HR: 16:15h
AN: A52G-02    [PDF]
TI: The Long-Term Change in Stratospheric Water Vapor Isotopes
AU: * Coffey, M T
EM: coffey@ucar.edu
AF: National Center for Atmospheric Research, PO Box 3000, Boulder, CO 80307 United States
AU: Hannigan, J W
EM: jamesw@ucar.edu
AF: National Center for Atmospheric Research, PO Box 3000, Boulder, CO 80307 United States
AU: Goldman, A
EM: goldman@ucar.edu
AF: University of Denver, 2112 E. Wesley Avenue, Denver, CO 80208 United States
AB: More than 20 years of observations from high altitude aircraft of high-resolution infrared absorption have been analyzed, using non-linear least squares spectral fitting, to retrieve stratospheric column amounts of H$_{2}$$^{16}$O, H$_{2}$$^{17}$O, H$_{2}$$^{18}$O and HDO. Total vertical column amounts above 12 km are retrieved. However, analysis of the information content of the solar viewing geometry shows that most of the contribution to the column comes from altitudes below 25 km. So the measured column amounts may be considered as lower stratospheric amounts. The lower stratosphere is a difficult region to observe, especially for H$_{2}$O. It is above the in situ sampling range for most aircraft. The strong absorption by H$_{2}$O makes the lower stratosphere difficult to measure remotely by both surface and satellite techniques. Observations by our remote sounding spectrometer, from a platform at the base of the stratosphere, are optimum for determining lower stratospheric water vapor amounts. The advantage of having deployed the same instrument over such a long measurement period and the uniform analysis of all the data make this data set extremely useful for long-term trend analyses. Water vapor plays an important role in chemical and radiative processes in the lower stratosphere and upper troposphere. We expect lower stratospheric water to have a latitudinal and a seasonal variation, as well as a long-term trend. However, the dominant component of the water variation is found to be a linear long-term trend. Monthly averaged column amounts of H$_{2}$$^{16}$O, H$_{2}$$^{17}$O, H$_{2}$$^{18}$O and HDO for the period from 1978 to 2000 are presented to show the latitudinal distribution of these isotopes in both hemispheres. Results show an increase at mid-latitudes of approximately 3 % / year in all isotopes. Annual trends diverge at low latitudes for the four isotopes with the increase in HDO being much depressed.
DE: 0341 Middle atmosphere--constituent transport and chemistry (3334)
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting