Chapter 1 Earth and Its Atmosphere - PowerPoint Presentation

Chapter 1 Earth and Its Atmosphere © 2019 Cengage Learning, Inc. All rights reserved .

The Atmosphere and the Scientific Method (1 of 2)Our understanding of the atmosphere and weather is built on knowledge obtained using the scientific method.Pose a question, propose a hypothesis, predict the implications of an accurate prediction, and perform tests.The hypothesis must be tested using quantitative methods (e.g., weather instruments and laboratory experiments).

The Atmosphere and the Scientific Method (2 of 2)Over the past 60 years, computerized numerical models have been used to test weather and climate forecasts and other atmospheric phenomena.

Overview of Earth’s AtmosphereRadiant energy (or radiation) from the sun drives everyday wind and weather on Earth.Earth’s atmosphere is a thin gaseous envelope that contains clouds made of liquid water and ice crystals.Approximately 99 percent of Earth’s atmosphere is located within 30 km of Earth’s surface.

The Early AtmosphereEarth’s first atmosphere contained mostly hydrogen and helium.The atmosphere evolved due to outgassing from Earth’s interior.Oxygen (O2) slowly increased from the photodissociation of water (H2O) and plant photosynthesis.

Composition of Today’s Atmosphere (1 of 7)Molecular nitrogen (N2), ~78 percent, and molecular oxygen (O 2), ~21 percentThese percentages hold up to ~80 km (50 mi).Cycles for N 2 and O2 are balanced at Earth’s surface by production and destruction primarily due to bacterial processes.

Composition of the Atmosphere Near the Earth’s SurfaceTABLE 1.1Composition of the Atmosphere Near the Earth’s Surface PERMANENT GASES VARIABLE GASES Gas Symbol Percent (by Volume) Dry Air Gas (and Particles) Symbol Percent (by Volume) Parts per Million (ppm)* Nitrogen N 2 78.08 Water vaporH2 O0 to 4 OxygenO220.95Carbon dioxideCO20.041410* ArgonAr0.93MethaneCH40.000181.8NeonNe0.0018Nitrous oxideN2O0.000030.3HeliumHe0.0005OzoneO30.0000040.04** HydrogenH20.00006Particles (dust, soot, etc.)0.0000010.01–0.15 XenonXe0.000009Chlorofluorocarbons(CFCs) and hydrofluorocarbons (HFCs)0.000000010.0001 *For CO 2 , 410 parts per million means that out of every million air molecules, 410 are CO 2 molecules. **Stratospheric values at altitudes between 11 km and 50 km are about 5 to 12 ppm.

Composition of Today’s Atmosphere (2 of 7)Water vapor (H2O)Comprises up to 4 percent of total atmospheric gases in the tropics, while less than a percent in cold (e.g., arctic) regionsIs invisible until transformed into larger liquid or solid particles through condensation, and delivered to the surface as precipitation Transforms from a liquid to a vapor through a process called evaporation

Composition of Today’s Atmosphere (3 of 7)Water vaporReleases latent heat to the atmosphere when it changes from a vapor to a liquid or solid (ice)—resulting in atmospheric energy (e.g., storms)A greenhouse gas

Composition of Today’s Atmosphere (4 of 7)Carbon dioxide (CO2)Makes up ~0.04 percent of Earth’s atmosphereEnters the atmosphere mainly as a result of vegetation decay, volcanic eruptions, animal respiration, fossil fuel (e.g., coal, oil, and natural gas) burning, and deforestation Removed from the atmosphere during photosynthesis and as a result of dissolution in water

Atmospheric Carbon Dioxide Cycle

Composition of Today’s Atmosphere (5 of 7)Within the past few decades, the atmospheric concentration of CO2 (a greenhouse gas) has increased.This increase is thought to be due to the burning of fossil fuels and deforestation.Other greenhouse gases include methane (CH 4), nitrous oxide (N2O), and chlorofluorocarbons (CFCs).

The Average Yearly Measurements of CO2

Composition of Today’s Atmosphere (6 of 7)Ozone (O3) A primary component of photochemical smog at Earth’s surfaceThe majority (~97 percent) of O3 is found in the stratosphere, where it protects us from ultraviolet (UV) radiationDestroyed by CFCs in the stratosphere, leading to a loss of stratospheric O 3 and the formation of the ozone hole

The Area of Lowest Ozone Concentration

Composition of Today’s Atmosphere (7 of 7)AerosolsTiny solid or liquid particles of various composition suspended in airOriginate from the ocean’s surface (salt particles from ocean waves), volcanoes, forest fires and other types of burning, and dust from soil carried by wind Natural: aid the condensation of water vapor Human-made: sometimes labeled as a pollutant

Erupting volcanoes

Vertical Structure of the Atmosphere (1 of 2)In the vertical, Earth’s atmosphere can be divided into a series of layers. Layers may be defined by the following:Temperature Gas compositionElectrical properties Understanding air pressure and density is important for understanding the atmosphere.

Vertical Structure of the Atmosphere (2 of 2)Due to gravity, most of Earth’s atmosphere is located close to its surface.DensityThe mass of atoms and the space between themMolecular density of air: number of molecules in a given volume Greatest at Earth’s surface and decreases with height

A Brief Look at Air Pressure and Air Density (1 of 4)Weight = mass x gravityDensity = mass/volumePressure = force/areaAt Earth’s surface, the pressure of the atmosphere is 14.7 lbs/in2.Standard sea level pressure is 1013.25 mb = 1013.25 hPa = 29.92 in Hg. Atmospheric pressure decreases with an increase in height.

The Weight of all the Air Molecules

Atmospheric Pressure

Layers of the Atmosphere (1 of 6)Lapse rate: rate at which the air temperature decreases with height is called the lapse rate.The average (standard) lapse rate is 6.5°C for every 1000 m.Temperature inversion: a measured increase in air temperature with height is called temperature inversion.

The Air Temperature Lapse Rate

Layers of the Atmosphere (2 of 6)TroposphereExtends from Earth’s surface to ~11 km; location of weather systems; temperature decreases with height to the isothermal (equal temperature) zoneStratosphereExtends from ~11 km to ~50 km; temperature increases with height; contains O3 maximum at ~25 km TropopauseSeparates the troposphere from the stratosphere; height varies

Layers of the Atmosphere (3 of 6)MesosphereBegins near 50 km; 99.9 percent of Earth’s atmosphere is below this level; high levels of UV light; temperature decreases with heightThermosphereBegins at ~85 km; temperature increases with height; has low density; has charged particlesExosphereBegins ~500 km above Earth’s surface; gases can escape to space

Layers of the Atmosphere (4 of 6)Earth’s atmosphere may also be divided based on composition instead of temperatureHomosphere: well-mixed atmosphereHeterosphere: stratified (heavy gases settle at the bottom) atmosphereIonosphere: electrified region where ions and free electrons exist; begins at ~60 km above Earth’s surface; mostly located in the thermosphere

Layers of the Atmosphere (5 of 6)

Layers of the Atmosphere (6 of 6)

Weather and ClimateWeather is the condition of the atmosphere at any particular time and place.Comprises air temperature, air pressure, humidity, clouds, precipitation, visibility, and windClimate is the average weather of a particular region.

Meteorology—A Brief History (1 of 2)Meteorology: study of the atmosphere and its phenomenaMajor historical eventsAristotle and his Meteorologica1400s: hygrometers 1500s: thermometers1600s: barometers1800s: telegraph; concepts of wind flow and storm movement1920s: concept of air masses1940s: daily air measurements

Meteorology—A Brief History (2 of 2)More history1950s: scientists developed computerized numerical models for weather prediction 1960: launching of the first weather satellite1990s: Doppler radars in use by the National Weather Service Today, more sophisticated satellites are in use and accurate forecasts—extending weeks into the future—may be possible.

A Satellite’s View of Weather (1 of 2)Geostationary satellitesMove at the same rate as Earth spinsRemain above a particular area to monitor weather and other phenomenaUsed for weather observation and prediction

A Satellite’s View of Weather (2 of 2)

Storms of All Sizes (1 of 2)Types of storms experienced in the United StatesMiddle-latitude cyclonic storm systems (also called extratropical cyclones)—form outside the tropicsHurricanes—swirling band of sustained surface winds greater than 74 miles/hr; winds are calm in the eyeThunderstorms—grow from cumulus clouds; accompanied by thunder, lightning, strong gusty winds, and heavy rain

Storms of All Sizes (2 of 2)Types of storms experienced in the United States:Tornadoes—intense rotating columns of air that extend downward from the base of a thunderstorm with a circulation that reaches the groundGenerally have winds below 100 knots (1 knot = 1.15 miles/hr)

A Glimpse at a Weather Map (1 of 2)Wind: horizontal movement of airWind direction: direction from which the wind is blowingWind speed: rate of movement past a stationary observerA low: region of low atmospheric pressure (L)A high: region of high atmospheric pressure (H)A front: area of sharp changes in temperature, humidity, and wind direction

A Glimpse at a Weather Map (2 of 2)

Weather and Climate in Our LivesWeather and climate impact our lives in terms of economic efficiency and public safety:ClothingCropsUtilitiesExtreme cold and heat Tornados and hurricanesConstant availability of forecasts