Tropospheric zonal temperature

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]. 

Figure 3.7. Zonally averaged distribution of the potential temperature unbroken lines, in K) from the surface to approximately 30 km altitude 10 hPa). The isolines for the absolute temperature (dashed lines, in K) are also shown. The tropopause is represented by the dotted line. Note that isentropes corresponding to potential temperatures larger than 380 K are located exclusively in the stratosphere (an area called the overworld ). Air parcels located in the lowermost stratosphere between the tropopause and the 380 K isentrope (an area called the middle world) are susceptible to crossing the tropopause when adiabatically transported, and entering the troposphere also called the underworld). From Holton et al. (1995), based on Appenzeller 1994).

This prediction can be checked with the help of radiosonde data. The instrumentation normally is not suitable to measure the low abundance of water in the upper troposphere and stratosphere, so that the data are restricted to altitudes below 7 km. Oort and Rasmussen (1971) have compiled zonally averaged, mean monthly specific humidities (H20 mass mixing ratios) as a function of height for the northern hemisphere. Average water vapor pressures computed from their values are shown in Fig. 8-1 as a function of temperature. If, as a precaution, one uses only data for altitudes... 

The radiosonde data also provide the total amount of precipitable water in the atmosphere. Zonal mean values are shown in Fig. 8-2. The data are based mainly on the maps of Bannon and Steele (1960). More recent data presented by Newell et al. (1972) are in good agreement. The amount of precipitable water decreases from the equator to the poles due to the poleward decrease of temperature in the troposphere. 

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