Why is a certain frost called Horefrost?

Question

I have always heard that it was usually around the late fall when we get a moderate to light frost.

Answer 1

It is called "hoarfrost" and the name comes from the same root as "hoary" which refers to being white, particularly the white of hair or beards that comes with old age. If is caused by direct deposition of ice crystals without an intervening water stage, and so the frost is particularly white.

Answer 2

Its called "hoarfrost". Also called radiation frost.
It is the white ice crystals, loosely deposited on the ground or exposed objects, that form when the air is moist, the wind is weak or absent and surfaces are cold.
It is often seen on clear winter nights, especially in valleys and hollows. Hoar frost can form in these areas even when the reported temperature is above the freezing point of water.

Answer 3

Source: Webster's Revised Unabridged Dictionary (1913)

Hoarfrost \Hoar"frost`\, n.
The white particles formed by the congelation of dew; white
frost. [Written also horefrost. See Hoar, a.]

He scattereth the hoarfrost like ashes. --Ps. cxlvii.
16.

Answer 4

Radiation frost (also called hoar frost or, sometimes, hoarfrost) refers to the white ice crystals, loosely deposited on the ground or exposed objects, that form when the air is moist, the wind is weak or absent and surfaces are cold. It is often seen on clear winter nights, especially in valleys and hollows. Hoar frost can form in these areas even when the reported temperature is above the freezing point of water.

One can distinguish between some types of hoar frost, depending on where it forms. For example, air hoar is a deposit of hoar frost on objects above the surface, such as tree branches, plant stems, wires; surface hoar is formed by fernlike ice crystals directly deposited on snow, ice or already frozen surfaces; crevasse hoar consists in crystals that form in glacial crevasses where water vapour can accumulate under calm weather conditions; depth hoar refers to cup shaped, faceted crystals formed within dry snow, beneath the surface.

Depth hoar is a common cause of avalanches when it forms in air spaces within snow, especially below a snow crust, and subsequent layers of snow fall on top of it. The layer of depth hoar consists of angular crystals that do not bond well to each other or other layers of snow, causing upper layers to slide off under the right conditions, especially when upper layers are well bonded within themselves, as is the case in a slab avalanche.

Hoar frost does not occur exclusively in nature. Hoar frost is also found in and around freezers particularly in industrial cold storage facilities. It occurs in adjacent rooms that are not well insulated against the cold and around entry locations where humidity and moisture will enter and freeze instantly depending on the freezer temperature.

White frost is a relatively heavy coating of hoar frost with big and interlocking crystals. It forms when the air has a relative humidity above 90% and a temperature below -8 °C (18 °F).

Regards and good luck from Oulu Finland

Julian OH8GEJ

Answer 5

Frost occurs when moist air comes into contact with a colder surface.
Hoar frost forms in damp air.The water vapour freezes directly onto a cold surface.The surface must be colder than the air and below freezing.

Answer 6

hoar frost is caused by radiation cooling

Saturated air freezes and deposits ice crystals on twigs for example