Idealized Tracer Transport Models with Time-Varying Transport: Applications to Ocean boundary-current
Abstract
One-dimensional advection-diffusion and advection-diffusion-dilution (or "leaky-pipe") analytical models have been widely used to interpret a variety of geophysical phenomena, such as the propagation of tracers (e.g., CFCs) in the North Atlantic Deep Western Boundary Current (DWBC). In all applications we are aware of, transport is assumed to be in steady state. Here, we relax this assumption, and solve analytically for tracer signals in both models with small-amplitude time-varying transport. For a tracer boundary condition that steadily increases in time, the resulting tracer field exhibits fluctuations due to the transport acting on the gradients induced by boundary forcing. We compare the transport-induced tracer fluctuations to "propagated fluctuations" occurring in steady-state models when the tracer at the boundary is fluctuating in time. Using coefficients fit to DWBC tracer observations we find that in the North-Atlantic propagated tracer fluctuations are larger but by the sub-tropics transport-induced fluctuations dominate. This is in contrast to the common that subtropical and tropical DWBC fluctuations in tracer such as CFCs, temperature and salinity are propagated signals from the northern formation region. However, even the transport-induced fluctuations are smaller than observed sub-tropical DWBC CFC fluctuations.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.H21B0818T
- Keywords:
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- 0341 Middle atmosphere: constituent transport and chemistry (3334);
- 1829 Groundwater hydrology;
- 1845 Limnology (0458;
- 4239;
- 4942);
- 4536 Hydrography and tracers;
- 4808 Chemical tracers