Lapse rate Dry adiabatic Lapse rate Wet adiabatic Lapse rate Stability condition

1. Lapse rate and Stability
conditions
Presented by,
Asst. Prof. Krishna Parmar
Environmental Engineering
Diwaliba Polytechnic, Mahuva

2. Lapse rate
• Lapse rate is rate of change in temperature
observed while moving upward through the
Earth’s atmosphere (troposphere to be specific).
• Lapse rate is also defined as negative of
temperature gradient (dT/dZ) in the atmosphere.
The lapse rate is considered positive when the
temperature decreases with elevation, zero when
the temperature is constant with elevation,
and negative when the temperature increases
with elevation.

3. Temperature profiles in various atmospheric
levels
Source: http://apollo.lsc.vsc.edu/classes/met130/notes/chapter1/vert_temp_all.html

4. What is air parcel?
• An air parcel refers to a volume of air, large
enough to contain a great number of molecules,
but small enough so that energy (heat) and mass
(air molecules) are nearly constant within its
boundaries.
• An air parcel is commonly portrayed as a three
dimensional cube or sphere. Air parcels can be
expanded and compressed, but the outside air is
assumed not to be able to mix with air inside;
essentially making an air parcel a sealed
container.

5. Adiabatic process
• In thermodynamics, an adiabatic process is
one that occurs without transfer
of heat between a thermodynamic system and
its surroundings.( dq=0 )

6. Adiabatic lapse rate
• Adiabatic Lapse Rate is the rate of fall in
temperature of a rising or a falling air parcel
adiabatically.
• Adiabatic or adiabatically: Heat doesn’t enter
or leave the system. All temperature changes
are internal.
• Adiabatic lapse rates are usually differentiated
as dry or wet (moist).

7. Dry Adiabatic Lapse Rate (DALR)
• Assume the atmosphere to be a stationary
column of air in gravitational field, and the air
is approximated as a dry ideal gas.
• The expansion is rapid enough that we
assume that no heat transfer takes place.
• The change in temperature with elevation is
due to adiabatic expansion is determined in
the following manner.

8. Wet adiabatic lapse rate (WALR)
• When an air parcel that is saturated with water
vapour rises, some of the vapour will condense
and release latent heat [Additional Heat from
inside]. This process causes the parcel to cool
more slowly than it would if it were not
saturated.
• The moist adiabatic lapse rate varies considerably
because the amount of water vapour in the air is
highly variable. The greater the amount of
vapour, the smaller the adiabatic lapse rate.

9. • Approximately, the saturated lapse rate or
WALR is roughly 3.4° F/1000ft or 6 °C/1000m.

10. Significance in meteorology
• The difference between the normal lapse rate
in the atmosphere (environmental lapse rate)
and the dry and moist adiabatic lapse rates
determines the vertical stability of the
atmosphere.

11. Environmental lapse rate
• The environmental lapse rate (ELR), is the rate
of decrease of temperature with altitude in
the atmosphere at a given time and location.
• Temperature at various elevation can be
measured using radiosonde.
• The normal or standard lapse rate based on
international convention is 0.66°C/100 m or
3.6° F/1000ft.

12. Radiosonde
• A radiosonde is a battery-
powered instrument package
carried into the atmosphere
usually by a weather balloon that
measures various atmospheric
parameters and transmits them
by radio to a ground receiver.
Modern radiosondes measure or
calculate the following
variables: altitude, pressure, tem
perature, relative humidity, wind
speed and wind direction, cosmic
ray readings at high altitude
and geographical position
(latitude / longitude). Source: http://radioclubtigullio.weebly.com/radio-sonde.html

13. Stability conditions
• The degree of stability of the atmosphere
must be known if we wish to estimate the
ability of atmosphere to disperse pollutants it
receives from man made sources.
• Mixing in atmosphere depends upon
1. The temperature gradient
2. Mechanical turbulence

14. Unstable atmosphere
Source: https://laulima.hawaii.edu/access/content/group/2c084cc1-8f08-442b-80e8-
ed89faa22c33/book/chapter_5/stability.htm

15. If the ELR > DALR , then the atmosphere is said
to be superadiabatic.
Source: http://mytutorial.srtcube.com/air-pollution-dispersion/environment-science/693-446#7393

16. Stable atmosphere
Source: https://laulima.hawaii.edu/access/content/group/2c084cc1-8f08-442b-80e8-
ed89faa22c33/book/chapter_5/stability.htm

17. If the ELR < DALR , then the atmosphere
is said to be subadiabatic.
Source: http://mytutorial.srtcube.com/air-pollution-dispersion/environment-science/693-446#7393

18. Neutral atmosphere
• When the ELR=DALR , the stability of
atmosphere is said to be neutral.
• Any parcel of air is carried rapidly downwards
or upwards will have the same temperature at
the new height. Hence there is no tendency
for any further vertical movement and the
displaced particle remains in displaced
motion.

19. Potential temperature Gradient
• The stability of atmosphere is also frequently
characterised by the potential temperature
gradient.
• The gradient of environmental temperature
may be expressed in terms of gradient of ELR
and DALR.

20. When the value for the above equation is
1. Negative: unstable atmosphere
2. Positive: stable atmosphere
3. Zero: neutral atmosphere

21. References
1. Wikipedia
2. https://www.pmfias.com/adiabatic-lapse-
rate-latent-heat-condensation/
3. Air Pollution, Its Origin and Control,Book by
Cecil Francis Warner and Kenneth Wark
4.https://hs.umt.edu/physics/documents/BORE
ALIS/Lapse%20Rate%20Terms%20and%20For
mulas2012.pdf

22. THANK YOU