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tokens: origin ( t = 61 minutes) up to its decay phase ( t = 70.7 minutes) in the vertical experiment for the three LOSs. (An animation of this figure is available.) To extend the analysis, it is also of interest to consider the total emitted intensity for each vertical column, i.e.,which, following Equation ( 1 ), is equal to the column density of the emitting species along the LOS (except for a constant factor). Equation ( 5 ) has been calculated separately for Si iv and O iv and with the emissivities obtained assuming either NEQ or SE ionization, to better gauge the importance of disregarding the NEQ effects. The results are shown in the middle and bottom panels of Figure 10 for Si iv and O iv , respectively. The top panel of the image contains the 2D map of the emissivity for Si iv for context identification. Combining Figures 9 and 10 , we are able to discern and describe characteristic features of the spectral profiles: 1. The most prominent feature in the synthetic profiles of Figure 9 is the brightening associated with the location of the internal footpoint of the surge. In the corresponding movie, we can see how that footpoint is formed at around t = 64 minutes, as the surge detaches from the emerged dome. During those instants, the associated synthetic profiles are characterized by large intermittent intensities and bidirectional behavior with velocities of tens of kilometers per second, as apparent, e.g., in the (b0) and (c0) panels at x ∈ [15, 16] Mm. In Si iv and O iv (panels (b) and (c)), we find that the internal footpoint is usually the brightest region, although there are some instants in which the brightest points can be located in the crests or the external footpoint. This is a potentially important result from the observational point of view because it can help us to unravel the spatial geometry of the surge in future observational studies: if strong brightenings are detected in Si iv and also in O iv within the surge, it would be reasonable to think that they correspond to the internal footpoint of the surge. In this region, the intensity ratio between Si iv and O iv ranges between 2 and 7, approximately. Note that, in general, the intensity ratio values vary depending on the observed region and features (Martínez-Sykora et al. 2016 ). In Section 5.2 we will see that LOS effects play a major role in causing the large brightness of the internal footpoint (and other bright features) compared to the rest of the surge. Here we consider the parallel question of the role of NEQ: what would be obtained for the intensity of the internal footpoint if SE were assumed? Comparing the values for Si iv in Figure 10 (middle panel, 13.8 ≤ x ≤ 16.1), there is roughly a factor of two, on average, between the NEQ and SE intensities; for O iv (bottom panel), there is no major difference in the intensity between both calculations. One could conclude that while NEQ is important for the Si iv diagnostics, SE could be applied for the O iv case;