We introduce harmonic cross-correlation decomposition (HCD) as a tool to detect and visualize features in the frequency structure of multivariate time series. HCD decomposes series into spatiotemporal modes with leading representing dominant oscillatory patterns data. is closely related data-adaptive (DAHD) [Chekroun Kondrashov, Chaos 27, 093110 (2017)] that it performs an eigendecomposition gr...