BASIC
METEOROLOGICAL
PROCESSES
Objectives
What is atmospheric thermodynamics?
What are the variables of atmospheric thermodynamics?
What is lapse rate?
Explain the potential temperature.
What is atmospheric stability and the various methods that
define atmospheric stability?
What is boundary layer development?
What are the effects of meteorology on plume dispersion?
What is wind velocity profile?
What is wind rose diagram and what are the uses of it?
Determination of mixing height.
A
IR
P
OLLUTION
M
ETEOROLOGY
Atmospheric thermodynamics
Atmospheric stability
Boundary layer development
Effect of meteorology on plume dispersion
A
TMOSPHERE
Pollution
cloud
is
interpreted
by
the
chemical
composition
and
physical
characteristics
of
the
atmosphere
Concentration
of
gases
in
the
atmosphere
varies
from
trace
levels
to
very
high
levels
Nitrogen
and
oxygen
are
the
main
constituents
.
Some
constituents
such
as
water
vapor
vary
in
space
and
time
.
Four
major
layers
of
earth’s
atmosphere
are
:
Troposphere
Stratosphere
Mesosphere
Thermosphere
A
TMOSPHERIC
T
HERMODYNAMICS
A parcel of air is defined using the state variables
Three important state variables are density, pressure
and temperature
The units and dimensions for the state variables are
Density
(mass/volume)
gm/cm
3
ML

3
Pressure (Force/Area)
N/m
2
( P
a
)
ML

1
T

2
Temperature
o
F,
o
R,
o
C,
o
K
T
Humidity is the fourth important variable that gives the
amount of water vapor present in a sample of moist air
E
QUATION
OF
S
TATE
Relationship between the three state variables may be
written as:
f ( P, ρ ,T) = 0
For a perfect gas:
P = ρ .R .T
R is Specific gas constant
R for dry air = 0.287
Joules / gm /
o
K
R for water vapor = 0.461 Joules / gm /
o
K
R for wet air is not constant and depend on mixing ratio
Exercise
Calculate the density of a gas with a molecular weight of 29 @ 1
atm (absolute) and 80
o
F. Gas constant, R = 0.7302 ft
3
atm/lb

mole
o
R.
Solution
Absolute Temperature = 80
o
F + 460 = 540
o
R
Density = P ( molecular weight) / RT
Density = ( 1atm. )*(29 lb/lb mole) / ( 0.7302 ft
3
atm/lb

mole
o
R)*(540
o
R)
Density = 0.073546 lb/ ft
3
.
Exercise
Determine the pressure, both absolute and gauge, exerted at the
bottom of the column of liquid 1 meter high, with density of 1000
kg / m3.
Solution
Step 1
:
Pgauge = (density of liquid) * ( acceleration due to gravity)
*(height of liquid column)
Step 2
:
Pabsolute = Pgauge + Patmospheric
Pabsolute = 111.11 kPa
L
AWS
OF
T
HERMODYNAMICS
First Law of Thermodynamics:
This law is based on law of conservation of total energy.
Heat added per unit mass =
(Change in internal energy per unit mass)
+ (Work done by a unit mass)
δH = δU+δW
Second Law of Thermodynamics:
This law can be stated as "no cyclic process exists having the
transference of heat from a colder to hotter body as its sole
effect"
S
PECIFIC
H
EAT
Defined as the amount of heat needed to change the
temperature of unit mass by 1
o
K.
Specific heat at constant volume
C
v
= lim
δQ
δT
→
0 δT
α = const
Specific heat at constant pressure
C
p
= lim
δQ
δT
→
0 δT
p = const
Relationship between C
v
and C
p
is given by Carnot’s law:
For perfect gas, C
p
–
C
v
= R
For dry air C
p
= (7/2)*R (Perfect diatomic gas)
C
v
= (5/2)*R (Perfect diatomic gas)
Ratio of C
p
and C
v
for dry air is 1.4
C
pd
= 1.003 joules/gm/
o
K ;
C
vd
= 0.717 joules/gm/
o
K
P
ROCESSES
IN
THE
A
TMOSPHERE
An air parcel follows several different paths when it
moves from one point to another point in the
atmosphere. These are:
Isobaric change
–
constant pressure
Isosteric change
–
constant volume
Isothermal change
–
constant temperature
Isentropic change
–
constant entropy (E)
Adiabatic Process
–
δQ = 0
(no heat is added or
removed )
The adiabatic law is P. α
γ
= constant
E =
S
TATICS
OF
THE
A
TMOSPHERE
Vertical variation of the parameters = ?
Hydrostatic Equation:
Pressure variation in a "motionless" atmosphere
Pressure variation in an atmosphere:
Relationship between pressure and elevation using gas law:
S
TATICS
OF
THE
A
TMOSPHERE
Integration of the above equation gives
Using the initial condition Z=0, P = P
0
The above equation indicates that the variation of
pressure depends on vertical profile of temperature.
For iso

thermal atmosphere
Therefore, pressure decreases exponentially with
height at a ratio of 12.24 mb per 100m.
Lapse Rate:
Lapse rate is the rate of change of temperature with
height
Lapse rate is defined as Γ =

δT
δz
Value of
Γ varies throughout the atmosphere
Potential Temperature:
Concept of potential temperature is useful in comparing two air
parcels at same temperatures and different pressures.
C
ONCEPT
OF
P
OTENTIAL
T
EMPERATURE
θ
A
TMOSPHERE
S
TABILITY
The ability of the atmosphere to enhance or to resist
atmospheric motions
Influences the vertical movement of air.
If the air parcels tend to sink back to their initial level after
the lifting exerted on them stops, the atmosphere is
stable
.
If the air parcels tend to rise vertically on their own, even
when the lifting exerted on them stops, the atmosphere is
unstable
.
If the air parcels tend to remain where they are after lifting
stops, the atmosphere is
neutral
.
A
TMOSPHERIC
S
TABILITY
The stability depends on the ratio of suppression to
generation of turbulence
The stability at any given time will depend upon static
stability ( related to change in temperature with height ),
thermal turbulence ( caused by solar heating ), and
mechanical turbulence (a function of wind speed and
surface roughness).
A
TMOSPHERIC
S
TABILITY
Atmospheric stability can be determined using adiabatic
lapse rate.
Γ >
Γ
d
Unstable
Γ = Γ
d
Neutral
Γ <
Γ
d
Stable
Γ is environmental lapse rate
Γ
d
is dry adiabatic lapse rate (1
0
c/100m) and
dT
/
dZ
=

1
0
c /100 m
A
TMOSPHERIC
S
TABILITY
C
LASSIFICATION
Schemes to define atmospheric stability are:
P

G Method
P

G / NWS Method
The STAR Method
BNL Scheme
Sigma Phi Method
Sigma Omega Method
Modified Sigma Theta Method
NRC Temperature Difference Method
Wind Speed ratio (U
R
) Method
Radiation Index Method
AERMOD Method (Stable and Convective cases)
P
ASQUILL

GIFFORD
S
TABILITY
C
ATEGORIES
Surface Wind
Speed (m/s
)
Daytime Insolation
Nighttime cloud
cover
Strong
Moderate
Slight
Thinly
overcast or 4/8
low cloud
3/8
< 2
A
A

B
B


2

3
A

B
B
C
E
F
3

5
B
B

C
C
D
E
5

6
C
C

D
D
D
D
> 6
C
D
D
D
D
Source: Met Monitoring Guide
–
Table 6.3
S
IGMA
T
HETA
STABILITY
CLASSIFICATION
CATEGORY
PASQUILL CLASS
SIGMA THETA (ST)
EXTREME UNSTABLE
A
ST>=22.5
MODERATE UNSTABLE
B
22.5>ST>=17.5
SLIGHTLY UNSTABLE
C
17.5>ST>=12.5
NEUTRAL
D
12.5>ST>=7.5
SLIGHTLY STABLE
E
7.5>ST>= 3.8
MODERATE STABLE
F
3.8>ST>=2.1
EXTREMELY STABLE
G
2.1>ST
Source: Atmospheric Stability
–
Methods & Measurements (NUMUG

Oct 2003)
T
EMPERATURE
D
IFFERENCE
(∆T)
Source: Regulatory guide; office of nuclear regulatory research

Table 1
T
URBULENCE
Fluctuations in wind flow which have a frequency of
more than 2 cycles/ hr
Types of Turbulence
Mechanical Turbulence
Convective Turbulence
Clear Air Turbulence
Wake Turbulence
L
OCAL
CLIMATOLOGICAL
DATA

T
OLEDO
W
EATHER
CONDITIONS
OF
TOLEDO
Weather Station
Home, Professional, and Live
Weather Balloon
Pressure, Temperature, Wind Speed, Wind Direction, &
Humidity
Use of Towers
Velocity, Temperature, & Turbulence
L
OCAL
CLIMATOLOGICAL
DATA

T
OLEDO
Greatest snowfall
–
73.1” (1997

1998)
Least snowfall
–
6.0” (1889

1890)
Average number of days with a tenth of an inch or more
snowfall
–
27 days
Annual
38.3”
D散emb敲
9.1”
January
9.8”
䙥Fruary
8.0”
䵡r捨
6.3”
Snowfall
Annual
49.6
°
F
January
25.7
°
F
July
73.2
°
F
Temperature
Annual
31.62”
䩡nuary
2.18”
䩵ne
3.45”
Precipitation
National Weather Map
US Forecast
National Air Quality
Ozone
Climate
Temperature
N
ATIONAL
W
EATHER
M
AP
H
–
High Pressure Area
L
–
Low Pressure Area
•
A high pressure area forecasts clear skies.
•
A low pressure area forecasts cloudiness and precipitation
B
OUNDARY
L
AYER
D
EVELOPMENT
B
OUNDARY
L
AYER
D
EVELOPMENT
Thermal boundary Layer (TBL) development depends on
two factors:
Convectively produced turbulence
Mechanically produced turbulence
Development of TBL can be predicted by two distinct
approaches:
Theoretical approach
Experimental studies
B
OUNDARY
L
AYER
D
EVELOPMENT
Theoretical approach may be classified into three
groups:
Empirical formulae
Analytical solutions
Numerical models
One layer models
Higher order closure models
TBL
USING
A
NALYTICAL
S
OLUTION
Time
Time
Time
Time
E
FFECTS
OF
M
ETEOROLOGY
ON
P
LUME
D
ISPERSION
E
FFECTS
OF
M
ETEOROLOGY
ON
P
LUME
D
ISPERSION
Dispersion of emission into atmosphere depends on
various meteorological factors.
Height of thermal boundary layer is one of the
important factors responsible for high ground level
concentrations
At 9 AM pollutants are pulled to the ground by
convective eddies
Spread of plume is restricted in vertical due to thermal
boundary height at this time
W
IND
V
ELOCITY
A power law profile is used to describe the variation of
wind speed with height in the surface boundary layer
U = U
1
(Z/Z
1
)
p
Where,
U
1
is the velocity at Z
1
(usually 10 m)
U is the velocity at height Z.
The values of p are given in the following table.
Stability Class
Rural p
Urban p
Very Unstable
0.07
0.15
Neutral
0.15
0.25
Very Stable
0.55
0.30
B
EAUFORT
S
CALE
This scale is helpful in getting an idea on the magnitude
of wind speed from real life observations
Atmospheric
condition
Wind speed
Comments
Calm
< 1mph
Smoke rises vertically
Light breeze
5 mph
Wind felt on face
Gentle breeze
10 mph
Leaves in constant motion
Strong
25 mph
Large branches in motion
Violent storm
60 mph
Wide spread damage
W
IND
R
OSE
D
IAGRAM
(WRD)
Wind Direction (%)
Wind Speed (mph)
W
IND
R
OSE
D
IAGRAM
(WRD
)
WRD provides the graphical summary of the
frequency distribution of wind direction and wind
speed over a period of time
Steps to develop a wind rose diagram from hourly observations
are:
Analysis for wind direction
Determination of frequency of wind in a given wind
direction
Analysis for mean wind speed
Preparation of polar diagram
Calculations for Wind Rose
% Frequency =
Number of observations * 100/Total Number of
Observations
Direction: N, NNE,

,NNW, Calm
Wind speed: Calm, 1

3, 4

6, 7

10,

D
ETERMINATION
OF
M
AXIMUM
M
IXING
H
EIGHT
Steps to determine the maximum mixing height for a
day are:
Plot the temperature profile, if needed
Plot the maximum surface temperature for the day
on the graph for morning temperature profile
Draw dry adiabatic line from a point of maximum
surface temperature to a point where it intersects
the morning temperature profile
Read the corresponding height above ground at the
point of intersection obtained. This is the
maximum
mixing height for the day
D
ETERMINATION
OF
M
AXIMUM
M
IXING
H
EIGHT
P
OWER
PLANT
P
LUMES
IN
M
ICHIGAN
Monroe Power Plant
P
OWER
PLANT
P
LUMES
IN
M
ICHIGAN
Trenton Channel
P
OWER
PLANT
P
LUMES
IN
M
ICHIGAN
Belle River Power Plant
River Rouge Power Plant
Photo credit:
Kimberly M. Coburn
PROBLEMS
During an air pollution experiment the lapse rate was a
constant at 1.1
°
C per 100 m. If the atmosphere is assumed
to behave as a perfect gas and the sea level temperature
and pressure were 16
°
C and 1 atm, at what altitude was
the pressure one

third the sea level?
S
OLUTION
Step1:
Step 2:
Calculate Temperature
Step 3:
Substitute for temperature
Step 4:
Integrate between P = 1 and P = 0.333, and between z = 0, and z = z.
Z = 7817.13m
R
EFERENCES
Met Monitoring Guide:
http://www.webmet.com/met_monitoring/toc.html
Regulatory Guide
–
office of nuclear regulatory research:
http://www.nrc.gov/reading

rm/doc

collections/reg

guides/power

reactors/active/01

023/01

023r1.pdf
NOAA

National Climate Data Center
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