Air masses, high and low pressure sysems, warm and cold fronts SCIENCE 10: WEATHER Air masses, high and low pressure sysems, warm and cold fronts

Air is usually in motion BUT (Convection and the Coriolis effect) BUT Large portions of air often remain in nearly the same place long enough to take on the temperature and moisture characteristics of the land or ocean below

Air masses can interact as they move and even collide, and when they do…. We get weather! The zone b/w interacting air masses is called a front Eventually moves due to worldwide wind currents

Cold Fronts We said rain often occurs with cold fronts…why? Warm air is pushed up by cold air and condenses If the cold front is fast moving intense thunderstorms may develop sometimes bringing hail and tornadoes

Cold Fronts

Warm Front Warm air mass overtakes a cooler one Warm air gently rides up over the trailing end of the cold air mass Precipitation may last longer than with a cold front Once it passes, the air is left warmer than before the front arrived

Warm Fronts

Stationary Fronts Two air masses (warm/cold) in contact but neither is moving Some warm air rises and condenses creating stratus clouds and often rain The front may remain this way for several days = dreary, gloomy sky

Occluded Fronts A faster moving cold front catches up to a slower moving warm front All the warm air is pushed up, away from the ground, contacting the leading cold air mass Many types of clouds are present, one after another Often cause a period of steady precipitation

High Pressure Systems Air descends into a region, which puts more pressure on that region. An air mass cooled by conduction and convection when it forms over cold ground becomes more dense and settles lower to the ground Creates more pressure, continues to settle, draws more air from above

High Pressure Systems Air is also pushed out toward low pressure areas at the perimeter in all directions This air curves to the right due to the Coriolis Effect High pressure systems create a clear sky (since air is descending not rising) May be 100’s of kms across

Low Pressure Systems 1. Very intense heating of the ground heats air above it (conduction) Air rises, pulling more, less dense air in beneath it Air curves to the right (Coriolis Effect) so rising air rotates

Low Pressure Systems 2. Warm air rises in a frontal system creating low pressure systems Generally smaller than high pressure systems Likely to occur b/w air masses Bring unstable weather conditions (cause precipitation and often storms)

Why do we get nice weather with high pressure systems and storms and rain happen with low pressure systems?

Wind Let’s hear it from Bill If time, let’s review weather office website to see what the high and low pressure systems can look like!

Next Class: Storms! Let’s ask Bill Nye!