Water vapor in the stratosphere

An entirely new level of sophistication—not only in experiments but also in modeling—will be required for particles, aerosols, and the associated radiation field sets. New mid-IR laser-based instrumentation and use of long-duration balloons have helped make major advances in observations. The balloons can sit in the upper stratosphere and then be lowered to the lower stratosphere with power from fuel cells and solar panels. The modeling elements are equally important it is necessary to test the model and its validity, and the model must link the measurements. The observations must be linked to trajectories, the trajectories must be initialized, and sources of specific chemicals must be identified along with the positions of those sources. Considerable progress has been made on observations and refinement of models to help explain low ozone loss at the mid-altitudes, the increase in UV dosage, the appearance of water vapor in the stratosphere, and possibly, of climate changes 50 million years ago. 

Harries, J. E. (1976). The distribution of water vapor in the stratosphere. Rev. Geophys. Space Phys. 14, 565-575. 

Whereas the troposphere contains abundant water vapor, little H20 makes it to the stratosphere the low temperatures at the tropopause lead to an effective freezing out of water before it can be transported up (a cold trap at the tropopause). Mixing ratios of H20 in the stratosphere do not exceed approximately 5-6 ppm. In fact, about half of this water vapor in the stratosphere actually results from the oxidation of methane that has leaked into the stratosphere from the troposphere. Between 20 and 50 km the total rate of... 

Methane in the troposphere contributes to the photochanical production of carbon monoxide and ozone. The photochemical oxidation of methane is a major source of water vapor in the stratosphere. 

The sources of active species containing H atom like OH, HO2, etc. in the stratosphere are H2O, H2, and CH4. Although water vapor (H2O) exists at 0.1-1 % in the troposphere, the vapor pressure drops when it passes through the cold tropopause (at 195 K, above tropics), and the mixing ratio of water vapor in the stratosphere is typically 5-6 ppmv. It should be noted, however, the half of H2O present in the stratosphere is that produced in situ by the oxidation of CH4. Stratospheric H2O is a source of OH by the reaction with 0( D) formed in the photolysis of O3 just the same as in the troposphere (Sect. 5.1.4). 

The turnover time of water vapor in the atmosphere obviously is a function of latitude and altitude. In the equatorial regions, its turnover time in the atmosphere is a few days, while water in the stratosphere has a turnover time of one year or more. Table 7-1 Qunge, 1963) provides an estimate of the average residence time for water vapor for various latitude ranges in the troposphere. Given this simple picture of vertical structure, motion, transport, and diffusion, we can proceed to examine the behavior of... 

K. R. Chan, Mechanisms Controlling Water Vapor in the Lower Stratosphere A Tale of Two Stratospheres, J. Geophys. Res., 100, 23167-23172 (1995b). 

Mote, P.W., K.H. Rosenlof, J.R. Holton, R.S. Harwood, and J.W. Waters, Seasonal variations of water vapor in the tropical lower stratosphere. Geophys Res Lett 22, 1093, 1995. 

Abbas, M.M., H.A. Michelsen, M.R. Gunson, M.C. Abrams, M.J. Newchurch, R.J. Salawitch, A.Y. Chang, A. Goldman, F.W. Irion, G.L. Manney, E.J. Moyer, R. Nagaraju, C.P. Rinsland, G.P. Stiller, and R. Zander, Seasonal variations of water vapor in the lower stratosphere inferred from ATMOS/ATLAS-3 measurements of H2O and CH4. Geophys Res Lett S3, 2401, 1996b. 

Gettelman, A., J.R. Holton, and A.R. Douglass, Simulations of water vapor in the lower stratosphere and upper troposphere, J Geophys Res 105, 9003, 2000. 

Simultaneous in situ measurements of CO2 and water vapor in the lower stratosphere in November 1992 and May 1993, for example, were analyzed to infer a mean transport time of 4 to 6 months from the tropical tropopause (—16 km) to — 18.5 to 19 km at midlatitudes (Boering et al., 1995). It takes many years for a species to reach the upper levels of the stratosphere from the time it crosses the tropopause. 

Although the percentage of water vapor in the atmosphere is small, only 3 g per 1000 g of the air on average in the troposphere and much less in the stratosphere, the presence of water in three different forms— vapor, liquid, and solid— has a profound effect on the motion of the atmosphere. Prediction of clouds and precipitation is an important aspect of weather forecasting. Unfortunately, the problem is also difficult because the time and space scales involved are much smaller than those of large-scale motions. 

In the very cold tropopause layer at the boundary between the troposphere and the stratosphere, water vapor in the atmosphere is condensed and forms ice crystals, a phenomenon that serves as a barrier to the movement of water into the stratosphere. Thns, little water is transferred from the troposphere to the stratosphere, and the main source of water in the stratosphere is the photochemical oxidation of methane ... 

In addition to the equipment listed in Table XIII, I must add that Nimbus 4 and 5 carry three other instruments (two spectrometers and one radiometer) for specialized meteorological experiments (atmospheric water vapor in the 1.2-2.4 pim and 3.2-6.4 //m band ozone distribution, 0.25 to 0.34 nm band thermal profile of the atmosphere and stratosphere, 13 to 15 /im bands, 6 different channels). To make the task of future researchers just that bit simpler, the instruments doing these various jobs are called, respectively FWS, BUV, and SCR. At the risk of repeating myself, I will say... 

About 51 percent of solar energy incident at the top of the atmosphere reaches Earth s surface. Energetic solar ultraviolet radiation affects the chemistry of the atmosphere, especially the stratosphere where, through a series of photochemical reactions, it is responsible for the creation of ozone (O,). Ozone in the stratosphere absorbs most of the short-wave solar ultraviolet (UV) radiation, and some long-wave infrared radiation. Water vapor and carbon dioxide in the troposphere also absorb infrared radiation. 

Other important catalysts are the free radicals OH and HO2, produced in the stratosphere by the decomposition of water vapor. 

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