Transcript Energy that Drives Storms, Isopleths

Tonight
Sept 7
• Weather Review
• Weather map basics
• Energy that Drives the Storms (chapter 2)
• More Weather Maps (Isopleths)
• Classwork (HW#3)
• Homework #4
Weather Review
Hrcn Earl
Visible
Weather Review
Hrcn Earl
Infrared (IR)
Weather Review
Hrcn Earl
Enhanced IR
Weather Review
Hrcn Earl
Visible
Weather 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 Review
TS Hermine
Visible
Weather Review
TS Hermine
Infrared
Weather Review
TS Hermine
Enhance
Infrared
Weather Review
TS Hermine
Radar
Weather Review
TS Hermine
QPF
Weather Symbols and Maps
Station model
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63
021
-23
Weather Symbols
Sky Symbols
Wind Symbols
Pressure Tendency
Station model
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Station model
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Temperature
Surface: ºF
Upper air: ºC
021
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Station model
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Dew point temperature
Surface: ºF
Upper air: ºC
Station model
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Total sky cover
** Depicted by shading
in circle
021
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Station model
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Current weather conditions
** If blank, “no weather”
Station model
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Wind direction – of wind
toward center
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Station model
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Wind speed
Long barb = 10 knots
Short barb = 5 knots
Flag = 50 knots
** Notice range of wind speeds (i.e., 28-32
knots)
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Station model
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Sea level pressure
**If first number is 5 or greater, then place 9 in
front
--Otherwise, place 10 in front
**Place decimal point between last two
numbers
Station model
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Change in surface pressure
during last 3 hours
** In tenths of mb
** Line describes how pressure changes over
time from left to right
Example 1
• Temperature: 76 ºF
• Dew point: 65 ºF
• Sky cover: Completely
overcast
• Current weather: Light rain
• Wind direction and speed:
Southwest at 15 knots
• Sea level pressure: 995.3 mb
• Pressure tendency: Increase
of 1.6 mb; rising steadily
76
65
953
+16
Example 2
•Temperature: 10ºF
•Dew point: 8ºF
•Sky cover: 7/10 or 8/10
•Current weather: Snow
shower
•Wind direction and speed:
North at 3-7 knots
•Sea level pressure: 1010.5
mb
•Pressure tendency: Decrease
of 0.4 mb; falling, then steady
10
8
105
-4
High & Low Pressure Systems
° Air pressure Patterns are main organizing
feature
° Circulation in Northern Hemisphere
° Clockwise around Highs (H)
° CCW around Lows (L)
° Clouds & Precip around Lows
° Temperature patterns result from latitude, wind
flow and cloud cover
Plotting Fronts
° Boundary
between
Different Air
Masses
° Types of
Fronts
Weather Maps
Weather Maps
Weather Maps
Weather Maps
Weather Maps
Weather Maps
Weather Maps
CHAPTER 2
ENERGY THAT DRIVES
THE STORMS
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
Cold Air vs. Warm Air
Slower and closer together ….. Faster and farther apart
Fig. 2.1, p. 37
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 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 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
Changes of State
Fig. 2.2, p. 37
ENERGY 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 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
Thermal Circulations
Fig. 2.5, p. 40
Thermal Circulations
Fig. 2.6, p. 40
ENERGY 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
Electromagnetic Radiation
Fig. 2.7, p. 41
ENERGY BALANCING ACT
• Radiation of the Sun and Earth
– Sun (6000 K) emits mostly shortwave radiation
– Earth emits mostly longwave radiation
SUN’S ELECTROMAGNETIC SPRECTRUM
Mostly shorter wavelengths
Fig. 2.8, p. 44
SUN
Electromagnetic
Radiation
EARTH
Fig. 2.9, p. 44
ENERGY 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
Atmospheric
Absorption of
Radiation
Fig. 2.10, p. 46
A GREENHOUSE
• Glass is transparent
to short visible
wavelengths (SW) but
opaque to long
infrared (LW)
wavelengths.
w/o GREENHOUSE GASES
w/ 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 Feedback
• When the response in a second variable reinforces
the change in the initial variable
• Example of positive feedback:
– Global temperatures increase
– Increase in temperature melts the ice and snow in
the upper latitudes
– Loss of ice and snow results in a lower albedo at
the surface in the upper latitudes
– Lower albedo leads to less reflection and more
insolation
– More insolation results in warmer temperatures
Negative Feedback
• When the response in a second variable lessens the
change caused by the initial variable
• Example of negative feedback:
– Global warming leads to more atmospheric water
vapor
– Increased water vapor leads to increased cloud
cover
– Increased cloud cover leads to a higher albedo
– Higher albedo results in less insolation at the
surface
– Reduced insolation at the surface leads to cooling
Solar Radiation
Fig. 2.13, p. 50
ALBEDO
• Percent of
sunlight
reflected from
clouds and
earth surfaces
• Earth average
albedo = 30%
Surface
Earth and Atmosphere
Clouds (Thick)
Albedo (%)
30
60-90
Clouds (Thin)
Fresh Snow
Ice
Sand
30-50
75-95
30-40
15-45
Grassy Field
Plowed Field
Water
10-30
5-20
10
Moon
7
Atmospheric Energy Balance
Fig. 2.14, p. 51
ENERGY 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
Global Energy Balance
Fig. 2.15, p. 52
ENERGY BALANCE
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.
Elliptical Orbit
Fig. 2.16, p. 52
Sun Angle
Fig. 2.17, p. 53
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
Sun Angle
Fig. 2.20, p. 56
Sun and the Seasons
Fig. 2.18, p. 53
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
Sun’s Seasonal Path
Stepped Art
Fig. 2.22, p. 58
Sun’s Seasonal Path
Fig. 2.19, p. 56
WHY THE EARTH HAS SEASONS
• Seasons in the Southern Hemisphere
– Opposite timing of N Hemisphere
– Closer to sun in summer but not significant
difference
ISOPLETHS
Contour Maps
Contour Maps
Contour Maps
ISOBARS
ISOTHERMS
ISOTACHS
ISOHYET
ISOPLETHS
°
°
°
°
Connects all points that have the same value
Iso = equal (Greek)
Also called “Isolines”
Types
°
°
°
°
°
°
°
°
Isobar = pressure
Isallobar = pressure change per time
Isotherm = temperature
Isohyet = rainfall
Isonif = snowfall
Isoryme = frost incidence
isoneph = cloudiness
isotach = wind speed
ISOPLETHS (cont’d)
° Rules
° Only through exact value of isopleth
° Higher side and lower side
° All higher should be on the same side of the
line
° Draw for all values
° Spacing by interpolation
° Spacing indicates rate of change (I.e., gradient)
° Isopleths form closed loops
° Isopleth never cross one another
ISOPLETHS (cont’d)
• DRAWING HINTS
– Note location of lowest and highest values
– Begin around these low or high values and
gradually work outward
– Sketch lightly to get spacing and orientation of
– Smooth the isopleths. Isopleths generally do
not have sharp bends
ISOPLETHS
Draw 6.5 contour
ISOPLETHS
ISOPLETHS
Draw even contours
ISOPLETHS
ISOTHERMS
Draw 10, 20, 30,40, 50,
60, 70 degree contours
ISOTHERMS
Isodrosotherms
Isodrosotherms
HOMEWORK #4
Due next week (9/14/09)
at the beginning of class.
Draw Isotherms at 10 degree intervals( i.e., 50, 60, 70, 80, 90 degrees).