Leading and following sunspots: their magnetic properties and ultra-violet emission above them

TL;DR

This study investigates the magnetic and ultraviolet emission differences between leading and following sunspots during solar cycle 24, revealing that leading spots generally have more vertical magnetic fields and larger flux densities.

Contribution

It introduces a more accurate algorithm for resolving magnetic field azimuth ambiguity and provides new insights into magnetic field asymmetries between sunspot pairs.

Findings

Leading spots have more vertical magnetic fields in ~78% of cases.

Umbral area-averaged angles are smaller in leading spots in ~83% of cases.

Magnetic flux densities depend on umbral area.

Abstract

Using SDO/HMI and SDO/AIA data for sunspot groups of the 24th solar cycle, we analyzed magnetic properties and He II 304 emission in leading and following sunspots separately. Simultaneous examination of umbral magnetic properties and atmospheric characteristics above the umbrae draws on average differences in He II 304 contrast over the umbrae of leading and following spots we discovered earlier for solar cycle 23 sunspot groups based on SOHO data as well as on the hypothetical relationship between contrast asymmetry and magnetic field asymmetry in umbrae. We use a more accurate and faster algorithm for solving the pi-uncertainty problem of the transverse magnetic field direction in this research producing new results on differences in magnetic field properties between magneto-conjugated leaders and followers. We found that, in ~78% of the cases, the minimum (over the umbra area) angle between the magnetic field line and the normal to the solar surface, a_min, is smaller in the leading spots, so the magnetic field there is more vertical than that in the counterpart following spot. It was also found that umbral area-averaged angle <a> in ~83% of the spot groups examined is smaller in the leader compared to the follower and the maximum and mean magnetic flux densities inside the umbra depend on the umbral area.