Properties of sunspot oscillations and wave propagation in NOAA AR 12470 as observed with ALMA and BBSO instruments

Waves and oscillations are important phenomena not only because they can propagate and dissipate energy in the chromosphere, but also because they carry information about the structure of the atmosphere in which they propagate. The nature of the three-minute oscillations observed in the umbral region of sunspots is considered to be an effect of propagation of magnetohydrodynamic (MHD) waves from the photosphere to the corona. We present a study of sunspot oscillations and wave propagation in NOAA AR 12470 using an approximately one-hour long data set acquired on December 17, 2015 by the Atacama Large Millimeter/submillimeter Array (ALMA), the Goode Solar Telescope (GST) operating at the Big Bear Solar Observatory (BBSO), the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO), and the Interface Region Imaging Spectrograph (IRIS). The ALMA data are unique in providing a direct temperature measurement in the chromosphere. The high cadence of ALMA images (2 s) allows us to well resolve the three-minute oscillations of temperature in the chromosphere above the sunspot. Fourier analysis was applied to ALMA band 3 ( 100 GHz) and GST H-alpha data sets to obtain power spectra as well as phase information. We analysed properties of wave propagation by comparing power spectra maps as well as phase information derived for multiple wavelengths that probe physical parameters of solar atmosphere at different heights. We discuss implications of these results on understanding sunspot oscillations and wave propagation in the highly coupled low solar atmosphere.