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What is a monsoon? This word comes from the Arabic word “mausim” (or Mausam) that means “season” and commonly refers to the reversing of winds in the ocean located between the Arabian Sea and India that changes the precipitation pattern of the zone.

Broadly speaking, monsoons are significant variations in the direction of the strongest winds of a region, during a season. Thus, they are responsible for seasonal changes and torrential rains in areas with hot and humid climates, like South and Southeast Asia, but they can also happen in other parts of the world like Australia, West Africa, and even America.

A broader definition describes a thermal effect caused by heat differences between large landmasses and seas. In the tropics, monsoons bring moisture and the seasons become dryer, but as there are various monsoon systems on the planet, the seasons they cause vary. For example, in northern Australia, monsoon season extends from December to March, while in parts of India and Southeast Asia, summer monsoons and winter monsoons significantly influence the climate in the region.

Monsoons are the result of temperature differences between land and sea because the heat from solar radiation.

Causes of Monsoons
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Monsoons are the result of temperature differences between land and sea because the heat from solar radiation. It happens because the land and the ocean waters absorb heat differently. During the hot season, the surface of the land warms faster than water, a difference that causes a low-pressure area over land and higher pressure at sea.

In all cases, winds blow from the sea toward warm areas, which get loaded with moisture, and this, is what causes abundant and frequent rains because this moist air rises and returns to the sea but while being on the Earth’s surface it cools and reduces its capacity to retain water.

Effects of monsoons.
Monsoon in Ratangad, India.

We can identify three mechanisms that cause monsoons:


1. Heat and the cooling differential between land and water.

2. Wind deflection. This phenomenon is a result of the Coriolis effect, which is due to Earth’s rotation, causing winds in the Northern Hemisphere to deflect to the right, and winds in the Southern Hemisphere to diverge to the left.

3. Heat exchange, or energy exchange that occurs as water changes from liquid to gas or gas to liquid.

Asian monsoons are the most popular. In the south, monsoon season runs from April to September. Note that in this particular part of the planet, solar radiation hits vertically during the summer so hot air rises and creates an area of low pressure over Central Asia. Meanwhile, the water in the Indian Ocean is relatively cold, creating a high-pressure area.

Such temperature difference causes the air from the ocean to move toward South and Southeast Asia because the wind moves from an area of high pressure toward an area of low pressure. Then during autumn, water and land begin to cool, but the latter loses heat faster than the ocean, so during winter, the Indian Ocean becomes a low-pressure area.

In Australia, the monsoon season arrives when the wind gets loaded with moisture from the Indian Ocean, moving toward the north of the country. Additionally, America is hit once a year by the summer monsoon. It happens the same time that the Asian monsoon, but in a different region: the temperature difference occurs between the land and the Pacific Ocean and it usually affects parts of Mexico along the Sierra Madre Occidental, New Mexico, Arizona, Nevada, Utah, Colorado, California, and western Texas.

Torrential rains can have adverse effects such as flooding and landslides.

Effects.

The straight effect of the monsoons is the abundance and intensity of precipitation. Torrential rains can have adverse effects such as flooding and landslides that often cause destruction in urban and rural areas, and sometimes death of people in that region.

However, rains have a positive side as well, as some economic activities depend on monsoon season in South and Southeast Asia. For example, many farmers rely on monsoon rains for growing rice, tea, and other important produces, and aquifers replenish guaranteeing fresh water supplies for all living beings in the area, including humans.

The simplest definition of Precipitation is any form of water that falls from the sky. Evidently, any precipitation develops in Earth’s atmosphere and then falls to the surface, usually as rain.

Precipitation is part of the water cycle, and thanks to this component, living organisms get the freshwater they need to survive. After falling, it evaporates and rises into the atmosphere as a gas, condenses, and falls again. This process repeats over and over again.

Each year about 505,000 km3 of water fall to the Earth´s surface; 398,000 km3 on oceans and 107,000 km3 on land. It means that on average, annual rainfall is about 99 centimeters. 
But precipitation is different in each region of the world. For example in Georgia, USA, the rain falls evenly during the year, about 102-107 centimeters annually, while in Arica, Chile, it didn’t rain for 14 consecutive years. Then, rainfall can vary across a region, area, or even a city.

It means the conversion of water vapor into a liquid that accumulates around tiny dust particles, forming clouds.

Causes of Precipitation.

Precipitation falls to Earth after a condensation process. It means the conversion of water vapor into a liquid that accumulates around tiny dust particles, forming clouds. When the droplets become too heavy, gravity pulls them down. Let´s explain it further:

During the water cycle, the process of evaporation causes liquid water from the oceans, rivers, lakes, and other bodies of water and even plants to become water vapor in the air. This vapor rises and accumulates in the atmosphere, forming clouds. Clouds are made mainly of water droplets, dust, ice, and salt. When they rise high enough, they become cirrostratus clouds, high-level clouds composed of ice crystals, and altostratus clouds, thick clouds made of ice and water.

Eventually, clouds fill with microscopic water droplets, which grow heavier; this happens due to air turbulence that moves droplets around and joins them. When they’re eventually heavy enough to overcome air resistance, they fall to Earth surface. All types of precipitation originate in the clouds.

Rain, a type o precipitation.

Types of Precipitation.

Rain.
It is the precipitation in the form of drops of liquid water. Unlike its traditional representation, drops are spherical and not shaped like teardrops. They can have a diameter up to 6 mm; if drops are less than 0.5 mm, it is called drizzle.

Snow.

Snow is precipitation in the form of ice crystals. Its formation takes place in clouds when water vapor is sublimated and forms delicate ice crystals. When they fall, they join and form snowflakes, and therefore each flake has a complex structure based on crystals of frozen water, but they are soft if touched. According to the temperature and humidity, the snowflakes develop diverse patterns.

Precipitation allows plants to grow and agriculture to be successful provinding food for humans.


Hail.

It is the precipitation in the form of pieces of ice, created when chilling water droplets freeze at the top of the clouds. When they become larger, due to the binding of the frozen drops, air currents can’t hold them in the clouds, and these ice pieces fall. Given their size, they do not melt before reaching the Earth’s surface. Most Hail has a diameter of 25 mm, but they can be as large as 150 mm or as small as 5 mm.

hail

Sleet.

Sleet is rain and snow mixed that freezes before it hits the ground, creating ice pellets.

Another lesser-known kind of precipitation is diamond dust, which is composed of small ice crystals formed at temperatures not exceeding -30°C.

Needless to say, that precipitation is the basis of life. If the water vapor in the air just remained suspended there, bodies of water would dry up, and life would be impossible. Precipitation allows plants to grow and agriculture to be successful provinding food for humans.