Schematic representation of the effects of vertical temperature structures on the N₂H⁺ emission. Left panels: the snow surfaces of CO and N₂ in the disks with the same midplane temperatures but different vertical temperature structures; in the upper panel the VIRaM layer extends through a substantial part of the disk, while in the lower panel the VIRaM layer is thin, and instead there is a vertical temperature gradient from the midplane to the disk surface. The solid blue shading shows the disk regions where N₂ is in the gas phase and CO is frozen out, and thus where N₂H⁺ should be abundant. Right panels: the expected corresponding N₂H⁺ column density distributions. The thick VIRaM layer case results in sharp edges at the CO and N₂ midplane snowline, while the opposite is true for disks with a thin VIRaM layer.