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.

Observation of the supercritical Pearl River plume front under the downwelling-favorable winds

“…From Figure 6, we can see the plume water area is occupied by the downwelling-favorable wind. According to Pan et al (2014), the supercritical, distinct plume front is easily produced in the downwelling-favorable wind and spring tide. The front observed in the SAR image shall be a supercritical one.…”

“…The pattern of the front suggests that the plume water was trapped by this front as a bulge lying near the river mouth. The bulge near the estuary mouth was observed by Pan et al (2014) using numerical model results. The bulge is formed under downwelling-favorable wind and strongly affected by the Earth's rotation as well as the momentum of the river discharge.…”

“…Impacted by the river discharge, tides, and topography, the Pearl River plume front shows tidal mixing front and salinity front characteristics (Luo et al, 2008). The supercritical, distinct plume front appears in downwelling-favorable wind and spring tide; in contrast, the subcritical, diffusive front occurs in southwesterly wind and neap tide (Pan et al, 2014). The supercritical front has a distinct boundary and strong velocity convergence in the surface layer, which can be easily observed.…”

River bulge evolution and dynamics in a non-tidal sea – Daugava River plume in the Gulf of Riga, Baltic Sea

“…Observational studies confirm that the bulge is a naturally occurring phenomenon with many rivers (Chant et al, 2008;Horner-Devine et al, 2008;Horner-Devine, 2009;Valente and da Silva, 2009;Saldías et al, 2012;Hopkins et al, 2013;Mendes et al, 2014;Pan et al, 2014;Fernández-Nóvoa et al, 2015), but an anti-cyclonic rotation inside a bulge is observed seldom (Kudela et al, 2010;Horner-Devine, 2009;Chant et al, 2008). Observations of the evolution of the bulge over a certain time period are almost non-existent, with the ex-418 E. Soosaar et al: River bulge evolution and dynamics in a non-tidal sea ception of the Niagara River plume (Horner-Devine et al, 2008) and the Tagus estuary plume (Valente and da Silva, 2009).…”

Different approaches to model the nearshore circulation in the south shore of O'ahu, Hawaii

“…On average, the influence of the canal on the coastal dynamics is small; however, sporadic, heavy rainfall events can force an outflow of freshwater into the coastal zone that alters the stratification. Although numerous modeling studies on large discharge rivers exist (Gracia Berdeal et al, 2002;Pan et al, 2014), the same is not true for rivers with small volume and aperiodic discharge.…”