1. MET 61 Introduction to Meteorology - Lecture 5
Moisture (II)
Dr. Eugene Cordero
San Jose State University
Stull: Pg 43-48, pg , 104,
W&H: Chap 3, Pg 85-93
Class Outline:
LCL
Moist Lapse Rate
Normand’s rule
MET 61 Introduction to Meteorology

2. Eulerian vs. Lagrangian
Refer to different perspectives or frames of reference:
Eulerian refers to:
Lagrangian means that
Examples:
MET 61 Introduction to Meteorology

3. Eulerian vs. Lagrangian
Refer to different perspectives or frames of reference:
Eulerian refers to:
examining a fixed volume in space.
Lagrangian means that
we following an air parcel as it moves in the atmosphere.
Examples:
MET 61 Introduction to Meteorology

4. Adiabatic/pseudoadiabatic
A parcel of air rises in the atmosphere at the dry adiabatic lapse rate until air is saturated.
If all condensation products (rain,snow) remain in the parcel –
MET 61 Introduction to Meteorology

5. Adiabatic/pseudoadiabatic
A parcel of air rises in the atmosphere at the dry adiabatic lapse rate until air is saturated.
Further lifting results in condensation releasing latent heat.
If all condensation products (rain,snow) remain in the parcel – adiabatic process
MET 61 Introduction to Meteorology

6. Adiabatic/pseudoadiabatic
If condensation products fall out (rain out), then not an adiabatic (or reversible) process, rather a -
However, the amount of heat lost is relatively small, thus the saturated adiabatic lapse rate is similar to pseudoadiabatic lapse rate.
MET 61 Introduction to Meteorology

7. Adiabatic/pseudoadiabatic
If condensation products fall out (rain out), then not an adiabatic (or reversible) process, rather a - -pseudoadiabatic
MET 61 Introduction to Meteorology

8. Saturated adiabatic lapse rate
The dry adiabatic lapse rate applies to moist air provided it’s unsaturated.
The saturated-adiabatic lapse rate is less than the dry rate because of: -
MET 61 Introduction to Meteorology

9. Saturated adiabatic lapse rate
The dry adiabatic lapse rate applies to moist air provided it’s unsaturated.
Saturated air: e.g. clouds and fog
The saturated-adiabatic lapse rate is less than the dry rate because of:
-release of latent heat during condensation
Dry adiabats: constant potential temperature
Moist or saturated adiabats: constant equivalent potential temperature
MET 61 Introduction to Meteorology

10. Thermodynamic Diagram
Green
Dry Adiabats
Red
Moist Adiabats
Yellow
Saturation
Mixing
Ratio
MET 61 Introduction to Meteorology

11. MET 61 Introduction to Meteorology
Skew-T Log-p Diagram
MET 61 Introduction to Meteorology

12. Equivalent potential temperature
The equilivant potential temperature, e, refers to the case where a parcel is expanded pseudoadiabatically until all the vapor has condensed, released its latent heat and fallen out. Then the parcel is compressed dry adiabatically to the 1000mb. The final temperature at 1000mb is the equivalent potential temperature.
MET 61 Introduction to Meteorology

13. MET 61 Introduction to Meteorology
Wet bulb temperature
Is defined as Tw.
Example:
MET 61 Introduction to Meteorology

14. MET 61 Introduction to Meteorology
Wet bulb temperature
Is defined as Tw.
By definition it is the lowest temperature a volume of air can be cooled through evaporation.
Example:
MET 61 Introduction to Meteorology

15. Wet bulb potential temperature
Is defined by w.
If the moist adiabat is followed through the wet-bulb temperature of the parcel back to 1000mb, the temperature is called the wet-bulb potential temperature, w
MET 61 Introduction to Meteorology

16. MET 61 Introduction to Meteorology
Normand’s rule
This rule states that on a pseudoadiabatic chart, the lifting condensation level of an air parcel is at the intersection of three other lines:
the potential temperature line which passes through the
The equivalent potential temperature line which passes through the
Saturation mixing ratio line which passes through
MET 61 Introduction to Meteorology

17. MET 61 Introduction to Meteorology
Normand’s rule
This rule states that on a pseudoadiabatic chart, the lifting condensation level of an air parcel is at the intersection of three other lines:
the potential temperature line which passes through the
Temperature and pressure of parcel
The equivalent potential temperature line which passes through the
Web bulb temperature and pressure of parcel
Saturation mixing ratio line which passes through
Dew point and pressure of the parcel
MET 61 Introduction to Meteorology

18. MET 61 Introduction to Meteorology
Skew-T
MET 61 Introduction to Meteorology

19. MET 61 Introduction to Meteorology
Normand’s rule
LCL
pressure
Constant 
Constant rs P
Td Tw T
Constant e
1000mb w
temperature
MET 61 Introduction to Meteorology

20. MET 61 Introduction to Meteorology
Skew-T
MET 61 Introduction to Meteorology

21. MET 61 Introduction to Meteorology

22. Irreversible condensation processes
Consider a parcel lifted above its LCL so that condensation occurs. If precipitation falls out and the parcel returns to original pressure (adiabatically), then how does the following change? Increase, decrease of stay the same?
a) T
b) 
r (mixing ratio) RH Td Tw
MET 61 Introduction to Meteorology

23. Irreversible condensation processes
Net increase in temperature and 
Decrease in moisture (i.e. dew point, wet bulb temp etc.)
No change in equivalent potential temperature or wet-bulb potential temp
MET 61 Introduction to Meteorology

24. MET 61 Introduction to Meteorology

25. MET 61 Introduction to Meteorology
In the figure below, explain why the temperature and dew point on the windward side of the mountain are different from the leeward side.
MET 61 Introduction to Meteorology

26. MET 61 Introduction to Meteorology
Question 1a
A parcel of air with initial temperature of 40°C and dew point of 20°C is lifted adiabatically from the 1000 hPa level.
Determine it’s thermodynamic state (Temp, 800 hPa
If the parcel raises further, determine the lifting condensation level and temperature at that level.
If the parcel is lifted further up to 500 hPa, what is the final temperature and how much water is condensed during the rise?
If 2g/kg of precipitation falls out during the rise, then if the parcel descends, what is the new LCL and what is the thermo state (Temp, RH) at 800 hPa?
At 800 hPa, determine the wet bulb temperature and the wet bulb potential temperature.
MET 61 Introduction to Meteorology

27. MET 61 Introduction to Meteorology
Activity 4 (Due Feb 21st)
An air parcel at 800mb has a temperature of 20°C and a dew point temperature of –2.5°C.
Determine the LCL of the parcel
Determine the state of the parcel if lifted to 400mb. How much water is condensed out?
If 1 g/kg of water is rained out, what is the new LCL and thermodynamic state of the parcel at 800mb?
I think that it would be worthwhile at this introductory lecture to provide some definitions that you may have never thought of before
Go through.....
Climatology also has a distinctly Geographical component to it - we often consider what gives one region or locality a different climate from another. However, although this course is put on by Geography and Environmental Science, there are clear components of meteorology and climatology in it. In the course we will not be taking a particularly mathematical approach to atmospheric science, but everything we will talk about will be based on sound physical principles.
MET 61 Introduction to Meteorology

28. MET 61 Introduction to Meteorology
Question 2
An air parcel at 800mb has a temperature of 20°C and a dew point temperature of –2.5°C.
Determine the LCL of the parcel
Determine the state of the parcel if lifted to 400mb. How much water is condensed out?
If 1 g/kg of water is rained out, what is the new LCL and thermodynamic state of the parcel at 800mb?
MET 61 Introduction to Meteorology

29. MET 61 Introduction to Meteorology
Quiz #2: Part B
The saturation mixing ratio can be described as:
For typical values of the Earth’s temperature, show that
MET 61 Introduction to Meteorology

30. MET 61 Introduction to Meteorology
Activity:
An air parcel at 950 mb has a temperature of 14°C and a saturation mixing ratio of 4.5g/kg.
A) What is the wet bulb potential temperature of the air?
The air parcel is lifted a further 200mb by passing over a mountain, and 70% of the water vapor that is condensed out by the ascent is removed by precipitation.
B) Determine the temperature, potential temperature, mixing ratio and web-bulb potential temperature of the air after it has returned to the 1000 mb level on the other side of the mountain.
MET 61 Introduction to Meteorology

31. MET 61 Introduction to Meteorology
Question 1
A parcel of air with initial temperature of 15°C and dew point of 2°C is lifted adiabatically from the 1000mb level.
Determine its lifting condensation level and temperature at that level.
If the parcel is lifted a further 200 mb above it’s lifting condensation level, what is its final temperature and how much water is condensed during the rise?
MET 61 Introduction to Meteorology