Lapse Rates (Elr, Dalr, Salr)

[Andy_]

Hi, i've got an a level geography exam tomorrow, and still don't really understand lapse rates, we have to learn about the dry adiabatic lapse rate, the environmental lapse rate, and the saturated adiabatic lapse rate. Any help from anyone with a decent knowledge of weather and climate would be much appreciated, thanks

[johnholmes]

try our Guides section, the one especaiily about the skew-t daigrams should help you. If still stuck ask and I'll try and answer or someone else will for you

[Andy_]

thanks mate i'll have a look

[Nick L]

DALR - This is the rate of change of temperature that an unsaturated air parcel experiences when it ascends adiabatically. This means as it rises, no energy is gained or lost to the surroundings, the only temperature change is caused by the air parcel expanding, so by the ideal gas law it cools. It is approximately 9.8c/km.

ELR - This is basically the actual rate of temperature decrease/increase as you go up through the atmosphere.

SALR - This is the same as the DALR, but for an air parcel saturated with water vapour (that is, it can't hold any more moisture). It is typically around 5c/km, it is less because as the water in the parcel condenses, it releases latent heat causing the temperature of the parcel to increase, therefore lessening the rate of decrease.

Hope this is an OK explanation and somebody please point out any glaring errors I have probably made :lol:

[johnholmes]

seems ok to me Nick although I can never remember the numbers other DALR=3C per 1000ft and SALR is approx half that!

[Andy_]

DALR - This is the rate of change of temperature that an unsaturated air parcel experiences when it ascends adiabatically. This means as it rises, no energy is gained or lost to the surroundings, the only temperature change is caused by the air parcel expanding, so by the ideal gas law it cools. It is approximately 9.8c/km.

ELR - This is basically the actual rate of temperature decrease/increase as you go up through the atmosphere.

SALR - This is the same as the DALR, but for an air parcel saturated with water vapour (that is, it can't hold any more moisture). It is typically around 5c/km, it is less because as the water in the parcel condenses, it releases latent heat causing the temperature of the parcel to increase, therefore lessening the rate of decrease.

Hope this is an OK explanation and somebody please point out any glaring errors I have probably made :lol:

yeah i think i'm starting to understand now, the SALR has less temperature change per 100m because its condensation is releasing latent heat, so offsets the normal decrease of temperature with height? so the DALR is more affected by increasing height because it is dry and its temperature can only be changed by an increase in altitude... i think haha.