Mechanism or name?
Zlin & RatherBeFlying together have the mechanism right. The air cools through adiabatic expansion as it rises on the western side of the slope. At first it cools at 3 degrees per thousand feet, but once it has cooled to the dewpoint, water begins to condense, warming the air, (just think of the opposite of evaporative cooling), so that subsequent cooling is only at 1.5 degrees per thousand feet.
When the air sinks down the eastern side of the slope, it has lost its moisture and warms at the dry adiabatic rate (3 degrees/1000') all the way down. It makes a profit, as it were, and ends up warmer than it started.
But Alexis asked for a fancy name, not the mechanism.