Weather and Climate

1
Weather and Climate

• 31 January 2007
• Temperature

2
Temperature

• Temperature is a measure of the average speed of
  atoms and molecules comprising a matter.
• Higher Temperature gt Faster Molecules
• Lower Temperature gt Slower Molecules
• Temperature is a measure of the average kinetic
  energy.

3
What is Energy?

• Energy is the ability or capacity to do work on
  some form of matter.
• Energy has many different forms
• Kinetic energy
• Potential energy
• Radiant energy
• Chemical energy
• Electric energy
• Magnetic energy

The ones that are important in the atmosphere
4
Potential Energy

• Energy that a body possesses because of its
  position with respect to other bodies in the
  field of gravity.
• Easier way energy of position -- increases as
  something rises
• PEmgh
• Where mmass of object,
• g gravity
• hheight of object above ground

5
Kinetic Energy

• The energy within a body that is the result of
  its motion.
• KE1/2 mvxv1/2mv2
• mmass of object
• vvelocity of object
• If a volume of water and an equal size volume of
  air were moving at the same speed, which would
  have the greater kinetic energy?

6
1st Law of Thermodynamics

• Energy cannot be
• created or destroyed.
• Energy can only change form
• Energy lost during one process must equal the
  energy gained during another
• Example throw a ball up in the air
• It loses Kinetic Energy, but gains potential
  energy as it rises
• As the ball falls, it loses potential energy, but
  gains Kinetic Energy

7
2nd Law of Thermodynamics

• You cannot finish any real physical process with
  as much useful energy as you had to start with
  some is always wasted
• Perpetual Motion machines are impossible

8
Temperature Scales

• Absolute zero occurs when molecules are cooled to
  the point where they no longer move (Remember
  temperature measures the kinetic energy of the
  molecules)
• At absolute zero there is a minimum amount of
  energy, and theoretically no thermal motion.
• Absolute zero is
• -459 oF (Fahrenheit)
• -273oC (Celsius)
• 0 K (Kelvin)

9
What is heat?

• Heat is energy that is being transferred from one
  object to another because of temperature
  differences between the the two objects.
• Heat flows from Warm to Cold, always
• (unless you add energy, in which case you can
  move cold to warm, like in a refrigerator)

10
Heat Capacity

• Heat capacity is the ratio of the heat absorbed
  (released) by a system to the corresponding
  temperature rise (fall).
• How long can you add energy to a substance before
  the temperature rises a given amount
• This varies for different substances. Water, for
  example, has a high heat capacity. Sand has a
  low heat capacity. Wet sand has a heat capacity
  in between water and sand.

11
Convection
12
How is heat transferred in the Atmosphere?

• Conduction
• Convection
• Advection
• Radiation
• Energy propagated in the form of electro-magnetic
  waves

13
Types of Radiation
14
Incoming vs. Outgoing Radiation
Poles are cooling, equator is warming
15
The Sun at the Poles
A man builds a house that is a perfect square,
with a window on each side. At 6am, noon, 6pm,
and midnight the sun is in the middle of a south
facing window. If the man sees a bear outside his
window, what color will it be?
16
How is temperature controlled
Note how temperature and outgoing radiation are
in phase
17
What controls temperature?

• Altitude (Colder as you go up)
• Latitude (Colder as you go north)
• Surface Type (Sand vs. Marsh)
• Location with respect to water
• Cloud Cover

18
Diurnal Temperature Ranges
19
Where is the range smallest?

• Right next to the Ocean coast of N. California,
  coastal North Carolina (vs. inland N. Carolina)
  where there is lots of water nearby
• Downwind of Great Lakes and downwind of oceans
  affects of nearby water
• Regions that are wetter/cloudier

20
Annual Temperature Changes
21
Where is the range smallest?

• Next to the Ocean -- oceanic effects
• Regions in the south
• Continentality -- A climate is said to have
  continentality if it is far from the ocean --
  expect to see extreme temperature variability for
  a very continental climate

22
Do diurnal/annual changes vary?

• Yes -- interannual variability is caused by El
  Nino, Volcanism, annual snow cover, annual cloud
  cover, . . .

23
Temperatures in January
24
Temperatures in July
25
Annual Temperatures

• Northern Hemisphere gets warmer in summer than
  southern Hemisphere
• More land, which warms faster than water, is
  present
• Oceans cooler on West sides of continents
• West side of continents warmer than east side of
  continents
• Reflects the west-to-east motion of airmasses.
  The airmasses will move warm oceanic air inland

26
Temperature at a location is controlled by the
prevailing wind
Local Effects
27
Solar intensity also changes with season because
the angle of the sun changes.
Sun is highest in sky on Summer Solstice June 21
Solar intensity can also change as you change
latitude -- those changes can be amplified or
mitigated by daylight length changes
Sun is lowest in sky on Winter Solstice December
21
28
What is the global annual mean day length? 12
hours!
29
(No Transcript)
30
Diurnal Range in July
Diurnal Range in January
31
Whose woods these are I think I know His house is
in the Village though He will not see me stopping
here To watch his woods fill up with snow
My little horse must think it queer To stop
without a farmhouse near Between the woods and
frozen lake The darkest evening of the year
He gives his harness bells a shake To ask if
there is some mistake The only other sounds the
sweep Of easy wind and downy flake
Stopping by the woods one snowy Evening Robert
Frost
The woods are lonely, dark and deep But I have
promises to keep And miles to go before I
sleep And miles to go before I sleep
32
LAPSE RATE

• Lapse Rate temperature change with height
• Positive if temperatures fall with height
• Environmental Lapse Rate varies in space and time
• You have to measure temperature to determine the
  Environmental lapse rate!
• The average environmental lapse rate is 6.5 C/km
• If the lapse rate increases, the atmosphere is
  destabilizing done by warming the ground or
  cooling upper levels. A less stable atmosphere
  is more prone to vertical motions

33
Parcels in the atmosphere

• Theoretical, isolated blob of air that moves
  without mixing with its environment
• As parcels move in the vertical, they warm or
  cool at specific rates
• Rising, unsaturated parcels cool at 9.8 oC/km
• Sinking parcels warm at 9.8 oC/km
• Rising, saturated parcels cool at about 6 oC/km
• Cooling is slower than for unsaturated parcels
• Cooling is slower for parcels that have more
  moisture
• Cooling is faster (but still slower than dry
  parcels) for parcels with less moisture

34
Parcels in the atmosphere

• Dry Adiabatic Lapse Rate
• Rising, unsaturated parcels cool at 9.8 oC/km
• Moist Adiabatic Lapse Rate
• Rising, saturated parcels cool at about 6 oC/km
• What causes the difference?
• LATENT HEAT IN PARCEL -- this is the heat
  associated with a phase change.

35
Heat in the Atmosphere

• Sensible Heat The heat you can feel and measure
  with a thermometer
• Latent Heat Heat in the air associated with a
  phase change
• When water evaporates, the now-gaseous vapor
  carries with it energy that will be released when
  the vapor re-condenses to liquid
• Energy comes from surrounding air -- its why you
  feel cool when water evaporates from you that
  (warmth) energy is carried away in the water vapor

36
Latent Heat and parcels

• Latent Heat of Vaporization 600 calories/gram
• Latent Heat of Melting 80 calories/gram
• As a saturated parcel rises, it cools.
• Saturated condensation evaporation. But
  evaporation is a function of temperature as the
  parcel cools, evaporation slows.
• More condensation in the rising saturated parcel,
  which releases latent heat, so the rising parcel
  doesnt cool as fast as it would if it were dry

37
Why do rising parcels cool?

• As a parcel rises, the pressure surrounding the
  parcel will drop -- pressure always drops as you
  rise in the atmosphere
• Therefore, the parcel will expand -- there is a
  smaller force acting to confine it because the
  pressure surrounding it dropped
• Expansion requires work, and an energy source.
  The energy source used is the parcels internal
  energy (heat) -- it loses that to expansion and
  cools

38
Summary

• Latent Heat is due to phase changes
• Rising Parcels Cool
• Environmental Lapse Rate always varies
• Parcel Lapse Rate is always the same
• 9.8 oC/km DRY or about 6 oC/km WET

39
Remember Cold Air is denser and will sink
40
Note how in the saturated lifting example on the
right, the parcel becomes warmer than its
environment
41
IF a parcel is..

• Warmer than its environment
• The parcel will move upwards
• If its saturated, it will cool and vapor will
  condense out

• Cooler than its environment.
• The parcel will move downward
• If its saturated, it will warm and become
  unsaturated

42
Change in temperature as the Sun rises and the
nocturnal inversion dissipates.
43
What can an inversion do?
Inhibit Mixing!
44
Where do you think the top of the inversion layer
is?
45
Some things to Note

• Winter Solstice 21 December
• Madisons coldest day 14 January
• It takes time for the land to cool down, so there
  is a lag between the shortest day and the coldest
  day. The effect is more pronounced if youre
  near water (which takes even longer to cool down)
• Similar thing happens in summer. Solstice is 21
  June, hottest day is in mid-July

46
Time Lag

• To account for the lag, you can define
  meteorological winter and also meteorological
  summer to be the coldest 3 months and warmest 3
  months, respectively.
• Meteorological winter is about 5 December - 5
  March
• Meteorological summer is about 5 June - 5
  September

47
Contouring
EXAMPLE
48
Contouring
49
Contouring
50
Daytime Warming
On a clear, windless day, joggers may experience
a temperature of 122oF near their feet, and a
temperature of 90oF near their waist.
51
Daytime Warming
52
Nighttime Cooling
53
Radiation Inversion Ingredients

• Windless night
• Wind mixes the air with turbulent eddies
• A long night
• Cloudless night
• Clouds radiate infrared energy back to surface
• A dry night
• If dew forms, then latent heat of condensation is
  released.

54
Radiational Inversion
55
Heating Degree-Day
56
Cooling Degree-Day
57
Growing Degree-Day
58
Mean Annual Temperature
59
Measuring Temperature
60
Wind Chill

• Why does the wind make it feel colder?
• On cold days our body warms a thin layer of air
  around us.
• When the wind blows, this warm layer is replaced
  by cold air. The body expends energy to recreate
  the lost boundary layer
• The faster the wind blows the colder we feel.

61
The wind chill equivalent temperature tells us
how cold it would have to be with no wind, in
order for us to lose the same amount of heat.

• This is new as of 2001!
• - Replaces Paul Siples original work in
  Antarctica
• - A bit warmer than the old formula
• -Will be updated in the near future for sunshine

62
Controls of Temperature

• Latitude
• Land and Water
• Ocean Currents
• Elevation
• Cloud Cover

63
Urban Heat Island
Stanley Park
Downtown Vancouver
64
(No Transcript)
65
Urban Heat island

• Decrease in
• Wind speed
• Humidity (drainage systems take away water!)
• Increase in
• Temperatures
• Cloudiness
• Precipitation
• Fog
• Pollution

66
Causes of Urban Heat Island

• Human produced heat
• In buildings, automobiles
• Particulates and Smog
• Greenhouse enhancer, traps heat
• Snow Removal
• Decreases the albedo

67
Heat Island Example
Areas that are warm appear in white/light gray.
Areas that are cool appear dark.
Atlanta
68
Heat Island Example
Trees and vegetation appear in red. Buildings,
streets and urban land cover is
white/blue-green/black.
Note the shape of the downtown region.
Atlanta
69
Heat Island Example
Remember the shape of the downtown!
70
Heat Trapping