Weather and Climate

Weather Weather: the atmospheric conditions of a certain place at a certain time; including temperature, pressure, humidity, precipitation and wind. Temperature: the measure of the average kinetic energy of the particles in a material Pressure: pressure caused by the weight of a column of air pushing down on an area

Weather Humidity: the amount of water vapor in the air Precipitation: water, in liquid, or solid form, that falls from the atmosphere Wind: The horizontal movement of air from an area of high pressure to an area of low pressure Climate: the long-term average weather conditions that occur in a particular region

Air Air is all around us, and although we cannot see it, it has mass. Recall that mass is the amount of matter in an object, and that matter is anything that has mass and takes up space. Because air has mass, it also has pressure

What is the atmosphere? The atmosphere is the outermost Earth System of gases and particles of matter

Why is the atmosphere important? The atmosphere is essential to life on Earth: contains oxygen and carbon dioxide, and water necessary for life acts like insulation on a house to keep the Earth warm protects living organisms from some of the Sun’s harmful rays protects Earth’s surface from being hit by meteoroids

Layers of the Atmosphere The atmosphere has several different layers Each layer has unique properties, including composition of gases and how temperature changes with altitude Altitude is height above sea level

Layers of the Atmosphere

The Troposphere Troposphere: The atmospheric layer closest to Earth’s surface Extends from the face of Earth’s surface to altitudes between 8 – 15km Temperature decreases as you move away from the surface This is the layer where most of Earth’s weather occurs

The Stratosphere Stratosphere: The atmospheric layer directly above the troposphere Extends from about 15 km to about 50 km Contains the ozone layer The area of the stratosphere with a high concentration of ozone Due to the ozone layer, temperature increases as altitude increases within the stratosphere

The Mesosphere and Thermosphere The mesosphere extends from the stratosphere (50 km) to about 85km The thermosphere can extend from the mesosphere to more than 500 km above Earth’s surface Combined these layers are much broader than the troposphere and stratosphere, yet only 1% of the atmosphere’s gas molecules are found here

The Mesosphere and Troposphere The ionosphere is region within the mesosphere and thermosphere that contains ions Between 60 km and 500 km The ions in this layer reflect AM radio waves transmitted at ground level Auroras- stunning display of lights in the ionosphere Ions from the Sun strike air molecules, causing them to emit vivid colors of light (can be viewed at higher latitudes)

The Exosphere Exosphere: The atmospheric layer furthest from Earth’s surface Extends from 500 km out to space It has no definite end, the molecules here can escape Earth’s gravity and travel into space Pressure and density is so low here that individual gas molecules rarely strike each other Molecules here move at incredibly fast speeds after absorbing the Sun’s radiation

Energy in the Atmosphere Energy in the form of heat is transferred throughout the atmosphere Recall that there are three types of heat transfer Radiation – transfer of heat through space Conduction – transfer of heat through direct contact Convection – transfer of heat within a fluid/air The troposphere is heated mostly through convection

Wind Winds are caused by differences in air pressure Winds are described by their direction and speed The name of a wind tells you where it is coming from, a south wind blows from the south towards the north Wind direction is determined with a wind vane Wind speed is measured with an anemometer

Local Winds Local Winds: winds that blow over short distances Local winds are caused by the unequal heating of Earth’s surface within a small area

Global Winds Global winds: winds that blow steadily from specific directions over long distances Like local winds they are created by unequal heating of earth’s surface, but unlike local winds they occur over a large area Recall that areas near the equator receive the most direct sunlight, and are therefore warmer than the poles. This difference in temperature creates giant convection currents Warm air rises at the equator and cold air sinks at the poles, therefore air pressure tends to be lower near the equator and greater near the poles

Coriolis Effect Coriolis Effect: change that Earth’s rotation causes in the motion of objects and that explain how winds curve Global winds in the Northern Hemisphere gradually turn towards the right and in the Southern Hemisphere winds curve to the left

Global Wind Belts Doldrums: areas near the equator with little or no winds; calm areas where warm air rises Horse Latitudes: areas at 30 degrees north and south of the equator; calm areas of falling air. Trade Winds: blow from the horse latitudes toward the equator; generally blow from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemisphere.

Global Wind Belts Prevailing Westerlies: blow west to east and away from the horse latitudes; play an important role in the weather of the United States. Polar Easterlies: cold air near the poles sinks and flows back toward the lower latitudes; blow east to west; major effect on the weather in the U.S. Jet Streams: bands of high-speed winds about 10 kilometers above Earth's surface.

Wind Belts

Air Masses Scientists classify air masses according to two characteristics: temperature and humidity Temperature affects air pressure Cold, dense air has a higher pressure, while warm, less dense air has a lower pressure

Types of Air Masses Tropical: warm, form in tropics, low air pressure Polar: cold, form at the poles, high air pressure Maritime: humid, form over oceans Continental: dry, form over land

Air Masses Maritime Tropical: warm, humid air mass Air masses are referred to as either maritime or continental, and as either tropical or polar Maritime Tropical: warm, humid air mass Maritime Polar: cold, humid air mass Continental Tropical: dry, warm air mass Continental Polar: dry, cold air mass

Fronts Front: the boundary where two different air masses meet cold – colder air mass move towards a warmer air mass showers and thunderstorms form along cold fronts warm – warm air moves toward cold air creates a wide blanket of clouds, steady rain or snow for several hours/days stationary – when an approaching front stalls for several days cloudy skies and light rain occluded – faster moving cold front catches up with a slow-moving warm front usually brings precipitation

Fronts