Water vapor's contribution to Earth's radiative forcing is most sensitive to changes in its lower stratosphere concentration. One recognized pathway for rapid increases in stratospheric water vapor is tropopause-overshooting convection. Since this pathway has been rarely sampled, the NASA Dynamics and Chemistry of the Summer Stratosphere (DCOTSS) field project focused on obtaining in situ...
Jason St.Clair's Publications
Homeyer, C. R., J. B. Smith, K. M. Bedka, K. P. Bowman, D. M. Wilmouth, R. Ueyama, J. M. Dean-Day, J. M. St. Clair, R. Hannun, J. Hare, A. Pandey, D. S. Sayres, T. F. Hanisco, A. E. Gordon, and E. N. Tinney, Extreme altitudes of stratospheric hydration by midlatitude convection observed during the DCOTSS field campaign. Geophys. Res. Lett., 50, e2023GL104914, 2023, doi: 10.1029/2023GL104914.
Sayres, D.S., L. Pfister, T.F. Hanisco, E.J. Moyer, J.B. Smith, J.M. St. Clair, A.S. OBrien, M.F. Witinski, M. Legg, J. G. Anderson, Influence of Convection on the Water Isotopic Composition of the Tropical Tropopause Layer and Tropical Stratosphere, J. Geophys. Res. 115, D00J20, doi:10.1029/2009JD013100, 2010.
We present the first in situ measurements of HDO across the tropical tropopause, obtained by the integrated cavity output spectroscopy (ICOS) and Hoxotope water isotope instruments during the Costa Rica Aura Validation Experiment (CR-AVE) and Tropical Composition, Cloud and Climate Coupling (TC4) aircraft campaigns out of Costa Rica in winter and summer, respectively. We use these data to explore...
Sayres, D.S., E.J. Moyer, T.F. Hanisco, J.M. Clair, F.N. Keutsch, A. O’Brien, N.T. Allen, L.Lapson, J.N. Demusz, M. Rivero, T. Martin, M. Greenberg, C. Tuozzolo, G.S. Engel, J.H. Kroll, J.B. Paul, and J.G. Anderson, A New Cavity Based Absorption Instrument for Detection of Water Isotopologues in the Upper Troposphere and Lower Stratosphere, Review of Scientific Instruments, 80, 2009.
We describe here the Harvard integrated cavity output spectroscopy (ICOS) isotope instrument, a mid-IR infrared spectrometer using ICOS to make in situ measurements of the primary isotopologues of water vapor (H2O, HDO, and H218O) in the upper troposphere and lower stratosphere (UTLS). The long path length provided by ICOS provides the sensitivity and accuracy necessary to measure...
Weinstock, E. M., et al. (2009), Validation of the Harvard Lyman-α in situ water vapor instrument: Implications for the mechanisms that control stratospheric water vapor, J. Geophys. Res., 114, D23301, doi:10.1029/2009JD012427.
Building on previously published details of the laboratory calibrations of the Harvard Lyman-α photofragment fluorescence hygrometer (HWV) on the NASA ER-2 and WB-57 aircraft, we describe here the validation process for HWV, which includes laboratory calibrations and intercomparisons with other Harvard water vapor instruments at water vapor mixing ratios from 0 to 10 ppmv, followed by in-...
Sayres, D. S., and Coauthors, 2009: A new cavity based absorption instrument for detection of water isotopologues in the upper troposphere and lower stratosphere. Rev. Sci. Instrum., 80, 044102, doi:10.1063/1.3117349.
We describe here the Harvard integrated cavity output spectroscopy (ICOS) isotope instrument, a mid-IR infrared spectrometer using ICOS to make in situ measurements of the primary isotopologues of water vapor (H2O, HDO, and H218O) in the upper troposphere and lower stratosphere (UTLS). The long path length provided by ICOS provides the sensitivity and accuracy necessary to measure...
E.J. Moyer, D.S. Sayres, G.S. Engel, J.M.St. Clair, F.N. Keutsch, N.T. Allen, J.H. Kroll, J.G. Anderson, Design considerations in high-sensitivity off-axis integrated cavity output spectroscopy. Phys. B 92, 467 (2008)
CT Off-axis integrated cavity output spectroscopy(OA-ICOS) has generated much interest because it potentially allows highly sensitive field measurements with robustoptical alignment. We discuss here design choices involvedin design of an OA-ICOS instrument and how these choicesimpact instrument sensitivity, using as our example the design of the Harvard ICOS isotope instrument, which demonstrates...
J.M. St. Clair, T.F. Hanisco, E.M. Weinstock, E.J. Moyer,D.S. Sayres, F.N. Keutsch, J.H. Kroll, J.N. Demusz,N.T. Allen, J.B. Smith, J.R. Spackman, J.G. Anderson, A new photolysis laser-induced fluorescence instrument for the detection of H2O and HDO in the lower stratosphere. Sci. Instrum. 79, 064101 (2008). doi:10.1063/1.2940221.
We present a new instrument, Hoxotope, for the in situ measurement of H2O and its heavy deuterium isotopologue (HDO) in the upper troposphere and lower stratosphere aboard the NASA WB-57. Sensitive measurements of δD are accomplished through the vacuum UV photolysis of water followed by laser-induced fluorescence detection of the resultant OH and OD photofragments....
Hanisco, T. F., et al. (2007), Observations of deep convective influence on stratospheric water vapor and its isotopic composition, Geophys. Res. Lett., 34, L04814, doi:10.1029/2006GL027899.
In situ observations of H2O and HDO in the midlatitude stratosphere are used to evaluate the role of convection in determining the stratospheric water budget. The observations show that water vapor in the overworld stratosphere (potential temperature > 380 K) is isotopically heavier than expected. Measurements in an airmass with anomalously high concentrations of water vapor show isotopic...