introduction to meteorology

1. Meteorology
Background
concepts

2. Meteorology
chapter 3 of text
CCE 524
January 2011
Meteorology is the study and
forecasting of weather changes
resulting from large scale
atmospheric circulation

3. Introduction
Once emitted pollutants:
 Transported
 Dispersed
 concentrated
By meteorological conditions

4. Layer nomenclature in the atmosphere

8.
Light scattering

9. Orographic rainfall

10. Emission
Transport
Diffusion or
concentration
Deposition onto
vegetation, livestock,
soil, water, or escape into
space
Air Pollutant Cycle

11. Transport
Pollutants moved from source
May undergo physical and chemical
changes
 Smog – interaction of NOx, HC, and solar
energy
 Ozone formation

12. Concentration & Dispersion
Disperse based on meteorological &
topographic conditions
Concentration --- usually stagnant conditions
Dispersion
 Topological conditions
 Affected by presence of large buildings
 Meteorological conditions
 prevailing wind speed & direction
Pollutants disperse over geographic area
Any location receives pollutants from different
sources in different amounts
Need to understand how pollutants disperse
to predict concentrations and predict
violations at a particular location

13. Prediction
Mathematical models of local atmosphere
determine transport and dispersion patterns
With emission data – predict concentrations
throughout region
Should correlate with data from monitoring
locations
Effect of sources can be estimated &
regulations set

14. Dispersion
General mean air motion
Turbulent velocity fluctuations
Diffusion due to concentration gradients –
from plumes
Aerodynamic characteristics of pollution
particles
 Size
 Shape
 Weight

15. Atmosphere
Gas composition (changes very little with time
or place in most of atmosphere
 78% nitrogen
 21% oxygen
 1% argon & other trace gases
Moisture content
 Water vapor
 Water droplets
 Ice crystals

16. Atmosphere
Relative humidity (RH): ratio of water
content to air
Increases with increasing temperatures

17. Atmosphere
Has well-defined lower boundary with water &
land
Upper boundary becomes increasingly
thinner
50% of atmospheric mass is within 3.4 miles
of earth
99% is within 20 miles of earth
Large width & small depth
Most motion is horizontal
Vertical motion ~ 1 to 2x less than horizontal

18. Solar Radiation
At upper boundary of atmosphere, vertical
solar radiation = 8.16 J/cm2
min (solar
constant)
Maximum intensity at λ = 0.4 to 0.8 μm =
visible portion of electromagnetic spectrum
~ 42% of energy
 Absorbed by higher atmosphere
 Reflected by clouds
 Back-scattered by atmosphere
 Reflected by earth’s surface
 Absorbed by water vapor & clouds
47% adsorbed by land and water

19. Insolation
Quantity of solar radiation reaching a
unit area of the earth’s surface
 Angle of incidence
 Thickness of the atmosphere
 Characteristics of surface
Albedo: fraction of incident radiation
that is reflected by a surface

20. Solar Incidence Angle
angle between sun’s
rays and an imaginary
line perpendicular to the
surface (0º)
maximum solar gain is
achieved when incidence
angle is 0º
Tangent in morning and
approximately
perpendicular
angle depends on surface
Information and image source: http://www.visualsunchart.com/VisualSunChart/SolarAccessConcepts/

21. Wind Circulation
Sun, earth, and atmosphere form dynamic
system
Differential heating of gases leads to
horizontal pressure gradients → horizontal
movement
Large scale movement
 Poles
 Equator
 Continents
 oceans
Small scale movement
 Lakes
 Different surfaces

22. Wind Circulation
Average over a year, solar heat flow to the
earth’s surface at equator is 2.4x that at poles
Air moves in response to differences
Heat transports from equator to poles
 Like air circulation from a heater in a room
Without rotation
Air flows directly from high to low pressure
areas (fp)

23. Wind Circulation
Average over a year, solar heat flow to the
earth’s surface at equator is 2.4x that at poles
Air moves in response to differences
Heat transports from equator to poles
 Rises from equator, sinks at poles
 Equator to pole at high altitudes
 Pole to equator at low altitudes
 Like air circulation from a heater in a room

24. Wind Circulation
Air flows directly from
high to low pressure
areas (fp)

26. Wind Circulation
Same principle as room heater but not
as neat because atmosphere is so thin
 Height vs width
 Flow is mechanically unstable
 Breaks into cells

28. Note differences in flow between cells

29. Sinking
boundaries
Rising
Boundaries

30. Wind Circulation
Rising air cools & produces rain
Sinking air is heated and becomes dry
Rising boundaries are regions of of higher
than average rainfall
 Equator
 Rain forests
 Temperate forests
Sinking boundaries are regions of lower than
average rainfall
 Most of world’s deserts
 Poles – small amounts of precipitation remains
due to low evaporation

31. Rotation
Without rotation
Air flows directly from high to low
pressure areas (fp)
Rotation of earth affects movement

32. Effect of rotation on
baseball thrown at
North Pole
Space observer
sees straight path
Catcher moves –
ball appears to
curve to the left

33. Coriolis forces

34. Inertial atmospheric rotation
Schematic representation
of inertial circles of air
masses in the absence of
other forces, calculated
for a wind speed of
approximately 50 to 70
m/s. Note that the
rotation is exactly
opposite of that normally
experienced with air
masses in weather
systems around
depressions.

35. Low-pressure area flows
Schematic represen-
tation of flow around a
low-pressure area in
the Northern hemi-
sphere. The Rossby
number is low, so the
centrifugal force is
virtually negligible. The
pressure-gradient force
is represented by blue
arrows, the Coriolis
acceleration (always
perpendicular to the
velocity) by red arrows

36. Low-pressure system If a low-pressure area
forms in the atmosphere,
air will tend to flow in
towards it, but will be
deflected perpendicular
to its velocity by the
Coriolis force.
This low pressure system
over Iceland spins
counter-clockwise due to
balance between the
Coriolis force and the
pressure gradient force.

37. Hurricane

38. Atmospheric regions & cells

39. Regions and cells

40. Rotation
Coriolis force –
horizontal deflection
force (fcor)
Acts at right angles to
the motion of the body
Is proportional to the
velocity of the moving
body
Northern hemisphere
turns body to the right
Southern hemisphere
turns body to the left

41. Isobar
Areas of equal
pressure

42. Frictional Force
Movement of air near surface is retarded by
effects of friction (ff) due to surface roughness
or terrain
Opposite to wind direction
Wind direction is perpendicular to Coriolis
Directly reduces wind speed and
consequently reduces Coriolis force (which is
proportional to wind speed)

43. Frictional Force

44. Friction force is maximum at earth’s surface
Decreases as height increases
Effect on tall stack not consistent
Effect negligible with strong winds > 6 m/s
Effect at lower speeds < 6 m/s more
significant
Frictional Force

45. Frictional Force
Ф = 5 to 15° over
ocean
Ф = 25 to 45° over land
As pollutants move
downstream they
diffuse outwardly in y
direction
Disperse vertically in
the z direction

46. Influence of Ground & Sea
Figure 5-2, simplistic
representation
In reality, land & water do
not respond to solar
heating similarly
Terrain is uneven
 Highest mountains rise
above most of atmosphere
 Large mountain ranges
are major barriers to
horizontal winds
 Even small mountain
ranges influence wind
patterns

47. Influence of Ground & Sea
Water adsorbs and transfer heat
differently than rock & soil
Rock and soil radiate heat differently
summer to winter

48. Vertical Motion
Any parcel of air less dense than
surrounding air will rise by buoyancy
any parcel more dense will sink
Most vertical movement is due to
changes in air density
The pressure at any point in the
atmosphere = pressure required to
support everything above that point

49. Properties of Gases
If volume of gas is held constant and heat is
applied, temperature and pressure rise
if volume is not held constant and pressure
is held constant, gas will expand and
temperature will rise
Adiabatic expansion or contraction: an
amount of gas is allowed to expand or
contract due to a change in pressure (such as
it would encounter in the atmosphere)
assuming no heat transfer with atmosphere

50. Lapse Rate
Important characteristic of atmosphere is
ability to resist vertical motion: stability
Affects ability to disperse pollutants
When small volume of air is displaced upward
 Encounters lower pressure
 Expands to lower temperature
 Assume no heat transfers to surrounding
atmosphere
 Called adiabatic expansion

51. Adiabatic expansion
To determine the change in temp. w/ elevation due to adiabatic
expansion
 Atmosphere considered a stationary column of air in a
gravitational field
 Gas is a dry ideal gas
 Ignoring friction and inertial effects
(dT/dz)adiabatic perfect gas = - vpg
Cp
T = temperature
z = vertical distance
g = acceleration due to gravity
p = atmospheric density
v = volume per unit of mass
Cp = heat capacity of the gas at constant pressure

52. Adiabatic expansion
If the volume of a parcel of air is held
constant and an incremental amount of heat
is added to the parcel, temperature of the
parcel will rise by an amount dT
Resultant rise in temperature produces a rise
in pressure according to ideal gas law
If the parcel is allowed to expand in volume
and have a change in temperature, while
holding the pressure constant, the parcel will
expand or contract and increase or decrease
in temp.
Parcel rises or falls accordingly

53. Adiabatic expansion
SI:
(dT/dz)adiabatic perfect gas = -0.0098°C/m
American:
(dT/dz)adiabatic perfect gas = -5.4°F/ft
Change in temp. with change in height

54. Lapse rate is the negative of temperature
gradient
Dry adiabatic lapse rate =
Metric:
Γ = - 1°C/100m or
SI:
Γ = - 5.4°F/1000ft
Lapse rate

55. Lapse rate
Important characteristic of atmosphere is ability to
resist vertical motion: stability
Comparison of Γ to actual environment lapse rate
indicates stability of atmosphere
Degree of stability is a measure of the ability of the
atmosphere to disperse pollutants
Determines if rising parcel of air will rise high enough
for water to condense to form clouds

56. International lapse rate
Factors vary somewhat
 M
 Cp
Meteorologists and aeronautical engineers
have defined
 “standard atmosphere”
 Represents approximate average of all
observations over most of the world
 Summer & winter
 Day & night

57. International Lapse Rate
SI:
Γ = - 6.49°C/km or 0.65 o
C/100m
American:
Γ = - 3.45°F/1000ft
About 66% of adiabatic lapse rate

58. Lapse Rate Example
Assuming the surface temperature is 15° at
the surface of the earth, what is the
temperature at 5510.5 m?
Γ = 6.49°C/km
Solution:
5510.5 m = 5.5105 km
For each km the temperature decreases 6.49°
So the temperature decreases:
5.5105 x 6.49 = 35.76°
Original temp was 15°, temp at 5.5105 km =
15° - 35.76° = -20.76°C

59. Temperature change due to
atmospheric height
Lapse rate for “standard atmosphere”
Troposphere:
 0 to 36,150 feet
 Temperature decreases linearly
 75% of atmospheric mass
Not applicable above troposphere
Stratosphere
 36,150 to 65,800 feet
 Temperature does not decrease further with
increasing height
 Chemical reaction occur to absorb heat from the
sun
 Adiabatic assumption is not followed

61. Atmospheric Stability
Affects dispersion of pollutants
Temperature/elevation relationship principal
determinant of atmospheric stability
Stable
 Little vertical mixing
 Pollutants emitted near surface tend to stay there
 Environmental lapse rate is same as the dry
adiabatic lapse rate
4 common scenarios

62. Neutral
 Environmental lapse rate is same as the dry
adiabatic lapse rate
 A parcel of air carried up or down will have same
temp as environment at the new height
 No tendency for further movement

63. Superadiabatic --- Unstable
 Environmental lapse rate > Γ
 i.e. Actual temp. gradient is more negative
 Small parcel of air displaced approximates adiabatic
expansion
 Heat transfer is slow compared to vertical movement
 At a given point, Tparcel > Tsurrounding air
 less dense than surrounding air

64. Subadiabatic --- Stable
 Environmental lapse rate < Γ
 greater temp. gradient
 No tendency for further vertical movement due to temp. differences
 Any parcel of air will return to its original position
 Parcel is colder than air above – moves back

65. Inversion --- Strongly Stable
 Environmental lapse rate is negative
 Temp. increases with height
 No tendency for further vertical movement due to temp. differences
 Any parcel of air will return to its original position
 Parcel is colder than air above – moves back
 Concentrates pollutants

66. Inversions
Stability lessens exchange of wind energy
between air layers near ground and high
altitude winds
Horizontal & vertical dispersions of
pollutants are hampered
Influenced by:
 Time of year
 Topography
 Presence of water or lakes
 Time of day
Image source:
http://www.unc.edu/courses/2005fall/geog/011/001/AirPollu
tion/AirPollution.htm

67. From San Francisco Bay area: “Pollutants are
carried from the ocean through mountain
passes on an almost daily basis during the
summer months”
Image and text source:
http://www.sparetheair.
org/teachers/bigpicture/
IIIA1a.html

68. “Streams of air carrying Bay Area emissions mix with locally generated
pollution from automobile traffic, small engine exhaust, industry, and
agriculture in the Valley and are diverted both north and south”
Image and text source:
http://www.sparetheair.org/teach
ers/bigpicture/IIIA1a.html

69. “A warm inversion layer acts like a blanket on the
smog layer, preventing it from dissipating higher
in the atmosphere. Because of high pressure, the
Central Valley regularly experiences these
thermal inversions. The Valley, which is nearly at
sea level, often fills at night with cool heavy air
underneath a layer of warmer air. The cool air
layer grows through the night reaching up to 3000
feet thick. “
Image and text source:
http://www.sparetheair.org/teach
ers/bigpicture/IIIA1a.html

70. Two Types of Inversion
Radiation Inversion
 Surface layers receive heat
by conduction, convection,
and radiation from earth’s
surface
Subsidence Inversion
 Cloud layer absorbs incoming
solar energy or high-pressure
region with slow net
downward flow or air and light
winds
 Sinking air mass increases in
temp and becomes warmer
than air below it
 Usually occur 1,500 to 15,000
feet above ground & inhibit
atmospheric mixing
 Common in sunny, low-wind
Subsidence Inversion
Image Source:
http://apollo.lsc.vsc.edu/classes/met130/notes/chapter17/fav_con
ditions.html

71. Two more Types of Inversion
Cold Air Flowing Under
 Nighttime flow of cold air down valleys
 Col air flows under warm air
 Winter
 Presence of fog blocks sun and inversion persists
 Sea or lake breezes also bring cold air under
warm air
Warm Air Flowing Over
 Same as above but warm air flows over cold
trapping it
 Warm air frequently overrides colder more dense

72. Stability Classes
Developed for use in dispersion models
Stability classified into 6 classes (A – F)
 A: strongly unstable
 B: moderately unstable
 C: slightly unstable
 D: neutral
 E: slightly stable
 F: moderately stable

74. Wind Velocity Profile
Friction retards wind movement
Friction is proportional to surface roughness
Location and size of surface objects produce
different wind velocity gradients in the vertical
direction
Area of atmosphere influenced by friction –
planetary boundary layer – few hundred m to
several km above earth’s surface
Depth of boundary layer > unstable than
stable conditions

75. Wind Velocity Profile
Wind speed varies by height
International standard height for wind-
speed measurements is 10 m
Dispersion of pollutant is a function of
wind speed at the height where
pollution is emitted
But difficult to develop relationship
between height and wind speed

76. Wind Velocity Profile
Power law of Deacon
u/u1 = (z/z1)p
U: wind speed at elevation z
z: elevation
p: exponent based on terrain and surface cover
and stability characteristics

77. Wind Velocity Profile

80. Wind Direction
Does the wind blow from my house towards a
smelly feedlot or the other way?
High and low-pressure zones
 Formed from large scale instabilities
 Often near boundaries of circulation zones
 Air is rising or sinking
 Major storms often associated with low-pressure
Topography
 Air heats and cools differently on different
surfaces, causes air from
 Lake to shore, etc.
 Mountains block low-level wind

82. Predicting Wind Direction
Need to know distribution of wind direction for
estimating pollution concentrations
Need speed and direction
Wind Rose
 Average of wind speed and direction over time
 Shows
 Frequency
 Speed
 direction
 Wind direction is direction from which the wind is
coming

84. Mixing Height
Vigorous mixing to a certain height (z) and
little effect above that
Rising air columns mix air vertically &
horizontally
Rising air mixes and disperses pollutants
Only mixes to “mixing” height no above it
Different in summer vs winter, morning vs
evening
For inversions, mixing height can be close to
0
Thermal buoyancy determines depth of
convective mixing depth

85. Mixing Height
Usually corresponds to tops of clouds
Different shapes but reach about same height
Up to mixing height unstable air brings
moisture up from below to form clouds –
above mixing height there is no
corresponding upward flow
Strong delineation at
stratosphere/troposphere boundary
Stratosphere very stable against mixing
 Where commercial air lines fly, air clear and non
turbulent
 Very clear boundary

86. Mixing Height

88. Mechanics of Mixing Height
Parcel heated by solar radiation
at earth’s surface
Rises until temperature T’ = T
T’ = particle’s temp
T = atmospheric temp
Achieves neutral equilibrium, no
tendency for further upward
motion

89. Turbulence
Not always completely understood
2 types
 Atmospheric heating
 Causes natural convection currents --- discussed
 Thermal eddies
 Mechanical turbulence
 Results from shear wind effects
 Result from air movement over the earth’s surface,
influenced by location of buildings and relative
roughness of terrain

90. General Characteristics of
Stack Plumes
Dispersion of pollutants
 Wind – carries pollution downstream from source
 Atmospheric turbulence -- causes pollutants to
fluctuate from mainstream in vertical and cross-
wind directions
Mechanical & atmospheric heating both
present at same time but in varying ratios
Affect plume dispersion differently

92. Six Classes of Plume
Behavior
Looping:
 high degree of
convective turbulence
 Superadiabatic lapse
rate -- strong instabilities
 Associated with clear
daytime conditions
accompanied by strong
solar heating & light
winds
Image Source:
http://apollo.lsc.vsc.edu/classes/met130/notes/chapt

93. Six Classes of Plume
Behavior
Coning:
 Occurs under neutral
conditions
 Stable with small-scale
turbulence
 Associated with overcast
moderate to strong winds
 Roughly 10° cone
 Pollutants travel fairly
long distances before
reaching ground level in
significant amounts
Image Source:
http://apollo.lsc.vsc.edu/classes/met130/
notes/chapter17/fav_conditions.html

94. Six Classes of Plume
Behavior
Fanning:
 Occurs under large negative
lapse rate
 Strong inversion at a
considerable distance above
the stack
 Extremely stable atmosphere
 Little turbulence
 If plume density is similar to air,
travels downwind at
approximately same elevation
Image Source:
http://apollo.lsc.vsc.edu/classes/met130/
notes/chapter17/fav_conditions.html

95. Six Classes of Plume
Behavior
Fumigation:
 Stable layer of air lies a
short distance above
release point with
unstable air beneath
 Usually early morning
after an evening with a
stable inversion
 Significant ground level
concentrations may be
reached
Image Source:
http://apollo.lsc.vsc.edu/classes/met130/
notes/chapter17/fav_conditions.html

97. Six Classes of Plume
Behavior
Lofting
 Opposite conditions of fumigation
 Inversion layer below with unstable
layer through and above
 Pollutants are dispersed downwind
without significant ground-level
concentration
Trapping
 Inversion above and below stack
 Diffusion of pollutants is limited to
layer between inversions Image Source:
http://apollo.lsc.vsc.edu/classes/met130/
notes/chapter17/fav_conditions.html

98. Assignment 3
Problems:
 3.7
 3.9
 3.14
 Due Thu Feb. 3rd