Dynamics of Sunspot Shock Waves in the Chromosphere and Transition Region

Abstract

Abstract We study the dynamics of shock waves observed in the umbra of a sunspot using the spectroscopic observations from the Interface Region Imaging Spectrograph. The presence of a shock significantly deforms the shape of the spectral lines of Mg ii, C ii, and Si iv. We found that C ii 1335.71 Å and Si iv 1393.75 Å show double-peaked profiles that change to a single peak later on. However, the Mg ii h 2803.53 Å line first shows flat-top profiles that change into double peaks followed by the single peak. To study the shock dynamics, we isolate the shock component from the spectra by fitting two Gaussians. We find that the lifetime of the shock is largest in the Mg ii h 2803.53 Å line. Moreover, the plasma motion shows both the acceleration and deceleration phases of the shock. Yet, in C ii 1335.71 Å and Si iv 1393.75 Å, only the deceleration phase is observed. We observe a strong correlation between the largest blueshift of the shock and deceleration for all three spectral lines. We find a positive (negative) correlation between intensities contributed by the shocks in Mg ii and C ii (Si iv). This suggests that the shocks are first amplified in C ii, followed by a decline in the height range corresponding to Si iv. These results may indicate the dissipation of shocks above the formation height of C ii, and the shocks may have important roles in the dynamics of the upper chromosphere and transition region above sunspots.