WEATHER & CLIMATE
Dr. Matthew G. Letts
Associate Professor of Geography
Co-ordinator, Environmental Science Program
(matthew.letts@uleth.ca, WE 2052)
SESSION GOALS:
•Geography majors
Learn about the fundamentals of
meteorology to prepare you for
Weather & Climate 2300
•Non Geography majors
Understand the atmosphere around
you and interpret a surface weather
map
WEATHER & CLIMATE: Outline
1. Our Energy Source
- The Sun
- Radiation Emission
- What Causes Seasons?
- Earth’s Radiation Balance
2. Weather vs. Climate
- Weather & Climate Defined
- Why Study Weather?
3. Atmospheric Circulation
- Air Pressure is Everywhere
- Forces Acting to Create Wind
- Global Atmospheric Circulation
WEATHER & CLIMATE
WEEK CONTENTS
4. The Importance of Water Vapour
- Specific & Relative Humidity
- Vapour Pressure
5. Instability and Cloud Formation
- Causes of Instability
- Causes of Precipitation
6. Analysis of Surface Weather Maps
- Understanding Weather Symbols
- The Mid-latitude Cyclone
Readings: Chapters 2, 3, 4 and 5
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
http://www.goes.noaa.gov/FULLDISK/GWVS.JPG
Day and Night (Feb 28, 2011 06h31 UTC)
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
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
February 28,
2011
Current windchill
temperature = -27˚C
Cloudy
Temp.:
-17°C
Pressure:
Visibility:
101.2
kPa
8km
Humidity:
81%
DewPoint:
-19.5°C
Wind:
NW 21 G35
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
Weather Forecasting & Understanding Promote Preparedness
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
January Temperatures
July Temperatures
San Francisco
vs. Wichita
Note the daily range
Source: Ahrens (1994)
Source: Solomon, 2000
“Don’t try this at home”
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
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
convergence
divergence
H
L
divergence
convergence
Air tends to be unstable in low pressure (tendency to rise)
Air tends to be stable in high pressure (tendency to fall)
500 mb heights are higher in warm air masses
The PGF is directed from the equator poleward…
But winds get deflected to the right (west) by the
Coriolis effect (into the screen here)…
A jet stream forms along the polar front
(and helps to maintain the polar front)
Low pressure forms beneath divergence and
jet streaks (causes air to rise), and where cold and
warm air mix at the surface (warm air forced to rise).
High pressure forms beneath convergence (air descends).
37º
37º
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
Global Barometric Pressure
Global Barometric Pressure
Winter
monsoon
Summer
monsoon
Topography enhances monsoonal effects
Land–Water Heating Differences
Figure 3.20
The Sea Breeze
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
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
The distance between Earth and the Sun gradually
changes between perihelion and aphelion due to
a) the Solar System’s placement in the Milky Way.
b) the elliptical shape of Earth’s orbit.
c) solar fusion.
d) the solar wind.
e) variations in the speed of light.
The distance between Earth and the Sun gradually changes
between perihelion and aphelion due to
a) the Solar System’s placement in the Milky Way.
b) the elliptical shape of Earth’s orbit.
c) solar fusion.
d) the solar wind.
e) variations in the speed of light.
Which of the following statements about energy is
correct?
a) Earth emits less energy in the thermal infrared portion of
the EMS.
b) Energy in the form of near infrared radiation is emitted
by Earth.
c) The maximum energy output from the Sun is in the form
of UV radiation and visible light.
d) The maximum energy output from Earth is in the form of
UV radiation and visible light.
e) Both the Sun and Earth emit a large amount of energy in
the form of microwave radiation.
Which of the following statements about energy is
correct?
a) Earth emits less energy in the thermal infrared portion of
the EMS.
b) Energy in the form of near infrared radiation is emitted
by Earth.
c) The maximum energy output from the Sun is in the
form of UV radiation and visible light.
d) The maximum energy output from Earth is in the form of
UV radiation and visible light.
e) Both the Sun and Earth emit a large amount of energy in
the form of microwave radiation.
Which of the following statements regarding
seasonality is correct ?
a) Areas near 45º N latitude are experiencing “summer”
on December 21.
b) Areas near 45º N latitude are experiencing “winter” on
December 21.
c) Areas near 90º S latitude are experiencing equal
hours of day and night on March 21.
d) Areas near 90º N are experiencing 24 hours of
daylight on the winter solstice.
e) Areas near 45º S are experiencing equal hours of day
and night on June 21.
Which of the following statements regarding
seasonality is correct ?
a) Areas near 45º N latitude are experiencing “summer”
on December 21.
b) Areas near 45º N latitude are experiencing
“winter” on December 21.
c) Areas near 90º S latitude are experiencing equal
hours of day and night on March 21.
d) Areas near 90º N are experiencing 24 hours of
daylight on the winter solstice.
e) Areas near 45º S are experiencing equal hours of day
and night on June 21.
Temperature generally rises with height in the stratosphere
due to the presence of _____, which absorbs incoming
ultraviolet radiation.
a) methane
b) chlorofluorocarbons
c) nitrogen
d) positively charged ions
e) ozone
Temperature generally rises with height in the stratosphere
due to the presence of _____, which absorbs incoming
ultraviolet radiation.
a) methane
b) chlorofluorocarbons
c) nitrogen
d) positively charged ions
e) ozone
Nitrogen is the most abundant gas in the homosphere.
Which gas is the next most abundant?
a) carbon dioxide
b) oxygen
c) water vapor
d) argon
e) methane
Nitrogen is the most abundant gas in the homosphere.
Which gas is the next most abundant?
a) carbon dioxide
b) oxygen
c) water vapor
d) argon
e) methane
Albedo is the percentage of incoming shortwave
radiation that is _____.
a) absorbed
b) reflected
c) scattered
d) emitted
e) refracted
Albedo is the percentage of incoming shortwave
radiation that is _____.
a) absorbed
b) reflected
c) scattered
d) emitted
e) refracted
A wind moving out of the northeast toward the
southwest would be correctly termed a(an) _____
wind.
a) easterly
b) northeasterly
c) southerly
d) southeasterly
e) northerly
A wind moving out of the northeast toward the
southwest would be correctly termed a(an) _____
wind.
a) easterly
b) northeasterly
c) southerly
d) southeasterly
e) northerly
The circling of winds into a low-pressure area or out
of a high-pressure area is principally due to the
effects of _____.
a) movement parallel to isobars
b) friction with the surface
c) gravity
d) pressure gradient
e) Coriolis force
The circling of winds into a low-pressure area or out
of a high-pressure area is principally due to the
effects of _____.
a) movement parallel to isobars
b) friction with the surface
c) gravity
d) pressure gradient
e) Coriolis force
Deflection of movement due to the Coriolis force in
the Northern Hemisphere is _____.
a) downward and to the left
b) to the left over water and to the right over land
c) upward (away from the surface)
d) to the left
e) to the right
Deflection of movement due to the Coriolis force in
the Northern Hemisphere is _____.
a) downward and to the left
b) to the left over water and to the right over land
c) upward (away from the surface)
d) to the left
e) to the right