Fig. 6
From: A diagnosis of the plasma waves responsible for the explosive energy release of substorm onset
A demonstration of the algorithm to estimate frequency as a function of wavenumber. a The original along-arc keogram showing auroral beads propagating along the substorm onset arc in the Eastward direction and b their dynamic power spectral density calculated from a spatial Fourier transform of panel a in the longitudinal direction. c An example wavenumber of k = 0.8 × 10−4 m−1 (white vertical dashed line in panel b) as illustration of our methodology. Only information for an individual spatial scale is used to inverse Fourier transform to the spatial domain. This so-called ‘filtered’ keogram is then used to find the real frequency component as a function of wavenumber in order to construct the observational dispersion relation
