Lapse

[Understanding Weather & Climate, Books a la Carte Edition (6th Edition) #ISBN-13: 978-0321773227 #ISBN-10: 0321773225 CH 5 Atmospheric Moisture]

Lapse – refers to a decrease in temperature (or pressure) with altitude

Dry adiabatic lapse rate (DALR)
 – a parcel of unsaturated air rises, it encounters lower surrounding pressure, expends and cools at the rate nearly 3°C/1000 feet

Lifting condensation level (LCL)
– the altitude in which the temperature of parcel of air is cooled to the dew point/frost point as well as become saturated.

Saturated adiabatic lapse rate (SALR)
– is the lapse rate after LCL. After the LCL, the parcel of saturated air will be cooled by expansion, but the release of latent heat from condensation cause the lapse rate at approx. 1.5°C/1000 feet

SALR is not constant value – higher temperature with a higher specific humidity and more water content can be condensed. With the gaining in altitude, the lower temperature with a lower specific humidity, the less condensation occur. Therefore, the little latent heat is released and decrease more in temperature – the SALR will increase nearly to the DALR – higher SALR.

Environmental lapse rate (ELR) / Ambient lapse rate
– vertical change in temperature through still air – changes from day to day, place to place.

The more heat on the surface, the steeper ELR!!!
(p.s – steeper ELR has lesser -ve slope)


Extension Reading:

(Ref. CH 6 p.167)
3 Factors Influencing the ELR

  1. Heating or cooling of the lower atmosphere
    – e.g solar radiation heats the Earth’s surface – more heat, steeper ELR
  2. Advection of (Cold and Warm) air at different level
    – different wind direction with distinct temperature
  3. Advection of an air mass with a different ELR

ISA – International Standard Atmosphere

Leave a Reply

Your email address will not be published. Required fields are marked *