Height of the Polar Chromosphere in 2012–2023 According to Observations with the Ernest Gurtovenko Telescope

Abstract

Based on observations conducted at the Ernest Gurtovenko Horizontal Solar Telescope, the height of the polar chromosphere of the Sun was determined for the period 2012–2023. The measurement was calculated as the difference between the positions of the maximum radial brightness gradients in the continuum and at the core of the H_α line. The results indicate that the height of the polar chromosphere is lower near the maximum of the solar cycle (approximately 4500 km, or 6.3″) and higher near the minimum of the cycle (approximately 5000 km, or 6.9″). The chromosphere’s height at the southern pole in 2012–2013 and, particularly, 2016–2017 was higher than at the northern pole. This north–south asymmetry is likely related to differences in the dynamics and magnitude of the polar magnetic fields during Solar Cycle 24. The findings demonstrate that the time changes in the chromosphere’s height closely correlate with sunspot numbers, the strength of the polar magnetic field, and chromospheric indices of solar activity. The correlation coefficient between the average annual height of the chromosphere and the smoothed relative sunspot number is –0.64 for the northern hemisphere and –0.75 for the southern hemisphere. The correlation coefficient between the average annual height of the chromosphere and the smoothed values of the polar magnetic field strength (based on data from the Wilcox Solar Observatory) is 0.86 for the northern hemisphere and 0.53 for the southern hemisphere (the latter value increases to 0.77). The correlation coefficient between the average annual height of the chromosphere and the chromospheric index I_K2 reaches the highest values, 0.91, for the northern pole and 0.80 for the southern pole.