Unit 5 – The AtmosphereChapters 11, 12, 13

Vocabulary1. Atmosphere2. Temperature3. Humidity4. Relative humidity5. Dew point6. Condensation nuclei7. Orographic lifting8. Coalescence9. Meteorology10.Air mass11.Jet stream12.Front13.High pressure system14.Low pressure system15.Thermometer

16.Barometer17.Anemometer18.Hygrometer19.Isopleths20.Supercells21.Tornado22.Fujita tornado intensity

scale23.Tropical cyclones

(hurricanes)24.Saffir-simpson scale25.Storm surge26.Climate27.Köppen classification

system28.Temperate zone29.Tropic zone30.Polar zone

• About 99 percent of the atmosphere is composed of nitrogen and oxygen, with the remaining one percent consisting of small amounts of argon, hydrogen, carbon dioxide, water vapor, and other gases.

Atmospheric Composition

Atmospheric Composition

Atmospheric Composition

Key Atmospheric Gases– Water is the only substance in the

atmosphere that exists in three states: solid, liquid, and gas.

– When water changes from one state to another, heat is either absorbed or released which greatly affects weather and climate.

Structure of the Atmosphere• The atmosphere is made up of several

different layers.

Atmospheric Composition

Lower Atmospheric Layers

– The troposphere – where most weather takes place and most air pollution collects

– The stratosphere - made up primarily of concentrated ozone.

Atmospheric CompositionUpper Atmospheric Layers

– The exosphere, the outermost layer of Earth’s atmosphere – composed of mostly hydrogen and helium.

– There is no clear boundary between the atmosphere and space.

– The mesosphere is above the stratosphere.

– The thermosphere is above the mesosphere.

What is Climate?• Climate describes annual variations of

temperature, precipitation, wind, and other weather variables. – The data used to describe an area’s

climate include daily high and low temperatures, amounts of rainfall, wind speed and direction, humidity, and air pressure.What Causes Climates?

• Climates vary greatly due to:• Latitude, topography, closeness to

lakes and oceans, global wind patterns, ocean currents, and air masses.

What Causes Climates?

Latitude– Earth is tilted on

its axis which affects how the Sun’s rays strike Earth’s surface and the amount of solar radiation received at any given place on Earth.

What Causes Climates?Topographic Effects– Large bodies of water heat up and cool down

more slowly than land. – Mountain climates are usually cooler because

temperature generally decreases with altitude.

Air Masses

– Two of the main causes of weather are the movement and interaction of air masses.

– Air masses form in one region and move to other regions.

How does the ocean effect climate?

•Over half the heat that reaches the earth from the sun is absorbed by the ocean's surface layer, so surface currents move a lot of heat.

•Currents that originate near the equator are warm; currents that flow from the poles are cold.

How does the ocean affect climate?

•Ocean water and currents affect the climate…it takes far more energy to change the temperature of water than land or air. Water warms up and cools off much more slowly than land or air.

• Inland climates are subject to more extreme temperature ranges than coastal climates, which are insulated by nearby water.

What about coastal regions?• Coastal regions experience a moderate

climate throughout the year.• The variation in specific heats of water and

land (soil) results in the unequal heating of the land and sea surfaces by sunlight.

• During the day land is heated quickly. The heated air rises and the comparatively cool air from the sea moves over the adjoining land area to replace the rising air. This air movement is called sea breeze.

• The reverse thing happens at night (land breeze). Thus the days are cooler and nights are warmer in coastal regions making a moderate climate throughout the year.

Koeppen Classification System• Koeppen distinguished different climatic zones

by natural vegetation.

Koeppen Classification SystemTropical Climates– Characterized by constant high temperatures. – Tropical wet and dry zones include savannas,

which are tropical grasslands.

Dry Climates

– Cover about 30 percent of Earth’s land area, make up the largest climatic zone.

– Precipitation is low, and vegetation is scarce.

Koeppen Classification SystemMild Climates– Mild climates can be classified into three

subtypes: humid subtropical climates, marine west coast climates, and mediterranean climates.

Continental Climates– Classified into three subtypes: warm summer

climates, cool summer climates, and subarctic climates.

– Both summer and winter temperatures can be extreme.

Koeppen Classification SystemPolar Climates– The polar climates are the coldest regions on

Earth. – Precipitation is generally low because cold air

holds less moisture than warm air.

Solar Fundamentals•The Sun is the source of all energy in the

atmosphere transferred through radiation, conduction and convection.

Temperature Versus Heat• Heat is the transfer of energy that fuels

atmospheric processes.• Temperature is used to measure and

interpret that energy.

•The temperature of the lower atmosphere decreases with increasing distance from Earth’s surface.

Vertical Temperature Changes

Temperature Versus HeatMeasuring Temperature– Fahrenheit (°F)– Celsius (°C)– Kelvin (K) – measures

absolute zero – where molecular motion stops

A Question of Balance•In meteorology, a crucial question is how

solar radiation is distributed around the planet. • The Sun feels hotter in the tropics because its rays strike Earth more directly, than it does in the polar regions where its rays strike Earth at a low angle.

• Because the Sun’s rays are more spread out when they strike Earth at a low angle, the same amount of energy is spread over a larger area.

What causes weather?

Balancing the Budget

– The continual motion of air and water reallocates heat energy among Earth’s surface, oceans, and atmosphere and brings it into balance.

– Virtually everything that we consider to be weather is part of a constant redistribution of Earth’s heat energy.

Air Masses

Air Mass Modification

– Air masses move, transferring heat from one area to another and thus establishing the heat balance.

– As an air mass moves, it starts to acquire some of the characteristics of the new surface beneath it.

Classifying Air Masses

– Air masses are classified according to their source regions. Ex. Polar, tropical, arctic

What are the classifications?•4 general air mass classifications

categorized according to the source region. ▫polar latitudes P - located poleward of 60

degrees north and south ▫tropical latitudes T - located within about 25

degrees of the equator ▫continental c - located over large land

masses--dry ▫marine m - located over the oceans----moist

•We can then make combinations of the above to describe various types of air masses.

Describing air mass types

▫cP continental polar - cold, dry, stable

▫cT continental tropical - hot, dry, stable air aloft--unstable surface air

▫mP maritime polar - cool, moist, and unstable

▫mT maritime tropical - warm, moist, usually unstable

FrontsCold Fronts– In a cold front, cold, dense air displaces warm

air and forces the warm air up along a steep front.– Clouds, showers, and thunderstorms

FrontsWarm Fronts– In a warm front, advancing warm air displaces

cold air.– A gradual frontal slope. – Characterized by

cloudiness and steady, widespread precipitation.

FrontsStationary Fronts– A stationary front is the result of two air masses

meeting and neither advancing into the other’s territory, stalling the boundary between them.

FrontsOccluded Fronts– An occluded front is the result of a cold air mass

overtaking a warm front, wedging the warm air upward.– Precipitation is common

Pressure SystemsHigh-Pressure Systems– In a high-pressure system, air sinks, so that

when it reaches Earth’s surface it spreads away from the center.

Pressure SystemsLow-Pressure Systems– In low-pressure systems, air rises, causing an

inward net flow toward the center and then upward.

Air Pressure and Density• Air pressure increases as you near the

bottom of the atmosphere because of the greater mass of the atmosphere above you. Wind

• Wind can be thought of as air moving from an area of high pressure to an area of low pressure.

• Wind speed generally increases with height in the atmosphere because there is less friction.

Pressure-Temperature-Density Relationship

•Temperature, pressure, and density are related.

• In the atmosphere, temperature is directly proportional to pressure.

• The relationship between temperature and density is inversely proportional.

Relative Humidity•Relative humidity varies

with temperature because warm air is capable of holding more moisture than cool air.

• Relative humidity is expressed as a percentage.

Global Wind Systems•There are three basic zones, or wind systems,

in each hemisphere.• Trade winds• Prevailing westerlies - responsible for

most of the weather movement in US and Canada

• Polar easterlies – characterized by cold air

Global Wind Systems

Jet StreamsLarge-Scale Weather Systems– Weather systems generally follow the path of the

jet stream. – The jet stream affects the intensity of weather

systems by moving air of different temperatures from one region to another.

Cloud Formation•Buoyancy is the tendency for air to rise or

sink as a result of differences in density. • Clouds form when warm, moist air rises,

expands, and cools in a convection current resulting in cloud formation.

Types of Clouds

Gathering Weather Data•Meteorologists measure the atmospheric

variables of temperature, air pressure, wind, and relative humidity to make accurate weather forecasts.

• Two of the most important factors in weather forecasting are the accuracy and the density of the data, or the amount of data available.

Weather Radar

Doppler Radar

– Meteorologists use Doppler radar, which is based on the Doppler effect, to plot the speed at which raindrops move toward or away from a radar station.

• A weather radar system is used to pinpoint where rain is falling.

Weather Satellites•One of the main uses of satellites in orbit

around Earth is to observe weather.

• Satellites track clouds but not necessarily precipitation.

Weather SatellitesInfrared Imagery– Infrared images allow meteorologists to

determine the temperature of a cloud and infer the type it is and estimate its height, which is related to strength.

Surface Analysis•To plot data nationwide or globally,

meteorologists use isopleths.• Isopleths are lines that connect points of

equal or constant values, such as pressure

or temperature. – Lines of equal pressure are called isobars.– Lines of equal temperature are called

isotherms.

Surface Analysis•Isobars also indicate the locations of high-

and low-pressure systems.

Short-Term Forecasts•Weather systems change directions, speed,

and intensity with time in response to changes in the upper atmosphere.

ForecastsDigital Forecasts– Digital forecasting is the main method used by

modern meteorologists and it is highly dependent on the density of the data available.

Analog Forecasts– Analog forecasting is useful for conducting

monthly or seasonal forecasts, which are based mainly on the past behavior of cyclic weather patterns.

Long-Term ForecastsAccuracy Declines with Time– Long-term forecasts involving months

and seasons are based largely onpatterns or cycles involving changes in the atmosphere, ocean currents, and solar activity.

• The most accurate and detailed forecasts are short-term in nature.

The Weather Station Model

©Steve Kluge 2007 Some images from the NYSED Earth Science Reference Tables

Get accompanying notes here

Draw a Station Model

Decoding the Coded Pressure

196

Insert a decimal point to the left of the last digit

19.6

Put a “9” or “10” in front of the result

Place a “9” in front if the value is higher than 500.Place a “10” in front if the value is lower than 500.

Coded pressure 196= 1019.6 mbDecode these coded pressures: 002 993 280

000

1000.2

999.3 1028.0

1000.0

Back to the Station Model

How to encode pressures

©S. Kluge 2007

Encoding the Pressure

1013.5

Remove the decimal point

10135 Report the last 3 digits

135

Pressure 1013.5 = 135 encoded pressureEncode these pressures: 1032.7 987.3 1012.2 1000.1

327 873 122 001

Back to the Station Model Back to Decoding Pressures

©S. Kluge 2007

The Barometric Trend + 19 /

+ means “Higher now than it was 3 hours ago”(- means “Lower now than it was 3 hours

ago”)19 means the pressure has changed by

1.9 mb / means the pressure is currently rising

( \ means the pressure is currently

falling)

Back to the Station Model

What was the pressure 3 hours ago?

Here?

1017.7 1003.5

©S. Kluge 2007

Back to the Station Model

©S. Kluge 2007

Back to the Station Model

NE at 25 Knots

E at 5 Knots

SE at 10 Knots

©S. Kluge 2007

Temperature= 45FDewpoint= 32FWind NE at 20 knotsOvercastVisibility= 1.5 milesRain ShowersPressure Now= 997.3 mbPressure 3 hrs. ago= 1000.2mbBarometer FallingPrecipitation in last 6 hrs.= .53 in.

Draw a Station Model for These Conditions:

©S. Kluge 2007

Back to the Station Model

How Thunderstorms Form•For a thunderstorm to form, three

conditions must exist. 1. An abundant source of moisture. 2. The lifting of air so that the moisture can condense and

release latent heat. 3. The portion of the atmosphere through which the cloud

grows must be unstable.

All thunderstorms, regardless of intensity, have certain characteristics in common.

Stages of Development•A thunderstorm usually has three stages: the

cumulus stage, the mature stage, and the dissipation stage.

The stages are classified according to the direction in which the air is moving.

Tornadoes•A tornado is a violent, whirling column of

air in contact with the ground. Before a tornado reaches the ground, it is

called a funnel cloud.

The air in a tornado is made visible by dust and debris drawn into the swirling column, or by the condensation of water vapor into a visible cloud.

Tropical CyclonesFormation of Tropical Cyclones– Tropical cyclones require two basic conditions to form:

1. An abundant supply of very warm ocean water2. Some sort of disturbance to lift warm air and

keep it rising

– They occur most frequently in the late summer and early fall, when Earth’s oceans contain their greatest amount of stored heat energy.

Tropical CyclonesMovement of Tropical Cyclones– Tropical cyclones move according to the wind currents that steer

them.

Classifying Hurricanes

The Saffir-Simpson hurricane scale ranges from Category 1 hurricanes to Category 5 storms, which can have winds in excess of 155 mph.

Hurricane HazardsStorm Surges– A storm surge occurs when hurricane-force winds drive a

mound of ocean water, sometimes as high as 6 m above normal sea level, toward coastal areas where it washes over the land.

– Floods are an additional hurricane hazard.

Test Review•Terms: Storm surge, exosphere,

troposphere, mesosphere, stratosphere, thermosphere, doppler effect, station model, dew point, condensation nuclei, coalescence

•What do severe thunderstorms need to form?•What are associated with severe

thunderstorms?•Weather vs. climate•Compare and contrast characteristics of low

pressure systems and high pressure systems. What are types of weather associated with each? Draw the symbols of each.

Test Review•What are the 2 main gases making up the

atmosphere?•Air masses – what are they? Know the types

and how to place them on a map (cT, cP, cA, mT, mP)

•What are the 3 methods of energy transfer?•Atmosphere layers - describe temp. changes in

each layer; why does the temperature increase with height in the stratosphere?

•Is weather forecasting more accurate today than 100 years ago? Why?

•What are isopleths? Isobars? Isotherms?

Test Review•Be able to draw a station model from

given data.

The Weather Station Model

©Steve Kluge 2007 Some images from the NYSED Earth Science Reference Tables

Get accompanying notes here

Draw a Station Model

Decoding the Coded Pressure

196

Insert a decimal point to the left of the last digit

19.6

Put a “9” and a “10” in front of the result

919.6 1019.6Test the results against the range of normal atmospheric pressures 919.6 is below the range of normal pressures….

REJECTED!

1019.6 is within the range of normal pressures….

ACCEPTED!

Coded pressure 196= 1019.6 mbDecode these coded pressures: 002 993 280

000 1000.2

999.3 1028.0

1000.0

Back to the Station Model

How to encode pressures

©S. Kluge 2007

Encoding the Pressure

1013.5

Remove the decimal point

10135 Report the last 3 digits

135

Pressure 1013.5 = 135 encoded pressureEncode these pressures: 1032.7 987.3 1012.2 1000.1

327 873 122 001

Back to the Station Model Back to Decoding Pressures

©S. Kluge 2007

The Barometric Trend + 19 /

+ means “Higher now than it was 3 hours ago”(- means “Lower now than it was 3 hours

ago”)19 means the pressure has changed by

1.9 mb / means the pressure is currently rising

( \ means the pressure is currently

falling)

Back to the Station Model

What was the pressure 3 hours ago?

Here?

1017.7 1003.5

©S. Kluge 2007

Back to the Station Model

©S. Kluge 2007

Back to the Station Model

NE at 25 Knots

E at 5 Knots

SE at 10 Knots

©S. Kluge 2007

Temperature= 45FDewpoint= 32FWind NE at 20 knotsOvercastVisibility= 1.5 milesRain ShowersPressure Now= 997.3 mbPressure 3 hrs. ago= 1000.2mbBarometer FallingPrecipitation in last 6 hrs.= .53 in.

Draw a Station Model for These Conditions:

©S. Kluge 2007

Back to the Station Model