Cloud and Precipitation Notes

Temperature affects water in the atmosphere Water is always in the atmosphere It can be a solid (snow), a liquid (rain) or a gas (water vapor)

Water in the Air Most of the Earth’s water is recycled Oceans hold most of the water

Water Vapor condenses and forms clouds Clouds are made of condensed water vapor – Air cools as it rises and condenses into tiny droplets or ice crystals – These tiny droplets/ice crystals are so light they either float as clouds or fall very slowly Water must condense on something solid. In the air, water condenses on the particles found in it (dust, smoke, salt, etc.)

Characteristics of clouds Clouds form under different conditions The shapes and sizes are determined by air movement Location also is a factor – Higher altitude clouds are made of tiny crystals – Lower altitude clouds are made of droplets of water or a mixture of droplets and ice crystals

3 Main Types of Clouds Cirrus Cumulus Stratus

Two prefixes that help to describe clouds further are: Nimbo/nimbus – Produce precipitation Alto – Medium altitude

Cirrus Clouds Means “curl of hair” Form at high altitudes in very cold air It is made of ice Wispy or feathery in appearance Normally found in fair weather but can be a sign that a storm is approaching

Cumulus Clouds Means “heap ” or “pile ” Puffy white clouds with darker bases Usually appear in the daytime when warm air rises and its water vapor condenses Cooler air sinks along the sides of these clouds keeping them apart Cumulonimbus clouds are ones that produce thunder storms, they are also called thunderheads

Stratus Clouds Means “spread out ” These are the clouds that produce ‘grey’ skies They form in flat layers when air cools over large area without rising They are smooth because they form without strong air movement

Fog A cloud that rests on the ground or a body of water If forms when a surface is colder than the air above it Fog tends to be heaviest at dawn, after the ground has cooled overnight, it clears as the ground is heated by the sunlight It can be a safety hazard while driving because it makes it hard to see what is in front of you

Precipitation forms from water droplets or ice crystals Precipitation is any form of water that falls from the clouds and reaches Earth’s surface Cloud droplets are much smaller than a typical raindrop Precipitation always comes from clouds but not all clouds form precipitation What types of clouds do?

For precipitation to occur… Cloud droplets (water) or ice crystals must grow heavy enough to fall through the air. They get heavier by colliding or combining with other droplets.

Measuring Precipitation Rain Gauge Measuring snow

Types of Precipitation Rain Sleet Freezing Rain Snow Hail

Rain Most common form.5mm in diameter Fall from nimbostratus clouds

Rain

Sleet When there are layers of warm air and cold air in the sky. As droplets fall they freeze into solid ice particles

Sleet

Freezing Rain Raindrops falling through cold air that don’t freeze until they reach a cold surface (the ground) Looks like sleet as it falls but freezes on the surface instead of right before it hits the surface

Freezing Rain

Freezing Rain vs. Sleet What is the difference between the two pictures? Which is freezing rain and which is sleet? WHY?

Snow Ice crystals grow and merge to form snowflakes Variety of shapes and sizes Most have 6 sides or branches When they fall through moist air that is near freezing they clump together When falling through colder drier air they don’t

Hail Only forms inside cumulonimbus clouds Strong updrafts carry the ice pellets up and down causing the pellet to get bigger When it gets to heavy it falls to the ground

Hail

Precipitation carries pollution Acid rain forms when factories, power plants, automobiles and some natural sources release sulfur dioxide and nitrogen oxides into the air The combine with the water to form sulfuric acid and nitric acid This acid rain can affect trees, lakes and damage the surface of buildings and sculptures

Acid Rain damage

How Acid Rain Forms