Precipitation, Forms, Processes, rainfall types and significance

 

Definition/ what is PRECIPITATION?

Precipitation refers to any form of water, whether liquid or solid, that falls from the atmosphere and reaches the Earth's surface. It is a vital part of the Earth's water cycle and plays a crucial role in replenishing freshwater resources. Precipitation occurs when atmospheric water vapor condenses into liquid or solid water droplets and falls to the ground under the influence of gravity. The most common forms of precipitation include rain, snow, sleet, and hail.

FORMS AND TYPES OF PRECIPITATION:

Precipitation can occur in various forms and involves several processes. The different forms of precipitation include: Precipitation can occur in various forms, including:

1) Rain: Precipitation in the form of water droplets whose size is larger than 0.5mm is called rain. The sizes of such water droplets during rainfall can be measured up to 6mm. These water droplets are formed due to condensation of water vapor around some cloud nuclei such as small dust particles which become heavier on further condensation due to the lowering of atmospheric temperature and ultimately fall back to the earth in the form of water droplets or rain. Rainfall is the most dominant form of precipitation.

2) Drizzle:It is a form of precipitation in which the water droplets are of size smaller than 0.5mm. These droplets can be seen to float in the air freely. The intensity of drizzle is also less than 1mm/hr.

3) Glaze: Glazes are thin sheets or coating of ice which are formed when drizzle or rain falls on the cold ground surface whose temperature is around the freezing point of water ie. 0°C and freezes.

4) Sleet: Sleet are forms of precipitation which are formed when rain drops pass through the atmosphere at subfreezing temperature (temperature below freezing point) and gets frozen. Initially sleets are liquid raindrops that freezes only with it fall through the atmosphere at sub-freezing temperature.

5) Snow: Snow consists of unique ice crystals which are individually formed in clouds. But they fall in the form of clusters during precipitation. Snow has an average density of 0.1g/cc which makes them seem to float in the air. Snow usually occurs in the presence of cold weather and humidity in the winter season, whereas in the Himalayas above 5000m altitude snowfall occurs the whole year.

6) Hails: Hailstones are irregular lumps of ice that are more than 8mm in diameter. They are formed by repeated freezing and melting of ice. They usually occur during cold storms.

These forms of precipitation can have varying effects on the environment and human activities. Understanding the type of precipitation is important for meteorologists, hydrologists, and various other fields that study weather patterns and water resources.

 

The process of precipitation involves several steps:

1.       Condensation: Precipitation begins with the process of condensation, where water vapor in the air cools and changes into liquid water droplets or ice crystals. This typically occurs when warm, moist air rises and encounters colder temperatures.

2.       Nucleation: Water vapor needs a surface on which it can condense into liquid droplets or freeze into ice crystals. Nucleation provides these surfaces, which can be tiny particles such as dust, salt, or aerosols in the atmosphere. The water vapor attaches to these particles and forms droplets or crystals.

3.       Coalescence/Growth: Once nucleation occurs, the water droplets or ice crystals continue to grow through a process called coalescence. As the droplets or crystals collide with one another, they merge and form larger particles.

4.       Precipitation and fall: When the droplets or crystals become large enough to overcome the upward air currents, they fall to the ground under the force of gravity. The type of precipitation (rain, snow, sleet, hail) depends on the temperature profile in the atmosphere.

It's important to note that the exact process and forms of precipitation can vary depending on atmospheric conditions, such as temperature, humidity, and the presence of certain particles in the air.

 

WHAT IS RAINFALL

Rainfall refers to the meteorological phenomenon of water falling from the atmosphere to the Earth's surface in the form of liquid water droplets. It is a type of precipitation that occurs when atmospheric moisture condenses and accumulates into larger droplets, becoming heavy enough to fall under the force of gravity.

There are different types of rainfall based on the mechanisms that cause the ascent and condensation of moist air. The main types of rainfall include:

Types of Rainfall has been classified into three main types based on the origin

1.       Convectional Rainfall: Convectional rainfall occurs when the Sun heats the Earth's surface, causing the air near the surface to warm and rise rapidly. As the warm air rises, it cools, and water vapor within it condenses, forming clouds. These clouds can develop into cumulonimbus clouds, which produce heavy showers or thunderstorms. Convectional rainfall is common in tropical regions with intense heating and can be localized, occurring in the afternoon or evening.

 

 

2.       Orographic Rainfall:  Orographic rainfall is associated with the lifting of moist air by topographic barriers such as mountains. When moist air encounters a mountain range, it is forced to rise, leading to the cooling and condensation of the air. As the air rises over the mountain, it releases moisture in the form of rainfall on the windward side (the side facing the wind). On the leeward side (the side sheltered from the wind), the air descends and warms, resulting in a rain shadow effect, where the area experiences reduced rainfall and drier conditions.

 

3.       Frontal Rainfall and Cyclonic Rainfall: Frontal rainfall occurs at the boundary (front) between two air masses with different characteristics, such as temperature and humidity. When a warm air mass and a cold air mass meet, the warm air is forced to rise over the colder air. As the warm air rises, it cools and condenses, leading to the formation of clouds and precipitation. Frontal rainfall can be prolonged and widespread, often associated with weather systems like cold fronts, warm fronts, and occluded fronts.

Cyclonic or Precipitation Rainfall: Cyclonic or precipitation rainfall is associated with the movement and interaction of large-scale weather systems, such as cyclones or low-pressure systems. These systems cause the ascent of moist air and the formation of clouds, leading to widespread rainfall. The rain is often stratiform (continuous and widespread) and can last for an extended period, particularly in areas influenced by the cyclonic system.

 

  

 

 

 

Types of Rainfall based on Intensity. The types of rainfall based on intensity can be classified as:

Rainfall can be classified on the basis of rainfall intensity.

1. Light rain: Intensity <= 2.5mm/hr
2. Moderate rain: Intensity>2.5mm/hr and <= 7.5mm/hr 
3. Heavy rain >7.5mm/hr

Importance of Precipitation:

§  It is a fundamental part of the water cycle of the Earth. Subsequently, it is necessary for keeping up with the natural balance.

§  It is a significant source of fresh water on the earth.

§  Precipitation, for example, Rainfall, and its distribution forms a leading feature of the environment.

§  It is essential for regulating the global energy flow for example the movement of heat and intensity.

Rainfall is an essential component of the Earth's water cycle, replenishing water sources such as rivers, lakes, and groundwater. It plays a crucial role in shaping climate patterns, supporting ecosystems, and influencing various aspects of human activities, including agriculture, hydrology, and weather forecasting. Rainfall is measured using instruments such as rain gauges, and its amount and distribution are key factors in understanding and managing water resources and the environment.