Trends and variability of midlatitude stratospheric water vapour deduced from the re-evaluated Boulder balloon series and HALOE M. Scherer1, H. Vömel2,3, S. Fueglistaler4, S. J. Oltmans3, and J. Staehelin1 1Atmospheric and Climate Science, Eidgenössische Technische Hochschule, Zürich, Switzerland 2Cooperative Institute for Research in Environmental Science, University of Colorado, Boulder, CO, USA 3Global Monitoring Division, Earth System Research Laboratory, NOAA, Boulder, CO, USA 4Applied Mathematics and Theoretical Physics, Cambridge University, Cambridge, UK
Abstract. This paper presents an updated trend analysis of water vapour in the
lower midlatitude stratosphere from the Boulder balloon-borne NOAA
frostpoint hygrometer measurements and from the Halogen Occulation
Two corrections for instrumental bias are applied to homogenise the
frostpoint data series, and a quality assessment of all soundings after
1991 is presented.
Linear trend estimates based on the corrected data
for the period 1980–2000 are up to 40% lower than previously reported.
Vertically resolved trends and variability are calculated with a multi
regression analysis including the quasi-biennal oscillation and equivalent
latitude as explanatory variables.
In the range of 380 to 640 K potential temperature
(≈14 to 25 km), the frostpoint data from 1981 to 2006 show
positive linear trends between 0.3±0.3 and 0.7±0.1%/yr.
The same dataset shows trends between −0.2±0.3 and 1.0±0.3%/yr
for the period 1992 to 2005.
HALOE data over the same time period suggest negative trends ranging
from −1.1±0.2 to −0.1±0.1%/yr.
In the lower stratosphere, a rapid drop of water vapour is observed in
2000/2001 with little change since.
At higher altitudes, the transition is more gradual, with slowly
decreasing concentrations between 2001 and 2007.
This pattern is consistent with a change induced by a drop of water
concentrations at entry into the stratosphere.
Previously noted differences in trends and variability between frostpoint
and HALOE remain for the homogenised data.
Due to uncertainties in reanalysis temperatures and
stratospheric transport combined with uncertainties in
observations, no quantitative inference about changes of water entering the
stratosphere in the tropics could be made with the mid latitude
measurements analysed here.
Citation: Scherer, M., Vömel, H., Fueglistaler, S., Oltmans, S. J., and Staehelin, J.: Trends and variability of midlatitude stratospheric water vapour deduced from the re-evaluated Boulder balloon series and HALOE, Atmos. Chem. Phys., 8, 1391-1402, doi:10.5194/acp-8-1391-2008, 2008.