Rotation rates of the coronal holes and their probable anchoring depths

TL;DR

This study analyzes the rotation rates of coronal holes using SOHO/EIT data from 2001-2008, revealing they rotate rigidly and their initial rotation matches the solar interior below the tachocline.

Contribution

It provides the first detailed analysis of coronal hole rotation rates across latitudes, showing rigid rotation and linking initial rotation to the solar interior.

Findings

Coronal holes rotate rigidly across latitudes.

Initial rotation rates match the solar interior below the tachocline.

Coronal holes follow a rigid body rotation law during their evolution.

Abstract

For the years 2001-2008, we use full-disk, SOHO/EIT 195 $\AA$ calibrated images to determine latitudinal and day to day variations of the rotation rates of coronal holes. We estimate the weighted average of heliographic coordinates such as latitude and longitude from the central meridian on the observed solar disk. For different latitude zones between $40^{o}$ north - $40^{o}$ south, we compute rotation rates, and find that, irrespective of their area, number of days observed on the solar disk and latitudes, coronal holes rotate rigidly. Combined for all the latitude zones, we also find that coronal holes rotate rigidly during their evolution history. In addition, for all latitude zones, coronal holes follow a rigid body rotation law during their first appearance. Interestingly, average first rotation rate ($\sim 438 nHz$) of the coronal holes, computed from their first appearance on the solar disk, match with rotation rate of the solar interior only below the tachocline.