It is useful for masking land vertically. 🙂
Because, continental self has only white color in vertical session, so it seems to look like value sometimes.
< Example of vertical session of Pacific Ocean >
yes? use levitus_climatology
yes? let pac_temp = temp[x=180e,y=90s:90n]
yes? let mask = missing(pac_temp, 999) ! set missing value as “999” which is far from real value
yes? let landmask = if mask eq 999 then mask else 0/0 ! erasing real value except masking area.
yes? shade pac_temp
yes? shade/overlay/pal=grey landmask
then, you can see the difference between value and land clearly.
So, Simple. 🙂