Sluggishness of the Ionosphere: Characteristic time-lag in Response to Solar Flares

The term “sluggishness” is used to describe the time delay between maximum radio absorption in the ionosphere following the time of maximum irradiance during a solar flare. Sluggishness is one of the characteristic properties that can be used for studying lower ionospheric (D-region) and mesospheric chemistry. In this study, we propose a novel approach to estimate the ionospheric sluggishness from riometer and SuperDARN radar observations following a solar flare. In addition, we analyze sluggishness observed in riometer data. We find that sluggishness is anticorrelated with the peak solar X-ray flux and positively correlated with solar zenith angle and geographic latitude.