Hoar Frost on Prunus trees of Loška Dolina/Lož Valley; Notranjska/Internal Karst-Dinaric Region, Slovenija
21-January-2024
Hoar Frost is due to the sublimation of water vapor into ice crystals contained in the dense mists and fogs freezing close to the ground of a basin, plain or valley floor after a clear and freezing night without wind and with high humidity.
This is a composition very similar to snow crystals (and Hard Rime) within clouds, which, in this case, are represented by freezing fog.
It is therefore white frost and not almost transparent ice or black ice which occurs when the valley is at temperatures below zero but fog is made up of supercooled droplets.
The formation process of Hoar Frost is basically similar to that of simply Rime, which however forms only on the ground by sublimation of water vapor on lawns (20-50cm thick, as Dew), but HF affects a greater thickness of the air column, depending on the line of temperature inversion altitude, under which stratified fog forms, generally from a few meters to a few dozen meters in height.
For this reason, trees and all surfaces that have been in contact with the freezing fog during the night, which then tends to dissolve with the sun, also turn white.
Hoar Frost on Prunus trees of Loška Dolina/Lož Valley; Notranjska/Internal Karst-Dinaric Region, Slovenija
21-January-2024
Hoar Frost is due to the sublimation of water vapor into ice crystals contained in the dense mists and fogs freezing close to the ground of a basin, plain or valley floor after a clear and freezing night without wind and with high humidity.
This is a composition very similar to snow crystals (and Hard Rime) within clouds, which, in this case, are represented by freezing fog.
It is therefore white frost and not almost transparent ice or black ice which occurs when the valley is at temperatures below zero but fog is made up of supercooled droplets.
The formation process of Hoar Frost is basically similar to that of simply Rime, which however forms only on the ground by sublimation of water vapor on lawns (20-50cm thick, as Dew), but HF affects a greater thickness of the air column, depending on the line of temperature inversion altitude, under which stratified fog forms, generally from a few meters to a few dozen meters in height.
For this reason, trees and all surfaces that have been in contact with the freezing fog during the night, which then tends to dissolve with the sun, also turn white.