  Umbral flashes (UFs) are most common phenomenon of wave processes in
sunspots. Studying the relationship between wave time dynamics and the origin
of UFs requires further investigation of their fine spatial and height
structure. We investigated the association between a short time increase in the
variations of three-minute extreme ultraviolet (EUV) emission at footpoints of
coronal magnetic loops and the UF emergence in sunspot umbra. We applied the
pixelized wavelet filtering (PWF) technique to analyse a cube of the images
obtained by SDO/AIA at 1600A, 304A, and 171A to study the spatio-temporal
oscillation power distribution in individual magnetic loops. Time-distance
plots were used to obtain the wave front propagation velocity. For the first
time, we obtained the 2D images of the fine wave processes in magnetic
structures of different spatial scales related to the UFs in sunspot. We
revealed two types of the UFs as background and local. The background UFs
associated with random increasing of separate parts of wave fronts. These UFs
are seen as weak and diffuse details that ride the wave fronts without stable
shapes and localization in space. The local UFs sources mainly localize near to
the footpoint of magnetic loops, anchored in an umbra, along which the
propagation of three-minute waves was observed. It is shown that the maxima of
three-minute oscillation trains coincide with the peak intensity of UFs. The
sunspot three-minute wave dynamics showed a relation between the localization
of oscillations power peak at the coronal magnetic loop footpoints and the UFs
origin. The spatial structure of the UFs sources, their power, and lifetime are
determined by the cut-off frequency of the waves for the detected waveguides.
We concluded that UFs are a global process of short-time increase of the wave
activity.
