The state of Haryana and Punjab have experienced first frost of the season. Skymet Meteorology division has issued frost alert for Bhiwani, Hisar, Kaithal, Karnal and Sirsa in Haryana for the next 24 hours. Amritsar, Fatehgarh Sahib, Firozpur, Gurdaspur, Hoshiarpur, Jalandhar, Kapurthala, Ludhiana, Moga and Sangrur districts in Punjab are also under frost alert.
This has been done as temperatures in Haryana and Punjab have dropped appreciably in the last 24 hours, as evident from the following table:
However to understand Frost formation & its other aspects, let us look at it in little detail.
What is Frost?
Frost is the term for several types of coatings or deposits of ice that may form in humid air in cold conditions, usually overnight. In temperate climates like India, it most commonly appears as fragile white crystals or frozen dew drops near the ground, but in cold climates it occurs in a greater variety of forms.
Frost is known to damage crops or reduce future crop yields, therefore farmers in those regions often invest substantial means to prevent its forming.
Frost forms when the temperature of a solid surface in the open cools to below the freezing point of water and for the most clearly crystalline forms of frost in particular, below the frost point in still air. In most temperate countries such temperatures usually are the result of heat loss by radiation at night, so those types of frost sometimes are called radiation frost.
Types of frost
This include crystalline hoar frost from deposition of water vapor from air of low humidity, white frost in humid conditions, window frost on glass surfaces, advection frost from cold wind over cold surfaces, black frost without visible ice at low temperatures and very low humidity, and rime under super cooled wet conditions.
The size of frost crystals varies depending on the time they have been building up and the amount of water vapor available. Frost crystals may be clear or translucent, but, like snow, a mass of frost crystals will scatter light in all directions, so that a coating of frost appears white.
Many plants can be damaged or killed by freezing temperatures or frost. This varies with the type of plant, the tissue exposed, and how low temperatures get:
"light frost" of −2 to 0 °C (28 to 32 °F) will damage fewer types of plants
"hard frost" below −2 °C (28 °F).
Effect on Vegetation
Plants likely to be damaged even by a light frost include vines—such as beans, grapes, squashes, melons—along with night shades such as tomatoes, eggplants and peppers. Plants that may tolerate (or even benefit) from frosts include.
• root vegetables (e.g. beets, carrots, parsnips, onions)
• leafy greens (e.g. lettuces, spinach, chard, cucumber)
• Cruciferous Vegetables (e.g. cabbages, cauliflower, broccoli, Brussels sprouts, radishes, mustard, turnips,)
Protection methods
Typical measures to prevent frost or reduce its severity include one or more of:
• Deploying powerful blowers to simulate wind, thereby preventing the formation of accumulations of cold air. There are variations on this theme. One of them is the selective inverted sink prevents frost by drawing cold air from the ground and blowing it up through a chimney. It was originally developed to prevent frost damage to citrus fruits In other places helicopters are used in a similar function, especially in the vine yard. By dragging down warmer air from the inversion layers, and preventing the ponding of colder air on the ground, the low-flying helicopters prevent damage to the fruit buds. For high-value crops, farmers may wrap trees and cover crops.
• Heating to slow the drop in temperature. This is not practical except for high value crops grown over small areas.
• Production of smoke to reduce cooling by radiation
• Spraying crops with a layer of water that releases latent heat, preventing harmful freezing of the tissues of the plants that it coats.
Such measures need to be applied with discretion, because they may do more harm than good; for example, spraying crops with water can cause damage if the plants become overburdened with ice. An effective low cost method for small crop farms and plant nurseries, exploits the latent heat of freezing. A pulsed irrigation time delivers water through existing overhead sprinklers at a low volumes to combat frosts down to −5 °C (23 °F) If the water freezes it giving off its latent heat, preventing the temperature of the foliage from falling much below zero.
