TonightTonightSept 7Sept 7

• Weather Review Weather Review

• Weather map basics Weather map basics

• Energy that Drives the Storms (chapter 2)Energy that Drives the Storms (chapter 2)

• More Weather Maps (Isopleths)More Weather Maps (Isopleths)

• Classwork (HW#3)Classwork (HW#3)

• Homework #4Homework #4

Weather ReviewWeather ReviewHrcn Earl

Visible

Weather ReviewWeather ReviewHrcn Earl

Infrared (IR)

Weather ReviewWeather ReviewHrcn Earl

Enhanced IR

Weather ReviewWeather ReviewHrcn Earl

Visible

Weather ReviewWeather Review

“Hurricane Force Wind Gusts”•Criteria: 1-minute sustained winds ≥ 74 mph•Peak 3 to 5-second gusts ~ 30% higher

•Exerted Force: proportional to the square of the wind speed

• Force from a 74 mph gust = 14.0 psf• Force from a 96 mph gust = 23.6 psf

• 69% higher.

Weather ReviewWeather ReviewTS Hermine

Visible

Weather ReviewWeather ReviewTS Hermine

Infrared

Weather ReviewWeather ReviewTS Hermine

Enhance Infrared

Weather ReviewWeather ReviewTS Hermine

Radar

Weather ReviewWeather ReviewTS Hermine

QPF

Weather Symbols and MapsWeather Symbols and Maps

Station modelStation model

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Weather SymbolsWeather Symbols

Sky SymbolsSky Symbols

Wind SymbolsWind Symbols

Pressure TendencyPressure Tendency

Station modelStation model

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Station modelStation model

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TemperatureTemperatureSurface: Surface: ºFºFUpper air: ºCUpper air: ºC

Station modelStation model

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Dew point temperatureDew point temperatureSurface: Surface: ºFºFUpper air: ºCUpper air: ºC

Station modelStation model

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TotalTotal sky coversky cover** Depicted by shading** Depicted by shading

in circlein circle

Station modelStation model

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Current weather conditionsCurrent weather conditions** If blank, “no weather”** If blank, “no weather”

Station modelStation model

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Wind direction – of wind Wind direction – of wind toward centertoward center

Station modelStation model

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Wind speedWind speedLong barb = 10 knotsLong barb = 10 knotsShort barb = 5 knotsShort barb = 5 knotsFlag = 50 knotsFlag = 50 knots** Notice range of wind speeds (i.e., 28-32 ** Notice range of wind speeds (i.e., 28-32 knots)knots)

Station modelStation model

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Sea level pressureSea level pressure**If first number is 5 or greater, then place 9 in **If first number is 5 or greater, then place 9 in frontfront --Otherwise, place 10 in front--Otherwise, place 10 in front**Place decimal point between last two **Place decimal point between last two numbersnumbers

Station modelStation model

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Change in surface pressure Change in surface pressure during last 3 hoursduring last 3 hours** In tenths of mb** In tenths of mb** Line describes how pressure changes over ** Line describes how pressure changes over time from left to righttime from left to right

Example 1Example 1• Temperature: 76 Temperature: 76 ºFºF• Dew point: 65 ºFDew point: 65 ºF• Sky cover: Completely Sky cover: Completely

overcastovercast• Current weather: Light rainCurrent weather: Light rain• Wind direction and speed: Wind direction and speed:

Southwest at 15 knotsSouthwest at 15 knots• Sea level pressure: 995.3 mbSea level pressure: 995.3 mb• Pressure tendency: Increase Pressure tendency: Increase

of 1.6 mb; rising steadily of 1.6 mb; rising steadily

7676

6565

953953+16+16

Example 2Example 2

1010

88

105105-4-4

•Temperature: 10ºFTemperature: 10ºF•Dew point: 8ºFDew point: 8ºF•Sky cover: 7/10 or 8/10Sky cover: 7/10 or 8/10•Current weather: Snow Current weather: Snow showershower•Wind direction and speed: Wind direction and speed: North at 3-7 knotsNorth at 3-7 knots•Sea level pressure: 1010.5 Sea level pressure: 1010.5 mbmb•Pressure tendency: Decrease Pressure tendency: Decrease of 0.4 mb; falling, then steadyof 0.4 mb; falling, then steady

High & Low Pressure SystemsHigh & Low Pressure Systems

° Air pressure Patterns are main organizing Air pressure Patterns are main organizing featurefeature

° Circulation in Northern HemisphereCirculation in Northern Hemisphere° Clockwise around Highs (H)Clockwise around Highs (H)° CCW around Lows (L)CCW around Lows (L)

° Clouds & Precip around LowsClouds & Precip around Lows° Temperature patterns result from latitude, wind Temperature patterns result from latitude, wind

flow and cloud coverflow and cloud cover

Plotting FrontsPlotting Fronts

° Boundary Boundary between between Different Air Different Air MassesMasses

° Types of Types of FrontsFronts

Weather MapsWeather Maps

Weather MapsWeather Maps

Weather MapsWeather Maps

Weather MapsWeather Maps

Weather MapsWeather Maps

Weather MapsWeather Maps

Weather MapsWeather Maps

CHAPTER 2

ENERGY THAT DRIVES THE STORMS

CHAPTER 2

ENERGY THAT DRIVES THE STORMS

ENERGY AND HEAT TRANSFER ENERGY AND HEAT TRANSFER • Energy is the capacity to do

work on some form of matter– Potential energy: The total

amount of energy stored in any object is capable of doing

– Kinetic energy: Any moving substance possesses energy of motion

Fig. 2.1, p. 37

Cold Air vs. Warm AirCold Air vs. Warm Air

Slower and closer together ….. Faster and farther apart

ENERGY AND HEAT TRANSFER

• Atoms and molecules have kinetic energy due to their motion (heat energy)

• Most important energy in terms of weather and climate is radiant energy from the sun

• Air temperature is a measure of the average kinetic energy of its molecules

ENERGY AND HEAT TRANSFERENERGY AND HEAT TRANSFER

• Heat is energy being transferred from one object to another because of a temperature difference

• After heat is transferred, it is stored as internal energy

• Heat is transferred in the atmosphere by – Conduction– Convection– Radiation

ENERGY AND HEAT TRANSFERENERGY AND HEAT TRANSFER

• Latent heat: energy required to change a substance, such as water, from one state to another

• Evaporation is a cooling process due to absorption of latent heat from the environment

• Condensation is a warming process due to a release of latent heat to the environment

Fig. 2.2, p. 37

Changes of State

ENERGY AND HEAT TRANSFERENERGY AND HEAT TRANSFER

• Conduction: the transfer of heat from molecule to molecule– Always flows from warmer to colder– Air is an extremely poor conductor of heat

ENERGY AND HEAT TRANSFERENERGY AND HEAT TRANSFER

• Convection: transfer of heat by the mass movement of a fluid (water or air)– Example: Pan of boiling water

• Convection circulation: warm air expands and rises then cools and sinks– Thermal cell, convection, thermals

Fig. 2.5, p. 40

Thermal CirculationsThermal Circulations

Fig. 2.6, p. 40

Thermal CirculationsThermal Circulations

ENERGY AND HEAT TRANSFERENERGY AND HEAT TRANSFER

• Radiation: Energy in the form of electromagnetic waves

• Radiation and Temperature– Hotter objects

• Emit shorter wavelengths• Emit radiation at a greater rate or intensity

Fig. 2.7, p. 41

Electromagnetic RadiationElectromagnetic Radiation

ENERGY BALANCING ACTENERGY BALANCING ACT

• Radiation of the Sun and Earth– Sun (6000 K) emits mostly shortwave radiation– Earth emits mostly longwave radiation

Fig. 2.8, p. 44

SUN’S ELECTROMAGNETIC SPRECTRUMSUN’S ELECTROMAGNETIC SPRECTRUM

Mostly shorter wavelengths

Fig. 2.9, p. 44

SUNSUN

EARTHEARTH

ElectromagneticElectromagneticRadiationRadiation

ENERGY BALANCING ACTENERGY BALANCING ACT

• Selective Absorbers:– Good absorbers are good emitters at a particular

wavelength, and vice versa.– Greenhouse effect: the atmosphere selectively

absorbs infrared radiation from the Earth’s surface but acts as a window and transmits shortwave radiation

Fig. 2.10, p. 46

Atmospheric Atmospheric Absorption of Absorption of

RadiationRadiation

A GREENHOUSEA GREENHOUSE• Glass is transparent to Glass is transparent to

short visible short visible wavelengths (SW) but wavelengths (SW) but opaque to long opaque to long infrared (LW) infrared (LW) wavelengths.wavelengths.

w/o GREENHOUSE GASESw/o GREENHOUSE GASES

w/ GREENHOUSE GASESw/ GREENHOUSE GASES

ENERGY BALANCING ACT

• Greenhouse Enhancement– Global warming is occurring due to an increase in

greenhouse gases• Carbon dioxide, methane, nitrogen oxide,

chloroflourocarbons (CFCs)

– Positive feedbacks continue the warming trend.– Negative feedbacks decrease warming.

Positive FeedbackPositive Feedback• When the response in a second variable reinforces the When the response in a second variable reinforces the

change in the initial variablechange in the initial variable• Example of positive feedback:Example of positive feedback:

– Global temperatures increaseGlobal temperatures increase– Increase in temperature melts the ice and snow in Increase in temperature melts the ice and snow in

the upper latitudesthe upper latitudes– Loss of ice and snow results in a lower albedo at the Loss of ice and snow results in a lower albedo at the

surface in the upper latitudessurface in the upper latitudes– Lower albedo leads to less reflection and more Lower albedo leads to less reflection and more

insolationinsolation– More insolation results in warmer temperaturesMore insolation results in warmer temperatures

Negative FeedbackNegative Feedback• When the response in a second variable lessens the When the response in a second variable lessens the

change caused by the initial variablechange caused by the initial variable• Example of negative feedback:Example of negative feedback:

– Global warming leads to more atmospheric water Global warming leads to more atmospheric water vaporvapor

– Increased water vapor leads to increased cloud coverIncreased water vapor leads to increased cloud cover– Increased cloud cover leads to a higher albedoIncreased cloud cover leads to a higher albedo– Higher albedo results in less insolation at the surfaceHigher albedo results in less insolation at the surface– Reduced insolation at the surface leads to coolingReduced insolation at the surface leads to cooling

Fig. 2.13, p. 50

Solar RadiationSolar Radiation

ALBEDOALBEDO• Percent of Percent of

sunlight sunlight reflected from reflected from clouds and clouds and earth surfacesearth surfaces

• Earth average Earth average albedo = 30%albedo = 30%

SurfaceSurface Albedo (%)Albedo (%)Earth and Atmosphere 30Clouds (Thick) 60-90Clouds (Thin) 30-50Fresh Snow 75-95Ice 30-40Sand 15-45Grassy Field 10-30Plowed Field 5-20Water 10Moon 7

Fig. 2.14, p. 51

Atmospheric Energy BalanceAtmospheric Energy Balance

ENERGY BALANCING ACTENERGY BALANCING ACT

• Annual Energy Balance– 50% of insolation reaches the earth’s surface– Earth absorbs 147 units, radiates 117 units

• 30 unit surplus, warm

– Atmosphere absorbs 130 units, radiates 160 units• 30 unit deficit, cool

– Tropics have a surplus of energy

Fig. 2.15, p. 52

Global Energy BalanceGlobal Energy Balance

ENERGY BALANCEENERGY BALANCE

WHY THE EARTH HAS SEASONS WHY THE EARTH HAS SEASONS

• Earth revolves in elliptical path around sun every 365 days.

• Earth rotates counterclockwise or eastward every 24 hours.

• Earth closest to sun (147 million km) in January, farthest from sun (152 million km) in July.

• Distance not the only factor impacting seasons.

Fig. 2.16, p. 52

Elliptical OrbitElliptical Orbit

Fig. 2.17, p. 53

Sun AngleSun Angle

WHY THE EARTH HAS SEASONS

• Energy reaching the earth’s surface, result of:– Distance from the sun– Solar angle– Length of daylight.

• Earth tilted toward the sun:– Higher solar angles and longer days

Fig. 2.20, p. 56

Sun AngleSun Angle

Fig. 2.18, p. 53

Sun and the SeasonsSun and the Seasons

WHY THE EARTH HAS SEASONS

• Seasons in the Northern Hemisphere– Summer solstice: ~ June 21

• Sun directly above Tropic of Cancer (23.5° N) • Longer days in N Hemisphere

– Winter solstice: ~ December 21• Sun directly above Tropic of Capricorn (23.5° S)• Shorter days in S Hemisphere

– Autumnal and Vernal Equinox: ~ Sep 22, Mar 20• Sun directly above Equator• All locations have a 12 hour day

Table 2.3, p. 57

Stepped Art

Fig. 2.22, p. 58

Sun’s Seasonal PathSun’s Seasonal Path

Fig. 2.19, p. 56

Sun’s Seasonal PathSun’s Seasonal Path

WHY THE EARTH HAS SEASONS

• Seasons in the Southern Hemisphere– Opposite timing of N Hemisphere– Closer to sun in summer but not significant

difference

ISOPLETHSISOPLETHS

Contour MapsContour Maps

Contour MapsContour Maps

Contour MapsContour Maps

ISOBARSISOBARS

ISOTHERMSISOTHERMS

ISOTACHSISOTACHS

ISOHYETISOHYET

ISOPLETHSISOPLETHS° Connects all points that have the same valueConnects all points that have the same value° Iso = equal (Greek)Iso = equal (Greek)° Also called “Isolines”Also called “Isolines”° TypesTypes

° Isobar = pressureIsobar = pressure° Isallobar = pressure change per timeIsallobar = pressure change per time° Isotherm = temperatureIsotherm = temperature° Isohyet = rainfallIsohyet = rainfall° Isonif = snowfallIsonif = snowfall° Isoryme = frost incidenceIsoryme = frost incidence° isoneph = cloudiness° isotach = wind speed

ISOPLETHS ISOPLETHS (cont’d)(cont’d)

° RulesRules° Only through exact value of isoplethOnly through exact value of isopleth° Higher side and lower sideHigher side and lower side° All higher should be on the same side of the All higher should be on the same side of the

lineline° Draw for all valuesDraw for all values° Spacing by interpolationSpacing by interpolation° Spacing indicates rate of change (I.e., gradient)Spacing indicates rate of change (I.e., gradient)° Isopleths form closed loopsIsopleths form closed loops° Isopleth never cross one anotherIsopleth never cross one another

ISOPLETHS ISOPLETHS (cont’d)(cont’d)

• DRAWING HINTSDRAWING HINTS– Note location of lowest and highest valuesNote location of lowest and highest values– Begin around these low or high values and Begin around these low or high values and

gradually work outwardgradually work outward– Sketch lightly to get spacing and orientation of Sketch lightly to get spacing and orientation of – Smooth the isopleths. Isopleths generally do Smooth the isopleths. Isopleths generally do

not have sharp bendsnot have sharp bends

ISOPLETHSISOPLETHS Draw 6.5 contourDraw 6.5 contour

ISOPLETHSISOPLETHS

ISOPLETHSISOPLETHS Draw even contoursDraw even contours

ISOPLETHSISOPLETHS

ISOTHERMSISOTHERMS Draw 10, 20, 30,40, 50, Draw 10, 20, 30,40, 50, 60, 70 degree contours60, 70 degree contours

ISOTHERMSISOTHERMS

Isodrosotherms Isodrosotherms

IsodrosothermsIsodrosotherms

HOMEWORK #4HOMEWORK #4Draw Isotherms at 10 degree intervals( i.e., 50, 60, 70, 80, 90 degrees).

Due next week (9/14/09) Due next week (9/14/09) at the beginning of class.at the beginning of class.