Study of butterfly-shaped coronal hole evolution across the solar disk

Abstract

We studied the evolution of a butterfly-shaped coronal hole observed during its passage across the solar disk from 2025 September 8 to 14. We used SDO/AIA 193 Å images to identify the coronal-hole boundary and measure its area and mean intensity, and SDO/HMI line-of-sight magnetograms to examine the underlying photospheric magnetic field. The boundary was identied using a fixed intensity threshold of 100 DN, and the area, mean 193 Å intensity, and total unsigned magnetic flux were tracked from the eastern to the western limb. As the coronal hole approached the central meridian, its measured area increased from approximately 7.70 × 10¹⁶ to 1.63 × 10¹⁷ m² and its unsigned magnetic flux increased from 8.68 × 10²¹ to 1.91 × 10²² Mx, while the mean intensity decreased from approximately 61 to 45 DN. The area and unsigned magnetic flux followed similar temporal trends, whereas the mean 193 Å intensity varied in the opposite direction. Near central-meridian passage, all three quantities remained relatively stable for several days, suggesting that the coronal-hole properties did not change abruptly during this interval. OMNIWeb observations detected a high-speed solar-wind stream approximately 2-4 days later, with speeds reaching 600_750 km s⁻¹. The timing is consistent with the butterfly-shaped coronal hole being the likely solar source. These findings reveal a close relationship among coronal-hole area, 193 Å intensity, and unsigned magnetic flux, and support an association with the subsequent high-speed solar-wind stream measured near Earth.