Adiabatic Lapse Rate
What Is the Adiabatic Lapse Rate?
The adiabatic lapse rate is the rate at which an air parcel's temperature changes as it rises or falls without exchanging heat with its environment (Alok Kumar Patra et al., 2020). This process occurs because changes in atmospheric pressure cause the parcel to expand or compress (Gregory J. Hakim et al., 2017). As a parcel rises, pressure decreases, leading to expansion and cooling; conversely, descending air is compressed and warms (Alok Kumar Patra et al., 2020). This internal rate differs from the environmental lapse rate, which measures the surrounding air's temperature profile (Gregory J. Hakim et al., 2021).
Dry vs. Moist Adiabatic Lapse Rates
There are two primary types: the dry and moist adiabatic lapse rates. The dry adiabatic lapse rate (DALR) applies to unsaturated air and is constant at approximately 9.8°C to 10°C per kilometer (Michael B. Mcelroy et al., 2021)(R R Scorer et al., 2014). The moist adiabatic lapse rate (SALR) applies when air reaches saturation and condensation begins (Alok Kumar Patra et al., 2020). Because condensation releases latent heat, the cooling rate is reduced, typically ranging from 4°C/km to 9°C/km depending on moisture and temperature (John H. Seinfeld et al., 2016).
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Functional Application and Atmospheric Stability
Adiabatic lapse rates are essential for determining atmospheric stability and cloud formation (M. Karamouz et al., 2012). If the environmental lapse rate is steeper than the dry adiabatic rate, the atmosphere is considered unstable, as rising air parcels remain warmer and more buoyant than their surroundings (M. Karamouz et al., 2012). Conversely, a smaller environmental lapse rate indicates stability, where air parcels resist vertical movement (M. Karamouz et al., 2012). Conditional instability occurs when the environmental rate falls between the dry and moist adiabatic rates (M. Karamouz et al., 2012).
