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Solar chromospheric observations of sunspot umbrae offer an exceptional viewof magneto-hydrodynamic wave phenomena. In recent years, a wealth of wavesignatures related to propagating magneto-acoustic modes have been presented,which demonstrate complex spatial and temporal structuring of the wavecomponents. Theoretical modelling has demonstrated how these ubiquitous wavesare consistent with an m=0 slow magneto-acoustic mode, which are excited bytrapped sub-photospheric acoustic (p-mode) waves. However, the spectrum ofumbral waves is broad, suggesting that the observed signatures represent thesuperposition of numerous frequencies and/or modes. We apply Fourier filtering,in both spatial and temporal domains, to extract chromospheric umbral wavecharacteristics consistent with an m=1 slow magneto-acoustic mode. Thisidentification has not been described before. Angular frequencies of 0.037 +/-0.007 rad/s (2.1 +/- 0.4 deg/s), corresponding to a period approximately 170 sfor the m=1 mode are uncovered for spatial wavenumbers in the range of0.45<k<0.90 arcsec^-1 (5000-9000 km). Theoretical dispersion relations aresolved, with corresponding eigenfunctions computed, which allows the densityperturbations to be investigated and compared with our observations. Suchmagnetohydrodynamic modelling confirms our interpretation that the identifiedwave signatures are the first direct observations of an m=1 slowmagneto-acoustic mode in the chromospheric umbra of a sunspot.

An Inside Look at Sunspot Oscillations with Higher Azimuthal Wavenumbers