Observations and numerical modeling of the Pearl River plume in summer season

Abstract

A cruise survey of the Pearl River plume during southeasterly and southwesterly winds, two typical wind patterns in summer in Guangdong coastal waters, is reported and the cruise data are analyzed to unveil the plume dynamics. The Kelvin number is derived from the in situ data, revealing that the Pearl River plume exhibits two different scales in response to the two kinds of the wind forcing. Numerical model simulations based on the regional oceanic modeling system (ROMS) with nesting domains are implemented to explore details of the plume dynamics, validated by cruise observations and tidal gauge sea level data. Modeling results suggest that there is a subtidal, anticyclonic recirculation bulge on the west side out of the estuary mouth under southeasterly winds, showing a recirculating plume in the near-field. When the wind changes to the southwesterly, however, the recirculating plume vanishes. The distinct, supercritical tidal plume front occurs with southeasterly winds prevailing in spring tide due to the strong advection in the tidal plume. The tidal salt deficit flux can reach as high as 12.5% of the mean current flux, and illustrates the combined forcing of tide and wind. Key Points The paper clarifies the Pearl River plume anatomy under two typical winds Spring tide facilitates the supercritical Pearl River tidal plume front Tide determines tidal salt deficit flux strength; wind determines the direction