Plasma Characteristics of Active Region Footpoints before Eruptive and Confined Flares

Abstract Solar flares are powerful, explosive events that occur in solar active regions (ARs). They are typically classified as either eruptive or confined, depending on whether they are associated with coronal mass ejections. While many studies have focused on magnetic field evolution during flares or over the full AR lifecycle, less attention has been given to plasma conditions shortly before flare onset. In this study, we investigate plasma characteristics in AR footpoints during the 1 to 2 hr preceding flare onset, using high-cadence data from the Solar Dynamics Observatory Atmospheric Imaging Assembly and Hinode EUV Imaging Spectrometer. Through differential emission measure and spectral analyses, we examine temporal variations in Doppler velocity, nonthermal velocity, and plasma density across four footpoint regions for two representative events: an M2.6 eruptive flare and an M1.4 confined flare. The results reveal distinct preflare signatures: prior to the eruptive flare, we observe increasing upflow speeds and decreasing plasma density, while the confined flare exhibits decreasing upflow speeds and stable or increasing densities, depending on location. Although nonthermal velocities differ in magnitude between the two flares, they show no consistent temporal trend. These findings confirm and extend earlier observations, particularly by identifying new features in density evolution. We propose that loop expansion plays a critical role in shaping the distinct preflare behaviors of eruptive and confined events.