WEATHER & CLIMATE WEEKInstructor: Matt Letts (matthew.letts@uleth.ca, UHall C850)Office Hours: Tuesday 13h30 – 15h00

INTRODUCTION TO GEOGRAPHY

SESSION GOALS:•Geography majorsLearn about the fundamentals ofmeteorology to prepare you for Weather & Climate 2015

•Non Geography majorsUnderstand the atmosphere aroundyou and interpret a surface weathermap

WEATHER & CLIMATEWEEK CONTENTS

1. Our Energy Source- The Sun- Radiation Emission- What Causes Seasons?- Earth’s Radiation Balance

2. Weather vs. Climate- Weather & Climate Defined (p. 233)- Why Study Weather?

3. Atmospheric Circulation- Air Pressure is Everywhere (p. 271-273)- Forces Acting to Create Wind (p. 274-281)- Global Atmospheric Circulation (p. 281-290)

WEATHER & CLIMATEWEEK CONTENTS

4. The Importance of Water Vapour- Specific & Relative Humidity- Vapour Pressure

5. Instability and Cloud Formation- Causes of Instability (p. 238)- Causes of Precipitation (p. 237-243)

6. Analysis of Surface Weather Maps- Understanding Weather Symbols (p. 244)- The Mid-latitude Cyclone (p. 243-256)

Optional Reading:http://www.physicalgeography.net/fundamentals/chapter7.html

Stefan-Boltzmann Law

As the temperature of an object increases, more radiation is emitted each second

Energy emitted = (T0)4

Wien’s Displacement Law

As the temperature of a body increases, so does the proportion of shorter wavelengths

See: http://weather.msfc.nasa.gov/cgi-bin/post-goes

Day and Night (09h00 MDT, Oct 23, 2006)

http://www.fourmilab.ch/cgi-bin/uncgi/Earth/action?opt=-p

Source: NOAA

ABSORPTION

K TO SPACE=31

L<K !!

Heat transfer7+24=31 !Compensatesfor radiationimbalance atsurface

L

46+19+4=69

L TO SPACE=69

100

46-15=31

100-31-69=0

White snow 0.80-0.95Old snow 0.40-0.60Vegetation 0.15-0.30Light colour soil 0.25-0.40Dark colour soil 0.10Clouds 0.50-0.90Calm water 0.10 (midday)

0

5

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45

SW Facing

NW Facing

NE Facing

SE Facing

7.5

cm A

ir T

emp

erat

ure

(C

)

Aug 18 Aug 19 Aug 21 Aug 22, 2005Aug 20

7.5 cm Air Temperatures at Lakeview Ridge, WLNP

Current weather conditions                    

CloudyTemp.: +7°C

Pressure: 101.8kPa

Visibility: 48km

Humidity: 54%

DewPoint: -1°C

Wind: WNW 26km/h

09h00October 23, 2006

http://weatheroffice.ec.gc.ca/city/pages/ab-30_metric_e.html

Thermometer(thermister)held withina Gill RadiationShield

SENSIBLEHEAT

Radiation Sensors(PAR and K)

Raingauge

Datalogger

Hurricane Katrina (August 29, 2005)

Lethbridge, Alberta

Photo: CBC

Photos: National Snow and Ice Data Center

1928 1979 2000

                                                                                                                       

Upsala Glacier, Argentina

Source: IPCC

WeatherWeather ClimateClimatea) air temperature a) air temperature Long term averagesLong term averagesb) atmospheric pressure b) atmospheric pressure of weather (eg. 30 y)of weather (eg. 30 y)c) humidity c) humidity d) clouds d) clouds MeansMeanse) precipitation e) precipitation ExtremesExtremesf) visibilityf) visibility VariabilityVariabilityg) windg) wind

0

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J F M A M J J A S O N D

Month

Pre

cip

itat

ion

(m

m)

-10

-5

0

5

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25

Tem

per

atu

re (

deg

rees

C)

Precip

Temp

LETHBRIDGE, AB VANCOUVER, BC

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J F M A M J J A S O N D

Month

Pre

cip

itat

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m)

-10

-5

0

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25

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per

atu

re (

deg

rees

C)

Precip

Temp

Source: Ahrens (1994)

Source: Solomon, 2000

                                                                                                                                                                           

H L102.2 99.8

101.4 100.6

600 km

Pressure Gradient Force = 2.4 kPa / 600 km= 0.4 kPa / 100 km

Definition:

The difference inatmosphericpressure per unitdistance

PGF acts at rightangles to isobarsof equal pressure

“Don’t try this at home”

Where are winds strongest ?

Oct 18, 2004 Solution: HUDSON BAYCheck the spacing of the isobars of equal surface pressure

Source: NASA

Surface roughness decreases wind speedReduces impact of Inertial Coriolis Force

Winds cross isobars, spiralling out ofANTICYCLONES (H), and into CYCLONES (L)

H L

weather.unisys.com

H L

Air tends to be unstable in low pressure (tendency to rise)Air tends to be stable in high pressure (tendency to fall)

1. Equatorial Low Pressure Trough

2. Subtropical High Pressure Cells

3. Subpolar Low Pressure Cells

4. Weak Polar High Pressure Cells

RAIN FOREST

SAVANNA

SAVANNA

DESERT

DESERT

BROADLEAF

BOREALTUNDRAICE CAP

ICE CAP

TUNDRA

MIXED TEMPERATE

MIXED TEMPERATE

A ratio that compares the amount of water vapour in the air to the maximum water vapour capacity at that temperature

The relative humidity of saturated air is 100%

 RH = [H20 vapour content/H20 capacity] x 100

The portion of atmospheric pressure that is made up of water vapour molecules (mb or kPa)

SATURATION VAPOUR PRESSURE:The pressure that water vapour moleculeswould exert if the air were saturated(at a given temperature)

Absolute stability

Temperature decreases with altitudemore slowly than MALR (ELR > -6C/km)

Temperature decreases with altitudemore quickly than the DALR(ELR < -10C /km)

VANCOUVER LETHBRIDGE8°C 12°C

X X

CoolingAt MALR6°C/km

WarmingAt DALR10 °C/km

CoolingAt DALR10 °C/km

CoolingAt MALR6°C/km

WarmingAt DALR10 °C/km

More sensible heat

Cold advectionRadiational cooling of clouds

Solar heating of Earth’s surfaceWarm air advection at surfaceAir moving over a warm surface

See weather.unisys.com

SHARPCOLDFRONT

WARM,MOISTSOUTHERLYFLOW

NORTH-EASTWINDS

www.atmos.washington.edu

0600h GMTAPRIL 52003

GROWING DEGREE DAYSGROWING DEGREE DAYS

CORN HEAT UNITSCORN HEAT UNITS

Cumulative index of daily Tavg < 18C

Cumulative index of daily Tavg > 18C

Cumulative index of daily Tavg > 4C

Cumulative index of daily Tavg > 10C