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Holzer, M., T.M. Hall, and R.B. Stull, 2005: Seasonality and weather-driven variability of transpacific transport. J. Geophys. Res., 110, D23103, doi:10.1029/2005JD006261.
We quantify transport from the industrialized regions of E Asia using the transit-time probability density function (pdf ), G, to isolate the role of transport from any other factors, such as chemistry and deposition. Using the offline transport model MATCH driven by NCEP reanalyses, we calculate G, which is the time-evolving mass fraction of air that had its last contact with the E-Asian source region during each day of a three-year period. Ensemble means of G establish the timescales and pathways of the seasonal-mean climatological transport from E Asia. During spring E-Asian air is efficiently exported from E Asia and nearly all of it is involved in transpacific transport. In summer E-Asian air is transported aloft across the Pacific but also west over SE Asia to the Middle East in nearly equal measure. For all seasons E-Asian air arrives over N America first in the mid-to-upper troposphere after 6-8 days and approximately one week (two weeks for summer) later at the surface. The N-American signal is strongest in winter and spring. Daily variability of transpacific transport is quantified in terms of the E-Asian air burden over western N America as a function of its transit time. The variability peaks at a transit time of ~7 days, several days before the burden itself peaks. When scaled by the seasonal mean, the distribution of fluctuations has only weak seasonal dependence. Lagged event and non-event composites, conditioned on the western N-American burden of E-Asian air, reveal that transport events are associated with dipolar wind perturbations over the eastern Pacific that are positioned and phased to receive enhanced Asian outflow. Surface-pressure correlations are consistent with an associated strengthened Pacific High and weakened Aleutian Low.
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