Lapse rate and stability conditions

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

1. Lapse rate and S tability 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, temperature, 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 The temperature gradient 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 Negative: unstable atmosphere Positive: stable atmosphere Zero: neutral atmosphere

21. References Wikipedia 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/BOREALIS/Lapse%20Rate%20Terms%20and%20Formulas2012.pdf

22. THANK YOU