Rain
Rain is liquid water that falls from clouds as droplets after becoming large enough to overcome air resistance. It is a form of precipitation.
Collision-coalescence: A process in which cloud droplets collide and merge into larger drops. In warm clouds, it is the main route from tiny droplets to raindrops.
Water cycle: The continuous movement of water among the atmosphere, land, oceans, and living things. Rain returns atmospheric water to the surface within this planetary cycle.
Rain gauge: An instrument that collects and measures precipitation reaching a surface. It provides direct measurements of rainfall depth at a particular location.
Snow: Precipitation that falls as ice crystals, often joined into flakes. Snow reaches the surface frozen, unlike rain's liquid drops.
Groundwater recharge: The process by which water moves from the land surface into underground aquifers. Some rain infiltrates soil and replenishes groundwater stores.
Bergeron process: Ice crystals grow at the expense of supercooled water droplets in mixed-phase clouds. In cold clouds, this process produces ice particles that can melt into rain.
Evaporation: The change of liquid water into water vapor. It supplies much of the vapor that later condenses into rain-producing clouds.
Weather radar: A system that detects precipitation by measuring reflected radio waves. Radar maps rain over broad areas and tracks its movement.
Sleet: Small ice pellets formed when raindrops or melted snow refreeze before reaching the ground. It can form when falling rain passes through a sufficiently cold air layer.
Soil erosion: The detachment and transport of soil by water, wind, ice, or gravity. Raindrop impact and runoff can dislodge and carry away soil.