earth: portrait of a planet, 3 rd edition, by stephen marshakchapter 20: an envelope of gas:...

Earth: Portrait of a Planet, 3rd edition, by Stephen Marshak Chapter 20: An Envelope of Gas: Earth's Atmosphere and Climate

Chapter 20An Envelope of Gas:

Earth’s Atmosphere and Climate

©2008 W. W. Norton & Company, Inc.

Portrait of a PlanetThird Edition

earthearth

LECTURE OUTLINE

An Envelope of Gas:Earth’s Atmosphere and ClimateAn Envelope of Gas:Earth’s Atmosphere and Climate

Prepared by

Ronald Parker Earlham College Department of Geosciences

Richmond, Indiana

Prepared by

Ronald Parker Earlham College Department of Geosciences

Richmond, Indiana


IntroductionIntroduction Earth has a well-developed atmosphere.Earth has a well-developed atmosphere. The atmosphere consists of a mixture of gases called air.The atmosphere consists of a mixture of gases called air. Density and pressure variation causes air motion: wind. Density and pressure variation causes air motion: wind.

The atmosphere governs physical conditions of weather.The atmosphere governs physical conditions of weather.

Temperature.Temperature. Pressure.Pressure. Moisture content.Moisture content. Wind velocity. Wind velocity. Wind direction.Wind direction.

Climate is long-term Climate is long-term

weather behavior.weather behavior.


Atmospheric FormationAtmospheric Formation Earth’s atmosphere has changed through time.Earth’s atmosphere has changed through time. Changes have been coupled to biotic evolution.Changes have been coupled to biotic evolution.


Atmospheric FormationAtmospheric Formation The first atmosphere at planet formation (4.57 Ga):The first atmosphere at planet formation (4.57 Ga):

Hydrogen and helium.Hydrogen and helium. Quickly stripped off by the solar wind.Quickly stripped off by the solar wind.

A secondary atmosphere developed via volcanism.A secondary atmosphere developed via volcanism. Volcanic gases dominated.Volcanic gases dominated.

Water (HWater (H22O).O).

Carbon dioxide (COCarbon dioxide (CO22).).

Sulfur dioxide (SOSulfur dioxide (SO22).).

Nitrogen (NNitrogen (N22).).

Ammonia (NHAmmonia (NH33).).

Free oxygen (OFree oxygen (O22) was absent.) was absent.


Atmospheric FormationAtmospheric Formation The secondary atmosphere evolved as the planet cooled.The secondary atmosphere evolved as the planet cooled.

Condensed water fell as rain to form the oceans.Condensed water fell as rain to form the oceans. Atmospheric COAtmospheric CO22 decreased by dissolving in ocean water. decreased by dissolving in ocean water.

COCO2 2 is a powerful heat-trapping (greenhouse) gas.is a powerful heat-trapping (greenhouse) gas.

COCO2 2 removal permitted atmospheric cooling.removal permitted atmospheric cooling.

The relative abundance of stable NThe relative abundance of stable N22 increased. increased.


Atmospheric FormationAtmospheric Formation By 3.5 Ga, photosynthetic cyanobacteria added free OBy 3.5 Ga, photosynthetic cyanobacteria added free O22..

Atmospheric OAtmospheric O22 accumulated. accumulated.

By 2 Ga, OBy 2 Ga, O22 reached 1% of present value. reached 1% of present value.

Eukaryotic green algae (1.6 Ga) accelerated OEukaryotic green algae (1.6 Ga) accelerated O2 2 production.production.

By 600 Ma, OBy 600 Ma, O2 2 arrived at 10% of present concentrations. arrived at 10% of present concentrations.

Present OPresent O22 concentration (20.9%) by 400 to 250 Ma. concentration (20.9%) by 400 to 250 Ma.


Atmospheric FormationAtmospheric Formation OO22 buildup permitted diversification of life. buildup permitted diversification of life.

Aerobic (oxygenated) respiration is more energy-efficient.Aerobic (oxygenated) respiration is more energy-efficient. Aerobic respiration fueled multicellular life.Aerobic respiration fueled multicellular life. OO22 opened the possibility of land-dwelling biota. opened the possibility of land-dwelling biota.

OO22 made formation of the ozone layer possible. made formation of the ozone layer possible. Ozone absorbs deadly ultraviolet (UV) radiation.Ozone absorbs deadly ultraviolet (UV) radiation. Prior to the ozone layer, exposed land was bathed in UV. Prior to the ozone layer, exposed land was bathed in UV.


Atmospheric ComponentsAtmospheric Components The present atmosphere is comprised of a mix of gases.The present atmosphere is comprised of a mix of gases.

Nitrogen Nitrogen 78%78% Oxygen Oxygen 21%21% Other gasesOther gases 1% 1%

Argon.Argon.Carbon dioxide.Carbon dioxide.Methane.Methane.Sulfur dioxide.Sulfur dioxide.Ozone.Ozone.Radon.Radon.

Aerosols – Tiny suspended particles (< 1 micrometer).Aerosols – Tiny suspended particles (< 1 micrometer). Liquid droplets.Liquid droplets. Solid dusts.Solid dusts.


Atmospheric PollutantsAtmospheric Pollutants Humans add gases and aerosols to the atmosphere.Humans add gases and aerosols to the atmosphere.

Fossil fuel combustion.Fossil fuel combustion. Industrial processes.Industrial processes.

Often these additions cause environmental harm.Often these additions cause environmental harm. Acid rain – Sulfate and nitrate acidify precipitation.Acid rain – Sulfate and nitrate acidify precipitation. Greenhouse gases – COGreenhouse gases – CO22 and CH and CH44 trap atmospheric heat. trap atmospheric heat.


Atmospheric ColorationAtmospheric Coloration Atmospheric color is due to dispersion Atmospheric color is due to dispersion

of light energy.of light energy. Light is scattered as it passes through Light is scattered as it passes through

the atmosphere. the atmosphere. Some light returns to space.Some light returns to space.

Why is the sky blue?Why is the sky blue? When the Sun is overhead...When the Sun is overhead... Gases scatter blue light.Gases scatter blue light.

Why is the sky red?Why is the sky red? The setting Sun passes through thicker The setting Sun passes through thicker

atmosphere.atmosphere. Blue is scattered to space.Blue is scattered to space.


Pressure and DensityPressure and Density Air pressure – Force due to the weight of overlying air. Air pressure – Force due to the weight of overlying air.

Greatest near Earth’s surface.Greatest near Earth’s surface. Decreases upward.Decreases upward. 14.7 psi (1 atm) at sea level.14.7 psi (1 atm) at sea level.

Air density – Mass of air/volume.Air density – Mass of air/volume. Maximum at sea level.Maximum at sea level. Decreases upward.Decreases upward.

Both measures are proportional.Both measures are proportional.


P and T RelationsP and T Relations P and T conditions change with elevation.P and T conditions change with elevation.

Pressure is higher near Earth’s surface; lower aloft. Pressure is higher near Earth’s surface; lower aloft. When air moves from higher to lower pressure, it…When air moves from higher to lower pressure, it…

Expands, cools, and holds less water.Expands, cools, and holds less water. This occurs when air rises.This occurs when air rises.

Moving from lower to higher P, air…Moving from lower to higher P, air… Contracts, warms and absorbs water. Contracts, warms and absorbs water. This occurs when air descends. This occurs when air descends.

Called adiabatic cooling and heating.Called adiabatic cooling and heating.


Relative HumidityRelative Humidity Air contains varying amounts of water.Air contains varying amounts of water.

Dry desert Dry desert 0.3%0.3% Humid tropical rainforestHumid tropical rainforest 4.0%4.0%

Water content is described by the relative humidity.Water content is described by the relative humidity. Ratio (%) of measured water content to maximum possible.Ratio (%) of measured water content to maximum possible.

Dry air has a low relative humidity.Dry air has a low relative humidity.Humid air has a high relative humidity.Humid air has a high relative humidity.

Air with 100% relative humidity is called saturated.Air with 100% relative humidity is called saturated. Undersaturated air has less that 100% relative humidity.Undersaturated air has less that 100% relative humidity.


Relative HumidityRelative Humidity Maximum moisture content changes with temperature.Maximum moisture content changes with temperature.

Cold air holds less moisture; warm air holds more. Cold air holds less moisture; warm air holds more. Warm undersaturated air becomes saturated as it cools.Warm undersaturated air becomes saturated as it cools. This temperature is the dewpoint.This temperature is the dewpoint. Below the dewpoint…Below the dewpoint…

Water forms dew on surfaces.Water forms dew on surfaces. Water freezes to form frost.Water freezes to form frost.


Relative HumidityRelative Humidity Rising air adiabatically cools to form tiny water droplets.Rising air adiabatically cools to form tiny water droplets. This phenomenon is commonplace; it forms clouds.This phenomenon is commonplace; it forms clouds. Clouds may also dissipate by adiabatic heating.Clouds may also dissipate by adiabatic heating.


Latent HeatLatent Heat Water in the air is subject to changes of state.Water in the air is subject to changes of state.

Liquid to gas.Liquid to gas. Gas to liquid.Gas to liquid.

With changes of state, air temperature also changes.With changes of state, air temperature also changes. T change is T change is notnot due to external energy; hence, “latent.” due to external energy; hence, “latent.” Instead, it derives from the change in state alone.Instead, it derives from the change in state alone.

Evaporating water absorbs heat, cooling the air.Evaporating water absorbs heat, cooling the air. Condensing water releases heat, warming the air.Condensing water releases heat, warming the air.


Atmospheric LayersAtmospheric Layers The atmosphere is thermally layered.The atmosphere is thermally layered.

Troposphere (0 - 9 to 12 km).Troposphere (0 - 9 to 12 km).The mixing layer.The mixing layer.All weather occurs here.All weather occurs here.Thinner at poles (9 km).Thinner at poles (9 km).Thicker at equator (12 km).Thicker at equator (12 km).T decreases to – 55T decreases to – 55ooC.C.

Tropopause (9 - 12 km).Tropopause (9 - 12 km).Marked by T stabilization.Marked by T stabilization.

Stratosphere (12 - 30 km).Stratosphere (12 - 30 km).Does not convect.Does not convect.T stays the same for 10 km.T stays the same for 10 km.Then, T warms to 0Then, T warms to 0ooC.C.


Atmospheric LayersAtmospheric Layers The atmosphere is thermally layered.The atmosphere is thermally layered.

Stratopause (47 km).Stratopause (47 km). Mesosphere (47 to 82 km).Mesosphere (47 to 82 km).

T decreases to - 85T decreases to - 85ooC.C.Meteors start to burn.Meteors start to burn.

Mesopause (82 km).Mesopause (82 km).Marked by T shift.Marked by T shift.

Thermosphere (> 82 km).Thermosphere (> 82 km).Outermost layer. Outermost layer. Sparse gas concentrations.Sparse gas concentrations.

Layered by type of mixing.Layered by type of mixing. Homosphere.Homosphere. Heterosphere.Heterosphere.


Atmospheric LayersAtmospheric Layers The ionosphere is the interval between 60 and 400 km.The ionosphere is the interval between 60 and 400 km.

Most of the mesosphere.Most of the mesosphere. Lower part of the thermosphere.Lower part of the thermosphere.

Solar energy creates + ions by Solar energy creates + ions by

stripping electrons from N and O.stripping electrons from N and O. The ionosphere creates auroras.The ionosphere creates auroras.

Charged particles from solar flaresCharged particles from solar flares

interact with the ionosphere.interact with the ionosphere. Funneled to the polesFunneled to the poles

by Earth’s magnetic field.by Earth’s magnetic field. Aurora borealis (northern lights).Aurora borealis (northern lights). Aurora australis (southern lights).Aurora australis (southern lights).


Atmospheric CirculationAtmospheric Circulation The troposphere experiences almost constant motion.The troposphere experiences almost constant motion. Movement of air from one place to another is the wind.Movement of air from one place to another is the wind. Wind velocities vary widely, from 0 to > 100 km/h.Wind velocities vary widely, from 0 to > 100 km/h. Wind circulation has both local and global aspects.Wind circulation has both local and global aspects.

Local – Operates across 10s to 1,000s of kilometers.Local – Operates across 10s to 1,000s of kilometers. Global – Operates on a scale that encircles the planet. Global – Operates on a scale that encircles the planet.


PressurePressure Lateral pressure differences drive horizontal winds. Lateral pressure differences drive horizontal winds. Pressures are mapped by isobars – lines of equal P. Pressures are mapped by isobars – lines of equal P.

Isobars cannot cross.Isobars cannot cross. Air flows from high P to low P perpendicular to isobars.Air flows from high P to low P perpendicular to isobars. The steeper the gradient, the faster the airflow.The steeper the gradient, the faster the airflow.


Energy InputEnergy Input Air circulation is a consequence of thermal convection. Air circulation is a consequence of thermal convection.

Warm air expands, becomes less dense, and rises.Warm air expands, becomes less dense, and rises. This air is replaced by sinking, cooler, denser air. This air is replaced by sinking, cooler, denser air.

Convection is driven by differential solar heating. Convection is driven by differential solar heating. Solar energy = insolation, or Solar energy = insolation, or inincoming coming solsolar radiar radiationation..


Energy InputEnergy Input The solar energy bathing Earth is not equally distributed.The solar energy bathing Earth is not equally distributed.

The vertical ray of the Sun imparts more energy per area.The vertical ray of the Sun imparts more energy per area. An oblique ray imparts less energy.An oblique ray imparts less energy.

The tropics (vertical ray) receive more energy = hotter.The tropics (vertical ray) receive more energy = hotter. The poles (oblique ray) receive less energy = colder.The poles (oblique ray) receive less energy = colder.


SeasonsSeasons Seasons come from the 23.5Seasons come from the 23.5oo tilt of Earth’s axis of rotation. tilt of Earth’s axis of rotation. As Earth orbits the Sun, the vertical ray shifts.As Earth orbits the Sun, the vertical ray shifts.

North during the northern hemisphere summer.North during the northern hemisphere summer. South during the southern hemisphere summer.South during the southern hemisphere summer.


Seasons – Seasons – Earth in JanuaryEarth in January


Seasons – Seasons – Earth in JulyEarth in July


The Coriolis EffectThe Coriolis Effect Earth’s rotation causes deflection of prevailing winds.Earth’s rotation causes deflection of prevailing winds. Sense of deflection depends upon…Sense of deflection depends upon…

Initial direction of motion.Initial direction of motion. Position relative to the equator. Position relative to the equator.

Coriolis deflection can be modeled on a merry-go-round.Coriolis deflection can be modeled on a merry-go-round.


The Coriolis EffectThe Coriolis Effect Surface winds and high-altitude winds are both affected.Surface winds and high-altitude winds are both affected. Northern hemisphere.Northern hemisphere.

North-moving winds deflected to the E.North-moving winds deflected to the E. South-moving winds deflected to the W.South-moving winds deflected to the W.

Southern hemisphere.Southern hemisphere. South-moving winds deflected to the E.South-moving winds deflected to the E. North-moving winds deflected to the W.North-moving winds deflected to the W.


Atmospheric MovementAtmospheric Movement Nonrotational circulation would yield 2 convection cells. Nonrotational circulation would yield 2 convection cells.

Maximum heating at the equator = rising air.Maximum heating at the equator = rising air. This air is pushed N and S.This air is pushed N and S. Cool polar air fills the gap.Cool polar air fills the gap.


Atmospheric MovementAtmospheric Movement Rotation, via Coriolis, complicates simple convection. Rotation, via Coriolis, complicates simple convection. The troposphere is divided into 6 circulation cells.The troposphere is divided into 6 circulation cells.

Hadley cells – Low-latitude (equator to 30Hadley cells – Low-latitude (equator to 30o o N or S).N or S). Ferrel cells – Mid-latitude.Ferrel cells – Mid-latitude. Polar cells – High-latitude.Polar cells – High-latitude.

Hadley cell – Rising Hadley cell – Rising

equatorial air creates equatorial air creates

low pressure. low pressure. N. hemisphere N. hemisphere

air flows S.air flows S. S. hemisphere S. hemisphere

air flows N.air flows N.


Hadley cell airflow is deflected to the west. Hadley cell airflow is deflected to the west. Form a convergence zone.Form a convergence zone.

Air masses move together.Air masses move together.Converging air is forced up.Converging air is forced up.

Rising equatorial air cools.Rising equatorial air cools. Moisture lost as rain.Moisture lost as rain. Air moves to N or S Air moves to N or S

at high altitude.at high altitude.

Atmospheric MovementAtmospheric Movement


Atmospheric MovementAtmospheric Movement Coriolis deflects the tropical high-altitude winds.Coriolis deflects the tropical high-altitude winds. After moving from the tropics to 30After moving from the tropics to 30o o N or S latitude…N or S latitude…

The former N- or S-directed winds are moving due E.The former N- or S-directed winds are moving due E. Cooling forces this high-altitude air to sink.Cooling forces this high-altitude air to sink.

At the surface, a divergence zone splits the flow. At the surface, a divergence zone splits the flow. Some flows N toward the poles. Some flows N toward the poles. Some flows S toward the equator.Some flows S toward the equator.


Prevailing Surface WindsPrevailing Surface Winds Global circulation dictates consistent wind directions.Global circulation dictates consistent wind directions. Consistent surface airflows are called prevailing winds.Consistent surface airflows are called prevailing winds.

Prevailing winds may be modified by local variability.Prevailing winds may be modified by local variability.


Winds AloftWinds Aloft Tropospheric thickness changes with latitude.Tropospheric thickness changes with latitude.

Warm equatorial air expands the tropospheric thickness. Warm equatorial air expands the tropospheric thickness. Frigid polar air forms a thinner troposphere. Frigid polar air forms a thinner troposphere.

At a given altitude, equatorial pressure will be higher. At a given altitude, equatorial pressure will be higher. This causes equatorial high-altitude air to flow north.This causes equatorial high-altitude air to flow north.

Air atop the Hadley cells spill over the top of the Ferrel cells.Air atop the Hadley cells spill over the top of the Ferrel cells.Coriolis deflects these high-altitude winds to the east. Coriolis deflects these high-altitude winds to the east.

Results in westerly high-altitude winds. Results in westerly high-altitude winds.


Winds AloftWinds Aloft The high-altitude pressure gradient is especially steep…The high-altitude pressure gradient is especially steep…

Over the polar front.Over the polar front. Over the horse latitudes.Over the horse latitudes.

High-altitude westerlies attain elevated velocities there.High-altitude westerlies attain elevated velocities there. Winds can move 200 to 400 km/hr.Winds can move 200 to 400 km/hr. These fast winds are known as the “jet streams.”These fast winds are known as the “jet streams.”


WeatherWeather Local-scale conditions of T, P, humidity, and wind speed.Local-scale conditions of T, P, humidity, and wind speed. Reflects prevailing winds and local heterogeneity. Reflects prevailing winds and local heterogeneity.

Variation in topography and vegetation.Variation in topography and vegetation. Land vs. sea.Land vs. sea.

A weather system affects a region for a time.A weather system affects a region for a time.


Air MassesAir Masses Packages of air with unique, recognizable properties.Packages of air with unique, recognizable properties. At least 1,500 km across, they flow over a region for days.At least 1,500 km across, they flow over a region for days. Characteristics reflect originating location and changes.Characteristics reflect originating location and changes. Weather changes dramatically when air masses change.Weather changes dramatically when air masses change.


FrontsFronts Boundaries between air masses are called fronts.Boundaries between air masses are called fronts. Fronts are curved surfaces that move with air masses.Fronts are curved surfaces that move with air masses. Cold front.Cold front.

Steep T and P gradient.Steep T and P gradient. Moves as a density underflow beneath warmer air.Moves as a density underflow beneath warmer air. Rapid uplift of warm humid creates large storms. Rapid uplift of warm humid creates large storms.


FrontsFronts Warm front.Warm front.

Warm fronts move more slowly than cold fronts. Warm fronts move more slowly than cold fronts. Warm air climbs up a gentle incline over the colder air.Warm air climbs up a gentle incline over the colder air.

Pushes the cold air as a a wedge.Pushes the cold air as a a wedge.Incline reflects less steep T and P gradients.Incline reflects less steep T and P gradients.

Warm air rising up the front produces broad cloud cover. Warm air rising up the front produces broad cloud cover.


FrontsFronts Occluded front.Occluded front.

A combination front.A combination front. A fast-moving cold front overtaken a slower warm front.A fast-moving cold front overtaken a slower warm front. The cold front lifts the warm front off the ground.The cold front lifts the warm front off the ground. Generates “combination weather.”Generates “combination weather.”


Rotational FlowRotational Flow Air flows away from high pressure; toward low pressure.Air flows away from high pressure; toward low pressure. High P – Departing air creates a void.High P – Departing air creates a void.

This is filled by pulling down cold, dry air from above. This is filled by pulling down cold, dry air from above. This air compresses and warms wicking moisture.This air compresses and warms wicking moisture. High pressure is associated with clear and dry weather.High pressure is associated with clear and dry weather.


Rotational FlowRotational Flow Air flows away from high pressure; toward low pressure.Air flows away from high pressure; toward low pressure. Low P – Converging air “piles up” in the center of Low P.Low P – Converging air “piles up” in the center of Low P.

This causes air to flow upward and spill outward.This causes air to flow upward and spill outward. Rising air cools, condensing moisture.Rising air cools, condensing moisture. This builds clouds causing rain.This builds clouds causing rain. Typically cloudy, rainy weather.Typically cloudy, rainy weather.


Rotational FlowRotational Flow Flowing air develops a spiral motion due to Coriolis.Flowing air develops a spiral motion due to Coriolis.

Cyclonic flow – Counterclockwise.Cyclonic flow – Counterclockwise. Anti-cyclonic flow – Clockwise.Anti-cyclonic flow – Clockwise.

Northern hemisphere - Cyclonic rotation toward low P; Northern hemisphere - Cyclonic rotation toward low P; anticyclonic rotation away from high P.anticyclonic rotation away from high P.


Wave cyclones are common across the mid U.S. Wave cyclones are common across the mid U.S. Develop via a “wrinkled” cold front. Develop via a “wrinkled” cold front. Shear parallel to a cold front, warps the front.Shear parallel to a cold front, warps the front. Upshear, warm air moves over cold to create a warm front. Upshear, warm air moves over cold to create a warm front. The cold front wraps around behind the warm front.The cold front wraps around behind the warm front.

Wave CyclonesWave Cyclones


Wave CyclonesWave Cyclones Wave cyclones are common across the mid U.S. Wave cyclones are common across the mid U.S.

The two fronts meet in a “V.”The two fronts meet in a “V.” The V is the center of the low P.The V is the center of the low P. The cold front catches up to the warm front.The cold front catches up to the warm front. The resulting occluded front eventually dies out.The resulting occluded front eventually dies out.


Clouds and PrecipitationClouds and Precipitation Water vapor in saturated air will change state by…Water vapor in saturated air will change state by…

Condensing as microscopic droplets of water.Condensing as microscopic droplets of water. Precipitating as microscopic crystals of ice.Precipitating as microscopic crystals of ice.

Condensation nuclei initiate this change.Condensation nuclei initiate this change. Microscopic solid of liquid aerosol particles.Microscopic solid of liquid aerosol particles.

Cloud-forming Cloud-forming

saturation occurs saturation occurs

when air is lifted.when air is lifted.


Clouds and PrecipitationClouds and Precipitation There are several air-lifting mechanisms. There are several air-lifting mechanisms.

Convective lifting – Warmed air is buoyed upward. Convective lifting – Warmed air is buoyed upward. Frontal lifting – Air is carried upward along fronts. Frontal lifting – Air is carried upward along fronts. Convergence lifting – Converging winds force air upward. Convergence lifting – Converging winds force air upward. Orographic lifting – Air must riase to pass over mountains.Orographic lifting – Air must riase to pass over mountains.


Clouds and PrecipitationClouds and Precipitation Rain, snow, and sleet form in two ways depending on T.Rain, snow, and sleet form in two ways depending on T.

Collison and coalescence – Smaller droplets collide to Collison and coalescence – Smaller droplets collide to create larger drops.create larger drops.Drops fall when too large to suspend.Drops fall when too large to suspend.

Typical raindrops are 2 mm.Typical raindrops are 2 mm. Drops larger than 5 mm break up.Drops larger than 5 mm break up.

Cold air near ground turns rain to sleet. Cold air near ground turns rain to sleet.


Clouds and PrecipitationClouds and Precipitation Bergeron process – Cold clouds contain water and ice.Bergeron process – Cold clouds contain water and ice.

Water evaporates faster than ice, fueling crystal growth.Water evaporates faster than ice, fueling crystal growth.Ice grows as delicate hexagonal flakes.Ice grows as delicate hexagonal flakes.

Snowflakes may change as they fall.Snowflakes may change as they fall.Cold air – Flakes remain as a powder.Cold air – Flakes remain as a powder.Near melting T – Flakes form clumps.Near melting T – Flakes form clumps.Above melting T – Flakes form rain.Above melting T – Flakes form rain.


Cloud TypesCloud Types Many cloud types form in the troposphere, controlled byMany cloud types form in the troposphere, controlled by

Air stability.Air stability. Elevation at which moisture condenses. Elevation at which moisture condenses. Wind conditions.Wind conditions.


Cloud TypesCloud Types Shape is used to describe clouds.Shape is used to describe clouds.

Cirrus – Wispy, thin, feathery.Cirrus – Wispy, thin, feathery. Cumulus – Puffy, cottony. Cumulus – Puffy, cottony. Stratus – Stable, layered.Stratus – Stable, layered.

Prefixes narrow cloud types.Prefixes narrow cloud types. Cirro – High-altitude.Cirro – High-altitude. Alto – Mid-altitude.Alto – Mid-altitude. Nimbo – Rain-producing.Nimbo – Rain-producing.


Cloud TypesCloud Types Cloud type depends on air stability.Cloud type depends on air stability.

Stable air, colder than surroundings, tends not to rise.Stable air, colder than surroundings, tends not to rise. Unstable air, warmer that surroundings, tends to rise.Unstable air, warmer that surroundings, tends to rise.

Stable air generates stratus clouds.Stable air generates stratus clouds.


Cloud TypesCloud Types Unstable air creates vertically building cumulus clouds.

Cumulonimbus – Immense rain-making cloud.Grows rapidly up to ~15 km.Spreads laterally at the top.Called “anvil clouds.”Generate thunderstorms.

Unstable air creates vertically building cumulus clouds. Cumulonimbus – Immense rain-making cloud.

Grows rapidly up to ~15 km.Spreads laterally at the top.Called “anvil clouds.”Generate thunderstorms.


StormsStorms Storms, episodes of severe weather, may be dangerous.Storms, episodes of severe weather, may be dangerous.

Lightning.Lightning. Wind.Wind. Rain.Rain. Hail.Hail. Sleet Sleet Snow.Snow.


StormsStorms Storms develop along steep pressure gradients.Storms develop along steep pressure gradients.

Centered by low pressure.Centered by low pressure. Fueled by warm, moist air.Fueled by warm, moist air.


ThunderstormsThunderstorms Short, local pulses of intense rain, wind, and lightning.Short, local pulses of intense rain, wind, and lightning. Form when warm, moist, unstable air is carried upward. Form when warm, moist, unstable air is carried upward.

Fronts.Fronts. Local conditions.Local conditions.


ThunderstormsThunderstorms Rising air forms cumulus clouds.Rising air forms cumulus clouds. Latent heat released by condensing water warms air.Latent heat released by condensing water warms air. Cumulus clouds build upward.Cumulus clouds build upward.

An anvil head develops.An anvil head develops. Heavy rains ensue.Heavy rains ensue. Downdrafts stop cycle.Downdrafts stop cycle.


ThunderstormsThunderstorms Lightning reflects electrical charge separation in clouds.Lightning reflects electrical charge separation in clouds.

Scientists do not fully understood why this happens. Scientists do not fully understood why this happens. The base of clouds develop a negative charge. The base of clouds develop a negative charge. This leads to a buildup of positive charge on the ground.This leads to a buildup of positive charge on the ground. Air is a good insulator; it prevents charge dissipation.Air is a good insulator; it prevents charge dissipation. Eventually, the charge imbalance overwhelms the air.Eventually, the charge imbalance overwhelms the air.


ThunderstormsThunderstorms A lightning leader advances from the base of the cloud.A lightning leader advances from the base of the cloud. A return stroke starts from the ground.A return stroke starts from the ground. They connect to form the bolt.They connect to form the bolt. Thunder is a direct result.Thunder is a direct result.

Bolt heats air 8K to 30K Bolt heats air 8K to 30K ooC.C. Air expands explosively.Air expands explosively.


TornadoesTornadoes A near-vertical rotating funnel-shaped vortex cloud.A near-vertical rotating funnel-shaped vortex cloud. Air moves with violent speed about rotational axis.Air moves with violent speed about rotational axis.

Can generate local winds of 500 km/h (300 mph).Can generate local winds of 500 km/h (300 mph). These winds are dangerously destructive.These winds are dangerously destructive.


TornadoesTornadoes Tornadoes develop along steep P gradients.Tornadoes develop along steep P gradients.

Strong W winds aloft carry polar air.Strong W winds aloft carry polar air. Strong SE surface winds carry warm moist air.Strong SE surface winds carry warm moist air.

Strong shear initiates horizontal rotation. Strong shear initiates horizontal rotation. Drafts tip the rotating cylinder upright.Drafts tip the rotating cylinder upright.


TornadoesTornadoes The funnel pulls air inward and upward.The funnel pulls air inward and upward. Touching down, debris darkens the funnel.Touching down, debris darkens the funnel. Destruction caused by winds and very low P.Destruction caused by winds and very low P.


TornadoesTornadoes Tornadoes are prevalent in the midwestern U.S. Tornadoes are prevalent in the midwestern U.S.

Proper conditions exist from March to September.Proper conditions exist from March to September.Cold polar air from Canada sweeps south.Cold polar air from Canada sweeps south.Warm moist air pushed north from the Gulf of Mexico.Warm moist air pushed north from the Gulf of Mexico.

The tornado-threatened region is called “Tornado Alley.”The tornado-threatened region is called “Tornado Alley.”


TornadoesTornadoes


TornadoesTornadoes Meteorologists track weather to predict tornadoes. Meteorologists track weather to predict tornadoes. Doppler radar maps severe weather conditions. Doppler radar maps severe weather conditions. Threatening conditions are broadcast by TV and radio.Threatening conditions are broadcast by TV and radio.

A tornado watch is issued when proper conditions exist.A tornado watch is issued when proper conditions exist. An observed tornado will elicit a tornado warning. An observed tornado will elicit a tornado warning. Tornado warning?Tornado warning?

Seek immediate cover. Seek immediate cover.


HurricanesHurricanes Huge low-P cyclonic storms from the tropical Atlantic.Huge low-P cyclonic storms from the tropical Atlantic.

Defined by sustained winds exceed 119 km/hr (74 mi/hr). Defined by sustained winds exceed 119 km/hr (74 mi/hr). Fueled by warm ocean water exceeding 27Fueled by warm ocean water exceeding 27ooC.C.

Originate in lower latitudes (< 20Originate in lower latitudes (< 20ooN) typified by warm water.N) typified by warm water.Do not form near the equator (insufficient lateral winds). Do not form near the equator (insufficient lateral winds).


HurricanesHurricanes Hurricanes develop in summer and late fall.Hurricanes develop in summer and late fall. Form over warm tropical ocean waters off W. Africa.Form over warm tropical ocean waters off W. Africa.

Cyclonic low-P “tropical disturbances” pull air inward.Cyclonic low-P “tropical disturbances” pull air inward. This air rises, cools, and condenses, releasing latent heat.This air rises, cools, and condenses, releasing latent heat. This heat buoys air, creates lower P, and pulls in more air. This heat buoys air, creates lower P, and pulls in more air. Over time, the storm gains Over time, the storm gains

size and strength.size and strength.Size range – 100 to 1500 km.Size range – 100 to 1500 km.Strength – 230 km/hr.Strength – 230 km/hr.


HurricanesHurricanes A storm is “named” after winds exceed 60 km/h.A storm is “named” after winds exceed 60 km/h.

Named in alphabetical order.Named in alphabetical order. Alternating male/female with varying national origin.Alternating male/female with varying national origin.

Hurricane tracks move W Hurricane tracks move W

and N, often crossing land.and N, often crossing land. Landfall removes the storm Landfall removes the storm

fuel; warm, moist air.fuel; warm, moist air.


HurricanesHurricanes Hurricane-like storms outside the Atlantic are called…Hurricane-like storms outside the Atlantic are called…

Typhoons – Western Pacific Ocean. Typhoons – Western Pacific Ocean. Cyclones (2Cyclones (2ndnd meaning) – Northern Indian Ocean. meaning) – Northern Indian Ocean.


HurricanesHurricanes Spiral arms (rain bands) mark rotating air pulled inward. Spiral arms (rain bands) mark rotating air pulled inward. Converging winds accelerate, rise up, and spill out. Converging winds accelerate, rise up, and spill out. A region of calm, the “eye,” is situated at storm center.A region of calm, the “eye,” is situated at storm center.

Cold, dry air is pulled down into the eye to create this calm.Cold, dry air is pulled down into the eye to create this calm. The “eye wall” forms a rotating vertical cylinder of wind. The “eye wall” forms a rotating vertical cylinder of wind. Wind velocity is highest in the eye wall.Wind velocity is highest in the eye wall.


HurricanesHurricanes


HurricanesHurricanes Hurricanes cause damage in a variety of ways.Hurricanes cause damage in a variety of ways.

Wind – High-velocity winds destroy structures.Wind – High-velocity winds destroy structures. Waves – Hurricanes generate enormous waves.Waves – Hurricanes generate enormous waves. Storm surge – Water moved inland by winds and low P.Storm surge – Water moved inland by winds and low P. Rainfall – Intense. Covers large regions resulting in...Rainfall – Intense. Covers large regions resulting in...

Flooding.Flooding.Mudslides.Mudslides.


HurricanesHurricanes Intensity is ranked according to the Saffir-Simpson Intensity is ranked according to the Saffir-Simpson

scale.scale. Category 1: Wind speed >119 km/h; pressure >980 mbars.Category 1: Wind speed >119 km/h; pressure >980 mbars. Category 5: Wind speed >250 km/h; pressure < 920 mbars.Category 5: Wind speed >250 km/h; pressure < 920 mbars.


HurricanesHurricanes The 2005 hurricane season set a number of new records.The 2005 hurricane season set a number of new records.

Most named storms (26) – Previous record 21 in 1933.Most named storms (26) – Previous record 21 in 1933. Most hurricanes (13) – Previous record 12 in 1969.Most hurricanes (13) – Previous record 12 in 1969. Most category 5s (3) – Previous record 2 in 1960 and 61.Most category 5s (3) – Previous record 2 in 1960 and 61. Most major hurricanes (Cat 3 or higher - 7).Most major hurricanes (Cat 3 or higher - 7). Most major hurricanes in the U.S. (4).Most major hurricanes in the U.S. (4).

Trends in storm activity likely reflect global warming.Trends in storm activity likely reflect global warming.

Hurricane KatrinaHurricane Katrina


Hurricane KatrinaHurricane Katrina Katrina is the most destructive hurricane recorded.Katrina is the most destructive hurricane recorded.

Tracked over the Gulf of Mexico for a week before landfall.Tracked over the Gulf of Mexico for a week before landfall. Dropped from a Category 5 to a 4 just before landfall.Dropped from a Category 5 to a 4 just before landfall. Struck the Mississippi and Louisiana coasts on Aug 30Struck the Mississippi and Louisiana coasts on Aug 30 thth..


Hurricane KatrinaHurricane Katrina Wreaked destruction on a grand scale. Wreaked destruction on a grand scale.

Reshaped barrier islands.Reshaped barrier islands. Destroyed coastal marsh and croplands. Destroyed coastal marsh and croplands. Devastated entire coastal communities.Devastated entire coastal communities.


Hurricane KatrinaHurricane Katrina Indirectly resulted in massive flooding of New Orleans.Indirectly resulted in massive flooding of New Orleans.

Estimated losses of $80 billion.Estimated losses of $80 billion. At least 1,300 deaths. At least 1,300 deaths.


Hurricane KatrinaHurricane Katrina


Global ClimateGlobal Climate The word “climate” refers to persistent weather patterns.The word “climate” refers to persistent weather patterns.

Patterns include long-term (30+ yrs.) regional trends.Patterns include long-term (30+ yrs.) regional trends. Trends include maxima, minima, ranges, timing, etc.Trends include maxima, minima, ranges, timing, etc.

Temperature.Temperature.Pressure.Pressure.HumidityHumidityPrecipitation.Precipitation.Wind conditions.Wind conditions.Storms.Storms.


Climate ControlsClimate Controls Climatic conditions are governed by several factors. Climatic conditions are governed by several factors.

Latitude – N or S position.Latitude – N or S position.Determines insolation.Determines insolation.Controls isotherms.Controls isotherms.

Hotter near the equator.Hotter near the equator. Colder near the poles.Colder near the poles. Seasonally varies.Seasonally varies.

Altitude – Height above SL. Altitude – Height above SL. Elevation linked to T.Elevation linked to T.For the same latitude.For the same latitude.

Lower elevations warmer. Lower elevations warmer. Higher elevations colder.Higher elevations colder.



Proximity to water influences T stability.Proximity to water influences T stability.Land heats and cools more rapidly that ocean water.Land heats and cools more rapidly that ocean water.Places near oceans have less T extremes; smaller T ranges.Places near oceans have less T extremes; smaller T ranges.



Proximity to ocean currents influences T conditions.Proximity to ocean currents influences T conditions.Warm currents produce warmer climates.Warm currents produce warmer climates.



Proximity to mountain ranges.Proximity to mountain ranges.Mountains alter air flow funneling or blocking winds.Mountains alter air flow funneling or blocking winds.Mountains modify moisture patterns.Mountains modify moisture patterns.

Heavy precipitation on windward side.Heavy precipitation on windward side. Rainshadow desert on leeward side. Rainshadow desert on leeward side.



Proximity to semi-permanent high- and low-pressure cells.Proximity to semi-permanent high- and low-pressure cells.Latitudinally controlled.Latitudinally controlled.Govern prevailing winds.Govern prevailing winds.Directly control humidity.Directly control humidity.


Climate BeltsClimate Belts Climatic belts are classified on the basis of temperature, Climatic belts are classified on the basis of temperature,

precipitation, and vegetation characteristics. precipitation, and vegetation characteristics.


Climate VariabilityClimate Variability Climate can change in cyclic patterns.Climate can change in cyclic patterns.

El NiEl Niñño – Oscillation of air and water circulation off Peru.o – Oscillation of air and water circulation off Peru. Normal oceanic circulation is driven by the trade winds.Normal oceanic circulation is driven by the trade winds.

Easterlies push equatorial surface water west.Easterlies push equatorial surface water west.Upwelling deep, cold, nutrient-rich water replaces this flow.Upwelling deep, cold, nutrient-rich water replaces this flow.


Climate VariabilityClimate Variability Climate can change in cyclical patterns.Climate can change in cyclical patterns.

During El NiDuring El Niñño events, low P develops off Peru, changing o events, low P develops off Peru, changing atmospheric and oceanic circulation. atmospheric and oceanic circulation.

El NiEl Niñño events are thought o events are thought

to change global climate.to change global climate.


Chapter 20An Envelope of Gas:

Earth’s Atmosphere and Climate

©2008 W. W. Norton & Company, Inc.

Portrait of a PlanetThird Edition

earthearth

LECTURE OUTLINE

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