PRECIPITATION AND ITS OCCURRENCE

Precipitation is a general term for a type of atmospheric water that originates from a cloud and falls to the ground. In other words, precipitation is the dropping of water from the atmosphere on the earth in the form of rain, snow, mist, and other forms that are helpful to humans, and it is measured in terms of depth on a horizontal land surface. The amount of precipitation that fell on a certain day, month, or year is referred to as daily, monthly, or yearly rainfall. Metrology counts the phenomena from cloud formation through their occurrence on the ground, while hydrology deals with the phenomena once the precipitation reaches the ground.

FORMS OF PRECIPITATION:

Based on the state, the precipitation is classified in following two forms-

(1) Liquid under precipitation

(2) Solid under precipitation.

The Other forms of precipitation under the above two are described as under -

1. Liquid precipitation- It refers to rainfall, which is the most important form of precipitation regarding an agricultural concern. In rain, the size of water droplets is more than 0.50 mm in diameter and goes a maximum of up to 6 mm. Based on the intensity the Rains are classified into the following three forms-

1. Light rain- Its falling rate is up to 2.5 mm per hour.

2. Moderate rain- Intensity ranges from 2.5 to 7.5 mm per hour.

3. Heavy rain involves an intensity greater than 7.5 mm per hour.

Drizzle - It's also a liquid kind of precipitation with water droplets smaller than 0.5 mm in diameter and an intensity of less than 1 mm per hour. Drizzles usually appear in the form of a floating cloud in the air.

2. Solid-state precipitation- It is also known as frozen precipitation, generally found in the following forms:

• Glaze- It is a type of frozen precipitation that is generated when drizzles or raindrops come into touch with cold things on the ground surface and freeze there. The glaze appears as a layer of frozen water on the ground surface, covering chilly things.
• Sleet- When raindrops fall through a medium at a sub-freezing temperature, the frozen raindrop is the most likely to form.
• Snow- It appears as branching, hexagonal, star-shaped, and other irregular ice crystals. Snow can fall in clumps or all at once. A snowflake is a clump of snow that has formed.
• Snowflake - It is the ice crystal fused during snowfall.
• Hail- It's a little ice lump with a diameter of 5 to 10 mm or more. When ice lumps fall through quickly blowing turbulent air currents, hails are generated by alternate freezing and melting processes.
• Dew- It is condensed moisture on cold objects.
• Frost- It is a feathering ice deposit generated by dew or water vapor and frozen on the ground or other surface items.
• Fog - Fog is a thin form of a cloud of changing density that forms near the earth's surface as a result of atmospheric moisture condensation.
• Mist - It is the thin fog.

TYPES OF PRECIPITATION:

Cloud is the source of precipitation that is formed due to adiabadic cooling of upward lifted warm air masses. Lifting of air masses takes place in several ways, such as the convection orographic effect and by fronts. Accordingly, the precipitation is classified as:

1.  Convective precipitation

2. Orographic precipitation

3. Frontal precipitation

4. Cyclonic precipitation

1. Convective precipitation:  The convection process lifts the air mass in this sort of precipitation. The main source of heat for the production of convection currents in the air is solar radiation. This precipitation occurs in hot weather when the earth's surface is intensely heated and there is a plentiful supply of moisture in the air to maintain sufficient relative humidity. Thunder and lightning accompany the convective precipitation, which comes in the form of rain and is accompanied by local winds. Because this precipitation is caused by the constant heating of the Earth's surface, the best conditions for it to occur are during the summer months.

2. Orographic precipitation: it occurs due to lifting of moisture Laden air mass along with the orographic plane and cooling of the same adiabadically to form a cloud. The orographic precipitation comprises the following two parts of the rising of the air mass.

1. Windward orographic precipitation
2. Leeward orographic precipitation

3. Frontal precipitation: When air masses are lifted by fronts that form between two different types of air masses, this sort of precipitation happens ( i.e. warm and cold air). Drizzle is the most common form of frontal precipitation. It is mostly found in temperate climates.

FRONTS: It's an imaginary boundary line produced by the temperature and moisture content of two nearby air masses. Layers or transition zones are central services. In comparison to the air masses, the front has a thin thickness. Surface frontal refers to the point where the frontal surface meets the earth.

Types of fronts:

1. Cold front: When a cold air mass pushes against a warm air mass, it forms. The cold front moves faster than the warm front, and it typically passes it.
2. Warm fronts: A warm front is generated when the air masses are moving in such a way that the warm air is displaced by the cold air.
3. Stationary front: A stationary front occurs when the cold air mass pushes the warm air mass beneath it, resulting in the formation of a front that does not move from its position.

Types of frontal precipitation:

1. Warm front precipitation: When a warm air mass rises steadily upward over a wedge of cold air mass that is worm gear replaced, this form of precipitation occurs.

2. Cold front precipitation: It occurs when the warm air masses are pushed higher by the cold air mass's approaching edge. The precipitation is mainly showery, and it is causing a cause at the surface front.

3. Stationary front precipitation: This form of precipitation occurs as a result of their bulk being lifted by any type of barometric depression. When a moving cold air mass collides with a stationary warm air mass, the warm air mass rises like a pod above the cold air.

4. Cyclonic precipitation: The pressure difference induced by unequal heating of the Earth's surface causes the mechanical lifting of the warm air mass, resulting in precipitation. Warm air moves from a high-pressure to a low-pressure environment.

OCCURRENCE OF PRECIPITATION:

Water vapor is present in the atmosphere at various levels at all periods and altitudes. It is, however, less at lower altitudes. Under the altitude of 2000 meters, roughly half of the total moisture is thought to be found. Temperature affects the amount of water vapor contained in the air. When opposed to cold air, warm air has higher moisture content and has less of a tendency to condense. When their temperature is lowered, however, the available moisture tends to condense and form a cloud, which falls as precipitation over the earth's surface.

Condensation: The process through which water vapor transforms into liquid form is known as condensation. The air is allowed to cool below the dew point during the condensation process, converting the available moisture in the air to liquid form. When the dew point falls below the freezing point, the sublimation process converts water vapor directly into ice. Condensation begins after the temperature is lowered in this situation.

PROCESS OF PRECIPITATION:

The processes through which clouds release the precipitation are mainly the following two.

1. Coalescence process: Water droplets in the air are subjected to two forces: gravity and frictional drag. When these forces are balanced, the water drops reach their maximum velocity, which is known as terminal velocity. On their way onward, the larger raindrop catches the smaller droplets. Smaller droplets fall at a faster rate and overtake the headed droplets as a result of falling raindrop leaves or turbulent wake behind them. Larger drops expand as a result of direct capture of small droplets on their forward path, while smaller drops develop as a result of wake capture of droplets of almost comparable size.

2. Ice-crystal process: At sub-freezing temperatures of around -40°C, the water droplets can stay in the cloud mass. Solidification of freezing nuclei happens at this temperature. When ice elements form in the cooled cloud mass during solidification, a balance is created because the equilibrium vapor pressure over the water droplets is greater than the ice crystal/elements. As a result, water droplets evaporate, and condensation forms on ice elements.

VARIABILITY OF PRECIPITATION:

Precipitation varies in time and intensity depending on meteorological conditions and local circumstances. The normal value is the long-term average of meteorological variables. It might be normal rain, normal temperature, and so forth. Many elements, such as elevation, slope, aspect, and prevailing wind directions, can influence the spatial variance of rainfall.

CONCLUSION:

We may conclude from the preceding essay that it covers the majority of the essential principles of precipitation, its forms, and types, as well as the reasons for its occurrence. Rainfall is the most common type of precipitation that causes streamflow, particularly flood flow in many rivers. Precipitation varies in intensity throughout time and space. Many hydrological problems, such as droughts and floods, are caused by this volatility. Precipitation is one of the most important aspects of hydrometeorology.

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