Overview of the Stratospheric Aerosol and Gas Experiment II water vapor observations: Method, validation, and data characteristics

Abstract

Water vapor observations obtained from the Stratospheric Aerosol and Gas Experiment II (SAGE II) solar occultation instrument for the troposphere and stratosphere are presented and compared with correlative in situ measurement techniques and other satellite data. The SAGE II instrument produces water vapor values from cloud top to approximately 1 mbar, except in regions of high aerosol content such as occurs in the low to middle stratosphere after volcanic eruptions. Details of the analysis procedure, instrumental errors, and data characteristics are discussed. Various features of the data set for the first $ years after launch (1985-1989) are identified. These include an increase in middle and upper tropospheric water vapor during northern hemisphere summer and autumn, thus at times of warmest sea surface temperature; minimum water vapor values of 2.5-3 ppmv in the tropical lower stratosphere, with lower values during northern hemisphere winter and spring; slowly increasing water vapor values with altitude in the stratosphere, reaching 5-6 ppmv or greater near the stratopause; extratropical values with minimum profile amounts occurring above the conventionally defined tropopause; and higher extratropical than tropical water vapor values throughout the stratosphere except in locations of possible polar stratospheric clouds. SAGE II data will be useful for studying individual water vapor profiles, tropospheric response to climate perturbations, troposphericstratospheric exchange (due to its inherent high vertical resolution), and stratospheric transports. It should also aid in the preparation, for the first time on a global scale, of climatologies of the stratosphere and the upper level cloud-free troposphere, for use in radiative, dynamical, and chemical studies.1.

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

“…In view of seasonal variations in the water vapor entry into the stratosphere with a minimum in January and maximum in July [e.g., Rind et aL, 1993;Boering et al, 1995;Mote et al, 1995], a close examination of ATMOS profiles of H20 leads to the following conclusions: …”

“…Measurements of H by other experiments for comparison are: 6.0 ppmv from LIMS and SAMS data [Jones et al, 1986]; 7.0 + 0.6 ppmv at 30 km from the ATMOS experiment on Spacelab 3 [Gunson et al, 1990]; 7.6 _+ 0.6 ppmv from data collected on the ER-2 aircraft [Dessler et al, 1994] et al, 1984;Jones et al, 1986;Kelly et al, 1989Kelly et al, , 1993 [Rind et al, 1993], HAI.DE and MLS [Mote et al, 1995], and instruments aboard the ER-2 aircraft [Boering et al, 1995]. Figure 4 shows good agreement at lower altitudes between ATMOS, HALOE, and in situ measurements of H20.…”

Variability of subtropical upper tropospheric humidity

“…Rind et al, 1993;Soden and Bretherton, 1993;Bates et al, 1996;Read et al, 2001;Gettelman et al, 2006). These measurements have also enabled examination of the processes causing variability in the water vapor distribution.…”

Tropical upper tropospheric humidity variations due to potential vorticity intrusions

“…However, this is one of the least well-measured parameters and significant uncertainties in the measurements remain a barrier to making reliable prediction about future climate change. In the past, satellite measurements, namely, the Stratospheric Aerosol and Gas Experiment, the Television Infrared Observation Satellite (TIROS), operational vertical sounder, 6.7 µm brightness temperature from a single Geostationary Operational Environmental Satellite, Microwave Limb Sounder, and Atmospheric Infrared Sounder (AIRS) have contributed significantly to the retrieval of water vapour in the upper troposphere from the radiances and also to the understanding of its variabilities (Rind et al, 1993;Soden and Bretherton, 1993;Soden and Fu, 1995;Liao and Rind, 1997;Gettelman et al, 2006). These humidity observations from satellites are important data sources for humidity assimilation in global data assimilation systems (Chen et al, 1999).…”