Rain

By:Daniel Bonnici 3.2

• Rain is liquid precipitation, as opposed to non-liquid kinds of precipitation such as snow, hail and sleet.

• Rain requires the presence of a thick layer of the atmosphere to have temperatures above the melting point of water near and above the Earth's surface.  

What is rain?

What is precipitation?• Precipitation is any form of moisture which falls to the

earth. This includes rain, snow, hail and sleet.• Precipitation occurs when water vapour cools. When the air

reaches saturation point (also known as condensation point and dew point) the water vapour condenses and forms tiny droplets of water. These tiny droplets of water from clouds.

• Complex forces cause the water droplets to fall as rainfall.• All rain is the same. It happens as the result of warm, moist

air being cooled, leading to condensation and in turn rain. The following examples show three different ways air is cooled causing rainfall.

The Water Cycle

• The sun, which drives the water cycle, heats water in oceans and seas. Water evaporates as water vapour into the air. Ice and snow can sublimate directly into water vapor.

• Rising air currents take the vapour up into the atmosphere where cooler temperatures cause it to condense into clouds. Air currents move water vapour around the globe, cloud particles collide, grow, and fall out of the sky as precipitation. Some precipitation falls as snow or hail.

• The sun warms up the ground, which warms up the air above it.

• The warm air rises, it cools, condenses, and rain falls.

What is convection rainfall?

Convectional Rainfall• The sun heats the ground and warm air

rises. • As the air rises it cools and water vapour

condenses to form clouds. • When the condensation point is reached

large cumulonimbus clouds are formed. • Heavy rain storms occur. These usually

include thunder and lightening due to the electrical charge created by unstable conditions.

Convectional rainfall

Frontal rainfall

• The sun heats the ground and warm air rises.

• As the air rises it cools and water vapour condenses to form clouds.

• Where the air meets the warm air is cooled and water vapour condenses.

• Clouds form and precipitation occurs.

Relief Rainfall

• Warm wet air is forced to rise over high land.

• As the air rises it cools and condenses. Clouds form and precipitation occurs.

• The drier air descends and warms. • Any moisture in the air (e.g. cloud)

evaporates.

Types of clouds:Cirrus

• Cirrus clouds generally refer to atmospheric clouds that are characterized by thin, wisplike strands, often bunched into tufts, leading to their common (non-standard) name of mare's tail.

• Cirrus clouds are formed when water vapour freezes into ice crystals at altitudes above 8,000 m.

Types of clouds: Cumulonimbus

• Cumulonimbus is a type of cloud that is tall, dense, and involved in thunderstorms and other intense weather.

• Cumulonimbus clouds usually form from cumulus coop at a much lower height, thus making them, like cumulus clouds, grow vertically instead of horizontally, thus giving the cumulonimbus its mushroom shape. The base of a cumulonimbus can be several miles across, and it can be tall enough to occupy middle as well as low altitudes.

Types of clouds: Stratus

• These clouds are among the lowest of cloud formations, and in fact sometimes they creep so low that they turn into ground-based fog. Stratus clouds are characterized by having horizontal layers with an extremely even, uniform bottom.

• Sometimes, stratus clouds will appear in a more

fragmented way, as is the case with stratus fractus.

• A rainbow is an optical and meteorological phenomenonon that causes a spectrum of light to appear in the sky when the Sun shines on to droplets of moisture in the Earth's atmosphere. It takes the form of a multicolored arc. Rainbows caused by sunlight always appear in the section of sky directly opposite the sun.

Lack of rain

• In desert climates, air from the equator falls toward earth's surface, which causes an absence of rain.

• Due to lack of rain live stock suffers, crops decrese and germination can’t take place, thus grasslands become desert.

Flood

• A flood is when there is too much rain to be absorbed by the earth and the water stays on top of the earth and runs off to the rivers and seas.

• The water fills up the rivers and then the rivers overflow their banks and the water comes onto the land and a flood devastates the land. In the spring when there is a big melt of the snow in the mountains the water makes its way to lower areas and the rivers and seas. Sometimes there is a blockage in the run off and again the water overflows and goes on the land and makes a flood.