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Wind Forcing (wind + forcing)
Selected AbstractsSimulating larval supply to estuarine nursery areas: how important are physical processes to the supply of larvae to the Aransas Pass Inlet?FISHERIES OCEANOGRAPHY, Issue 3 2004C. A. Brown Abstract Factors controlling the movement of fish larvae from coastal spawning environments to estuarine nursery areas are important to fish recruitment. In this paper, the role of physical processes in larval transport to estuarine nursery areas in the Aransas Pass region, Texas, is examined using a circulation model coupled with a fixed-depth particle transport model. Two phases of transport are examined: transport on the shelf to the tidal inlet and transport through the inlet to estuarine nursery areas. Observed pulsing in the supply of red drum (Sciaenops ocellatus) larvae to the tidal inlet is significantly correlated with modeled particle supply. This pulsing is not correlated with a specific physical process, but results from the interaction of several factors affecting water movement, including low-frequency variations in water level and wind forcing. Simulations suggest that the primary spawning region for red drum larvae that utilize nursery habitat in the Aransas Pass region is located north of the inlet. Patterns in the trajectories of particles that successfully enter the inlet reveal that they move alongshelf in the nearshore region and then move into the inlet, rather than moving directly across the shelf to the inlet. The approach path of particles outside the inlet determines the spatial transport patterns for inlets with branched channels and multiple bays. This study demonstrates that physical processes play an important role in determining larval supply to a tidal inlet. [source] Interaction between wind-induced seiches and convective cooling governs algal distribution in a canyon-shaped reservoirFRESHWATER BIOLOGY, Issue 7 2007RAFAEL MARCÉ Summary 1. Wind is considered the dominant factor controlling phytoplankton distribution in lentic environments. In canyon-shaped reservoirs, wind tends to blow along the main axis generating internal seiches and advective water movements that jointly with biological features of algae can produce a heterogeneous phytoplankton distribution. Turbulence generated by wind stress and convection will also affect the vertical distribution of algae, depending on their sinking properties. 2. We investigated the vertical and horizontal distribution of phytoplankton during the stratification period in Sau Reservoir (NE Spain). Sites along the main reservoir axis were sampled every 4 h for 3 days, and profiles of chlorophyll- a and temperature were made using a fluorescent FluoroProbe, which can discriminate among the main algal groups. Convective and wind shear velocity scales, and energy dissipation were calculated from meteorological data, and simulation experiments were performed to describe non-measured processes, like vertical advection and sinking velocity of phytoplankton. 3. Wind direction changed from day to night, producing a diel thermocline oscillation and an internal seiche. Energy dissipation was moderate during the night, and mainly attributed to convective cooling. During the day the energy dissipation was entirely attributed to wind shear, but values indicated low turbulence intensity. 4. The epilimnetic algal community was mainly composed of diatoms and chlorophytes. Chlorophytes showed a homogeneous distribution on the horizontal and vertical planes. Diatom horizontal pattern was also homogeneous, because the horizontal advective velocities generated by wind forcing were not high enough to develop phytoplankton gradients along the reservoir. 5. Diatom vertical distribution was heterogeneous in space and time. Different processes dominated in different regions of the reservoir, due to the interaction between seiching and the daily cycle of convective-mediated turbulence. As the meteorological forcing followed a clear daily pattern, we found very different diatom sedimentation dynamics between day and night. Remarkably, these dynamics were asynchronous in the extremes of the seiche, implying that under the same meteorological forcing a diatom population can show contrasting sedimentation dynamics at small spatial scales (approximately 103 m). This finding should be taken into account when interpreting paleolimnological records from different locations in a lake. 6. Vertical distribution of non-motile algae is a complex process including turbulence, vertical and horizontal advection, variations in the depth of the mixing layer and the intrinsic sinking properties of the organisms. Thus, simplistic interpretations considering only one of these factors should be regarded with caution. The results of this work also suggest that diatoms can persist in stratified water because of a synergistic effect between seiching and convective turbulence. [source] Wave and sediment dynamics along a shallow subtidal sandy beach inhabited by modern stromatolitesGEOBIOLOGY, Issue 1 2008J. E. ECKMAN ABSTRACT To help define the habitat of modern marine stromatolites, wave-dominated flow and sediment transport were studied in the shallow subtidal region (1,2 m depth) along the slightly concave, windward face of Highborne Cay, Exuma, Bahamas , the only face of the cay that includes a population of stromatolites concentrated near the region of highest curvature of the beach. Wave energy impacting this island's most exposed beach was driven by local wind forcing which increases largely in response to the passage of atmospheric disturbances that typically affect the region for periods of a few days. Although some wave energy is almost always noted (maximum horizontal orbital speeds at the bottom are rarely <10 cm s,1), wave conditions remain comparatively calm until local winds increase above speeds of ,3,4 m s,1 at which point maximum wave speeds rapidly increase to 50,80 cm s,1. Stromatolites, which are largely restricted to the shoreward side of a shallow platform reef, are sheltered by the reef beyond which wave speeds are one to four times higher (depending on tidal stage). Moreover, stromatolite populations are predominantly found along a region of this wave-exposed beach that experiences comparatively reduced wave energy because of the curved morphology of the island's face. Maximum wave speeds are 1.4 to 2 times higher along more northern sections of the beach just beyond the locus of stromatolite populations. A quantitative model of sediment transport was developed that accurately predicted accumulation of suspended sediment in sediment traps deployed in the shallow subtidal zone along this beach. This model, coupled with in situ wave records, indicates that gross rates of suspended sediment deposition should be two to three times higher northward of the main stromatolite populations. Regions of the beach containing stromatolites nevertheless should experience significant rates of gross suspended sediment deposition averaging 7,10 g cm,2 day,1 (,4,6 cm day,1). Results suggest that one axis of the habitat of modern marine stromatolites may be defined by a comparatively narrow range of flow energy and sediment transport conditions. [source] Intraseasonal variability of the ocean , atmosphere coupling in the Gulf of Guinea during boreal spring and summerTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue S1 2010Gaëlle de Coëtlogon Abstract Statistical analyses of the satellite TMI sea-surface temperature (SST) and QuikSCAT surface winds in boreal spring and summer are performed to investigate the intraseasonal variability of air,sea interactions in the Gulf of Guinea. There, empirical orthogonal function decomposition shows the existence of peaks around 15 days, and their lagged cross-correlation the signature of an expected 5-day lag wind forcing and 3-day lag strong negative SST feedback. Lagged linear regressions are performed onto a reference SST index of the cold tongue northern front in the Gulf of Guinea. A cold SST anomaly covering the equatorial and coastal upwelling is forced after about one week by stronger-than-usual south-easterlies linked to the St Helena anticyclone, suggesting that intraseasonal variability in the Gulf of Guinea is connected to large-scale fluctuations in the South Atlantic. Within about 5°S and 5°N, two retroactions between SST and surface wind appear to dominate near-surface atmosphere conditions. When the wind leads the SST, stronger monsoonal winds north of 2°N are partly sustained by the developing SST anomaly and bring more humidity and rainfall toward the continent. When the SST leads the wind, a reversal of anomalous winds is observed mainly south of 2°N, closing a negative feedback loop with a biweekly periodicity. Eventually, further investigation with an ocean model emphasizes the contribution of the horizontal advection in shaping these intraseasonal SST signals. The contribution of vertical processes may also be important but was more difficult to estimate. Copyright © 2010 Royal Meteorological Society [source] | ||||||||||