frimas

Frimas refers to a phenomenon of frost occurring on surfaces, typically at ground level, without any precipitation falling. It is formed when water vapor in the air comes into contact with a surface that is below the freezing point of water, and the vapor directly transforms into ice crystals. This process is known as deposition or desublimation. Frimas often appears as a thin, white layer of crystalline ice.

The formation of frimas is dependent on specific atmospheric conditions. Key factors include a clear sky, which allows for rapid radiational cooling of the ground surface, and a sufficient amount of moisture in the air. Calm or very light winds are also conducive to frimas development, as strong winds can mix the air and prevent the surface from cooling sufficiently. Dew point temperature is a critical factor; when the surface temperature drops below the dew point, frimas can form.

Common locations for frimas include open fields, grassy areas, and surfaces exposed to the night sky. It is distinct from frost that forms during freezing rain or sleet, as frimas is a dry frost. The presence of frimas can indicate that the temperature is at or below freezing, and it can sometimes be an early warning of more significant frost events.