Opposite Wind Directions Research Articles

Quantifying the influence of transmission path characteristics on urban railway noise.

Every ambient noise study employs the source-path-receiver structure to explore the overall behaviour of sound. Noise levels are affected by changes in distance, intervening barriers, and atmospheric conditions along the transmission path between the source and the receiver. The objective of this study is to quantify the influence of transmission path characteristics for a realistic time-varying moving line source. In this context, railway noise was considered to explore the variance of noise in an urban setting over a variety of measuring distances, including 25, 50, 100, and 200 m, with variables such as air temperature, humidity, and wind condition. The data corresponding to 106 trains was collected for analysis, and it was observed that the effect of the wind was more significant for larger distances between the source and the receiver. When the sound levels were measured in two opposite wind directions, a considerable noise level difference was observed. For every 1 m/s increase in wind speed, within a distance of 50 m, the average sound attenuation induced by the upwind phenomena was 0.2 dBA. The impact of air temperature changes on received sound level from a moving source was insignificant within the range of temperatures considered in the study. The effect of humidity is less at shorter distances but at larger distances, increasingly attenuates noise levels. Analysis of variance was performed on the selected variables to determine whether the means of each group were significantly different from each other and found that train speed had a more significant impact on railway noise compared to other parameters.

Quantification of CH<sub>4</sub> emissions from waste disposal sites near the city of Madrid using ground- and space-based observations of COCCON, TROPOMI and IASI

Abstract. The objective of this study is to derive methane (CH4) emissions from three landfills, which are found to be the most significant CH4 sources in the metropolitan area of Madrid in Spain. We derive CH4 emissions from the CH4 enhancements observed by spaceborne and ground-based instruments. We apply satellite-based measurements from the TROPOspheric Monitoring Instrument (TROPOMI) and the Infrared Atmospheric Sounding Interferometer (IASI) together with measurements from the ground-based COllaborative Carbon Column Observing Network (COCCON) instruments. In 2018, a 2-week field campaign for measuring the atmospheric concentrations of greenhouse gases was performed in Madrid in the framework of Monitoring of the Greenhouse Gases Concentrations in Madrid (MEGEI-MAD) project. Five COCCON instruments were deployed at different locations around the Madrid city center, enabling the observation of total column-averaged CH4 mixing ratios (XCH4). Considering the prevalent wind regimes, we calculate the wind-assigned XCH4 anomalies for two opposite wind directions. Pronounced bipolar plumes are found when applying the method to NO2, which implies that our method of wind-assigned anomaly is suitable to estimate enhancements of trace gases at the urban level from satellite-based measurements. For quantifying the CH4 emissions, the wind-assigned plume method is applied to the TROPOMI XCH4 and to the lower tropospheric CH4 / dry-air column ratio (TXCH4) of the combined TROPOMI+IASI product. As CH4 emission strength we estimate 7.4 × 1025 ± 6.4 × 1024 molec. s−1 from the TROPOMI XCH4 data and 7.1 × 1025 ± 1.0 × 1025 molec. s−1 from the TROPOMI+IASI merged TXCH4 data. We use COCCON observations to estimate the local source strength as an independent method. COCCON observations indicate a weaker CH4 emission strength of 3.7 × 1025 molec. s−1 from a local source (the Valdemingómez waste plant) based on observations from a single day. This strength is lower than the one derived from the satellite observations, and it is a plausible result. This is because the analysis of the satellite data refers to a larger area, covering further emission sources in the study region, whereas the signal observed by COCCON is generated by a nearby local source. All emission rates estimated from the different observations are significantly larger than the emission rates provided via the official Spanish Register of Emissions and Pollutant Sources.

Wind-Induced Resuspension and Transport of Contaminated Sediment from the Rove Canal into the Etang De Berre, France

The present study concerns the erosion and transport of severely contaminated sediments in a Canal. It begins in the context of an engineering project aimed to re-introduce a forced convection at the entrance of this Canal by pumping marine water. The local wind is often strong enough to overpass the resuspension threshold; thus, there is a serious risk of downstream contamination of a Mediterranean lagoon. So, the goal is to evaluate this risk as a function of the pumping rate; this contamination is transported by the fine suspended particles. Different scenarios are investigated to determine the downstream transport of suspensions in terms of runoff. These scenarios (of 24 h) contains a succession of 3 periods: constant wind speed, wind slowdown and calm, for two opposite wind directions. Special attention is devoted to the modeling of complex mechanisms of erosion and resuspension during wind periods, deposition during windless periods and sediment consolidation. The main results concern the total flux of the suspended particles through the exit of the Canal at the confluence with the lagoon. It is shown that even for moderate runoff (<6 m3/s) this total flux is large enough, not only during the wind period, but also after several hours of calm.

Influences of wind direction on the cooling effects of mountain vegetation in urban area

The mountain or hill with lots of natural vegetation in a city has obvious cooling effects, so it can play a significant role in the regulation of urban microclimate and mitigation of urban heat island (UHI). In this paper, the influences of wind direction on the cooling effects of the Zijin Mountain in Nanjing were evaluated. Firstly, the land surface temperature (LST) was obtained based on 15 Landsat-8 images from 2013 to 2020, and the wind directions in 4 h before the satellite crossing time were calculated. Then, two remote sensing images with opposite wind directions were compared and analyzed to explore the influences of wind direction on the cooling effects of the Zijin Mountain. The results showed that both the cooling buffer zone method and the cooling area method proposed in this paper had proved that the wind direction had great influences on the cooling effects of the mountain vegetation in urban area. In addition, it was also found that the larger the wind speed differences of group images, the greater the influences of the wind direction on the cooling effects. This study will be helpful and meaningful for urban microclimate analyses and urban planning research.

Aeroelastic load validation in wake conditions using nacelle-mounted lidar measurements

Abstract. We propose a method for carrying out wind turbine load validation in wake conditions using measurements from forward-looking nacelle lidars. Two lidars, a pulsed- and a continuous-wave system, were installed on the nacelle of a 2.3 MW wind turbine operating in free-, partial-, and full-wake conditions. The turbine is placed within a straight row of turbines with a spacing of 5.2 rotor diameters, and wake disturbances are present for two opposite wind direction sectors. The wake flow fields are described by lidar-estimated wind field characteristics, which are commonly used as inputs for load simulations, without employing wake deficit models. These include mean wind speed, turbulence intensity, vertical and horizontal shear, yaw error, and turbulence-spectra parameters. We assess the uncertainty of lidar-based load predictions against wind turbine on-board sensors in wake conditions and compare it with the uncertainty of lidar-based load predictions against sensor data in free wind. Compared to the free-wind case, the simulations in wake conditions lead to increased relative errors (4 %–11 %). It is demonstrated that the mean wind speed, turbulence intensity, and turbulence length scale have a significant impact on the predictions. Finally, the experiences from this study indicate that characterizing turbulence inside the wake as well as defining a wind deficit model are the most challenging aspects of lidar-based load validation in wake conditions.

A numerical study of hydrogen leakage and diffusion in a hydrogen refueling station

Studies focused on the behavior of the hydrogen leakage and diffusion are of great importance for facilitating the large scale application of the hydrogen energy. In this paper, the hydrogen leakage and diffusion in six scenarios which including comparison of different leakage position and different wind effect are analyzed numerically. The studied geometry is derived from the hydrogen refueling station in China. Due to the high pressure in hydrogen storage take, the hydrogen leakage is momentum dominated. The hydrogen volume concentration with the variation of the leakage time in different scenarios is plotted. More importantly, profiles of the flammable gas cloud at the end of the leakage are quantitatively studied. Results indicate that a more narrow space between the leakage hole and the obstacle and a smaller contact area with the obstacle make the profile of the flammable gas cloud more irregular and unpredictable. In addition, results highlight the wind effect on the hydrogen leakage and diffusion. Comparing with scenario which the wind direction consistent with the leakage direction, the opposite wind direction may result in a larger profile of the flammable gas cloud. With wind velocity increasing, the profile of the flammable gas cloud is confined in a smaller range. However, the presence of the wind facilitates the form of the recirculation zone near the obstacle. With an increase of the wind velocity, the recirculation zone moves downward along the obstacle. Thus, the hydrogen accumulation is more prominent near the obstacle.

Risk of wind-driven resuspension and transport of contaminated sediments in a narrow marine channel confluencing a wide lagoon

This work concerns the wind-driven resuspension in a narrow marine channel and the risk of transport of contaminated bottom sediments in a wide brackish lagoon in the context of a planned anthropogenic infrastructure (with forced convection, by pumping sea water). It is based on the modelling and 3D numerical simulation of salinity, current distributions and bottom shear stress (BSS). The goal is to demonstrate that, even for narrow channels of a few tens of meter of width, a wind of 10–20 m/s is sufficient to create intensive currents, to resuspend muddy bottom sediments and transport polluted sediments downstream. Several model scenarios are considered for such wind speeds in two dominant and opposite wind directions, for a channel whose bottom sediments are mainly constituted of fine particles, typically 85% of mud and 15% of fine sand. It is known that finer sediments usually play an important role to transport contaminants (due to larger surface area of smaller particles). Our main results concern the bottom shear stress along such a long and narrow channel; namely the Rove channel which confluences the Etang de Berre lagoon, and for which a project of forced current circulation is planned by pumping sea water. Our numerical results show that the mobility threshold can be easily overpassed for the muddy sediments in the Rove channel. For a bottom roughness of 5 μm (coarse silt) and a wind speed of 20 m/s, BSS can reach 0.18 N/m2 for the N-NW wind in the median part of the channel, and even 0.21 N/m2 in one enlargement for the S-SE wind, while BSScr is about 0.1 N/m2. We conclude that these local winds can permit floc erosion and even surface erosion of fine sediments in the Rove channel.Concerning the resuspension of muddy sediments, our results are consistent with the experimental study presented by Carlin et al. (2016) for a windy shallow lagoon. They are also consistent with the conclusion of Mengual et al. (2017), from erodimetry experiment for estuarine sediments, that the sediment behaves like a pure mud if the percentage of the mud fraction is more than 70%, and that the critical BSS for mobility of such bed sediments is of the order of 0.1 N/m2. Such a lower critical BSS when the mixture is muddier is opposite to trends most often published.

Performance Evaluation of the GRAPES Model in Wind Simulations Over South China

In the present study, the performance of the GRAPES model in wind simulation over south China was assessed. The simulations were evaluated by using surface observations and two sounding stations in south China. The results show that the GRAPES model could provide a reliable simulation of the distribution and diurnal variation of the wind. It showed a generally overestimated southerly wind speed especially over the Pearl River Delta region and the south of Jiangxi Province as well as the coastal region over south China. GRAPES also exhibited a large number of stations with the opposite surface wind directions over the east of Guangxi and the south of Jiangxi during the nocturnal-to-morning period, as well as an overall overestimation of surface wind over the coastal regions during the afternoon. Although GRAPES could simulate the general evolutional characteristics of vertical wind profile, it underestimated wind speed above 900 hPa and overestimated wind speed below 900 hPa. Though the parameterization scheme of gravity wave drag proved to be an effective method to alleviate the systematic deviation of wind simulation, GRAPES still exhibited large errors in wind simulation, especially in the lower and upper troposphere.

Pesticide contamination and associated risk factors at public playgrounds near intensively managed apple and wine orchards

BackgroundPesticide levels are generally monitored within agricultural areas, but are commonly not assessed at public places. To assess possible contamination of non-target areas, 71 public playgrounds located next to intensively managed apple and wine orchards were selected in four valleys of South Tyrol (northern Italy). Further, the impact of environmental site characteristics on the number and concentration of pesticides was assessed. Grass samples from the selected playgrounds were collected and screened for 315 pesticide residues using standard gas chromatography and mass spectrometry.ResultsNearly half of the playgrounds (45%) were contaminated by at least one pesticide and a quarter (24%) by more than one. Eleven of the 12 different detected pesticides are classified as endocrine-active substances including the insecticide phosmet and the fungicide fluazinam showing the highest concentrations (0.069 and 0.26 mg kg−1, respectively). Additionally, one disinfectant and one preservation agent was found. Playgrounds in Venosta valley were most often contaminated (76% of all investigated playgrounds), highest concentrations were found in the Low Adige (2.02 mg kg−1). Pesticide concentrations were positively associated with areal proportion of apple orchards in the surroundings, the amount of rainfall and wind speed. In contrast, increasing global irradiance, opposite wind direction, increasing distance to agricultural sites and high wind speeds when pesticide application was not allowed were associated with decreasing pesticide contamination.ConclusionThis study is among the first investigating pesticide contamination of public playgrounds together with environmental factors in areas with pesticide-intensive agriculture at the beginning of the growing season. It is likely that playgrounds will be affected by more pesticides and higher concentrations over the course of the crop season. The result, that the majority of the detected pesticides are classified as endocrine active is worrisome as children are especially vulnerable. Hence, we recommend that pesticide risk assessments should better include protection measures for non-target areas.

Wind velocity changes along the passage between two angled walls – CFD simulations and full-scale measurements

This paper presents a study on wind flow in the passage between the walls of a bell tower. The bell tower, raised above the church roof, consisted of two walls with the horizontal angle between them equal to 100°. Computational fluid dynamics (CFD) simulations were performed for 3D models of the entire church structure. Two opposite inflow wind directions, which corresponded to diverging and converging wall layouts, were used. Amplification factors of the wind velocity along the passage were calculated. Additionally, full-scale measurements were conducted using three ultrasonic anemometers and three cup anemometers placed along the horizontal centreline of the bell tower walls. The CFD results were validated with the use of in-situ data. Wind velocity amplification or reduction observed in CFD simulations and full-scale measurements were of the same order. The biggest amplification of the wind velocity behind the passage was obtained for diverging walls, whereas the biggest reduction occurred in the front of the contraction for converging walls. The influence of geometry simplification and changes in the description of the wind flow were also analysed. Considerable differences in CFD simulations results were caused by small changes in the geometry of the model rather than by changes in the terrain category, including the roughness of the terrain.

Influence of Wind Strength and Duration on Relative Hypoxia Reductions by Opposite Wind Directions in an Estuary with an Asymmetric Channel

Computer model experiments are applied to analyze hypoxia reductions for opposing wind directions under various speeds and durations in the north–south oriented, two-layer-circulated Chesapeake estuary. Wind’s role in destratification is the main mechanism in short-term reduction of hypoxia. Hypoxia can also be reduced by wind-enhanced estuarine circulation associated with winds that have down-estuary straining components that promote bottom-returned oxygen-rich seawater intrusion. The up-bay-ward along-channel component of straining by the southerly or easterly wind induces greater destratification than the down-bay-ward straining by the opposite wind direction, i.e., northerly or westerly winds. While under the modulation of the west-skewed asymmetric cross-channel bathymetry in the Bay’s hypoxic zone, the westward cross-channel straining by easterly or northerly winds causes greater destratification than its opposite wind direction. The wind-induced cross-channel circulation can be completed much more rapidly than the wind-induced along-channel circulation, and the former is usually more effective than the latter in destratification and hypoxia reduction in an early wind period. The relative importance of cross-channel versus along-channel circulation for a particular wind direction can change with wind speed and duration. The existence of month-long prevailing unidirectional winds in the Chesapeake is explored, and the relative hypoxia reductions among different prevailing directions are analyzed. Scenarios of wind with intermittent calm or reversing directions on an hourly scale are also simulated and compared.

Effects of cross-channel bathymetry and wind direction on destratification and hypoxia reduction in the Chesapeake Bay

A coupled estuarine hydrodynamic model and water quality model were used to analyze differences in destratification and anoxia/hypoxia reduction by wind directions in the north-south oriented Chesapeake estuary, USA. The predominant cross-channel bathymetry in the Bay's anoxic center is asymmetric with a steeper and narrower shoal on the eastern shore than on the western shore, which modifies wind-induced circulation differently for two opposite wind directions. Model experiments of winds for 2-day at 8 m/s indicated that, for a stratified water over the aforementioned asymmetric bottom topography, the easterly wind caused greater destratification and hypoxia reduction than the westerly wind. This is a result of differential modulations on the two wind-induced cross-channel circulations by the asymmetric cross channel bathymetry. The downwelling along the gentle slope in the easterly wind was characterized with stronger baroclinicity than the downwelling along the steep slope (nearly perpendicular to surfaces of constant density) in the westerly wind. On the broad slope, there undergo greater contrasting density readjustments to the vorticity changes around the bottom boundary layer (BBL) during upslope and downslope motions. During the upslope condition, the flow in BBL tends to decelerate under adverse pressure gradient which leads to a stable condition in the outer layer; whereas, during the downslope condition, the BBL tends to accelerate under favourable pressure gradient, which leads to unstable condition in the outer layer of the large scale flow. Overall, the easterly wind caused greater anoxia reduction than the westerly wind during the entire wind period. A similar case was found for northerly versus southerly winds in the early stages of the wind period; modulated by the aforementioned bathymetry on the wind-induced cross-channel circulation, the northerly wind caused greater anoxia reduction than the southerly wind. However, as wind continues, the wind-induced along-channel circulation influences a larger area of greater hypoxia in the mid-Bay, by which the southerly wind causes a greater destratification and anoxia reduction than the northerly wind. This can supersede the greater destratification and anoxia reduction by the northerly wind under the bathymetry-affected cross-channel circulation.

Energy Budget of a Small Convectively Driven Marginal Sea: The Gulf of Eilat/Aqaba (Northern Red Sea)*

Abstract Oceanic model simulations and model-based energy budget calculations have been used to quantitatively study the relative importance of different processes affecting the Gulf of Eilat/Aqaba dynamics and hydrographic conditions. Large seasonality among various energetic pathways is observed. Similar to other oceanic waters, a significant amount of energy is stored in the potential energy (PE) that is predominately in the form of background potential energy (BPE). During September–March PE/BPE gains energy by raising the center of mass due to atmospheric cooling. During April–August, PE decreases its strength due to the exchange of light, warmer water from the northern Red Sea through the Strait of Tiran. The available potential energy (APE) is stored in baroclinic modes that are linked to the along-gulf temperature gradient. During April–August, the APE is sustained by baroclinic energy flux through the straits, resulting from advective density fronts into the gulf, and during September–March, the APE is sustained by the differential heating at the surface. Part of the APE is converted into kinetic energy (KE) by vertical buoyancy flux and in smaller quantity to background potential energy by isopycnal mixing. The conversion from APE is the only source of KE, where losses are related to the work done by pressure at the straits and energy dissipation. The wind stress work subtracts energy from the buoyancy-driven flow, which explained by the opposite surface flow and mean wind directions. The authors found that temperature and salinity variations contribute to the dynamics, via the APE–KE conversion, by a ratio of 10:1.

Influence of ventilation conditions on the radon annual effective dose of the lungsimulatedfor radon prone areas of Ramsar

Ramsar of northern Iran located on the littoral of the Caspian Sea is considered one of the radon prone areas of the world. The annual effective dose in the district of Talesh-Mahalleh is higher than the dose limits for radiation workers by at least 13 times. In the present study, the indoor radon concentration and radon annual effective dose of the lung were estimated using a Prassi portable radon gas survey meter in a ventilated model house containing top soil samples from different parts of Ramsar. The average wind speed was maintained at 3.0 ms -1 matching the average wind speed of the region. For the extremely hot samples, the annual effective dose of the lung was 111±10.20mSv y -1 when the windows closed. However, when the windows opened in the wind direction and in the opposite wind direction, the annual effective doses of the lung were 2.46±0.86 and 4.16±0.81mSvy -1 , respectively. Also, when the crossed windows opened in no wind condition, the radon annual effective dose of the lung was 5.43±0.86mSvy -1 . The results suggest by opening the windows a significant reduction of the radon annual effective dose in buildings of Ramsar can be achieved.

On the characteristics of ASCAT wind direction ambiguities

Abstract. The inversion of the Advanced Scatterometer (ASCAT) backscatter measurement triplets generally leads to two wind ambiguities with similar wind speed values and opposite wind directions. However, for up-, down- and crosswind (with respect to the mid-beam azimuth direction) cases, the inversion often leads to three or four wind solutions. In most of such cases, the inversion residuals or maximum likelihood estimators (MLEs) of the third and fourth solutions (i.e. high-rank solutions) are substantially higher than those of the first two (low-rank) ambiguities. This indicates a low probability for the high-rank solutions and thus essentially dual ambiguity. This paper investigates the characteristics of ASCAT high-rank wind solutions under different conditions with the objective of developing a method for rejecting the spurious high-rank solutions. The implementation of this rejection procedure improves the effectiveness of the ASCAT wind quality control (QC) and ambiguity removal procedures.

Dune fields on Mars: Recorders of a climate change?

Dunes have similar morphologies on the Earth and Mars. The main differences between Martian and terrestrial dunes are their size, which is larger on Mars, and their duration of formation, which is longer on Mars. As the characteristic time of Martian dunes is in the same order as that of the Martian climatic oscillations, Martian dunes could be recorders of past winds regimes and past climates. In order to test this hypothesis, we performed a morphological study of 550 dune fields with high resolution images and we inferred the directions of the dune formative winds from the orientation of the dune slip faces. Our study shows that 310 dune fields record one to four distinct wind directions with some geometric patterns that do not exist on the Earth such as barchans built by opposite wind directions coexisting in the same dune field. Our study demonstrates that the inferred formative wind directions are only partially in agreement with the current wind-patterns predicted by General Circulation Models (GCM). Several possible causes for the misalignment between dunes and GCM outputs are discussed: these include the local variation of the global circulation due to local topographic effects or the possibility that these dunes could be in a transient geometry or fossil. Such bedforms are considered indeed to be not in equilibrium with the present-day atmospheric conditions. This latter hypothesis is supported by the presence, in some ergs, of closely spaced dunes showing nearly opposite slip face orientations. Therefore, we propose that Martian dune fields are constituted, in some cases, by active and fossil dunes and therefore have the potential to preserve information on paleoclimates over extensive periods.

Thermally induced wind patterns in the Sahelian city of Ouagadougou, Burkina Faso

The urban surface wind field in the dry-tropical city of Ouagadougou, Burkina Faso was studied based on data collected at one urban and one suburban station during early dry season. An intra-urban thermal breeze, creating almost opposite wind directions at the two sites, was found during nights with high atmospheric stability. The high atmospheric stability suggests a decoupling of the surface wind layer from the layer above, allowing the wind system to develop due to the strong intra-urban temperature gradients in the city. Frequent temporary breakdowns of the thermal wind system were noticed, generally generating a turn in wind direction towards that of the regional wind, thus indicating a re-coupling with a stronger wind flow in the wind layer above.

Long range propagation of high speed train noise: Sound level variations before and after the pass-bys

It has been observed relatively frequently that high speed train (TGV) noise could be heard tens of seconds before or after the actual train pass-bys. This study is aimed at characterizing this phenomenon and the conditions in which it occurs, both experimentally and numerically. Acoustic measurements of TGV pass-bys have been performed under controlled conditions. A relatively strong wind was blowing from the South during the experiment. The measurements show that the TGV noise can be heard before the pass-bys when the TGV was coming from the South (same wind and train directions), and after the pass-bys when the TGV was coming from the North (opposite wind and train directions). This noise is relatively low in frequency (around 400 Hz), and corresponds to propagation distances that can exceed 1 km. Levels associated with this phenomenon can vary significantly over short time intervals (5-10 minutes), which raises the issue of the representativeness of TGV measurements at long ranges. It will be shown using numerical prediction methods (parabolic equation in the frequency domain, linearized Euler equations in the time domain) that these acoustic variations are mostly due to variations in the meteorological conditions between the pass-bys.

Short‐term variations in development of a recurrent toxic Alexandrium minutum–dominated dinoflagellate bloom induced by meteorological conditions1

Development of an Alexandrium minutum Halim bloom affecting a Mediterranean harbor was monitored in detail using a multidisciplinary approach. A. minutum was by far the most abundant species at and near the bloom maximum, but always coexisted with members of three additional dinoflagellate genera and prasinophytes. Bloom initiation (early February) occurred during prolonged influences of sunny weather conditions, when day length exceeded 10.5 h and water temperatures reached 10.2°C. Subsequent development toward its maximum (end of March) also relied on good weather conditions, with specific wind directions favoring accumulation of cells. Arrival of rainy weather, associated with frontal boundaries of large‐scale low‐atmospheric‐pressure systems and characterized by reduced solar irradiance (heavy cloud coverage), opposite wind directions, and enhanced wind speeds, always caused temporal declines of the bloom. These declines were attributed to dispersal or displacement of algae, but a vertical migration of A. minutum cells toward the sediment was not excluded. Delayed inflows of excess terrestrial rainwater along the inner harbor wall strongly reduced salinity and prolonged a temporal decline far beyond influences of bad weather. The associated nutrient supply favored development of the phytoplankton population but reduced the toxin production of A. minutum cells. The HPLC‐determined Gonyautoxin (GTX) 1 + 4/GTX 2 + 3 ratio strongly increased toward the bloom maximum. This ratio was influenced by nutrient status and cell density and has a potential value for monitoring developmental stages of blooms. Prolonged bad weather conditions eventually hindered continuation of bloom development, and subsequent declines of algal biomass were attributed to grazing.

Effects of separation distance on wind-induced response of parallel box girders

Wind-induced response characteristics of parallel bridges were studied with various separation distances. Section models of box girders for a proposed and an existing cable-stayed bridges were tested in smooth flow. The two box girders have different cross-sections, and different response characteristics were observed with the opposite wind directions. Mostly, larger response was observed when the bridges were located in parallel than for the single bridge case; but in a few cases, smaller response was observed when the bluffer girder was located close leeward of the other girder. General conclusion could not be obtained, but the results of this study will serve as an example of complicated parallel bridge response characteristics. It was observed that the interference effects between the bridges built in parallel can be significant even with a separation distance as large as 8 times the deck width.