Example applications of RH 1.5D, calculated from a 3D MHD simulation. Panel a) is a velocity-time diagram from one column of the simulation, showing a shock pattern in the Ca ii H line. Panels b), c), and e) are a top view of the 24 × 24 Mm² simulation box, showing the properties of the radiation at 279.548 nm, approximately on the mean blue peak (k_2V) feature of the Mg ii k line. Panel b) shows the Stokes V intensity, a proxy for the vertical magnetic field in the chromosphere, while panel c) shows the squared root of the radiation intensity and panel e) shows z(τ = 1), the height where the optical depth reaches unity, scaled from 0.5 Mm (black) to 3.5 Mm (white). Panel d) shows the source function around the Mg ii k line for one column in the simulation, as a function of velocity and height. Additional lines are z(τ = 1) (cyan), atmospheric velocity (red), and in brightness temperature units (in kK, top scale) the source function at − 5km s^-1 (white dashed), and the LTE source function (white dotted). One can see that in this case the departures from LTE occur at around z ≈ 1 Mm. The bottom panelf) shows the spatially averaged spectrum around the Mg ii h&k lines from the same simulation snapshot, with many blending lines included (thick blue). Also included is the spatially averaged z(τ = 1) as a function of wavelength (thin red).