Composition and Structure of Atmosphere Composition and Structure of Atmosphere Weather Patterns and Forecasting Weather Patterns and Forecasting Factors Influencing Climate Factors Influencing Climate Severe Weather Severe Weather

Weather vs. Climate Weather- constantly changing, refers to the state of the atmosphere at any given time and place Weather- constantly changing, refers to the state of the atmosphere at any given time and place Climate- based on observations that have been collected over many years and describes a place or region Climate- based on observations that have been collected over many years and describes a place or region Both measure- air temperature, humidity, precipitation, air pressure, wind (speed and direction) Both measure- air temperature, humidity, precipitation, air pressure, wind (speed and direction) What is the climate of the Las Vegas valley? What is the climate of the Las Vegas valley? What is the weather today in the Las Vegas valley? What is the weather today in the Las Vegas valley?

Composition and Structure of Earth’s Atmosphere A mixture of gases with some suspended solids (dust, salt, ice) and liquids (water droplets in clouds). A mixture of gases with some suspended solids (dust, salt, ice) and liquids (water droplets in clouds). Extends from surface to outer space – hundreds of km’s. Extends from surface to outer space – hundreds of km’s. Very thin layer around Earth Very thin layer around Earth Earth Science Reference Table

Major Components 99% of atmosphere is 2 gases- nitrogen and oxygen 99% of atmosphere is 2 gases- nitrogen and oxygen.93% - Argon.93% - Argon.039% Carbon Dioxide.039% Carbon Dioxide

Variable Components Water vapor- source of clouds and precipitation Water vapor- source of clouds and precipitation Absorbs solar energy Absorbs solar energy Ozone- O km above earth. Absorbs UV radiation from sun Ozone- O km above earth. Absorbs UV radiation from sun Dust – fine grained particles can stay suspended for some time Dust – fine grained particles can stay suspended for some time

Changes in Earth’s Atmosphere Earth’s atmosphere thins as you travel from Earth until there are too few gas molecules to detect- this is space Earth’s atmosphere thins as you travel from Earth until there are too few gas molecules to detect- this is space As gas molecules decrease air pressure decreases As gas molecules decrease air pressure decreases

Layers of the Atmosphere Troposphere Stratosphere Mesosphere Thermosphere

Troposphere Contains 75% of atmospheric gases, Earth’s surface – 12 kilometers Weather, clouds, and smog found here

Temperature Trends Temp decrease with altitude in the Troposphere Temp decrease with altitude in the Troposphere - Temp rises in the Stratosphere Why? Why? - Ozone layer occurs in stratosphere - Remember Ozone absorbs UV radiation - Being destroyed by Clorofluorocarcbons (CFCs)

Pressure Trends  Gases in the atmosphere, like all matter, have mass.  Atmosphere is a sea of air – the deeper you are in it, the heavier it feels (more force exerted)  Sea level pressure is 1013 mb at STP  Denver pressure is 550 mb (1600 m)  Mt Everest pressure is 315 mb (8800 m)

Types of heat transfer Radiation (no molecules needed) Radiation (no molecules needed) transfer of energy without the involvement of a physical substance in the transmission. transfer of energy without the involvement of a physical substance in the transmission. Allows solar radiation to reach Earth as it travels through space Allows solar radiation to reach Earth as it travels through space Convection (air movement) Convection (air movement) transmits heat energy by transporting groups of molecules from one place to another within a substance transmits heat energy by transporting groups of molecules from one place to another within a substance - warmer less dense portions of the medium will rise while colder more dense areas will sink Conduction (direct contact) Conduction (direct contact) Transfer of energy between molecules until an even temperature is reached Transfer of energy between molecules until an even temperature is reached

What happens to solar radiation? When radiation strikes an object 1 of three things can happen When radiation strikes an object 1 of three things can happen 1) Energy is absorbed by the object (temperature of object increases) 2) Energy is transmitted by object (temperature of object does not increase) air and water transmit some radiation 3) Energy bounces off object without being absorbed or transmitted

Weather Patterns and Forecasting Sun is the external heat engine for our planet. Sun is the external heat engine for our planet. Three possibilities Three possibilities 1)Reflect to space Atmosphere Atmosphere Land (Albedo) Land (Albedo) 2)Absorbed by atmosphere 3)Absorbed by land or absorbed/transmitted by water surfaces

Albedo of Earth Surfaces

Weather The present state of the atmosphere The present state of the atmosphere Describes current conditions Describes current conditions Air Pressure Air Pressure Wind Wind Air Temperature Air Temperature Amount of Moisture Amount of Moisture

Water Cycle Evaporation/transpiration Evaporation/transpiration Condensation Condensation Precipitation Precipitation

Air Masses A large body of air that has the same properties as the surface over which it develops. A large body of air that has the same properties as the surface over which it develops. When you witness a change When you witness a change in the weather from one day to the next, it is due to the move- ment of air masses.

Prevailing Winds across U.S. Winds tend to move towards the right due to the Coriolis effect Winds tend to move towards the right due to the Coriolis effect Coriolis effect created by the rotation of the earth Coriolis effect created by the rotation of the earth Surface winds across U.S. consist of prevailing westerlies Surface winds across U.S. consist of prevailing westerlies Winds blow from southwest to northeast Winds blow from southwest to northeast These winds are responsible for movement of weather across the U.S. and Canada These winds are responsible for movement of weather across the U.S. and Canada

Fronts Boundary between two air masses Boundary between two air masses Cold Front Cold Front Warm Front Warm Front Occluded Front Occluded Front Stationary Front Stationary Front

Humidity Refers to the water vapor content in the atmosphere Refers to the water vapor content in the atmosphere Relative Humidity is the ratio of the amount of water vapor in air to the maximum amount it can hold at that temperature. (expressed as percentage) *Varies with temperature change Relative Humidity is the ratio of the amount of water vapor in air to the maximum amount it can hold at that temperature. (expressed as percentage) *Varies with temperature change

Dew Point Temperature at which air is saturated and condensation occurs. Temperature at which air is saturated and condensation occurs. Point where saturated vapor pressure equals actual vapor pressure Point where saturated vapor pressure equals actual vapor pressure Point where relative humidity equals 100% Point where relative humidity equals 100%

Clouds Classified mainly on shape and height Classified mainly on shape and height Form when warm air is forced upward, expands, and cools. Form when warm air is forced upward, expands, and cools. At the dew point, condensation occurs At the dew point, condensation occurs Aided by nuclei (dust, salt, smoke…) Aided by nuclei (dust, salt, smoke…)

Classification of Clouds

Weather Maps Cloud Cover and Precipitation

Weather Maps Isobar and Isotherm

Weather Map Symbols

Weather Map

Five Factors Influencing Climate

Factors Influencing Climate Climate is an average of the weather over a long period of time. Climate is an average of the weather over a long period of time. Influenced by: Influenced by: Global wind patterns Latitude Topographic Features Large bodies of water Mountains Large cities

Global Wind Uneven heating of the latitudes produces major convection currents. Uneven heating of the latitudes produces major convection currents. Deflect to the right in N.H. Deflect to the right in N.H. Coriolis Effect Coriolis Effect

Topographic Features

Severe Weather Tornado Tornado Hurricane Hurricane Lightning Lightning

Tornado Violent, whirling wind that moves in a narrow path over the land, usually in a direction from southwest to northeast. Violent, whirling wind that moves in a narrow path over the land, usually in a direction from southwest to northeast. Typically form along a front Typically form along a front Local storm, short duration Local storm, short duration Spin counterclockwise Spin counterclockwise Vortex extends from cloud Vortex extends from cloud Why can we see it? Why can we see it?

Tornado Occurrence < 1% of all thunderstorms ~ 770 per year April - June

Tornado Category Scale Fujita Scale Fujita Scale

Tornado Summary Lightning Lightning Damaging Hail Damaging Hail High Winds High Winds Torrential Rain Torrential Rain

Hurricane (Typhoon/Cyclone) Is a low pressure system that forms over tropical oceans. Is a low pressure system that forms over tropical oceans. The greatest storms on Earth – several 100 miles across! Wind speeds > 74 mph Wind speeds > 74 mph Spin counterclockwise Spin counterclockwise Average 6-10 per year Average 6-10 per year “Season” July – September “Season” July – September Produces: Torrential rain, Flooding, Damaging winds, Storm Surge

Anatomy of a Hurricane Warm ocean water with a minimum temp of 80° F Warm ocean water with a minimum temp of 80° F Minimum ocean depth of 200 m Minimum ocean depth of 200 m Converging winds near surface Converging winds near surface Humid air rises and condenses Humid air rises and condenses – Latent heat Condensation is a warming process, releasing stored heat. This heat warms the surrounding air, making it lighter Upper atmosphere high pressure removes rising air in storm Upper atmosphere high pressure removes rising air in storm

Hurricane Category Scale Winds greater than 155 mph have been recorded Winds greater than 155 mph have been recorded Tropical storms have winds mph Tropical storms have winds mph

Tracking Hurricanes Movement Movement Storms gets energy from warm ocean water Storms gets energy from warm ocean water Loses power when it moves over land Loses power when it moves over land Difficult to predict where it will make land Difficult to predict where it will make land Errors in prediction and evacuation can be costly! Errors in prediction and evacuation can be costly!

Lightning Polarization of + and – charges within a storm cloud by frictional charging and freezing. Polarization of + and – charges within a storm cloud by frictional charging and freezing. + charges carried to upper portions of cloud and – portions gravitate to bottom + charges carried to upper portions of cloud and – portions gravitate to bottom of clouds. Electric field from cloud induces movement of electrons upon Earth Electric field from cloud induces movement of electrons upon Earth Buildings, trees and people can experience a build up of static charge as electrons are repelled by the cloud’s bottom. Buildings, trees and people can experience a build up of static charge as electrons are repelled by the cloud’s bottom.

Anatomy of Lightning As static charge buildup increases, the electric field becomes stronger As static charge buildup increases, the electric field becomes stronger Ionization of surrounding air makes it more conductive Ionization of surrounding air makes it more conductive Begins with development of a step leader. Why zigzag? Begins with development of a step leader. Why zigzag? Induces a strong positive charge on earth surface. This charge begins migrating upward (streamer) through buildings, trees and people into the air. Induces a strong positive charge on earth surface. This charge begins migrating upward (streamer) through buildings, trees and people into the air. When step leader meets streamer, a complete conductive pathway is mapped out and lightning begins. When step leader meets streamer, a complete conductive pathway is mapped out and lightning begins.

Lightning Rods Pointed metal pole which extends upward above the building, is attached by a copper cable to a grounding rod buried in the Earth below. Pointed metal pole which extends upward above the building, is attached by a copper cable to a grounding rod buried in the Earth below. “leaks off” excess charges in the atmosphere, thus reducing the likelihood of a sudden and explosive discharge.

Myths about Lightning Never strikes the same place twice Never strikes the same place twice Only strikes very tall objects Only strikes very tall objects Does not strike water Does not strike water Could be used as a power source Could be used as a power source Rubber shoes or boots insulate and protect against a lightning strike Rubber shoes or boots insulate and protect against a lightning strike A metal vehicle is safe because of rubber tires A metal vehicle is safe because of rubber tires “Heat lightning” is a strange phenomenon caused by hot water or occurs after very hot summer days and poses no threat. “Heat lightning” is a strange phenomenon caused by hot water or occurs after very hot summer days and poses no threat. Lightning victims are electrified Lightning victims are electrified

Facts about Lightning The average flash could light a 100-Watt light bulb for more than three months The average flash could light a 100-Watt light bulb for more than three months Chances of being struck are estimated to be 1 in 600,000 Chances of being struck are estimated to be 1 in 600,000 Temperature of a flash is 5x hotter than sun’s surface Temperature of a flash is 5x hotter than sun’s surface Can travel over and through the Earth’s surface Can travel over and through the Earth’s surface ~20 million cloud to ground lightning strikes occur in the US per year ~20 million cloud to ground lightning strikes occur in the US per year ~2,000 thunderstorms active throughout the world at any given time, producing more than 100 flashes/second ~2,000 thunderstorms active throughout the world at any given time, producing more than 100 flashes/second ~26,400 lightning-induced fires/year in the US ~26,400 lightning-induced fires/year in the US 80% of livestock deaths attributed to lightning strikes 80% of livestock deaths attributed to lightning strikes Second largest storm killer in the US (#1 floods) Second largest storm killer in the US (#1 floods)

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Greenhouse Effect As heat is reflected back into the atmosphere it is absorbed by greenhouse Gases. More gases in the atmosphere means more heat is absorbed.