I am using GRADS (1, 2, 3) to plot ERA reanalysis relative humidity profile for latitudinal average of 15N to 37N, and along the longitude from 40E to 130E. The orography is quite obvious and thus some pressure levels like up to 700 hPa are not applicable in some regions with high altitude.
I need to know how to plot orography in the grads, thus the orography can be masked or shown in gray color, the image for reference is shown below. Thanks