- Related Topics:
- Rime
- air-mass freeze
- black frost
- wind frost
- radiation frost
Frost
News •
-
What is frost in meteorology?
In meteorology, frost refers to atmospheric moisture that crystallizes directly on the ground and on exposed objects when the temperature drops below freezing. This can also refer to subfreezing temperatures that harm plants and crops.
Frost crystals, often called hoarfrost, form when water vapor transforms into ice crystals without first becoming liquid. Rime, a granular form of frost, occurs when supercooled water droplets freeze on objects, common on mountaintops and aircraft. True crystalline hoarfrost appears in columnar or platelike forms, depending on the temperature.
In horticulture, frost is a high-risk element for commercial growers, especially for sensitive perennial fruit crops and transplants. Frost control methods include reducing radiational heat loss or conserving/adding heat. The frost point is the temperature below 0° C (32° F) at which moisture in the air will condense as frost on exposed surfaces.
4 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
How does frost form on the ground?
Frost is atmospheric moisture that crystallizes on the ground and exposed objects when the temperature drops below freezing. This occurs when water vapor transforms directly into ice crystals, skipping the liquid phase, in a process similar to dew formation, but at sub-freezing temperatures.
For frost to form, the air must be sufficiently damp to reach saturation upon cooling. The temperature at which moisture in the air will condense as frost on a surface is called the frost point. If there isn't enough moisture, "black frost" may occur, where water inside plant tissues freezes instead.
4 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
What weather conditions are needed for frost to appear?
Frost appears when atmospheric moisture crystallizes directly on exposed surfaces, like the ground or leaves. This happens when the air reaches its frost point, meaning the temperature is below 0° C (32° F), and the air is saturated with moisture.
For frost to form, the air needs to be damp enough to reach saturation upon cooling. Without sufficient moisture, frost won't form; instead, the water inside plant tissues may freeze, leading to black frost.
Hoarfrost is the name for frost crystals that form in these conditions.
5 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
What is the difference between frost and dew?
Both dew and frost are forms of atmospheric moisture that condense on exposed surfaces. Dew is the deposit of water drops, while frost is atmospheric moisture crystallized on the ground and exposed objects.
Dew forms when water vapor condenses on objects, typically on clear, calm nights, as surfaces lose heat to the sky through radiation, cooling the surrounding air below its dew point. Frost, however, occurs when the temperature of the exposed surface is below the freezing point. In this case, water vapor transforms directly into ice crystals without first becoming liquid.
6 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
How does frost affect plants and crops?
Frost affects plants and crops when subfreezing temperatures cause the aqueous solutions in plant cells to freeze, which can rupture the cells and destroy the plant. The most critical impact of frost is its determination of the growing season's length, from the last killing frost in spring to the first in autumn.
Two types of frost can affect plants: radiation frost, which occurs on clear, calm nights, and wind (or advection) frost, which can occur anytime when wind moves cold air in from other regions. Methods of protecting plants from frost include:
* Heating the plants
* Using wind machines to mix the air
* Flooding or sprinkling with water
* Using mulches
* Shielding plants from the wind5 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
What are some ways people protect crops from frost?
To protect crops from frost, several techniques can be employed based on the type of frost expected.
- Heating Supplying heat to an orchard or field is effective when there is a strong temperature inversion, where the air temperature increases with height above the ground. A large number of small heaters are more effective than a few large ones.
- Wind Machines Wind machines mix the air and return heat to the ground. They are most effective when there is a strong temperature inversion.
- Water Sprinkling Flooding and sprinkling with water prevents ground cooling. The temperature of the plant will not fall below freezing as long as water is freezing.
- Covers Shields of paper or aluminum foil can reduce radiation loss to the sky. Hot caps, cold frames, and mulches can also reduce radiational heat loss.
- Hardening Off Withholding water and fertilizer can prevent the formation of succulent tissue that is very frost-tender.
4 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
Frost, atmospheric moisture directly crystallized on the ground and on exposed objects. The term also refers to the occurrence of subfreezing temperatures that affect plants and crops.
Frost crystals, often called hoarfrost in the aggregate, form when the invisible water vapour of the atmosphere passes into the ice crystal phase without going through the intermediate liquid phase. Hoarfrost lightly covers fields and rooftops under conditions that would form dew if the temperature were above freezing at the point of formation. Sometimes the freezing temperature will be reached after dew has already formed, producing frozen dew, but this usually cannot be readily distinguished, because crystals ordinarily will start forming at about the same time the freezing starts.
The crystalline and other forms of frost deposit are a subject of aesthetic as well as scientific interest. The structures differ in some respects from those of snow. Granular forms are called rime and are produced by the freezing of droplets of liquid water (technically called supercooled droplets) that are carried in the air at temperatures below freezing. Rime is best developed on mountaintops enveloped in supercooled clouds. It is a common form of icing on aircraft. It also occurs in steam fogs around open springs, streams, lakes, or ponds in very cold weather and, in extreme conditions, around chimneys from the water vapour condensed in the flue gases.
" height="20" alt="HEW Logo">
True crystalline hoarfrost is of two classes, one of which assumes columnar forms and the other of which assumes tabular, or platelike, forms. Generally, the crystals of these two classes do not occur together on a single night; rather, one or the other will greatly predominate. Columnar or needlelike forms are found at the higher subfreezing temperatures, whereas plate crystals predominate under colder conditions. In their pristine state, both forms are hexagonal crystals, the columns having a hexagonal cross section and the plates appearing as flat hexagons. Because they must grow outward from some supporting object, they rarely assume the perfect symmetry found in many snow crystals. Over ice-covered ponds and rivers, beautiful clusters or rosettes of fernlike or jewel-like frost collect on the surface of the ice. At very low temperatures, cubical crystals are sometimes found.
In cold weather, striking frost forms are often found on the inner surfaces of windowpanes in buildings. In most cases with heated rooms, the vapour condenses as a liquid first, but if the conditions are right, as in an unheated room, the delicate, pure crystalline forms are predominant, evoking a variety of fanciful descriptions.
In gardening and horticulture, frost refers to the freezing of the aqueous solutions in the plant cells, causing these to burst and destroy the plant. Only plants containing plentiful and dilute solutions in their leaves, fruits, and so on, are easily damaged. The occurrence of a killing frost without a hoarfrost deposit is sometimes popularly called a black frost.
The most important aspect of frost in relation to plants is its determination of the length of the growing season: the period from the last killing frost in spring to the first killing frost in autumn, with reference to the tenderest crop plants. There are regions where the season reaches critically short duration for the maturing of most usable crops and others where the season is so long that more than one planting of such crops as corn (maize) and alfalfa can be brought to harvest. In regions where frost is rare or absent, other factors take on more importance.
The trusted destination for professionals, college students, and lifelong learners.
SUBSCRIBE
One of the most critical situations for frost is encountered in the citrus fruit regions. There the few killing frosts likely each winter are combated by a variety of methods, including heating the groves with special burners using oil or a petroleum-derived solid fuel, mixing the air with large fans mounted above the trees, or casting a fine water spray over and on the trees to keep the temperature at or very near the nondamaging level of 32 °F (0 °C).