Hard Rime
(Section 3.2.1.4.5)Definition: Hard rime: Granular rime, usually white, adorned with crystalline branches of grains of ice.
Hard rime is formed by the rapid freezing of supercooled water so that the droplets freeze more or less individually, leaving air gaps. Near the ground, it is deposited mainly on objects exposed to at least moderate wind. In the windward direction, the deposit may form a thick layer. In the free atmosphere, hard rime may form on the parts of aircraft exposed to the relative wind. Hard rime is rather adhesive, but can be scratched off the object. Hard rime mainly forms at temperatures between −2 °C and −10 °C.