Magnetic Evolution and Temperature Variation in a Coronal Hole

TL;DR

This study investigates the magnetic flux evolution and temperature changes in a coronal hole over several days, revealing that flux imbalance influences EUV brightness and coronal temperature, with the coronal hole disappearing during the observation period.

Contribution

It provides detailed observational analysis of magnetic flux and temperature evolution in a coronal hole, highlighting the relationship between flux imbalance and coronal heating.

Findings

Coronal hole's magnetic flux imbalance decreases as it disappears.

EUV brightness and temperature increase as the coronal hole diminishes.

Quiet region shows stable temperature and irregular brightness variation.

Abstract

We have explored the magnetic flux evolution and temperature variation in a coronal-hole region, using Big Bear Solar Observatory (BBSO) deep magnetograms and {\it SOHO}/EIT images observed from 2005 October 10 to 14. For comparison, we also investigated a neighboring quiet region of the Sun. The coronal hole evolved from its mature stage to its disappearance during the observing period. We have obtained the following results: (1) When the coronal hole was well developed on October 10, about 60 % of the magnetic flux was positive. The EUV brightness was 420 counts pixel$^{-1}$, and the coronal temperature, estimated from the line ratio of the EIT 195 {\AA} and 171 {\AA} images, was 1.07 MK. (2) On October 14, when the coronal hole had almost disappeared, 51 % of the magnetic flux was positive, the EUV radiance was 530 counts pixel$^{-1}$, and the temperature was 1.10 MK. (3) In the neighboring quiet region, the fraction of positive flux varied between 0.49 and 0.47. The EUV brightness displayed an irregular variation, with a mean value of 870 counts pixel$^{-1}$. The temperature was almost constant at 1.11 MK during the five-day observation. Our results demonstrate that in a coronal hole less imbalance of the magnetic flux in opposite polarities leads to stronger EUV brightness and higher coronal temperatures.