Air Masses and Weather

Air and the Sun For the most part, the Sun’s energy never actually reaches the Earth but is lost in space. The greenhouse effect is when the atmosphere traps heat like the glass of a greenhouse. If we did not have a greenhouse effect, the Earth would reflect back most of the energy back into space and the Earth would be very cold and could not support life.

The Greenhouse Effect is NOT global warming!! Greenhouse Effect is NATURAL!! Global Warming is NOT!!

Air Masses Air masses form in large clumps and move over the Earth’s surface and slowly change. An air mass has some of the same general properties as the land or water that it forms over. Air masses with moisture form over water and dry air masses form over land. Air masses that form at the poles are cold and the ones that form in the tropics (or near the equator) are warm. Two Properties of air masses are: Moisture content Temperature

Large Air Masses Huge volumes of air that can cover entire continents or oceans Several types and each has specific characteristics

Air mass classification involves two letters. The first letter describes its moisture properties: c for continental air masses (dry) m for maritime air masses (moist) The second letter describes the thermal characteristic of its source region: T for Tropical P for Polar A for Arctic or Antarctic M for Monsoon E for Equatorial

cP continental polar cold, dry, stable cT continental tropical hot, dry, stable air aloft, unstable surface air mP maritime polar cool, moist and unstable mT maritime tropical warm, moist usually unstable

Clouds are indicators of weather For clouds to form, air must be lifted Three types of lifting cause clouds. Convectional Orographic Frontal

Orographic lift occurs when an air mass is forced from a low elevation to a higher elevation as it moves over rising terrain. As the air mass gains altitude it quickly cools down, which can raise the humidity to 100% and create clouds and, under the right conditions, precipitation. Orographic Lifting

Convectional Lifting Earth’s surface is heated by the sun, which heats the air mass above it. The heated air will then rise. Cool air sinks.

Frontal Lifting One air mass (warm) is pushed upward by the other (cold).

What are Fronts?

Air Masses Meet When 2 air masses meet, they do not mix. What happens is that they form a border that is known as a front. Most of the weather that we think of happens along fronts.

Cold Fronts A cold front forms when a cold air mass catches up to a warm air mass. Colder air forces the warm air higher into the atmosphere. The warm air that is pushed up cools and forms clouds. This reaction causes rain and thunderstorms to occur along a cold front.

A warm front is when a warm air mass catches up to a cold air mass A warm front is when a warm air mass catches up to a cold air mass. ( Just the opposite of a cold front.) Warm Fronts Warm air slides over the cold, dense air. This also causes clouds to form, but many miles ahead of the front. As the front approaches and passes it can cause steady rain or snow to fall. After all of this happens, the sky becomes clear and this is also when the temperature starts to rise.

Stationary Front A front that stops moving is called a stationary front. This type of front can stay in the same place for days. When this front stays in the same place for a long time there is constant snow or rainfall and this leads to several inches of snow or it could even cause a flood.

Quick Review 1. What is the greenhouse effect? 2. What is an air mass? 3. Give me 3 types of fronts.