INTRODUCTION TO GEOGRAPHY
WEATHER & CLIMATE WEEK
Instructor: Matt Letts (matthew.letts@uleth.ca, UHall C850)
Office Hours: Tuesday 13h30 – 15h00
SESSION GOALS:
•Geography majors
Learn about the fundamentals of
meteorology to prepare you for
Weather & Climate 2015
•Non Geography majors
Understand the atmosphere around
you and interpret a surface weather
map
WEATHER & CLIMATE
WEEK 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 & CLIMATE
WEEK 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
K TO SPACE=31
L
L TO SPACE=69
100-31-69=0
100
Heat transfer
7+24=31 !
Compensates
for radiation
imbalance at
surface
ABSORPTION
46+19+4=69
L<K !!
46-15=31
Source: NOAA
White snow
Old snow
Vegetation
Light colour soil
Dark colour soil
Clouds
Calm water
0.80-0.95
0.40-0.60
0.15-0.30
0.25-0.40
0.10
0.50-0.90
0.10 (midday)
7.5 cm Air Temperatures at Lakeview Ridge, WLNP
7.5 cm Air Temperature (C)
45
SW Facing
40
NW Facing
NE Facing
35
SE Facing
30
25
20
15
10
5
0
Aug 18
Aug 19
Aug 20
Aug 21
Aug 22, 2005
Current weather conditions
09h00
October 23,
2006
Cloudy
Temp.:
+7°C
Pressure:
Visibility:
101.8
kPa
48km
Humidity:
54%
DewPoint:
-1°C
Wind:
WNW 26
km/h
http://weatheroffice.ec.gc.ca/city/pages/ab-30_metric_e.html
Radiation Sensors
(PAR and K)
Thermometer
(thermister)
held within
a Gill Radiation
Shield
SENSIBLE
HEAT
Raingauge
Datalogger
Hurricane Katrina (August 29, 2005)
Lethbridge, Alberta
Photo: CBC
1928
1979
2000
Photos: National Snow and Ice Data Center
Upsala Glacier, Argentina
Source: IPCC
Weather
Climate
a) air temperature
b) atmospheric pressure
c) humidity
d) clouds
e) precipitation
f) visibility
g) wind
Long term averages
of weather (eg. 30 y)
Means
Extremes
Variability
200
Precip
180
20
Temp
15
140
120
10
100
5
80
60
0
40
-5
20
0
-10
160
Precipitation (mm)
Precipitation (mm)
160
200
25
Temperature (degrees C)
180
VANCOUVER, BC
25
Precip
20
Temp
15
140
120
10
100
5
80
60
0
40
-5
20
0
-10
J F M A M J J A S O N D
J F M A M J J A S O N D
Month
Month
Temperature (degrees C)
LETHBRIDGE, AB
Source: Ahrens (1994)
Source: Solomon, 2000
Definition:
The difference in
atmospheric
pressure per unit
distance
PGF acts at right
angles to isobars
of equal pressure
H
L
102.2
99.8
101.4
100.6
600 km
Pressure Gradient Force = 2.4 kPa / 600 km
= 0.4 kPa / 100 km
“Don’t try this at home”
Where are winds strongest ?
Oct 18, 2004 Solution: HUDSON BAY
Check the spacing of the isobars of equal surface pressure
Source: NASA
Surface roughness decreases wind speed
Reduces impact of Inertial Coriolis Force
Winds cross isobars, spiralling out of
ANTICYCLONES (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
ICE CAP
TUNDRA
BOREAL
MIXED TEMPERATE
BROADLEAF
DESERT
SAVANNA
RAIN FOREST
SAVANNA
DESERT
MIXED TEMPERATE
TUNDRA
ICE CAP
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 molecules
would exert if the air were saturated
(at a given temperature)
Absolute stability
Temperature decreases with altitude
more slowly than MALR
(ELR > -6C/km)
Temperature decreases with altitude
more quickly than the DALR
(ELR < -10C /km)
Cooling
At MALR
6°C/km
Cooling
At MALR
6°C/km
X
VANCOUVER
8°C
Warming
At DALR
10 °C/km
Warming
At DALR
10 °C/km
Cooling
At DALR
10 °C/km
X
LETHBRIDGE
12°C
More sensible heat
Solar heating of Earth’s surface
Warm air advection at surface
Air moving over a warm surface
Cold advection
Radiational cooling of clouds
See weather.unisys.com
0600h GMT
APRIL 5
2003
NORTHEAST
WINDS
SHARP
COLD
FRONT
WARM,
MOIST
SOUTHERLY
FLOW
www.atmos.washington.edu
Cumulative index of daily Tavg < 18C
Cumulative index of daily Tavg > 18C
GROWING DEGREE DAYS
Cumulative index of daily Tavg > 4C
CORN HEAT UNITS
Cumulative index of daily Tavg > 10C