Adiabatic lapse rate

Fig. 8. Characteristic plume patterns where (--) represents dry-adiabatic lapse rate and (—), air (a) fanning (b) fumigation (c) lofting and (d) looping.

ADIABATIC LAPSE RATE ATMOSPHERIC LAPSE RATE... 

If an ascending air parcel reaches saturation, the addition of latent heat from condensing moisture will partially overcome the cooling due to expansion. Therefore, the saturated adiabatic lapse rate (of cooling) is smaller than y. ... 

Fig. 19-4. Vertical expansion of continuous plumes related to vertical temperature structure, The dashed lines correspond to the dry adiabatic lapse rate for reference.

Temperature change with altitude has great influence on the motion of air pollutants. For example, inversion conditions result in only limited vertical mixing. The amount of turbulence available to diffuse pollutants is also a function of the temperature profile. The decrease of temperature with altitude is known as the lapse rate. The normal or standard lapse rate in the United States is -3.5" F/1,000 ft. An adiabatic lapse rate has a value of -5.4" F/1,000 ft. Temperature as a function of altitude is expressed by the following equation ... 

Adiabatic lapse rate The adiabatic temperature change that takes place with height of a rising (or falling) parcel of air, approximately -1 C/100 m. 

Inversion The condition that occurs when the lapse rate is positive, i.e, temperature rises with height at a rate greater than the adiabatic lapse rate 3 °C per 300 m. In these conditions stagnant air pollution builds up and is trapped under this layer. 

Environmental lapse rate (ELR) Dry adiabatic lapse rate (DALR)... 

Dry air rising in the atmosphere has to expand as the pressure in the atmosphere decreases. This pV work decreases the temperature in a regular way, known as the adiabatic lapse rate, Td, which for the Earth is of order 9.8 Kkm-1. As the temperature decreases, condensable vapours begin to form and the work required for the expansion is used up in the latent heat of condensation of the vapour. In this case, the lapse rate for a condensable vapour, the saturated adiabatic lapse rate, is different. At a specific altitude the environmental lapse rate for a given parcel of air with a given humidity reaches a temperature that is the same as the saturated adiabatic lapse rate, when water condenses and clouds form Clouds in turn affect the albedo and the effective temperature of the planet. Convection of hot, wet (containing condensable vapour) air produces weather and precipitation. This initiates the water cycle in the atmosphere. Similar calculations may be performed for all gases, and cloud layers may be predicted in all atmospheres. 

The potential temperatiue 0 is that to which dry air originally in the state (T, p) would come if brought adiabatically to po- Adiabatic temperature profiles expressed in terms of 0 are vertical on a plot of z vs 0, facilitating comparisons of actual temperature profiles to the adiabatic lapse rate. 

Using the dry adiabatic lapse rate, by how much would you expect the temperature to change from the earth s surface to an altitude of 1000 feet, which, as seen in Fig. 2.19, sometimes corresponds to the bottom of the inversion layer in the Los Angeles area ... 

At the dry adiabatic lapse rate (9.8°C decrease in temperature per kilometer increase in altitude), a rising parcel of dry air that does not exchange heat with the environment will cool by expansion due to the decrease in air pressure and will achieve the same temperature as the surrounding air—a case of neutral stability. That is, air movement is then neither favored nor retarded by buoyancy. Observed lapse rates are usually -5 to -7°C km-1, reflecting heat exchange with the environment and the possibility of heat release due to water condensation at higher altitudes. 

The adiabatic lapse rate for a dry atmosphere, which may contain water vapor but which has no liquid moisture present in the form of fog, droplets, or... 

FIGURE 4-5 Illustration of the adiabatic lapse rate. As this air parcel is raised in altitude by 1000 m, the air pressure decreases and the parcel expands and cools by 9.8°C (5.4°F for an altitude increase of 1000 ft). Assuming no heat is lost or gained by the parcel (i.e., the process is adiabatic), its temperature will increase to its original value on being lowered to its original height. 

In Section 4.1.1, Eqs. [4-1] and [4-2] were used to estimate the relationship between air pressure and altitude, assuming temperature to be constant with height. When combined with a third equation, Eqs. [4-1] and [4-2] also can be used to calculate the dry adiabatic lapse rate. The third equation, presented as the following Eq. [4-7], is based on an adiabatic process for air that rises and expands due to a decrease in pressure. By definition for an adiabatic process, heat flow into the rising air is assumed to be zero. Therefore, conser-... 

It is important not to confuse this dry adiabatic lapse rate with the rate of change in temperature with height in a Standard Atmosphere. The latter represents average conditions in Earth s atmosphere, where heating, mixing, and wet adiabatic processes also are occurring. 

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