Analysis of seasonal and interannual variability in transpacific transport

Abstract

The purpose of our analysis is both to evaluate the meteorological component of the seasonal and interannual variability of transpacific transport and to identify meteorological features that can be used to estimate transpacific transport. To accomplish this goal, we simulate the transport of nine continental tracers with uniform emissions and two-week lifetimes using the global Model of Ozone and Related Tracers Version 2 (MOZART-2) driven with NCEP reanalysis meteorology from 1991-2001. In addition, we define a transpacific "transport potential,'' a measure of the quantity of a tracer transported from a particular region normalized by its total emissions from that region, across a meridional plane in the eastern Pacific at 130degreesW. We find that at midlatitudes, the east Asian and Indian tracers have the largest transport potentials, particularly in spring. The interannual variability of the transpacific transport potentials of most tracers is relatively high in winter and fall ( particularly in February and September) but is low from April to August. At high latitudes the former Soviet Union, east Asian, and European tracers have the largest transpacific transport potentials, especially in late summer and fall, when the lowest interannual variability is observed. We find that El Nino winters are associated with stronger eastward transport of east Asian emissions in the subtropical eastern Pacific. Transport of the east Asian tracer in the central North Pacific is well correlated with the North Pacific Index. However, we find that the interannual variability of transport across the west coast of North America is mostly driven by local meteorology. We therefore created a new index based on meteorology over the eastern Pacific, which we call the Eastern Pacific Index (EPI). The EPI captures most of the interannual variability of transpacific transport at both middle- and high-latitude regions across the west coast of North America.