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Moving Air and Water

Moving Air and Water. Fronts, Air Masses, Uplift and Jet Streams. Front. A boundary between air masses are called fronts. Three Basic Types of Weather Fronts. Cold Front Warm Front Stationary Front. Cold Front.

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Moving Air and Water

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  1. Moving Air and Water Fronts, Air Masses, Uplift and Jet Streams

  2. Front • A boundary between air masses are called fronts.

  3. Three Basic Types of Weather Fronts • Cold Front • Warm Front • Stationary Front

  4. Cold Front • In a cold front, cold air displaces warm air along a steeply-sloped boundary. The heavier cold air wedges under the warm air, pushing it upward. Precipitation is often heavy and occurs behind the front.

  5. Warm Front • In a warm front, warm air replaces cooler air. The warm air slides over the heavier cold air, creating a boundary with a gentle slope. As the warm front approaches, thin high clouds gradually grow thicker and lower. Precipitation is usually steady and falls ahead of the front.

  6. Stationary Front • In a stationary front the boundary between air masses is not moving. Warm air continues to move over the dense cooler air causing clouds to form. Precipitation if present is typically slow and steady.

  7. Air Masses • Air Masses are large volumes of air that remain in one place long enough to acquire humidity and temperature characteristics of the surface beneath them • Most weather is caused by the interaction of air masses in the lower atmosphere.

  8. Six Main types of Air Masses • Continental Arctic – cA • Continental Polar – cP • Continental Tropical – cT • Maritime Arctic – mA • Maritime Polar – mP • Maritime Tropical - mT

  9. Uplift • Uplift occurs when air masses are forced upward. • Uplift can be triggered by: • Topography • Weather Fronts • Winds (jet streams) • Convection Cells (non – frontal thunderstorms)

  10. Four Types of Uplift • Convection – Where an air mass moves over a warmer surface, expands and rises. • Frontal – Where denser, cooler air wedges under a warmer air mass and forces it upward. • Orographic – Where an air mass is forced up and over and landform such as a mountain (Rain Shadow Effect). • Disturbance – Where conditions in the upper atmosphere, often associated with the jet stream, produce uplift in the lower atmosphere.

  11. Jet Streams • High altitude “rivers of air” that play an important role in the formation and movement of storms. • There are two main jet steams in each hemisphere – Polar and Subtropical • The polar jet stream influences precipitation in the US more so than the tropical jet stream.

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