ABSTRACT - DRUM - University of Maryland

vapor mixing ratio with altitude in the stratosphere, is photochemical CH 4 oxidation
[Brasseur and Solomon, 1984; Letexier et al., 1988]. Oxidation of each CH 4 molecule
in the lower and mid stratosphere creates about 2 H 2 O molecules [Jones et al., 1986].
Otherwise, stratospheric H 2 O is transported from the troposphere through the tropical
tropopause.
Due to many technical difficulties, it is not easy to measure directly the amount
of [H 2 O] e , the entry level of water vapor to the stratosphere. Instead, simultaneous
measurements of CH 4 and H 2 O in the extratropics are used to estimate the entry
amount of water vapor through the topical tropopause. First, measurements of CH 4 in
the extratropical stratosphere are used to determine how much of the water vapor in
these regions was produced in the stratosphere. Subtracting this from the mid-latitude
H 2 O abundance yields an estimate for [H 2 O] e .
Table 1.1 shows a list of estimates of [H 2 O] e from various instruments. Estimates
are from 2.7 ppmv to 4.2 ppmv, mostly ranging between 3.6 ppmv and 3.8 ppmv. For
the same period, the saturation mixing ratios of water vapor at the tropical cold point
temperature are clearly over 4 ppmv [Zhou et al., 2001], suggesting additional
mechanisms for the hydration of the lower stratosphere.
Trend: Observations indicate rising concentrations of stratospheric water vapor
[Oltmans and Hofmann, 1995; Abbas et al., 1996; Evans et al., 1998; Nedoluha et al.,
1998; Michelsen et al., 2000; Oltmans et al. 2000]. Oltmans et al. [2000] used data
from frostpoint hydrometer measurements at Washington, D.C. and Boulder, to show
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