Three-minute oscillations over sunspot's umbra in AR 11131 were observed
simultaneously in UV/EUV emission by SDO/AIA and in radio emission by Nobeyama
Radioheliograph (NoRH). We use 24-hours series of SDO and 8-hours series of
NoRH observations to study spectral, spatial and temporal variations of
pulsations in the 5-9 mHz frequency range at different layers of the solar
atmosphere. High spatial and temporal resolution of SDO/AIA in combination with
long-duration observations allowed us to trace the variations of the cut-off
frequency and spectrum of oscillations across the umbra. We found that higher
frequency oscillations are more pronounced closer to the umbra's center, while
the lower frequencies concentrate to the peripheral parts. We interpreted this
discovery as a manifestation of variation of the magnetic field inclination
across the umbra at the level of temperature-minimum. Possible implications of
this interpretation for the diagnostics of sunspot atmospheres is discussed.Comment: 29 pages, 7 figures, in press ApJ, 201
