Water in the Atmosphere

evaporation – the process by which water molecules in liquid water escape into the air as water vapor

humidity – a measure of the amount of water vapor in the air relative humidity – the percentage of water vapor in the air compared to the maximum amount the air could hold Relative humidity can be measured with a psychrometer.

How Clouds Form - Water in the Atmosphere Clouds form when warm, moist air rises and cools. Water vapor condenses on tiny particles to form liquid water or ice crystals.

How Clouds Form Clouds of all kinds form when water vapor in the air becomes liquid or ice crystals. condensation – the process by which molecules of water vapor in the air become liquid water dew point – the temperature at which condensation begins

- Water in the Atmosphere Types of Clouds Scientists classify clouds into three main types based on their shape: cirrus, cumulus, and stratus. Clouds are further classified by their altitude.

Types of Clouds Meteorologists classify clouds into three main types: cumulus clouds that look like fluffy, rounded piles of cotton stratus clouds that form in flat layers cirrus wispy, feathery clouds

Precipitation

Water Droplets - Precipitation Droplets come in many sizes. A raindrop has about one million times as much water in it as a cloud droplet.

precipitation – any form of water that falls from clouds and reaches Earth’s surface

Common types of precipitation include: Rain – Most common type of precipitation. At least 0.5 mm in diameter. Rain made up of smaller particles of water is called drizzle. Sleet – Ice particles smaller than 5 mm in diameter. Freezing rain – Rain that falls through cold air near the ground and freezes when it touches a cold surface. Hail – Round pellets of ice larger than 5 mm in diameter. Snow – Falling ice crystals. They have an endless number of different shapes and all have 6 sides.

How Hail Forms - Precipitation Hailstones start as small pellets of ice in cumulonimbus clouds. They grow larger as they are repeatedly tossed up and down until they become so heavy they fall to the ground.

Measuring Precipitation Scientists measure precipitation with various instruments, including rain gauges.