Tropopause

Upward diffusion of water vapor through the cold temperatures of the tropopause is very inefficient in fact, the upper limit of cloud formation often occurs at the tropopause. Thus the stratosphere is so dry as to prevent rain formation, and particles and gases have very much longer residence times there than in the troposphere. Stratospheric removal requires diffusion back through the tropopause, which then may be followed by precipitation scavenging. 

The lapse rate in the PBL is imstable and vertical motion leads to the transport of significant amounts of energy upward, due to the buoyancy of air that has been in contact with the surface. A mixed layer forms up to a height where static stability of the air forms a barrier to thermally induced upward motion. This extreme occurs practically daily over the arid areas of the world and the barrier to upward mixing is often the tropopause itself. On the average in mid-latitudes, the imstable or mixed PBL is typically 1-2 km deep. 

The tropical regions of both of the hemispheres troposphere exhibit easterly flow called the trade winds. Finally the jet stream -sometimes described as a river of air - flows at mid-latitude of both hemispheres with velocities of 25 to 50 m/sec from west to east, often carrying material completely around the Earth at its altitude close to the tropopause. It is in this flow that balloonists attempt to circle the globe. 

The temperature inversion at the tropopause prevents mixing between the stratosphere and troposphere, with hotter air (less dense) sitting on top of cooler air (more dense). Pollutants (such as chlorofluorocarbons) present in the stratosphere have very long lifetimes (of order 30 years) and become persistent problems, especially... 

Tropopause The point of temperature inversion in the atmosphere at 10-15 km when the temperature stops falling and begins to rise. 

Troposphere The layer of the atmosphere closest to the Earth surface rising to the tropopause. 

Courtina R. and Kimb S. J. (2002). Mapping of Titan s tropopause and surface temperatures from Voyager IRIS spectra, Planetary and Space Science 50 309-321. Davis W. L. and McKay C. P. (1996). Origins of Life a comparison of theories and applications to Mars. Origins of Life and Evolution of the Biosphere 26 61-73. 

Sticksel discussed vertical profile measurements of ozone in the stratosphere and the troposphere over the last several years. Transient ozone maximums in the troposphere are illustrated and explained by three possible mechanisms a channel-like r on conducted ozone from the stratosphere into the troposphere ozone-laden air descended from the stratosphere and was compressed as it subsided and ozone-rich layers leaked through the break between the polar and middle tropopauses by differential advection. Surface variations of ozone soundings were mostly attributed to anthropogenic pollution however, relatively thick high-... 

Stratospheric methane collected over Japan gave a 8 C-value of —47.5%c at the tropopause and increased to —38.9%c at around 35 km (Sugawara et al. 1998). These authors suggested that reaction with Cl in the stratosphere might be responsible for the C-enrichment. 

Another oxygen isotope fractionation effect is documented in CO2 samples collected between 26 and 35 km altitude, which show a mass - independent enrichment in both 0 and 0 of up to about 15%c above tropospheric values (Thiemens et al. 1995). The enrichment of stratospheric CO2 relative to tropospheric CO2 should make it possible to study mixing processes across the tropopause. 

Triterpenes, structural chemistry, 136 Tropopause, emissions model, 605 Troposphere ozone analysis, 605 trifluoromethyl peroxynitrate, 743 Tryptophan... 

However, at the tropopause the temperature profile changes, increasing with altitude throughout the stratosphere. The reason for this increase is a critical series of photochemical reactions involving ozone and molecular oxygen. The Chapman cycle, reactions (l)-(4), hypothesized in the 1930 s by Sir Sydney Chapman,... 

The transition zones between the various regions of the atmosphere are known as the tropopause, stratopause, and mesopause, respectively. Their locations, of course, are not fixed, but vary with latitude, season, and year. Thus Fig. 1.1 represents an average profile for mid-latitudes. Specific temperatures, pressures, densities, winds, and the concentrations of some atmospheric constituents as a function of altitude, geographic position, and time are incorporated into a NASA model, the Global. Reference Atmosphere Model (GRAM) information on obtaining this model and data is included in Appendix IV. 

Brunner, D., J. Staehelin, and D. Jeker, Large-Scale Nitrogen Oxide Plumes in the Tropopause Region and Implications for Ozone, Science, 282, 1305-1309 (1998). 

Knop, G., and F. Arnold, Atmospheric Acetonitrile Measurements in the Tropopause Region Using Aircraft-Borne Active Chemical Ionization Mass Spectrometry, Planet. Space Sci., 35, 259-266 (1987b). 

Water vapor concentrations have also been used to show that stratospheric air in the midlatitudes cannot all have originated via the tropical pump, i.e., path I in Fig. 12.3. For example, Dessler et al. (1995b) have shown that water vapor concentrations in the lowermost stratosphere at 37.4°N, 122.1°W are higher than expected for an air mass that has passed through the cold tropical tropopause. Their data are consistent with path II, although as they point out, these measurements do not exclude path III, which represents convective transport from the troposphere to the stratosphere at mid and high latitudes. Lelieveld et al. (1997) report aircraft measurements of CO, 03, and HNO-, over western Europe that suggest that tropospheric air can be mixed into the lower stratosphere. 

This effect can be seen in the midlatitude stratospheric measurements of Keim et al. (1996) shown in Fig. 12.31. In the tropopause region (shown by the... 

Figure 12.44 shows the major organobromine compounds measured at the earth s surface from 1988 to 1996 (Wamsley et al., 1998). These compounds have also been measured at the tropopause in the tropics, i.e., at the point at which the air is believed to enter the stratosphere. Methyl bromide and the halons are the major species obseived. For example, in one set of measurements, of 17.4 ppt organic bromine, 55% was from CH3Br, 38% from the halons, 6% from CH2Br2, and 0.8% from the combination of CH2BrCl and CHBrCl2 (Schauffler et al., 1998). 

Keim et a.l. (1996) have shown that there is a significant reduction in NO and increase in NO. and CIO in a layer above the tropopause that has increased aerosol surface areas (Fig. 12.31). They attribute this to increased heterogeneous reactions of C10N02 on particles to form HN03 and active chlorine. 

Borrmann, S S. Solomon, L. Aval lone, D. Toohey, and D. Baumgardner, On the Occurrence of CIO in Cirrus Clouds and Volcanic Aerosol in the Tropopause Region, Geophys. Res. Lett., 24, 2011-2014 (1997a). 

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