A 3-D global simulation of the advective transport of passive tracers from various northern hemisphere sources

Two-year transport simulations are performed for passive tracers continuously emitted from Japan, Europe, North America and Amazon regions in order to study transport processes of anthropogenic gases such as CO₂ and halocarbons. Three-dimensional wind data produced by the Meteorological Research Institute global spectral model with rhomboidal 24 truncation and 23 levels are used. Globally, there are three regions within which the transport of tracer is relatively rapid. These are the tropics, and the northern/southern extratropics. Within the tropics, the Pacific and Indian Ocean regions may be considered as further subdivisions. Transports between regions are much slower. In the case of a Japanese source, an equatorward transport occurs mainly in the lower troposphere during winter associated with the Asian winter monsoon circulation. The tracers are advected upward over the equatorial Indian Ocean and transported into the southern hemisphere. A significant seasonal oscillation in tracer density develops in the Antarctic region with the maximum in early June. In the cases of European and North American sources, an equatorward transport is slow and a poleward transport is enhanced in winter. In all cases, transport to the southern extratropics occurs in the upper troposphere because of upward advection in the tropical region. The tracer density increases with altitude in the troposphere in the southern extratropics except over Antarctica. Over Antarctica, the tracer density decreases with altitude and the horizontal distribution is rather uniform at the surface, indicating downward transport of low-density stratospheric air.