9302370 Anderson Water vapor is the dominant greenhouse gas and, as the original Central Equatorial Pacific Experiment (CEPEX) proposal pints out, water vapor is therefore the dominant regulator of the Earth's energy budget and thus the critical regulator of climate. An understanding of the processes that dictate the distribution of water vapor and the processes that link the distribution of water in all its phases to the frequency-dependent divergence of flux and radiance constitutes a central element in any considered strategy to understand secular trends of the Earth's climate. The PIs will augment the array of CEPEX observations with in situ observations of water vapor, ozone, pressure and temperature from the ER-2 aircraft. Water vapor measurements will be carried out using the Lyman- alpha photofragmentionion technique: Water vapor + hv hydroxyl(A) + hydrogen hydroxyl radical(X) + hv + hydrogen that fragments a water vapor molecule with 121.6 nm radiation from a plasma discharge lamp and observes 308 nm radiation from the electronically excited product hydroxyl radical. This experiment is done both in absorption and in fluorescence to provide a dynamic range of five orders of magnitude in water vapor concentration and an absolute calibration of the instrument during each flight. Ozone observations will be done using ultraviolet absorption in the Hartley continuum at 257nm. The instrument uses an on-board Hg resonance lamp; a MnO2 getter to establish the absorption cell count rate in the absence of ozone in the sample; a Roots blower to actively aspirate the measurement cell; and counting electronics to obtain fractional absorption levels of one part in 105. This research is important because it will provide water vapor and ozone observations needed to help interpret climate processes in a climate-sensitive part of the world. ***
