Read a report about a rare meteorological phenomenon that is beautiful and fascinating: Rime ice.  The report is the work of Dave Whiteman, Research Professor at the University of Utah and Rolando Garibotti, an expert on the mountains of Patagonia.

Specific conditions are necessary for the formation of rime.  Supercooled water droplets must be suspended in the atmosphere, (water that is liquid below 0C).  This occurs during rapid topographic uplifting of wet, maritime airmasses downwind of water.  They must not cool much below -10c because then the water tends to freeze independent of a surface to stick to.  The rock surface of a mountain must be below freezing, and rime collides with it during high winds, and is accreted in layers.  Above is a photo of Cerro Torre, a mountain in Argentine Patagonia.  Conditions are conducive to rime formation for much of the year, and the formations can grow to huge proportions. Here is Dave Whiteman’s formula for the mass growth of rime ice:

dM/dt=awUA [kg/s]       where w is the supercooled liquid water content of the passing cloud, U is the wind velocity in m/s, A is the area of the obstacle perpendicular to the wind, and a is the droplet-obstacle collision efficiency, between 0 and 1.

Throughout the course of a year wet weather deposits rime steadily on the faces of exposed, windswept ridges and summits.  In the photo above, these ‘mushrooms’ can grow to thicknesses of over 30m.