Science News

What is WIND? The horizontal motion of air across Earth’s surface; movement produced by differences in air pressure from an area of high pressure (warm air) to an area of low pressure (cool air)

GLOBAL WINDS

Global Winds The atmosphere balances differences of unequal heating by acting as a giant heat-transfer system. This system moves warm air toward high latitudes and cool air toward the equator

GLOBAL Direction of WIND

3 WIND SYSTEMS “ZONES” Polar easterlies 60 DEGREES – POLES N & S LATITUDES 60 DEGREES – POLES N & S LATITUDES Dense cold air sinking from the polar high toward the sub polar low. These winds are not constant like the trade winds. Dense cold air sinking from the polar high toward the sub polar low. These winds are not constant like the trade winds.

Westerlies 30 – 60 DEGREES N & S LATITUDES 30 – 60 DEGREES N & S LATITUDES Dominant and steady surface wind moving west-to-east towards the POLES. Move much of the weather across USA & Canada. Dominant and steady surface wind moving west-to-east towards the POLES. Move much of the weather across USA & Canada.

Trade winds  30 degrees N – 30 degrees S LATITUDES  Two belts of winds, air in this region sinks, warms and moves toward the equator in an easterly direction.

Boundaries of Wind Systems JET STREAM: A narrow band of fast moving wind that varies with seasons Result of the difference between air masses (Temperature & Pressure) at the wind zone boundaries. Result of the difference between air masses (Temperature & Pressure) at the wind zone boundaries.

2 Types of JETSTREAMS Major POLAR JET STREAM Separate polar easterlies from prevailing westerlies Separate polar easterlies from prevailing westerlies Move East to West Move East to West Latitudes 40 N- 60 N & Latitudes 40 N- 60 N & 40 S-60 S

MinorSubtropical Separate trade winds from westerlies Separate trade winds from westerlies Latitudes 20 N – 30 N & Latitudes 20 N – 30 N & 20 S – 30 S

GLOBAL WIND SYSTEMS Result of Earth’s rotation & uneven heating of surface Result of Earth’s rotation & uneven heating of surface Transports colder air to the Equator & warmer air to the Poles Transports colder air to the Equator & warmer air to the Poles Help to equalize the thermal energy on Earth Help to equalize the thermal energy on Earth

Forces Influencing Wind Speed & Direction Gravitational Force: equal compression density decrease with altitude Gravitational Force: equal compression density decrease with altitude Friction Force: Earth’s rough surface adds to Pressure & Coriolis Friction Force: Earth’s rough surface adds to Pressure & Coriolis Coriolis Force: Earth’s rotation deflecting wind Coriolis Force: Earth’s rotation deflecting wind Pressure Gradient Force: High/Low systems Pressure Gradient Force: High/Low systems

Why are the winds systems broken into zones?? Coriolis effect

Coriolis Effect Earth’s rotation breaks air masses into smaller cells Earth’s rotation breaks air masses into smaller cells Moving air curves to the right in the N. Hemisphere & to the left in the S. Hemisphere Moving air curves to the right in the N. Hemisphere & to the left in the S. Hemisphere

PRESSURE SYSTEMS Low Pressure system air coming up either cloud cover / precipitation or no clouds because no moisture Low Pressure system air coming up either cloud cover / precipitation or no clouds because no moisture High pressure system air coming down generally fair skies High pressure system air coming down generally fair skies

Pressure Differences

970 mb. 950 mb. 930 mb. 960 mb. H L Wind & Pressure Relationship WINDS ALWAYS MOVE FROM HIGH PRESSURE AREAS TO LOW PRESSURE AREAS!!!!!!!

Pressure Centers Cyclones: centers of low pressure, Storm & Clouds Storm & Clouds (L) the pressure decreases from the outer isobars toward the center (L) the pressure decreases from the outer isobars toward the center Anticyclones: centers of high pressure, Anticyclones: centers of high pressure, Calm & Clear Calm & Clear (H) the pressure increases from the outside toward the center (H) the pressure increases from the outside toward the center

Cyclonic & Anticyclonic Winds Anticyclones Winds in a high pressure area move clockwise (S Hemisphere) Winds in a high pressure area move clockwise (S Hemisphere)Cyclones Winds in a lower pressure area move counter-clockwise (N Hemisphere) Winds in a lower pressure area move counter-clockwise (N Hemisphere)

CYCLONE

ANTICYCLONE

Pressure Centers & Winds  Weather and Air Pressure Rising air is associated with cloud formation and precipitation, whereas sinking air produces clear skies. Rising air is associated with cloud formation and precipitation, whereas sinking air produces clear skies.  Weather Forecasting Weather reports emphasize the locations and possible paths of cyclones and anticyclones. Weather reports emphasize the locations and possible paths of cyclones and anticyclones. Low-pressure centers can produce bad weather in any season. Low-pressure centers can produce bad weather in any season.

Pressure Systems Collisions Collision forms a front, boundary that separates air masses of different densities  Air masses retain their identities  Warmer, less dense air forced aloft  Cooler, denser air acts as wedge

4 Types of Fronts Warm front  Warm air replaces cooler air Clouds become lower as the front nears Clouds become lower as the front nears Slow rate of advance Slow rate of advance Light-to-moderate precipitation Light-to-moderate precipitation

Warm front

Cold Fronts  Cold air replaces warm air Advances faster than a warm front Advances faster than a warm front Associated weather is more violent than a warm front Associated weather is more violent than a warm front Intensity of precipitation is greaterIntensity of precipitation is greater Duration of precipitation is shorterDuration of precipitation is shorter

Cold front

Stationary front Flow of air on both sides of the front is almost parallel to the line of the front Surface position of the front does not move Surface position of the front does not move Occluded front Active cold front overtakes a warm front Precipitation is associated with warm air being forced up Precipitation is associated with warm air being forced up

Formation of an Occluded front