Air Movement Pressure Systems/Cyclones Local Winds Air Pressure Air Movement Pressure Systems/Cyclones Local Winds

Air Pressure Basics Air pressure = weight of atmosphere pressing down Most of Earth’s air mass is in the lower atmosphere. Moving from space to Earth’s surface, air pressure increases. Change in atmospheric pressure = change in weather.

Mapping Air Pressure Meteorologists use isobars to identify high pressure and low pressure air systems. Isobars  lines that connect areas of equal air pressure

Low Pressure Systems = Cyclones The center of the isobar rings with lowest pressure Marked with “L” Air moves: UP INTO COUNTERCLOCKWISE Rising air cools, condenses, & precipitates = cloudy & stormy weather Bird’s Eye View L Profile View L

High Pressure Systems = Anticyclones The center of isobar rings has highest pressure Marked with “H” Air moves: DOWN OUT CLOCKWISE Sinking air warms and retains (keeps) its moisture = clear, dry weather Bird’s Eye View H Profile View H

Low vs. High Pressure

Winds Wind is air in motion. The way air moves depends on 3 things: Air pressure Coriolis Effect Shape of the land (topography)

1. Air Pressure Air ALWAYS flows from high to low pressure. Closer isobars = faster changes in pressure = faster air movement = stronger wind!!!

1. Air Pressure: Global Winds Caused by temperature/pressure differences Poles—cold—dense air sinks—pushes out air Equator—hot—less dense air rises—leaves space

2. Coriolis Effect Rotation of Earth causes winds to deflect/spin Northern Hemisphere = deflected to the right (clockwise) Southern Hemisphere = deflected to the left (counterclockwise)

3a. Shape of the Land: Land and Sea Breezes Sea Breeze Land Breeze (Day time) (Night time) Warm air rises Cool land breeze Cooler Land Warmer Ocean Warm air rises Cool sea breeze Warmer Land Cooler Ocean Caused by low pressure over land Caused by low pressure over water

3b. Shape of the Land: Local Winds—Mountain and Valley Breezes (Day time) Mountain Breeze (Night time)