Air Pressure and Wind Pages 523 537 WHAT

Air Pressure and Wind Pages 523 -537

WHAT IS AIR PRESSURE? • Air Pressure is the weight of the atmosphere per unit area. • At the surface, the atmospheric pressure is about 1 kg/cm 2

Air Pressure is exerted in all directions

Atmospheric Pressure = Barometric Pressure •

Measuring Air Pressure p 523 • Air pressure is measured with an instrument called a Barometer. • There are two main types of barometers

Measuring Air Pressure p 523 • Aneroid barometer measures the atmospheric pressure using the expansion of a metal.

Measuring Air Pressure p 523 • Mercury barometer measures the atmospheric pressure by adjusting the height of mercury inside a tube.

Air Pressure is measured in millibars p 524 • Millibar is a measure of the actual force of the atmosphere pushing down on a surface. • Standard pressure at sea level is 1013. 2 millibars

Air Pressure decreases with altitude • At higher elevations, there are fewer air molecules above a given surface than a similar surface at lower levels. • An altimeter is an instrument used by air craft to measure height above sea level.

Factors Affecting Air Pressure p 525 • Changing temperature: warm air is lighter than cold air because the molecules of warm air are farther apart. • So when warm air replaces an equal volume of cold air, the air pressure at the ground falls. • Conversely, the arrival of colder air higher up causes the pressure at ground to rise.

Factors affecting Pressure p 525 • Changing humidity: the more water vapor in the air the lighter it is. • When water vapor enters the atmosphere, it pushes out an equal volume of dry air. • Water vapor is lighter than the nitrogen and oxygen it pushes out. Therefore, humid air weighs less than dry air and exerts less pressure.

Pressure indicates weather • High pressure associated with “fair weather” • Low pressure associated with “rain” • Falling pressure associated with increasing cloudiness • Rising pressure associated with clearing conditions

Indicating Pressure • pressure reading in millibars (mb).

Isobars • Isobars are lines that connect areas of equal air pressure. • Pressure Gradient is the spacing between the lines, indicate pressure change over a given distance.

What is the isobar interval on this map? •

What is the isobar interval on this map? • The isobar interval or pressure gradient is 4 millibars.

Cyclones and Anticyclones A cyclone is a large air mass that rotates around a strong center of low atmospheric pressure. • characterized by inward spiraling winds that rotate about a zone of low pressure. • Isobars decrease in value inward indicate a low-pressure center (L) • low pressure in center, spin inward • Effects: heavy rain, strong wind, storms, tornadoes.

Anticyclones • a weather system with high atmospheric pressure at its center, around which air slowly circulates in a clockwise (northern hemisphere) or counterclockwise (southern hemisphere) direction. • Anticyclones are associated with calm, fine weather. • spin outward. • high-pressure center (H) • Associated with calm, fine weather.

What's the difference between cyclone and hurricane or typhoon? • the location where the storm occurs. • same weather phenomenon; • “typhoon” occur in Northwest Pacific • “hurricanes” occur in the Atlantic and Northeast Pacific • “cyclones” occur in the South Pacific and Indian Ocean

Where are the areas of high and low pressures? • Is A an area of high pressure or Low? • B? A B

Practice • Read pages 523 -526 • Answer 1 -5 p 526

Wind Direction and Isobars • Winds flow roughly parallel to the isobars.

How does a barometer work? • Ted Ed • https: //www. youtube. com/watch? v=Ek. Dhlz. A-lw. I

WHAT IS PRESSURE? • Pressure is the amount of Force per unit area.

Example: • What pressure does a 50 kg person exert on the ground when standing on one foot that measures 20 cm x 8 cm? • Pressure = weight/area

Answer: • What pressure does a 50 kg person exert on the ground when standing on one foot that measures 20 cm x 8 cm? • 50 kg/ (20 cmx 8 cm) = 0. 31 kg/cm 2 • What if person is standing on both feet?

Answer: • What pressure does a 50 kg person exert on the ground when standing on one foot that measures 20 cm x 8 cm? • 50 kg/ (20 cmx 8 cm) = 0. 31 kg/cm 2 • What if person is standing on both feet? • Half the pressure: 0. 156 kg/cm 2