We provide:

(1) the complete processed experimental data on which the paper is based: the density field ('rho') and three-component velocity ('u', 'v', 'w') field in three spatial coordinates ('x', 'y', 'z') and in time ('t'). The fields are given as four seperate four-dimensional matlab arrays, in addition to the one-dimensional coordinate arrays. All data are given on the same grid (density has been subsampled on the velocity grid as explained in the paper). A few slices and isosurfaces of these data are plotted in figures 2, 3, 4a-b. The vorticity field (curl of the velocity field) is not given due to space restrictions.

(2) the base flow, U(y,z) and R(z) upon which the 3P-2B stability analysis is based, as well as U(y=0,z) upon which the 2P-1B analysis is based (see figure 5). These are grouped in the structure BASE_FLOW, with subfields 'U', 'R', 'U0', 'y', 'z'.

(3) the phase-averaged confined Holmboe wave (CHW) plotted in figures 4c-d and 8, given as the matlab structure called 'CHW', consisting of the subfields: density ('rho') three-dimensional velocity ('u', 'v', 'w'), spanwise vorticity ('omega_y') subfields and corresponding coordinates ('x', 'y', 'z')

(4) the reconstructed confined Holmboe instability (CHI) to which we compare the CHW in the article, plotted in figures 7 and 9, given as the matlab structure 'CHI' with the respective subfields named as in the 'CHW' structure.