Abstract; This Letter presents first observations of distinct solar atmospheric oscillations from signals collected by the Extreme Ultraviolet and X-ray Irradiance Sensors EUVS-C instrument, which is part of each Geostationary Observational Environmental Satellite R-Series instrument payload. The EUVS-C instrument is a full-disk, normal-incidence spectrograph that covers a narrow band in the mid-ultraviolet between 276 and 284 nm, where it can measure the magnesium ii emission doublet at ∼280 nm and the photospheric continuum. The primary goal of EUVS-C data is to construct the well-known Mg ii index, which is often used as a proxy for chromospheric activity. Because of the high temporal and spectral resolution of EUVS-C measurements, the data provide a unique opportunity to observe discernible solar atmospheric waves that have definite signatures of 3 and 5 minute oscillation periods, where the frequency response of these signals is dependent on what part of the spectrum is analyzed (e.g., Mg emission lines). Furthermore, both photospheric and chromospheric waves can simultaneously be examined. With the recent increase in solar activity for Solar Cycle 25, these waves exhibit enhanced amplitudes and phase shifts during the impulsive shock of strong solar flares. This Letter will discuss the analysis for deriving these waves, and results from both a quiescent Sun and an X-class solar flare event will be presented.
