavior and hemispheric asymmetry using SPEAR catalog data and magnetic field maps for Solar Cycle 24.

Findings

41-48% of AR magnetic flux found in hemispheric nests

Nests have average lifetimes of 3.3 to 4.0 months

Strong hemispheric asymmetry in nest patterns

Abstract

Solar Cycle 24 data are used to determine how often the Sun emerges sunspots in `activity nests', i.e., regions where sunspots and active regions (ARs) repeatedly emerge. We use the Solar Photospheric Ephemeral Active Region (SPEAR) catalog created from Helioseismic and Magnetic Imager (HMI) data as well as the HMI Carrington Rotation maps of radial magnetic field, $B_r$. The Sun shows moderate nesting behavior with 41\% (48\%) of AR magnetic flux found in Northern (Southern) hemispheric nests that are short-lived (average lifetimes $\sim$3.3 - 4.0 months). Different rotation rates are used to search for nests that may not be evident `by eye'. The maximum number of nests are found with slightly prograde rotational velocities, with significant nest flux also found at synodic 451--452 nHz prograde and 409--411 nHz retrograde frequencies. Nest patterns show strong hemispheric asymmetry, indicating that the physical origin of nests identified herein must also be asymmetric or antisymmetric across the equator.