Seasonal variations of water vapor in the lower stratosphere inferred from ATMOS/ATLAS‐3 measurements of H₂O and CH₄

Abstract

Stratospheric measurements of H2O and CH4 by the Atmospheric Trace Molecule Spectroscopy (ATMOS) Fourier transform spectrometer on the ATLAS‐3 shuttle flight in November 1994 have been examined to investigate the altitude and geographic variability of H2O and the quantity H = (H2O + 2CH4) in the tropics and at mid‐latitudes (8 to 49°N) in the northern hemisphere. The measurements indicate an average value of 7.24±0.44 ppmv for H between altitudes of about 18 to 35 km, corresponding to an annual average water vapor mixing ratio of 3.85±0.29 ppmv entering the stratosphere. The H2O vertical distribution in the tropics exhibits a wave‐like structure in the 16‐ to 25‐km altitude range, suggestive of seasonal variations in the water vapor transported from the troposphere to the stratosphere. The hygropause appears to be nearly coincident with the tropopause at the time of observations. This is consistent with the phase of the seasonal cycle of H2O in the lower stratosphere, since the ATMOS observations were made in November when the H2O content of air injected into the stratosphere from the troposphere is decreasing from its seasonal peak in July–August.

Stratospheric water vapour in the vicinity of the Arctic polar vortex

“…In the upper stratosphere, methane oxidation accounts for the primary water vapour source within the stratosphere (Abbas et al, 1996;Michelsen et al, 2000), generally leading to an increase of H 2 O from the lowermost stratosphere to the stratopause. In the tropics, vertical transport from the troposphere provides the other important source of stratospheric water vapour, limited by freeze drying at the cold tropical tropopause (Brewer, 1949).…”

O{sub 3} and stratospheric H{sub 2}O radiative forcing resulting from a supersonic jet transport emission scenario

“…Setting the minimum water vapor mixing ratio in the LLNL 2-D model a few kilometers above the tropopause was done to represent the hygropause. A recent study (Abbas et al, 1996), primarily using water vapor measurements from the Atmospheric Trace Molecule Spectroscopy (ATMOS) Fourier transform spectrometer on the ATLAS-3 Shuttle flight (in November 1994) suggest that between 8"N and 49"N, the minimum water vapor mixing ratio is at or very near the tropopause. Therefore, to assess the uncertainty in forcing due to the uncertainty in the water vapor profile, a modified background water vapor profile was constructed by arbitrarily holding the mixing ratio at a constant value between the model prescribed hygropause and the tropopause.…”

ATMOS version 3 water vapor measurements: Comparisons with observations from two ER‐2 Lyman‐α hygrometers, MkIV, HALOE, SAGE II, MAS, and MLS

“…During NH winter, tropopause temperatures are the lowest, and [H 2 O] at the tropical tropopause is at a minimum; during the NH summer, tropical tropopause temperatures and [H 2 O] are at a maximum. As air masses ascend in the tropical stratosphere, this oscillation in [H 2 O] is maintained, leading to oscillations in the vertical profile of [H 2 O] in the tropics [e.g., McCormick et al , 1993; Mote et al , 1995, 1996; Abbas et al , 1996b; Randel et al , 1998, Randel et al , 2001; Michelsen et al. , 2000], as shown in Figure 1b.…”