Basic meteorological processes

1. BASIC
METEOROLOGICAL
PROCESSES

2. 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.

3. AIR POLLUTION METEOROLOGY
 Atmospheric thermodynamics
 Atmospheric stability
 Boundary layer development
 Effect of meteorology on plume dispersion

4. ATMOSPHERE
 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

5. ATMOSPHERIC THERMODYNAMICS
 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/cm3 ML-3
Pressure (Force/Area) N/m2 ( Pa ) ML-1T-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

6. EQUATION OF STATE
 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 /oK
 R for water vapor = 0.461 Joules / gm /oK
 R for wet air is not constant and depend on mixing ratio

7. Exercise
 Calculate the density of a gas with a molecular weight of 29 @ 1 atm
(absolute) and 80 oF. Gas constant, R = 0.7302 ft3atm/lb-moleoR.

8. Solution
Absolute Temperature = 80 oF + 460 = 540 oR
Density = P ( molecular weight) / RT
Density = ( 1atm. )*(29 lb/lb mole) / ( 0.7302 ft3atm/lb-moleoR)*(540 oR)
Density = 0.073546 lb/ ft3.

9. 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.

10. Solution
 Step 1 :
Pgauge = (density of liquid) * ( acceleration due to gravity)
*(height of liquid column)
Step 2 :
Pabsolute = Pgauge + Patmospheric
Pabsolute = 111.11 kPa

11. LAWS OF THERMODYNAMICS
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"

12. SPECIFIC HEAT
 Defined as the amount of heat needed to change the
temperature of unit mass by 1oK.
 Specific heat at constant volume
Cv = lim δQ
δT→0 δT α = const
 Specific heat at constant pressure
Cp = lim δQ
δT→0 δT p = const
Relationship between Cv and Cp is given by Carnot’s law:
 For perfect gas, Cp – Cv = R
 For dry air Cp = (7/2)*R (Perfect diatomic gas)
Cv = (5/2)*R (Perfect diatomic gas)
 Ratio of Cp and Cv for dry air is 1.4
Cpd = 1.003 joules/gm/o K ; Cvd = 0.717 joules/gm/o K

13. PROCESSES IN THE ATMOSPHERE
 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. αγ = constant
 E =  T
Q

14. STATICS OF THE ATMOSPHERE
 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:
g
z
p
org
z
p








1
.
2
2
1
dt
zd
z
p
g 




TR
g
z
p
p d



1

15. STATICS OF THE ATMOSPHERE
 Integration of the above equation gives
 Using the initial condition Z=0, P = P0
 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.





 
 
 zT
R
g
p
p
o
do
.exp 1







 









z
do
dzT
R
g
p
p
0
1
.ln

17.  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.

18. CONCEPT OF POTENTIAL TEMPERATURE
θ

19. ATMOSPHERE STABILITY
 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.

20. ATMOSPHERIC STABILITY
 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).

21. ATMOSPHERIC STABILITY
 Atmospheric stability can be determined using adiabatic
lapse rate.
Γ > Γd Unstable
Γ = Γd Neutral
Γ < Γd Stable
 Γ is environmental lapse rate
 Γd is dry adiabatic lapse rate (10c/100m) and dT/dZ = -10c /100 m

22. ATMOSPHERIC STABILITY CLASSIFICATION
 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 (UR) Method
 Radiation Index Method
 AERMOD Method (Stable and Convective cases)

23. PASQUILL-GIFFORD STABILITY CATEGORIES
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

24. SIGMA THETA 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)

25. TEMPERATURE DIFFERENCE (∆T)
Source: Regulatory guide; office of nuclear regulatory research- Table 1

26. TURBULENCE
 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

27. LOCAL CLIMATOLOGICAL DATA - TOLEDO

28. WEATHER CONDITIONS OF TOLEDO

29. Weather Station
 Home, Professional, and Live

30. Weather Balloon
 Pressure, Temperature, Wind Speed, Wind Direction, &
Humidity

31. Use of Towers
 Velocity, Temperature, & Turbulence

32. LOCAL CLIMATOLOGICAL DATA - TOLEDO
 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”
December 9.1”
January 9.8”
February 8.0”
March 6.3”
Snowfall
Annual 49.6°F
January 25.7°F
July 73.2°F
Temperature
Annual 31.62”
January 2.18”
June 3.45”
Precipitation

33. National Weather Map
 US Forecast

34. National Air Quality
 Ozone

35. Climate
 Temperature

36. NATIONAL WEATHER MAP
H – High Pressure Area
L – Low Pressure Area
•A high pressure area forecasts clear skies.
•A low pressure area forecasts cloudiness and precipitation

37. BOUNDARY LAYER DEVELOPMENT

38. BOUNDARY LAYER DEVELOPMENT
 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

39. BOUNDARY LAYER DEVELOPMENT
 Theoretical approach may be classified into three
groups:
 Empirical formulae
 Analytical solutions
 Numerical models
 One layer models
 Higher order closure models

40. TBL USING ANALYTICAL SOLUTION
Time
Time
Time
Time

41. EFFECTS OF METEOROLOGY ON PLUME
DISPERSION

42. EFFECTS OF METEOROLOGY ON PLUME
DISPERSION
 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

43. WIND VELOCITY
 A power law profile is used to describe the variation of
wind speed with height in the surface boundary layer
U = U1 (Z/Z1)p
Where,
U1 is the velocity at Z1 (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

44. BEAUFORT SCALE
 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

45. WIND ROSE DIAGRAM (WRD)
Wind Direction (%)
Wind Speed (mph)

46. WIND ROSE DIAGRAM (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

47. 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, -----------

48. DETERMINATION OF MAXIMUM MIXING
HEIGHT
 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

49. DETERMINATION OF MAXIMUM MIXING
HEIGHT

50. POWER PLANT PLUMES IN MICHIGAN
Monroe Power Plant

51. POWER PLANT PLUMES IN MICHIGAN
Trenton Channel

52. POWER PLANT PLUMES IN MICHIGAN
Belle River Power Plant
River Rouge Power Plant
Photo credit: Kimberly M. Coburn

53. PROBLEMS

54.  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?

55. SOLUTION
 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

56. REFERENCES
 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