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We analyse sunspot oscillations using Interface Region Imaging Spectrograph(IRIS) slit-jaw and spectral data and narrow-band chromospheric images from theNew Solar Telescope (NST) for the main sunspot in NOAA AR 11836. We report thatthe difference between the shock arrival times as measured the Mg II k2796.35\AA\ and Si IV 1393.76\AA\ line formation levels changes during theobserved period and peak-to-peak delays may range from 40~s to zero. Theintensity of chromospheric shocks also displays a long term (about 20~min)variations. NST's high spatial resolution \ha\ data allowed us to conclude thatin this sunspot umbral flashes (UFs) appeared in the form of narrow brightlanes stretched along the light bridges and around clusters of umbral brightpoints. Time series also suggested that UFs preferred to appear on thesunspot-center side of light bridges, which may indicate the existence of acompact sub-photospheric driver of sunspot oscillations. The sunspot's umbra asseen in the IRIS chromospheric and transition region data appears bright abovethe locations of light bridges and the areas where the dark umbra is dottedwith clusters of umbral dots. Co-spatial and co-temporal data from theAtmospheric Imaging Assembly on board Solar Dynamics Observatory showed thatthe same locations were associated with bright footpoints of coronal loopssuggesting that the light bridges may play an important role in heating thecoronal sunspot loops. Finally, the power spectra analysis showed that theintensity of chromospheric and transition region oscillations significantlyvary across the umbra and with height, suggesting that umbral non-uniformitiesand the structure of sunspot magnetic fields may play a role in wavepropagation and heating of umbral loops.

Dynamics in Sunspot Umbra as Seen in New Solar Telescope and Interface Region Imaging Spectrograph Data