Tropopause density

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. 

Fig. VIII—1-4. Proposed temperature profile of Jupiter s Atmosphere. The tropo-pause is chosen as height reference since there is no evidence of a solid surface. The temperature at the tropopause is 9S.5°K and the number density is 2 x I01 cm 3. Contrary to the case of the upper atmosphere of earth, there appears to be no boundary between stratosphere and mesosphere. The observed cloud deck is believed to be solid ammonia. (M) signifies the number of molecules per cm3. From Hunten (490b), reprinted by permission of the American Meteorological Society. 

Figure 9. Zonal/seasonal averages of aerosol volume density V as a function of altitude and latitude. Dotted lines mark the tropopause plus 2 kilometers. Upward-pointing triangles on the x-axis mark the eruptions of Kelut (Feb. 1990 - 8 S), Knatubo (Jun. 1991 - 15 N) and Hudson (Aug. 1991 - 46 S).

Accomplishment of the complex observational experiment LACE-98 made it possible to obtain extensive information about atmospheric aerosol (aircraft measurements of the size distribution and number density of fine aerosols, coefficients of aerosol absorption, backscattering and depolarization, chemical composition of aerosol, as well as surface observations of the spectral optical thickness of the atmosphere, coefficients of extinction and backscattering). Fiebig et al. (2002) compared the observational data on optical parameters obtained from the results of numerical modeling for total H2S04 aerosol near the tropopause as well as for the ammonium sulfate/soot mixture in the remainder of the air column (Osborne et al., 2004). 

Bolin and Bischof (23) found a 25- to 30-day phase lag between the seasonal variations of carbon dioxide number densities at the tropopause and those at the surface layer. Assuming that vertical eddy diffusion is responsibl for the transport from the ground to the tropopause, they... 

The atmosphere is composed of a number of layers in which temperature either decreases or increases with increasing altitude. This thermal stratification can be likened to that of the ocean (Fig. 3.1). The lowest two layers are the troposphere (c.0-15km altitude, where weather occurs) and the stratosphere (c.15-50km altitude). The boundary between these two layers is the tropopause (Fig. 7.1), the altitude of which is greatest at the equator (c. 18 km) and least at the poles (c.8km). With increasing altitude in the troposphere air density and temperature both decrease until the tropopause is reached then temperature increases again in the stratosphere, until the stratopause. 

From the foregoing parts of this book it is clear that solar radiation in the stratosphere is primarily attenuated by ozone (see Subsection 3.4.3) and at a lesser extent by the stratospheric sulfate aerosol layer (see Subsection 4.4.3). This means that any change in the stratospheric 03 burden or aerosol concentration involves modification of radiative transfer in this atmospheric domain. We should remember that the residence time of trace constituents above the tropopause is rather long because of the thermal structure and the absence of wet removal. Furthermore at these altitudes the density of the air is low as compared to that of lower layers. For this reason even an insignificant quantity of pollutants can produce relatively long and significant effects. 

Some of the earliest proposed descriptions of stratospheric transport were based on observations of chemical species. The first observations of stratospheric water vapor densities showed that the stratosphere was extremely dry, exhibiting mixing ratios of the order of a few parts per million by volume, in marked contrast to the troposphere, where water vapor abundance reaches a few percent. Brewer (1949) suggested that the dryness of the stratosphere was determined primarily by condensation and that the water vapor content of an air parcel rising from the troposphere to the stratosphere would therefore be determined by the lowest temperature experienced by the parcel, which would normally correspond to the tropopause. He also noted that the tropopause temperatures in the tropics were low enough to yield stratospheric water vapor densities as low as those observed, while the... 

Figure 4-19b. Vertical profiles of chemical compounds retrieved from satellite observations based on occultation methods. Upper Panel Nighttime ozone number density (cm-3) measured on 24 March 2002 from the tropopause to the mesopause levels (15°N, 115°E) by the GOMOS instrument on board the ENVISAT spacecraft (stellar occultation). Courtesy of J.L. Bertaux and A. Hauchecorne, Service d Aeronomie du CNRS, France. Lower Panel Water vapor mixing ratio (ppmv) between the surface and 50 km altitude (33°N, 125°W) measured by SAGE II on 11 January 1987 (solar occultation). Courtesy of M. Geller, State University of New York.

Table 1-5. Tropopause Temperatures, Pressures, Densities, and Number Densities...

Here, nT is the number density of air molecules at the tropopause and ptr the corresponding air density. These data may be taken from Table 1-5. Values for the eddy diffusion coefficients in the lower stratosphere are 1 m2/s in the equatorial updraft region and 0.3 m2/s at higher latitudes. The second of the above equations gives the flux in units of kg/m2 s. The global flux is obtained after converting from seconds to years and integrating over the Earth s surface area. This yields loss rates for the tropical and extratropical latitudes of 29 and 31 Tg/yr, respectively. 

Assuming an average tropopause height of 12 km, one obtains by integration over height the following approximate column densities. 

The mass content is estimated from a model distribution assuming a uniform background mixing ratio superimposed by a boundary layer component. The vertical concentration profile is c = c0 exp[ - (1/h + 1/H)z] with H = 9.1 km, and the average tropopause level is 11 km. The mass content is the product of integrated column density and surface area A. 

Mean formula weight. Pressure scale height. Column density. Properties given at the 1 bar pressure level. Observed P-T profiles are adiabatic below the tropopauses. assuming0.80, - 0.19, andX= 0.01. 

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