Troposphere lapse rate

Figure 23.10 illustrates the differences between the no-feedback surface temperature response ATo and the ultimate equilibrium response AT,. AT0 tends to be directly proportional to the adjusted forcing this proportionality provides the rationale for using the adjusted forcing as a measure of the expected climate response to the perturbation. This proportionality assumes that the lapse rate in the troposphere is fixed (and that in the stratosphere is determined by radiative equilibrium). Ultimately, the question is whether AT, is proportional to the adjusted forcing, when the tropospheric lapse rate is allowed to change in response to climate feedbacks such feedbacks include changes in clouds and precipitation. 

In a normal troposphere that has a positive lapse rate, i.e., where the temperature is falling with altitude, warm air close to the earth s surface, being less dense, rises and is replaced by cooler air from higher elevations. This results in mixing within the troposphere. 

In some situations, however, the temperature of the air, at some height within the troposphere, may start to rise with increasing altitude before reversing itself again that is, the lapse rate changes from positive to negative to positive (Fig. 2.18). This region, with a... 

FIGURE 2.18 Variation of temperature with altitude within the troposphere (a) normal lapse rate (b) change in lapse rate from positive to negative, characteristic of a thermal inversion. 

The model tropopause is defined by a PV level of 3.5 pvu poleward of 20° latitude, and by a -2 K km 1 temperature lapse rate equatorward of 20° latitude. Consequently, in this study the troposphere is defined as the volume between the surface and the simulated tropopause. Because the model does not consider typical stratospheric chemical reactions explicitly, ozone concentrations are prescribed from 1-2 levels above the model tropopause up to the top of the model domain at 10 hPa. In both hemispheres we apply monthly and zonally averaged distributions from a 2D stratospheric chemistry model [31]. In the present version of the model, we use the simulated PV and the regression analysis of the MOZAIC data (Section 2) to prescribe ozone in the NH extratropical lower stratosphere, which improves the representation of ozone distributions influenced by synoptic scale disturbances [32, 33]. Furthermore, the present model contains updated reaction rates and photodissociation data [34]. 

The bulk of cloudiness is found in the lowest level of the atmosphere, which is called the troposphere. The thickness of the troposphere is 8 km at high latitudes, 12km at mid-latitudes, and 16km at low latitudes (Buseck and Schwartz 2004). In our simulations, we assumed a 12 km troposphere and a lapse rate of 6.5°C/km (Lide, 1994). We also assumed a starting point of 0.0 km and 25 °C (Fig. 5.8) for our two solutions, which were then lofted to colder (higher) altitudes. 

I would like to congratulate Dr. Crutzen on one of the most impressive papers that I have heard in the last 43 years. With regard to its policy implications, it stands certainly in a class all by itself. I would simply underscore Dr. Crutzen s emphasis on the conservativeness of his estimates. Having looked at thousands of vertical temperature profiles, it is clear, I believe, that the residence time will be of about an order of magnitude difference between the stratosphere rather than the troposphere, and also the lapse rates, would no longer apply. So as you say, it is just an entirely different atmosphere. This would inhibit the precipitation and the fallout, so that I just really wanted to underscore the conservative nature of your calculations. 

The regions of the atmosphere are defined by the vertical temperature profile. At the bottom is the troposphere where temperature decreases with height from the surface (which is warmed by the sun). The rate of change of temperature (the lapse rate) depends on the amount of moisture in the air since the latent heats of condensation and evaporation affect the heat of a rising or descending air parcel. For dry air the dry adiabatic lapse rate is — 9.8 K km but a more typical value of the environmental lapse rate (for air containing some water vapor) is — 6.5 K km The troposphere extends up to about 10 km, though this varies with... 

Absorption of solar ultraviolet radiation by O3 causes the temperature in the stratosphere to be much higher than expected, based on simply extending the troposphere s lapse rate into the stratosphere. 

The boundary between the troposphere and the stratosphere (about 8 km in polar regions and about 15 km in tropical regions), usually characterized by an abrupt change of lapse rate. The regions above the troposphere have increased atmospheric stability than those below. The tropopause marks the vertical limit of most clouds and storms, troposphere... 

Lapse rate The rate of decrease of tropospheric temperature with height. 

The temperature throughout most of the troposphere is observed to decrease with height. This temperature gradient, called the lapse rate, is denoted by T and is defined by... 

The lapse rate is defined as the rate of temperature change with height. With an increase in altitude in the troposphere, the temperature of the ambient air usually decreases. Temperature decreases an average of 6 to 7°C/km. This is the normal lapse rate, but it varies widely depending on location and time of day. We define a temperature decrease with height as a negative lapse rate and a temperature increase with height as a positive lapse rate. 

A rising parcel of dry air containing water vapor will continue to cool at the dry adiabatic lapse rate until it reaches its condensations temperature, or dew point. At this point, the pressure of the water vapor equals the saturation vapor pressure of the air, and some of the water vapor begins to condense. Condensation releases latent heat in the parcel, and thus the cooling rate of the parcel slows. This new rate is called the wet adiabatic lapse rate. Unlike the dry adiabatic lapse rate, the wet adiabatic lapse rate is not constant but depends on temperature and pressure. In the middle troposphere, however, it is assumed to be approximately -6 to -7°C/1000 m. 

It might be inferred from the preceding discussion that, based on its average lapse rate, the Standard Atmosphere is stable with little vertical mixing yet, on average, the troposphere is reasonably well mixed. Tropospheric mixing occurs in part because of atmospheric variability although... 

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