The Role of Weather Systems in Coastal Current

This study examines the influence of weather systems on coastal currents through the analysis of observational data collected from moving vessels, moorings, scaling analysis, and theoretical modeling. The velocity field in the coastal ocean is driven by factors such as tides, wind, and density gradients, which are largely influenced by river discharge and heterogeneous heat or buoyancy flux. Among these, the density gradient and buoyancy flux exhibit significant seasonal variability, while wind variability spans a broad spectrum, including both super-inertial and sub-inertial frequencies.

These variations are linked to changing weather patterns as systems move across the region, influenced by large-scale atmospheric circulations such as the meandering jet stream and the positioning of subtropical highs, which in turn affect the motion of tropical and extratropical cyclones. These atmospheric dynamics drive wind variations over the coastal ocean, ultimately influencing coastal current variations across a wide frequency range.

The data used in this study were primarily obtained from our own ship-based observations and mooring instruments, as well as from instruments mounted on offshore oil platforms and NOAA's weather data. Our analyses highlight the relationship between moving weather systems and oceanic responses, including spectral characteristics, time series variations, and spatial patterns. A theoretical model is presented that establishes a general relationship between the velocity field and forcing functions, represented as mathematical convolutions between the forcing functions and a complex frictional-rotary inertial function. Inertial oscillations are identified as the outcome of this convolution, acting as a natural filter that amplifies motions near the inertial frequency. Both moored data and observations from moving vessels demonstrate significant variability in coastal currents in response to passing weather systems.