Pittman, J. V., et al. (2007), Transport in the subtropical lowermost stratosphere during the Cirrus Regional Study ofTropical Anvils and Cirrus Layers – Florida Area Cirrus Experiment, J. Geophys. Res., 112, D08304, doi:10.1029/2006JD007851.
We use in situ measurements of water vapor (H2O), ozone (O3), carbon dioxide(CO2), carbon monoxide (CO), nitric oxide (NO), and total reactive nitrogen (NOy)obtained during the CRYSTAL-FACE campaign in July 2002 to study summertimetransport in the subtropical lowermost stratosphere. We use an objective methodology todistinguish the latitudinal origin of the sampled air masses despite the influence ofconvection, and we calculate backward trajectories to elucidate their recent geographicalhistory. The methodology consists of exploring the statistical behavior of the data byperforming multivariate clustering and agglomerative hierarchical clustering calculationsand projecting cluster groups onto principal component space to identify air masses of likecomposition and hence presumed origin. The statistically derived cluster groups are thenexamined in physical space using tracer-tracer correlation plots. Interpretation of theprincipal component analysis suggests that the variability in the data is accounted forprimarily by the mean age of air in the stratosphere, followed by the age of the convectiveinfluence, and last by the extent of convective influence, potentially related to the latitudeof convective injection (Dessler and Sherwood, 2004). We find that high-latitudestratospheric air is the dominant source region during the beginning of the campaign whiletropical air is the dominant source region during the rest of the campaign. Influence ofconvection from both local and nonlocal events is frequently observed. The identificationof air mass origin is confirmed with backward trajectories, and the behavior of thetrajectories is associated with the North American monsoon circulation.