Data/hora: 12/06/2024 15:14:50

Provedor de dados: | 5
País: | France
Título: | Year-long measurements of flow-through the dover strait by HF radar and acoustic doppler current profilers (ADCP)
Autores: | Prandle, D.
Data: | 1993
Ano: | 1993
Palavras-chave: | DOVER STRAIT; HF RADAR; ACOUSTIC DOPPLER; CURRENT PROFILER; TIDAL FLUX.
Resumo: | Contaminants from the Channel flow through the Dover Strait into the North Sea where they represent a significant fraction of the enhanced concentrations observed along the continental coast. Despite numerous previous investigations, the magnitude of this net flow and its dependency on various forcing factors remain uncertain. The new UK H.F. Radar system, OSCR (Ocean Surface Current Radar) developed for measuring nearshore surface currents offers a clear opportunity of establishing the magnitude and nature of this flow. Starting in July 1990, H.F. Radar observations were made in the Dover Strait for five months from the French coast overlapping (for two months) with five months from the English coast. These measurements involved fully-automised monitoring of surface currents at 700 locations every 20 minutes. A bottom-mounted ADCP was moored continuously for die same period in the middle of the Strait. Tidal current atlases were produced from the radar measurements showing ellipses for seven major constituents at up to 160 locations in the strait, examples for the two major constituents M2 and S2, are shown in Figures 2 and 3. A net tidal (M2) residual flow of 36,000 m3 s-1 into the North Sea was calculated from a combination of the M2 tidal ellipse data with the M2 tidal elevation distribution. The localised response of surface currents to wind forcing is shown to follow the classical pattern of Ekman veering, with angles of up to 45-degrees to die wind direction in deep water. In addition to this localised surface response, wind-forced residual currents, persistent through depth and coherent spatially, flow through the strait amounting, on average, to 45,000 m3 s-1. In addition a steady (non-tidal, non wind-driven) component was observed of approximately 6000 m2 s-1. Thus net longterm flow into the North Sea was estimated as 87,000 m3 s-1. i.e. 40% of earliest estimates and 60% of the value assumed in many present-day North-Sea models. The time-averaged residual currents revealed a gyre of approximately 20 km diameter off the westerly edge of Cap Gris Nez rotating anticlockwise with a period of approximately seven days. These residual flow time-series obtained from the radar measurements are correlated against corresponding time-series obtained from: a) wind measurements; b) the bottom-mounted ADCP; c) flows through the Dover Strait computed by the UK numerical model used operationally to predict storm surges Significant correlations are found in all cases with a maximum value of 0.8, between the depth-averaged ADCP residual current and the flow through the Strait calculated by the model. These correlations indicate that the low-frequency flows through the Dover Strait determined from the radar measurements on the French and English coasts are generally in opposing directions. Additional preliminary comparisons with observed sea-surface slopes were restricted by the availability of tide gauge data.
Tipo: | Text
Idioma: | Inglês
Identificador: | http://archimer.ifremer.fr/doc/00099/21070/18695.pdf
Editor: | Gauthier-Villars
Relação: | http://archimer.ifremer.fr/doc/00099/21070/
Formato: | application/pdf
Fonte: | Oceanologica Acta (0399-1784) (Gauthier-Villars), 1993 , Vol. 16 , N. 5-6 , P. 457-468