In situ measurements of water vapor in the Arctic winter lower stratosphere.

摘要

The Harvard Lyman-alpha photofragment fluorescence hygrometer measured water vapor aboard the NASA ER-2 aircraft during the SAGE III Ozone Loss and Validation Experiment (SOLVE), based from Kiruna, Sweden (68°N, 20°E), during January--March 2000. In situ measurements of water vapor, CH4, and N2O, acquired during SOLVE, are used to examine (1) dehydration in the Arctic vortex and (2) transport into the lowermost stratosphere in the context of middle- and high-latitude ozone declines.; Knowledge of the total hydrogen budget of the Arctic winter stratosphere is pertinent to understanding the processes of formation of polar stratospheric clouds (PSCs) and quantifying the reactive uptake coefficients of the relevant cold aerosols, factors determining how fast reservoir halogen species (i.e., ClONO2, HCl) are converted to active forms (i.e., ClO, ClOOCl). Although the data indicate only isolated dehydration and rehydration episodes along ER-2 flight tracks (i.e., between 400 and 470 K) in the vortex, the relationship between H2O and CH4 for all flights during SOLVE suggests that subtle, widespread dehydration occurred above the ER-2 flight tracks, consistent with meteorological reanalysis data.; Isentropic transport from the tropics plays a major role in redistributing ozone and water vapor at middle and high latitudes. Analysis of tracer-tracer correlations of the observed quantities H2O + 2*CH 4 and N2O indicates that rapid, poleward isentropic transport from the lower tropical stratosphere coupled with diabatic descent between the subtropical jet and polar jet delivers very young air to the high-latitude lowermost stratosphere during winter, while descent from the vortex and subsequent transport to lower latitudes is very limited. No evidence of isentropic mixing from the upper tropical troposphere survives in the high-latitude lowermost stratosphere except below 350 K, where markedly higher water vapor mixing ratios indicate mixing from the extratropical troposphere. The balance of all of these transport processes poses dynamical and chemical consequences for ozone. Transport from the lower tropical stratosphere (1) exports ozone-poor air to midlatitudes and the subvortex region and (2) distributes seasonally variable water vapor to the middle- and high-latitude lower stratosphere, potentially enhancing halogen-catalyzed ozone destruction through heterogeneous processing.