Atmospheric Temperature Lapse Rate

In the atmosphere, warm air parcels tend to occupy a greater volume than surrounding cooler air parcels. Because the warm air parcels are less dense than their immediate 

air is not a very good conductor of heat, so the expansion is effectively adiabatic. This means that q = 0, w 0, and AE 0. The net result is that as the energy of the rising air parcel decreases. Since AE still equals C AT, AT 0 and the air parcel cools off. The result is that the atmosphere cools off with increasing altitude above Earth s surface. 

The atmosphere s adiabatic lapse rate measures the rate at which a parcel of air cools as it rises in the atmosphere, in dry air, the lapse rate Is 9.8 C for an Increase In altitude of 1,000 meters, which is equivaient to 5.4°F every 1,000 feet. 

In dry air, this cooUng-off effect is called the adiabatic lapse rate of the atmosphere. Anyone who has hiked up or driven to the top of a mountain has experienced the effect of the air cooling off during the ascent. 

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The basis for the prediction system is as follows. Convection cells of sufficient strength arise only if the lower atmosphere is (sufficiently) unstable. The criterion for this is that the adiabatic lapse rate (rate of decrease in temperature from the sea surface upward) exceeds some threshold, the value of which depends on the moisture content because of its consequence for possible cloud formation. In case the lapse rate is smaller than 5.5 to 7.5°C/km, the lower atmosphere is stable here 6.5C/km is used as a representative critical value. Between approximately 10°C/km and (say) 6.5°C/km, it is conditionally unstable (depending on the moisture content), and a temperature lapse rate larger than 10°C/km results in an unstable atmosphere. Prediction of the lapse rate and moisture content using multi-layered atmospheric models is part of routine weather forecast systems. This, therefore, also allows operational prediction of the occurrence of significant seiche events on a routine basis, just like common weather prediction. 

When the actual temperature-decline-with-altitude is greater than 9.8°C/1000 m, the atmosphere is unstable, the Cj s become larger, and the concentrations of poUutants lower. As the lapse rate becomes smaUer, the dispersive capacity of the atmosphere declines and reaches a minimum when the lapse rate becomes positive. At that point, a temperature inversion exists. Temperature inversions form every evening in most places. However, these inversions are usuaUy destroyed the next morning as the sun heats the earth s surface. Most episodes of high poUutant concentrations are associated with multiday inversions. 

If the potential temperature decreases with height, the atmosphere is unstable- If the potential temperature increases with height, the atmosphere is stable. The average lapse rate of the atmosphere is about 6.5°C/km that is, the potential temperature increases with height and the average state of the atmosphere is stable. 

If the sphere of air mass moves upward in an adiabatic process but in an atmosphere with a subadiabatic lapse rate, the sphere follows a temperature change given by the adiabatic slope but when it arrives at point Zj, it is at a lower temperature than its surroundings, but at the same pressure. As a result, it is heavier than the surroundings and tends to fall back to its original position. This condition is called stable. In a stable atmosphere pollutants will only slowly disperse, and turbulence is suppressed. 

The temperature profile of a planetary atmosphere depends both on the composition and some simple thermodynamics. The temperature decreases with altitude at a rate called the lapse rate. As a parcel of air rises, the pressure falls as we have seen, which means that the volume will increase as a result of an adiabatic expansion. The change in enthalpy H coupled with the definition of the specific heat capacity... 

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 origin of the lapse rate can be understood on the basis of fundamental thermodynamics. That is, under the assumptions of a dry air parcel rising adia-batically in the atmosphere, the temperature is expected to fall about 10 degrees per kilometer increase in altitude. This drop in temperature is defined as a positive lapse rate. 

In reality, measured lapse rates are 6-7°C per km. This is due to the fact that atmospheric air is not dry but contains significant amounts of water vapor that also cools as the air parcel rises. When it reaches saturation, it condenses and releases its heat of vaporization, which warms the air somewhat, resulting in a less steep drop in temperature with altitude than expected for a dry air parcel. 

A large number of observations, both remote and in situ, confirm this qualitative picture of the loss of ozone over Antarctica. The in situ data have come from instruments carried on small balloons and the NASA ER-2 high-altitude aircraft. Small-balloon measurements are of particle distributions and sizes, ozone, and water vapor (23, 33). ER-2 measurements, listed in Table I, are of particle size and composition atmospheric parameters such as temperature, pressure, lapse rate, and winds and trace gas abundances of 03, N20, NOy or NO, CIO and BrO, and stable gases, including CH4, chlorofluorocarbons, halons, and others (34-45). 

Figure 2. Schematic vertical profiles (a) h (dashed) and h (solid) and (b) q (dashed) and q (solid), (c) The temperature profile, corresponding to cpT = h — gZ — Lyq, illustrates die constant lapse rate within the boundary layer and the reduced lapse rate above the boundary layer. The boundary level (1 km) is indicated by die horizontal dashed line in each panel. These profiles illustrate typical climatic values that are determined by moist convective adjustment in the free atmosphere and dry adiabatic convection in the boundary layer. [Used by permission of Geological Society of America, from Forest et al. (1999), Geol. Soc. Am. Bull., Vol. Ill, Fig. 2, p. 500.]...

The surface distribution for mean annual h results from two properties of atmospheric flow conservation of h following the large-scale flow and the maintenance of the vertical profile of h by convective processes. These features of the climate system allow one to quantify the expected errors for assuming that mean annual h is invariant with longitude and altitude for the present-day distribution. Forest et al. (1999) examined the distribution and calculated the expected error from assuming zonal invariance to be 4.5 kJ/kg for the mean annual climate. This error translates to an altitude error of 460 m and is compared with an equivalent error of 540 m from the mean annual temperature approach. Moreover, the uncertainty of the terrestrial lapse rate, y(, increases the expected error in elevation as elevations increase, particularly when small lapse rates are assumed. 

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