Skip to Content


« Back to Glossary Index

**Formation of Rain:**
– Air contains water vapor measured in mixing ratio.
– Relative humidity determines air’s moisture content.
– Warmer air can hold more water vapor before saturation.
– Dew point is the temperature for air to become saturated.
– Cooling mechanisms include adiabatic, conductive, radiational, and evaporative cooling.

**Characteristics and Impacts of Raindrops:**
– Raindrops vary in shape and size.
– Raindrop sizes range from 0.1 to 9mm.
– Final droplet size follows an exponential distribution.
– Raindrops impact at their terminal velocity, with larger drops impacting at higher speeds.
– Rainfall on certain surfaces can produce dimples that can be fossilized.

**Global Patterns and Changes in Rainfall:**
– Rainfall is crucial for the water cycle.
– Climate regimes are differentiated by average rainfall.
– Global warming affects precipitation patterns.
– Antarctica is the driest continent.
– Rainfall trends vary widely by region and over time.

**Causes and Types of Rainfall:**
– Frontal activity leads to different types of precipitation.
– Convection is associated with convective clouds.
– Orographic effects cause precipitation on the windward side of mountains.
– Virga is precipitation that evaporates before reaching the ground.
– Different regions experience rain due to various causes like frontal activity, convection, and orographic effects.

**Measurement and Monitoring of Rainfall:**
Rain is measured in units of length per unit time.
– Different types of rain gauges include standard gauges, tipping bucket gauges, and weighing gauges.
– Various networks exist for submitting rainfall measurements.
– Remote sensing technologies like weather radar and satellites aid in monitoring rainfall.
– Applications of rainfall data include flood control, dam construction, weather forecasting, and urban planning.

Rain (Wikipedia)

Rain is water droplets that have condensed from atmospheric water vapor and then fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides water for hydroelectric power plants, crop irrigation, and suitable conditions for many types of ecosystems.

Heavy rainfall on a roof

The major cause of rain production is moisture moving along three-dimensional zones of temperature and moisture contrasts known as weather fronts. If enough moisture and upward motion is present, precipitation falls from convective clouds (those with strong upward vertical motion) such as cumulonimbus (thunder clouds) which can organize into narrow rainbands. In mountainous areas, heavy precipitation is possible where upslope flow is maximized within windward sides of the terrain at elevation which forces moist air to condense and fall out as rainfall along the sides of mountains. On the leeward side of mountains, desert climates can exist due to the dry air caused by downslope flow which causes heating and drying of the air mass. The movement of the monsoon trough, or intertropical convergence zone, brings rainy seasons to savannah climes.

The urban heat island effect leads to increased rainfall, both in amounts and intensity, downwind of cities. Global warming is also causing changes in the precipitation pattern globally, including wetter conditions across eastern North America and drier conditions in the tropics. Antarctica is the driest continent. The globally averaged annual precipitation over land is 715 mm (28.1 in), but over the whole Earth, it is much higher at 990 mm (39 in). Climate classification systems such as the Köppen classification system use average annual rainfall to help differentiate between differing climate regimes. Rainfall is measured using rain gauges. Rainfall amounts can be estimated by weather radar.

« Back to Glossary Index