The Dry adiabatic Lapse rate is:

Question

Accepted Answer

The Dry Adiabatic Lapse Rate is 10°C per 1000 meters. Here's why:

*   **Why Option 1 (10°C per 1000 meters) is correct:** The dry adiabatic lapse rate (DALR) refers to the rate at which the temperature of a parcel of dry air decreases as it rises in the atmosphere. "Dry" in this context means unsaturated air (relative humidity less than 100%). The standard value for the DALR is approximately 10°C per kilometer (or 10°C per 1000 meters). This is because as the air parcel rises, it expands due to decreasing atmospheric pressure. This expansion causes the air parcel to cool. The rate of cooling is determined by the amount of work the air parcel does as it expands, and for dry air, this rate is consistently around 10°C/km.

*   **Why Option 2 (5°C per 1000 meters) is incorrect:** 5°C per 1000 meters is closer to the moist adiabatic lapse rate (MALR). The MALR is *always* less than the DALR because as moist air rises and cools, water vapor condenses, releasing latent heat. This latent heat partially offsets the cooling due to expansion, resulting in a slower rate of temperature decrease. Therefore, 5°C/1000m is not the dry adiabatic lapse rate.

*   **Why Option 3 (6.5°C per 1000 meters) is incorrect:** 6.5°C per 1000 meters is often cited as the average or standard lapse rate of the *environment*, not the dry adiabatic lapse rate. The environmental lapse rate is the actual temperature change with altitude at a specific time and location, and it varies greatly. It's not a fixed value like the DALR.

*   **Why Option 4 (9.5°C per 1000 meters) is incorrect:** While 9.5°C per 1000 meters is closer to the correct value than options 2 and 3, the standard and generally accepted value for the dry adiabatic lapse rate is 10°C per 1000 meters. Therefore, it's not the most accurate representation of the DALR.