Troposphere-Stratosphere transition

The Troposphere-Stratosphere Transition from a Chemical Perspective The... 

Example 5.3 The Troposphere/Stratosphere Transition The transition from troposphere to stratosphere is traditionally defined based on the reversal of the atmospheric temperature profile. That transition is also dramatically reflected in how the concentrations of trace species vary with altitude below and above the tropopause. Of trace species, HO2 and OH exhibit perhaps the most profound differences across the tropopause (Wennberg et al., 1995). In the lower stratosphere HO2 and OH participate in HO Cycle 4, which is the predominant cycle involved in O3 removal in that portion of the stratosphere. We saw in Chapter 4 that in the lower stratosphere the HO2/OH ratio is described by... 

Hydroxyl radical levels in the upper troposphere vary from about 0.01 to 0.1 ppt. In the lower stratosphere OH depends on solar zenith angle and ranges up to about 1 ppt. As noted above, OH is essentially independent of NO in the lower stratosphere, whereas in the upper troposphere OH decreases as NO decreases. This fundamentally different behavior of OH with respect to changes m NO characterizes the troposphere/stratosphere transition. 

The tropical tropopause, essentially defined by the 380 K potential temperature surface (see Chapter 21), is located at about 16-17 km. Tropical convection occurs up to an altitude of about 11-12 km. Between these two levels lies a transition region between the tropopause and the stratosphere, call the tropica tropopause layer (TTL). Together with the lowermost stratosphere, the region is referred to as the upper troposphere/lower... 

The boundaries between atmospheric layers are not rigidly fixed for example, the height of the transition from the troposphere to the stratosphere varies from an average of about 7500 m (25,000 ft) near the poles to 17,000 m (55,000 ft) near the equator and fluctuates seasonally. A reference profile, the Standard Atmosphere, is defined by the International Civil Aviation Organization to represent typical atmospheric conditions at midlatitudes (Table 4.1). At sea level, the Standard Atmosphere exerts a pressure of 760 mm of mercury (1 atm) and has a temperature of 15 °C (59 F). (Note that English units are still in widespread use in the meteorology and aviation communities in the United States.) Pressure decreases approximately exponentially with increasing altitude at 5500 m (18,000 ft), pressure is half that at sea level. 

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