Atmospheric Circulation

1. Global Convection Currents Equator = warm  rising air Poles = cold  sinking air

Air travels from H (high) to L (low) pressure H-L Pressure Zones: Horse latitudes and Doldrums are places where air flow slows and wind speed dies down Prevailing winds: Trade winds, Westerlies, and Polar Easterlies are characterized by winds that travel in one main direction (from H  L) 2. Global Winds

Hadley Cells - cells of atmospheric convection – Driven by solar heating – Air rises near equator – Air sinks near the poles

3. Air Movement Convergence – L pressure systems have a CCW rotation causing it to rise and cool inside – Condenses – Forms clouds – Cause of “bad weather” Divergence – H pressure systems have a CW rotation causing air to sink – Diverges – Form clear air – Cause of “good weather”

Jet Streams – form at boundaries between convection cells – Fast moving ribbons of air in the upper atmosphere

Air Masses – large uniform volume of air that has the same – Density – Temperature – Humidity 4 types - Maritime Polar - mP Maritime Tropical - mT Continental Polar - CP Continental Tropical - cT 4. Air Masses

Weather Formation

5. Wind Formation Variations of solar energy input lead to  temperature differences which lead to  pressure variations in the atmosphere The wind blows to try to correct these imbalances in pressure. Regions of L and H pressure moving through an area cause changes in weather as different air masses pass by.

6. Atmospheric Stability Unstable air – Temp of air mass > Temp of surrounding air = rising air Stable air – Temp of air mass < Temp of surrounding air = sinking air

7. Weather Fronts Air Fronts – boundaries where 2 different air masses meet and do not mix – Caused by density differences – Causes changes in elements of weather Temperature Dew Point Wind Direction Cloud Cover Type of Weather

4 main types – – Cold – Warm – Stationary – Occluded

Cold Front – leading edge of colder air that is replacing warmer air. – Warm air rises – Usually form with areas of L pressure – Weather: Heavy rain Hail Strong winds – Summer months: thunderstorms and severe storms

Warm Front – Leading edge of warmer air that is replacing cooler air. – Warm air rises slowly over colder air – Weather: Clouds Gradual to increasing rain Fog Clears and warm after – Winter months: hazardous weather conditions Sleet Freezing rain

Stationary Front – boundary between 2 different air mass with different densities but neither is advancing – Air masses do not move together – Weather: clear to partly cloudy If a lot moisture = rain/storms – Ice storms – Flooding

Occluded Front – when a cold front catches up to a warm front – Cold fronts move much faster than warm fronts – Cold takes over – Weather: Warm or cold Clear to partly cloudy If a lot of moisture = rain/storms – Ice storms – Flooding – Thunderstorms

Types of Weather

8. Types of weather Sunny – H pressure Clouds – Air is lifted and cooled Rain Snow Freezing Rain/Ice – Freezing air near Earth’s surface Hail – Supercooled water drops grow like snowballs Sleet – Frozen rain drops (transparent) Dust Storms – Strong, dry cold front Fog – Stratus cloud on the ground – Moist, warm front Hurricane Lightning – Discharge of electricity in the atmosphere Thunderstorm Tornado Wind – Imbalance of heating in the atmosphere

9. Elements of Weather and Weather Instruments Temperature  Thermometer Wind Speed  Anemometer Air Pressure  Barometer Moisture  Hygrometer Precipitation  Rain Gauge or Doppler Radar Cloud Cover  Satellite Imaging

10. Severe Weather Severe weather hazards – dangerous weather phenomena that threaten life and property

Thunderstorms – caused by unstable air masses – Form cumulonimbus clouds – Warm, moist air is forced up rapidly by fronts, mountains, or daytime heating

Tornadoes - violently rotating column of air – Forms in a severe thunderstorm called a supercell – Wind coming in starts to swirl and forms a funnel – The spinning air creates a L pressure area – Cold, dry polar air meets warm, moist tropical air – Unstable conditions exist

Hurricanes – giant, spiraling tropical storms with high wind speeds of 120 mph + – Spiral towards L pressure center – Form over oceans – Warm, moist air rises rapidly – The “eye of the storm” is calm

El Nino - a climate pattern representing an unusual warming of the eastern tropical Pacific Ocean sea surface temperatures – Trade winds weaken – Warmer water in the East – Occur every 3-7 years – Reduced upwelling of deep nutrient rich waters

La Nina - a climate pattern representing a cooling of the eastern tropical Pacific Ocean sea surface temperatures – Trade winds strengthen – Warmer water in the West (normal) – Usually occur after an El Nino – Enhanced upwelling of deep nutrient rich waters

Weather Maps

11. Weather Maps Weather maps – allow meteorologists to understand current weather and predict future weather Station Model – symbols used to show weather conditions – Temperature – Wind The wind barb (parts ff and dd combined) is like an arrow and points in the direction the wind is blowing. – Weather – Dew point – Sky cover – Pressure

Pressure/Front Map

Temperature/Front Map