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Climate Resilient Cities
Lecture 1
Introduction
• Heating and cooling sources of the earth
• Sun
• How does the earth balance the
temperature?
• Plants, rivers, oceans and the chemistry
of the atmosphere
Units
• Velocity
Km/hr to m/s
Units of energy
• 1 cal is the energy to heat up 1 g of
water molecule 1℃
• kCal=1000 cal
• 1 cal= 4.18 Joule
• Watt – rate of energy flow =
joules/second (flux)
• 1 kW . hr = 3.6 e6 joules
• You can heat up 3.6 e6 g (3600
tones) of water 1℃
Heat
• Heat
• Is the motion of the atoms that make up
the material (kinetic energy)
• Playing pool
• Temperature
• Is the average measurement of the atom
movements next to the thermometer
• Movement of the atoms
• Translation (fluids)
• Vibrations (bounded atoms)
• Rotation
Heat
• Energy= ½ k T
where
k, is the Boltzman constant
T, is the temperature in terms of Kelvin
Heat
• For single atom, 3 dimensions of
space
E=3/2 k T
• For 2 bounded atoms
• 1 vibrational mode
• 2 rotation modes
E= 6/2 k T
Heat
• Example – Thermal windows
Vacuum is the best
Argon is OK because it is a noble gas
Bad examples
Oxygen, nitrogen (more than one atom in a molecule)
Units of light
• Wave length, 𝜆, lambda cm/cycle=‘cm’
• Frequency, cycles/sec=sec-1, 𝜈, ‘nu’
• Wavenumber, n, number of waves in 1 cm
Light
• Sun is the source of energy in the earth
• The space between sun and earth is vacuum
• Energy transferred from the sun to the earth
via light
Blackbody radiation
• Spectrum – brightness in different ‘colors’
Y axis intensity W/m2 n
X axis n
Area under the curve is W/m2 (heat flux)
The smaller the area lower the energy of the object
Objects in room temperature are shining light
infrared
As the object gets hotter – red color
Really hot – white color
Blackbody radiation
• Total energy W/m2
𝑊
4
=
𝜀
𝜎
𝑇
𝑚2
where,
𝜀, 1 if black
𝜎, Stefan Boltzman constant
𝑇, temperature in Kelvin
Climate Resilient
Cities
Lecture 2
Naked Planet Climate Model
• Energy balance
• Coming energy should be balanced with the outgoing energy
• Outgoing is the earth’s blackbody radiation
𝑊
𝑒𝑛𝑒𝑟𝑔𝑦
= ! = 𝜀 𝜎 𝑇”
𝑚 ”
𝑒𝑛𝑒𝑟𝑔𝑦 𝑜𝑢𝑡 = 𝜀 𝜎 𝑇 . 𝐴
𝑜𝑢𝑡/𝑚!
A is the area of surface of the earth= 4𝜋𝑟 !
Naked Planet Climate Model
• Energy in is the light from the sun
𝑖𝑛 = 𝐿 1 − 𝛼 𝐴
L, solar constant (related with the intensity and the distance of the sun)
𝛼, albedo (reflection)
A, area of the shadow (projection) of the earth 𝜋𝑟 !
Table 3.1
Naked Planet Climate
Model
𝐸𝑛𝑒𝑟𝑔𝑦 𝑖𝑛 = 𝐸𝑛𝑒𝑟𝑔𝑦 𝑜𝑢𝑡
𝐿 1 − 𝛼 𝜋𝑟 ! = 𝜀 𝜎 𝑇 ” 4𝜋𝑟 !
Make simplifications and the unit becomes
watts/meter square sphere
𝐿 1−𝛼
= 𝜀 𝜎 𝑇”
4
The only unknown is the temperature
Temperatures and Albedos of the Terrestrial Planet
Isolar , W/m2
α(%)
Tbare K
Venus
2,600
71
240
Earth
1,350
33
253
Mars
600
17
216
The intensity of sunlight differs with distance from the sun.
Sunlight
E arthlight
(1−α)Isolar
4
ε σ T 4e arth
E arth
Figure 3-3 An energy diagram for Earth with no atmosphere, just a bare rock in space.
with the results of the calculation and the observed averag
Bare-Rock Layer Model has gotten it too cold.
Naked Planet Climate
Model
• The naked planet climate model results for
different planets vs observed
The L
Table 3.1
Temperatures and Albedos of the Terrestrial Planets.
Isolar , W/m2
α(%)
Tbare K
Tobserved K
Venus
2,600
71
240
700
Earth
1,350
33
253
295
Mars
600
17
216
240
The intensity of sunlight differs with distance from the sun.
Sunlight
• The model is very cold when compared with
the observations
E arthlight
(1−α)Isolar
4
ε σ T 4e arth
E arth
T
Greenhouse effect
24
CHAPTER 3
The Layer Model
Boundary to space
• An imaginary glass is added
• Some part of the energy out from the earth
surface reflected back to the earth
(1−α)Isolar
4
Iup, glass
Glass
Idown, glass
Iup, ground
E arth
Figure 3-4 An energy diagram for a planet with a single
pane of glass for an atmosphere. The glass is transparent
to incoming visible light but a blackbody to infrared light.
e of energy balance, where the rate of energy going out of the layer equals
to incoming visible light but a blackbody to infrared lig
coming in:
Iout = Iin
(3-6)
Greenhouse effect
Ioutof=the
Iin layers at which both energy budgets will
(3-6)be in
one
temperature
for
each
f energy balance, where the rate of energy going out of the layer
24
CHAPTER 3
The Layer Model
equ
temperature
for each of the layers at which both energy budgets will be in
ming
in:
rgy fluxes are depicted as arrows in Figure 3-4. The energy budget for the pane
• Energy budget for the glass
Boundary to space
euxes
written
as
are depicted
as arrows in Figure 3-4. The energy budget for the pane
Iout = Iin
tten as
Iup, glass + Idown, glass = Iup, ground
(3
(1−α)Isolar
4
Iup, glass
Iup, glass
+ Idown,
Iup, groundat which both energy budgets will be
glass =
perature
for
each
of
the
layers
are both IR light energy, the intensities can be written as
Glass
both IR light energy, the intensities
can4 be written as
4
= εσTground
2εσTglass
Idown, glass
(3-7)
s are depicted2εσ
asT 4arrows
in
4 Figure 3-4. The energy budget for the pa
(3-7)
glass = εσTground
nund
as and the glass have to be in a state of energy balance.
Iup, ground
E arth
and the glass have to be in a state of energy balance.
Iup, glass + Idown, glass = Iup, ground
Figure 3-4 An energy diagram for a planet with a single
pane of glass for an atmosphere. The glass is transparent
to incoming visible light but a blackbody to infrared light.
layers are in a state of energy balance, where the rate of energy going out of the layer equals
the rate of energy coming in:
get for the ground is different from in the Bare Rock Model because now there
I =I
g down from the pane of glass. The basic balance is
out
in
(3-6)
e are both IR light energy, the
= εσT 4can be written as
2εσT 4 intensities
glass
(3-7)
ground
4
4
= εσTground
2εσTglass
(3-7)
Greenhouse effect
and the glass have to be in a state of energy balance.
ound and the glass have to be in a state of energy balance.
24
CHAPTER 3
The Layer Model
for
ground
is isdifferent
from
inthe
the
Bare
Rock
Model
because
now there
dget the
for the
different
fromfor
in
Bare
Rock
Model
because
now there
• ground
Energy
budget
the
ground
wn
fromfrom
the the
pane
ofofglass.
basicbalance
balance
g down
pane
glass. The
The basic
is is
Boundary to space
(1−α)Isolar
4
=IIin,
ground=
in,solar
solar +
Iup,Iup,
+Idown,
Idown,glass
ground
glass
Iup, glass
ties can be expanded into
an be expanded into
(1 − α)
4
4
εσTground
=(1 − α) Isolar + εσTglass
4 Isolar + εσT 4
εσT 4
=
ground
4
glass
(3-8)
Glass
(3-8)
Idown, glass
Iup, ground
E arth
Figure 3-4 An energy diagram for a planet with a single
pane of glass for an atmosphere. The glass is transparent
to incoming visible light but a blackbody to infrared light.
layers are in a state of energy balance, where the rate of energy going out of the layer equals
the rate of energy coming in:
Iout = Iin
(3-6)
glass
ground
und and the glass have to be in a state of energy balance.
Greenhouse effect
get for the ground is different from in the Bare Rock Model because now there
down from the pane of glass. The basic balance is
TheThe
Layer
ModelModel
with Greenhouse
Effect 25
Layer
with Greenhouse
Effect 25
Iup, ground = Iin, solar + Idown, glass
C H A P T E R 3 The Layer Model
it is possible to combine Equations 3-7 and 3-8 in 24
such
as to eliminate one
ossible
toexpanded
combineinto
Equations 3-7 and 3-8 in sucha away
way
as to eliminate one
es can be
peratures, solving for the other, and then plugging back in to solve for the first.
res,
the other,
and
plugging
back
to solve
for the first.
Boundary to space
(1 −
α) then
niftysolving
trick thatfor
makes
it algebraically
much
easier
to
solveinand
is conceptually
4
4
I
εσ
T
=
+
εσ
T
(3-8)
solar
glass
rick that makes ground
it algebraically
much easier
to solve and is conceptually
4
(1−α)I
is to construct an energy budget for the Earth overall by drawing a boundary
4
I
osphere
andan
figuring
thatbudget
if energyfor
getsthe
across
this overall
line coming
it must aalso
be
construct
energy
Earth
by in,
drawing
boundary
out at the
rate. This
budget
canthis
be written
as
ethe
andline
figuring
thatsame
if energy
gets
across
line coming
in, it must also be
• There two unknows one is temperature of the ground the other is
temperature of the glass
solar
• One way is to solve with algebraic tricks
ne out at the same rate. This budget can be written as
• The other
way
to assume
Iup, glass
= Iin,is
solar
= Ithe
comprise individual Ifluxes
from
sun and from the atmosphere:
up, glass
in, solar
(1 −
α) and from the atmosphere:
4
rise individual fluxes
the
sun
εσTfrom
Isolar
=
glass
up, glass
Glass
Idown, glass
Iup, ground
E arth
4
α) also that this equation looks a lot like
contains only one unknown,
T(1
. Notice
glass−
4
εσTtemperature
Isolar
glass =
describing the surface
4of the Bare-Rock model. Solving for Tglass here
Figure 3-4 An energy diagram for a planet with a single
pane of glass for an atmosphere. The glass is transparent
to incoming visible light but a blackbody to infrared light.
t the top layer, where infrared radiates to space. We will call this
mperature of the Earth, and it comes up again in the next chapter.
erature of the Earth, and it comes up again in the next chapter.
eratures below the skin, in this case Tground ? Now that we know that the
ures
the skin, in this
case T we can
? Now
that we know that the
Greenhouse
Tglass ,below
is equal to the skin effect
temperature,ground
plug that into the budget
equal
to the skin temperature, we can plug that into the budget
ass , isto
phere
see that
re to see that
• The temperature of the ground
4
4
2εσTglass
= εσTground
4
4
2εσTglass
= εσTground
with the simplifications
√
4
Tground = 2 Tglass
Tground
√
= 4 2 Tglass
ground must be warmer than the skin temperature, by a factor of the
irrational number that equals about 1.189. The ground is warmer than
ound
be warmerModel
than calculation
the skin temperature,
byfor
a factor
of the
ut
19%.must
The One-Layer
is also repeated
Venus and
ational
number thatof equals
aboutright,
1.189.
The Mars
ground
is warmer
ets the temperature
Earth about
whereas
is too
warm andthan
9%.
The One-Layer Model calculation is also repeated for Venus and
enough.
The Layer Model with Green
Table 3.1
Temperatures and Albedos of the Terrestrial Planets.
Isolar , W/m2
α(%)
Tbare K
Tobserved K
T1 layer K
Venus
2,600
71
240
700
285
Earth
1,350
33
253
295
303
Mars
600
17
216
240
259
The intensity of sunlight differs with distance from the sun.
Sunlight
(1−α)Isolar
4
E arthlight
Greenhouse effect
ε σ T 4e arth of the glass layer
With the addition
Climate Resilient
Cities
Lecture 4
The Feedback Mechanism
• The feedback is a loop of cause and effect
• State variable is at the center of the feedback
• In the climate feedback loop the state variable is the
average temperature of the earth
Feedback Types
Positive Feedback
Makes the temperature change larger than
it would have been without the feedback
Negative Feedback
Counteracts some of the external forcing,
tending to stabilize the state variable
Amplifying the temperature change
If the incoming energy increases,
the outgoing energy via
Blackbody radiation increases
StefanBoltzman
Feedback
The earth tries to stabilize the
energy
Negative feedback
Ice Albedo Feedback
• The ice is an albedo material
• As the ice melts the albedo level of the
earth reduces
• The temperature increase
• The melting of ice increases
• Since the directions of the input
perturbation and the feedback loop agree
with each other it is a Positive Feedback
Water-Vapor
Feedback
• Water-vapor increase causes
greenhouse heat trapping
• As the water-vapor level in the earth
increases
• The condensation increases
• The amount of rain increases
• The water (rain) will tend to
evaporate
• Take energy from earth
• It is a negative feedback
74
CHAPTER 7
Feedbacks
a
Stefan-Boltzmann fe edback
−
Infrared radiation to space
+
b
T emperature
+
Ice albedo fe edback
Ice melts
Feedbacks
+
c
T emperature
−
Hydrological cycle
R ain evaporation
+
d
W ater vapor
concentration
+
W ater vapor fe edback
W ater vapor
concentration
+
T emperature
Figure 7-1 Feedback diagrams. (a) An example of a negative feedback resulting
from the Stefan-Boltzmann infrared energy flux !σT 4 . (b) An example of a positive
feedback. Some external perturbation increases the temperature. The increase in
Cloud
Feedback
Clouds
Cirrus
• The feedback mechanism of the
clouds is not straight forward
• Three types of clouds depending
on the weather characteristic
10 km
50–100 micron diameter ice
4 km
• High altitude cirrus clouds
• Low altitude cumulus clouds due
to unstable weather events
• Like a tower
• Can cause rain and
thunderstorms
• Low altitude stratus clouds
• Layered
C umulus
Stratus
ice
5 microns diameter
1 km
Figure 7-4
water
Schematic of the three main types of clouds.
with low tops have a smaller effect on the outgoing IR light. Table 7.1 records the conclusions
that the effect of clouds on IR light is to warm the planet and that high clouds warm the Earth
more than low clouds do.
The infrared effect of clouds (1) warms the Earth (2) depending on the
altitude (temperature) of the cloud tops.
The effect of clouds in the visible-light energy budget is to send solar energy back to space,
increasing Earth’s albedo and cooling the planet. Cloud particles (droplets and ice crystals) can
optically thick, capturing or scattering most of the visible light that tries to get through. Cirrus
clouds contain 10 or 100 times less water per volume than lower altitude clouds typically hold.
Table 7.1
High Clouds (Cirrus)
Low Clouds (Stratus and Cumulus)
Infrared effect
(warming)
Strong warming influence because
high-altitude cloud top
Weaker warming influence because
cloud tops are lower
Visible light effect
(cooling)
Weak cooling influence because they
are optically thin
Stronger cooling influence because
they are optically thicker
Overall effect
Warming
Cooling
Clouds reflect
Cloud Feedback
• The incoming radiation from the sun
• The outgoing radiation from the earth
Climate Resilient
Cities
Lecture 3
Atmosphere
44
CHAPTER 5
What Holds the Atmosphere Up?
• Mixture of gases that covers the earth
• Can be assumed as ideal gas
Visible
Infrared
• It is heated from ground via convection
• With the feedback mechanism it is heating back the ground
via blackbody radiation
Atmosphere
H e at
exchanger
E arth
Figure 5-1 The Layer Model from Chapter 3 with an
added heat exchanger, capable of partially or completely
equalizing the temperatures of the two layers.
(atm). Each 10-m depth interval increases the pressure by about the same 1 atm: descending
from 30 to 40 m would increase the pressure by the same 1 atm as going from 0 to 10 m. The
pressure can be calculated as44
What Holds the Atmosphere Up?
CHAPTER 5
−1 atm
Visible
Infrared
· z [m]
10 m
where the variable z is the vertical position, with positive numbers upward, as before, so a
Atmosphere
negative height is a depth.
Atmospheric
Temperature Structure
• Ideal gas law
P = 1 atm +
H e at
exchanger
The density of water does not change much with pressure, so the weight of the
water overhead (the pressure) depends linearly on the water depth.
Figure 5-1 The Layer Model from Chapter 3 with an
added heat exchanger, capable of partially or completely
equalizing the temperatures of the two layers.
𝑃𝑉 =𝑛𝑅𝑇
• Pressure is a function of altitude
• The ground temperature is higher
E arth
Because pressure is just a constant number multiplied by the depth, a graph of pressure
5-2), and it contains 90% of the air and all of the weather. The air temperature reaches
versus depth would be a straight line (Figure(Figure
5-4),
and
the
pressure
is said
to be
withabout
depth.
its coldest
point
at the
tropopause,
a boundary
of air about
10 kmlinear
high on average,
where
commercial airplanes fly. Above this, it gets warmer with altitude in the stratosphere because
The pressure in the atmosphere is nonlinear
with altitude in that a climb of 1 m at sea
of ozone which absorbs ultraviolet radiation from the sun (Chapter 10), and higher still are the
mesosphere
and
the
which do not affect The
the climate
story very much.
level changes the pressure much more than 1 m up atexosphere,
the tropopause.
equation
to describe
• The temperature at higher elevations are
lower
Altitude, km
LAPSE RATE
50
50
45
45
40
40
35
35
30
30
Stratosphere
25
25
20
20
Tropopause
15
15
Troposphere
10
10
5
5
0
180
Figure 5-2
tropics.
200
220
240
260
T emperature, K
280
300
0
0
0.2
0.4
0.6
Pressure, atm
0.8
1
Typical temperatures and pressures of the atmosphere as a function of altitude in the
Lapse Rate
• The temperature change with elevation
• Dry adiabatic Lapse Rate= cooling of a
parcel of air that rises adiabatically and
adjusts to the ambient Pressure
• Wet or Saturated or Moist Adiabatic
Lapse Rate= cooling of a parcel or air
that rises adiabatically and adjust to
the ambient Pressure while its
moisture is condensing
Lapse rates in the atmosphere
• Dry Lapse rate = 9.8 K/km
Lapse Rate
• Wet/ Saturated / Moist Adiabatic Lapse Rate =
5.5 K/km
Lapse
• Difference
caused rates
by latent in
heatthe
=
=
atmosphere
Latent Heat
• Liquid+ heat = vapor
• Latent heat is the heat that is
released from the vapor
while condensing
OR
• Latent heat is the heat that is
absorbed by the liquid while
evaporating
The Effect of Lapse Rate
• It determines the stability of the atmosphere
• If the lapse rate is higher than usual the air is unstable
• The density at the upper atmosphere is higher than
the lower parts
• Mixing at the atmosphere increases
• If the lapse rate is smaller than usual the air stable
• The density at the upper atmosphere is lower than
the lower parts
• Mixing at the atmosphere decreases
Skin Layer
Temperature
The Greenh
N ew skin altitude
M
ois
• The temperature of the glass
(skin) layer where we
consider in our layer model
Altitude
Skin altitude
ta
di
ab
at
• More greenhouse gas
s
higher skin altitude
T emperature
warmer ground
Skin
temperature
Ground
temperature
N ew ground
temperature
Figure 5-3 A demonstration of the effect of the lapse rate on the strength
of the greenhouse effect. If we increase the greenhouse gas concentration
of the atmosphere, the infrared radiation to space will originate from a
higher altitude (labeled Skin altitude), but the skin temperature at the
Weather
• Is the combination of
parameters which are firmly
connected to each other
• It is completely chaotic
• Small changes in the
parameters can generate
completely different
outcomes (butterfly effect)
Climate
• The long-run average of weather events
• Not chaotic
Weather and Climate
Climate
1200
Sunlight
Infrared
Total
1000
• The energy balance of the
earth
• Incoming= sunlight
• Outgoing= Blackbody
radiation
800
I, W/m 2
6
600
400
200
0
−200
−400
0
5
10
15
20
Hour in day
Figure 6-2 The surface of the Earth receives only
incoming solar radiation during the daytime (heavy solid
line), but it radiates infrared light all the time (thin solid
line). The energy budget for this location (dashed line) is
in Figure 6-4. The axes in this figure are day of the year in the x -direction and latitude in the
y -direction. The contours show the intensity of sunlight at the top of the atmosphere averaged
over 24 hours. Any location at some latitude, say 42 degrees north, which goes through Chicago,
Winter
Climate
Summer
Figure 6-3 The Earth’s tilt is responsible for the seasons. This is
southern hemisphere summer, northern hemisphere winter.
Earth is tilted relative to the orbit
• Changes the daily average sunlight energy
flux
• Causes the seasons
D aily average sunlight energy flux, W/m 2
90
0
100
60
100
200
300
400
200
300
400
30
Latitude
500
0
400
EQ
300
−30
200
500
−60
−90
500
100
0
J
F
M
A
M
J
J
A
S
O
N
D
Month of the ye ar
Figure 6-4
The Earth’s tilt determines how much heat the
Climate
62
CHAPTER 6
Weather and Climate
350
N et incoming solar
• There is an energy unbalance
• Earth always aims to balance itself
E nergy flux, W/m 2
300
250
O utgoing IR
200
H e at transport by winds and currents
150
100
50
0
−90
−60
−30
0
Latitude
30
60
90
Figure 6-5 The energy budget between incoming solar and outgoing infrared
radiation does not balance locally because heat is transported on Earth by winds
a circle of little dominos, which the pendulum knocks over as it swings. Over the course of the
day, the swing direction of the pendulum changes, knocking over a new little block every 10
minutes or some other crowd-pleasing rhythm. Leon Foucault installed the first of these into the
Pantheon in Paris for the 1850 Paris Exposition.
The pendulum is like a rotation meter, measuring the rate of rotation that drives the Coriolis
effect. Start with a Foucault pendulum on the North Pole (Figure 6-7). The Earth is spinning
Climate
Fixed stars
Fixed stars
Dominos
awaiting
their doom
• The rotational velocity is different throughout
the travel of the heat via wind and current
• The change in the rotational velocity causes a
change in the momentum
• It is called as Coriolis force
Rotating E arth
Fixed stars
• Coriolis force increases the mixing of the
weather and chaotic properties
Dominos
are safe
Rotating E arth
Figure 6-7 The Coriolis acceleration that we feel
on Earth depends on latitude. A Foucault’s pendulum is a rotation detector. A pendulum set in motion
at the pole would swing through 180 degrees in
Climate Resilient
Cities
Lecture 5
Layer Characteristics
From our flfSt breath, we spend most of our lives near the earth’s surface. We feel the
warmth of the daytime sun and the chill of the nighttime air. It is here where our crops
are grown, our dwellings are constructed, and much of our commerce takes place. We
grow familiar with our local breezes and microclimates, and we sense the contrasts when
we travel to other places.
Such near-earth characteristics, however, are not typical of what we observe in the rest
of the atmosphere. One reason for this difference is the dominating influence of the earth
on the lowest layers of air.
The earth’s surface is a boundary on the domain of the atmosphere. Transport
processes at this boundary modify the lowest tOO to 3000 m of the atmosphere, creating
what is called the boundary layer (Fig 1.1). The remainder of the air in the
troposphere is loosely called the/ree atmosphere. The nature of the atmosphere as
perceived by most individuals is thus based on the rather peculiar characteristics found in a
relatively shallow portion of the air.
Atmospheric Boundary Layer
• The earth’s surface is a boundary on the domain of the
atmosphere
_ _ _ Tropopause
——–r—-_
Free Atmosphere
• Transport processes at this boundary modify the lowest
100m to 3000m of the atmosphere
• It is called as Boundary Layer
A
Fig. 1.1 The troposphere can be divided into two parts: aboundary
layer (shaded) near the surface andedge
the free
of atmosphere
boundary layer
above it.
I
Figure 10.4 Displaccment thickntxr and sfmudine displacement
Atmospheric
Boundary Layer
Definition
• “The boundary layer as that part of
the troposphere that is directly
influenced by the presence of the
earth’s surface and responds to
surface forcings with a timescale of
about an hour or less”
• The forcings include
• Frictional drag
• Evaporation and transpiration
• Heat transfer
• Pollutant emission
• Terrain induced flow
These time-histories were constructed from rawinsonde soundings made every several
hours near Lawton, Oklahoma. They show a diurnal variation of temperature near the
ground that is not evident at greater altitudes. Such diurnal variation is one of the key
characteristics of the boundary layer over land. The free atmosphere shows little diurnal
variation.
Atmospheric Boundary Layer
Fig. 1.2
Evolution of
temperatures
measured near
the ground
(97.5 kPa) and
at a height of
roughly 1100 m
above ground
(85 kPa) .
Based on
rawinsonde
lauches from
Ft.SiII,OK.
30
U
0
.
.

GI
:J
20
i;
GI
Q.
E

85 (kPa)
10
Lawton,Oklahoma
1983
GI
0
Noon
Noon
Noon
June 7
June 10
Time
This diurnal variation is not caused by direct forcing of solar radiation on the boundary
layer. Little solar radiation is absorbed in the boundary layer; most is transmitted to the
Atmospheric Boundary Layer
also a boundary-layer phenomenon.
Thunderstorms, while not a surface forcing, can modify the boundary layer in a matte
of minutes by drawing up boundary-layer air into the cloud, or by laying down a carpet o
cold downdraft air. Although thunderstorms are rarely considered to be boundary laye
phenomena, their interaction with the boundary layer will be reviewed in this book.
Wind
1.2 Wind and Flow
Air flow, or wind. can be divided into three broad categories: mean wind
turbulence, and waves (Fig 1.3). Each can exist separately, or in the presence of an
of the others. Each can exist in the boundary layer, where transport of quantities such a
moisture, heat, momentum. and pollutants is dominated in the horizontal by the mean
wind, and in the vertical by turbulence.
• Is the mechanism of transport quantities such
as
• Moisture
• Heat
• Momentum
• Pollutants
• Transport is dominated in
• Horizontal by the mean wind
• Vertical by the turbulence
Fig. 1.3
Idealization of
(a) Mean wind
alone. (b) waves
alone. and (c)
turbulence alone .
In reality waves
or turbulence are
often superimposed on a
mean wind. U is
the component
of wind in the
x·direction.
—-
(a>
h
Kú=
(b)
•t
r
(e)
Wú g í ê j K =
4
t
Wind
• Horizontal transport via mean wind is
called as advection
• Horizontal wind is generally between 2
to 10 m/s in the boundary layer
• Turbulence near the ground is one of
the characteristics that makes
boundary layer different from the rest
of the atmosphere
Turbulent Transport
• Turbulence, the gustiness
superimposed on the mean
wind
• Can be visualized as
consisting of irregular swirls
of motion called eddies
Turbulence is several orders of
magnitude more effective at transporting
quantities than is molecular diffusivity
Turbulent
Transport
It is turbulence that allows the boundary
layer to respond to changing surface
forcings
The frequent lack of turbulence above
the boundary layer means that the rest
of the free atmosphere cannot respond
to surface changes
Wind Profile
• Due to the forcing at the surface of the earth, wind speed with
elevation changes
• The profile match with logarithmic scale
• Called as logarithmic wind profile
the layer in w
increases from zero near or at the surface to a maximum (and
Wind Profile
Climate Resilient
Cities
Lecture 6
(clear sky)
Diurnal Cycle
• End of night:
• Shallow nocturnal BL in which
• mixing is caused by wind friction. • Depth
depends on wind velocity
• and surface roughness
• Depth generally below 300 m
• Air above NBL is lightly stratified
• due to heat loss to space during night
Diurnal Cycle
(clear sky)
• Start of day:
• Solar radiation heats up earth
• surface which heats up the ABL
• from below
• Convective motions override wind• shear turbulence convective
• BL that develops upward
• Wind-induced turbulence is much
• weaker than convection-induced turbulence except in the
surface layer
• • Surface layer: more or less equal intensity of wind-induced
and convection-induced turbulence
(clear sky)
Diurnal Cycle
• End of day:
• Sunset stops heating of the ABL
• New NBL develops
• SynopCc scale (L > 2000 km)
Meteorological
scales
• Mesoscale – (200 km < L < 2000 km) • Mesoscale- (20km Purchase answer to see full attachment

  
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