OS41B-1213
Observations of Diurnal Period Wind-Driven and Wave-Driven Flows in Northern Monterey Bay
In July 2007, the Partnership for Interdisciplinary Studies of Coastal Oceans (PISCO) conducted a biophysical experiment with the goal of examining the physical processes that determine the delivery of invertebrate larvae and juvenile rockfish to communities in northern Monterey Bay. Simultaneous measurement of currents and waves are analyzed to isolate forcing mechanisms that drive cross-shelf flow and provide insight to the on/offshore transport of mass and momentum to the inner shelf. These mechanisms include wind- driven motions from large-scale and local diurnal winds as well as wave-driven motions. The work here focuses on the variability of wind-driven and wave-driven transports associated with a diurnal sea breeze in this part of Monterey Bay. An amplitude modulation technique is used to examine the relationship between the diurnal period winds, along- and cross-shelf transports, as well as wave-driven transports.
OS41B-1214
Sea Level Trends Along the Coast of the Gulf of Finland
Historical time series of monthly mean values of sea level were compiled for all stations in the Gulf of Finland for time periods starting from the beginning of sea level observations at each station and until station closing, or the year 2006 for Russian and Finnish and 1991 for Estonian stations. These data were analysed for trends for a common period from 1920 until 1991. It was found that along the northern coast of the Gulf of Finland, the sea level trends change from minus 3-4 mm/year in the west (at Turku and Hanko) to plus 1.5 mm/year in the east (at Lisiy Nos). Along the southern coast of the Gulf of Finland, the sea level trends also change from small negative values at the west (at Ristna, Poosaspea) to plus 1,4 mm/year at the east (at Lomonosov). At the head of the Gulf in Saint-Petersburg (at Port of Nevskaya), the positive trend was the largest: 3.3 mm/year. Relative to the global sea level rise (about 2 mm/year during the last century) trend values are negative in all points except Saint-Petersburg. Their spatial distribution is consistent with the map of post-glacial uplift in Fennoscandia (Ekman, 1996) and with the results of repeated levelings (in 1966 and 1985) across Saint-Petersburg and suburbs, which have shown that the land there is sinking.
OS41B-1215
The Impacts of Cold Front Passages on Louisiana Coastal Environments
Time-series measurements from stations along the Louisiana coast and inside the bays, estuaries and wetlands, from Atchafalaya Bay to the Mississippi River Delta, and synoptic satellite images from MODIS and other sensors, are used to investigate the impacts of cold front passages on the coastal aquatic environments and circulation. We examine the effects of wind on water level, currents, sediment resuspension and transport. Low-frequency water level usually decreases with cold front passages, both in the inner shelf, bays and estuaries, but the variations have different phases in different areas. Cross-shore and longshore winds may have different effects, depending on the orientation of fronts and the direction of wind with respect to the coastline. Strong cross-shore winds can directly induce set-up and set-down of water level, while water level variations from longshore winds occur through the Ekman transport. Surface current is with winds on the shelf, but inside the bays and estuaries, tidal currents may dominate.
OS41B-1216
COCMP Surface Current Mapping Reveals Eddy and Upwelling Jet off Cape Mendocino
Ocean surface currents are now being measured continuously over a roughly 2000 km stretch of the western US continental shelf from south of Tijuana, Mexico to the Columbia River. A long-standing gap in this coverage was finally filled on August 12, 2008, with the installation of a long-range Seasonde radar system at Shelter Cove, California (as a part of California's COCMP project). During its first three weeks of operation, this radar has revealed a large (~170 km diameter), stable, anticyclonic eddy southwest of Cape Mendocino in this poorly studied region. Upwelling-favorable winds appear to create an upwelling jet along the eastern edge of the eddy, leading to maximum daily-averaged current speeds up to 80 cm/s, and MODIS-derived chlorophyll concentrations up to 30 mg/m3 in the jet (compared to ~1 mg/m3 in the eddy center). AVHRR data reveal SST differences between the jet and the eddy center of 1.5 to 2.5 °C during these 3 weeks. These complex circulation structures modify water pathways and may interrupt nutrient delivery to locations farther south. We discuss the spatial and temporal evolution of these features.
OS41B-1217
Nearshore Circulation and Storm Surge Along the Mackenzie Delta Coast
The Mackenzie Delta is a 150 km long section of coastline characterized by muddy sediments where the Mackenzie River outflow, dispersed over 20 distributary channels, discharges into the southern Beaufort Sea. The marine environment in this region is an important and integral part of the lives of Canadian Northerners. The area is also undergoing hydrocarbon exploration with potential development within the next decade. Changes to Arctic climate, such as increasing ice-free western Arctic Ocean and intensifying storm activity, may endanger the coastal settlements and marine environment in the Mackenzie Delta region. The low gradient of the delta and the adjacent inner shelf makes it very susceptible to flooding during storms. Field observations in the nearshore zone collected in August of 2007 and 2008 indicate strong gradients in temperature and salinity in shallow water of 2-6 m. The fluctuations are associated with the movements of warm and fresh river plumes and wind-driven upwelling of cold and saline water below the thermocline. The observations are in agreement with 3D model simulations of the nearshore delta region using Delft3D, which includes wind, tidal, storm surge, buoyancy and river forcing. The results validate the model and indicate that it can be used to hindcast the nearshore oceanographic conditions during severe Arctic storms. As a case study we present preliminary model results for an Arctic storm from late 1999 that caused extensive vegetation die-off in the outer delta. This cyclone was a mesoscale Arctic storm that developed over the NE Pacific and western Bering Sea, intensified explosively in the Gulf of Alaska and developed into a meteorological bomb. The storm made landfall at Cape Newenham, Alaska, crossed the Rocky Mountains to the Yukon and Northwest Territories and re-intensified over a zone of high sea surface temperature gradients in the southern Beaufort Sea. Using the Canadian Mesoscale Compressible Community (MC2) atmospheric model, simulations of the storm pattern, track and intensity are in very good agreement with the NCEP re-analysis. This is model coupled to the Princeton Ocean Model (POM) and Hibler Ice Model, which are used to provide basin-scale driver fields and define the boundary conditions of the nearshore Delft3D model for the Mackenzie Delta region. Coastal damage was predominately caused by storm surge, and the high salinity flood waters that flowed over the surface of the outer delta.
OS41B-1218
Development of Three-Dimensional Storm Surges/Tide Prediction System by Regional Ocean Modeling System (ROMS)
Over the past 30 years, an average of 26 typhoons per year has originated in the northwestern Pacific Ocean, among which three on average have affected the Korean Peninsula. Typhoons are particularly frequent in summer in the Pacific Ocean and can pass or make landfall on the Korean Peninsula, often causing serious damage to property in the coastal region. In this study, we developed three-dimensional Storm surges/Tide prediction system based on ROMS (Regional Ocean Modeling System). ROMS is a free-surface, terrain-following, primitive equations ocean model widely used by the scientific community for a diverse range of applications. This prediction system covers 115¢®¨¡-150¢®¨¡E, 20¢®¨¡-52¢®¨¡N with 1/12¢®¨¡ horizontal resolutions and 20 vertical layers including the Yellow Sea, East China Sea and the East Sea, marginal seas around Korea. The newly developed three-dimensional Storm surges/Tide prediction system has been applied to hindcasting study for typhoon cases. Sea surface wind and pressure from the Korea Weather Research and Forecasting (KWRF) is used for forcing input of storm surge/tide prediction system. In this model, the level of storm surge calculated by the difference between tide level and sea level change caused by meteorological effects. The three-dimensional storm surges/tide prediction system simulates very well the storm surges/tide pattern around Korean Peninsular. The storm surges were hindcasted using pressure and wind field of Typhoon. The result showed that the storm surges by the three-dimensional model were in well agreement with the observed high storm surges height in the coastal areas.
OS41B-1219
Numerical Study on the Sea Winds on coastal regions using High Resolution WRF model
Sea winds are very difficult to predict, which are significantly important in predicting typhoon, waves, storm surges and are needed to be accurate with high resolution model. Especially, as accompanied with property damages and injuries caused by strong sea winds during typhoon days, more accurate prediction of sea winds is the thing requisite for the mitigated damages. At present, sea winds and sea level pressure of Regional Data Assimilation and Prediction System/Korean Meteorological Administration (RDAPS/KMA) is provided to operational ocean model such as wind waves and storm surge operational model of KMA. RDAPS has limitations in reproducing sea winds especially in the complex coastal areas due to low resolution. In this study, the next generation KWRF (Korea WRF) and high-resolution coastal WRF of 9 km and 3 km horizontal grid resolution are used to investigate the sea winds on coastal regions depending on the model resolution during typhoon periods. The model employed in this study is the Advanced Research WRF version 3.0 (ARW), which is developed by Mesoscale and Meteorology Division of National Center for Atmospheric Research and expected to be the next generation mesoscale numerical weather prediction model replacing MM5. The next generation operational weather prediction model (KWRF) in KMA was used as the initial and boundary conditions of the nested domains with 9 km resolution and 3 km resolution to reproduce more detailed sea winds on the coastal regions using one-way nesting. The experiments using high resolution regional WRF model were performed during typhoon MANYI from 1200 UTC 12 July to 0000 UTC 15 July 2008 and typhoon USAGI from 0000 UTC 1 August to 1200 UTC 3 August 2007. The comparisons of horizontal sea winds distributions between the model and the observations show high resolution WRF model with 3 km grid resolution represent the most accurate sea winds in two typhoon cases and produce the smallest differences with the observations. Even high resolution model has limitations to predict sea winds on the coastal regions exactly due to the complex coastal topography and numerical techniques. In the future study, the data assimilation system part and nesting techniques are expected to improve sea winds prediction.
OS41B-1220
Preliminary Study on Coupling Wave-Tide-Storm Surges Prediction System
The Korean Peninsula is surrounded by the Yellow Sea, East China Sea, and East Sea. This complex oceanographic system includes large tides in the Yellow Sea and seasonally varying monsoon and typhoon events. For Korea's coastal regions, floods caused by wave and storm surges are among the most serious threats. To predict more accurate wave and storm surge, the development of coupling wave-tide-storm surges prediction system is essential. For the time being, wave and storm surges predictions are still made separately in KMA (Korea Meteorological Administration) and most operational institute. However, many researchers have emphasized the effects of tides and storm surges on wind waves and recommended further investigations into the effects of wave-tide-storm surges interactions and coupling module on wave heights. However, tidal height and current give a great effect on the wave prediction in the Yellow sea where is very high tide and related research is not enough. At present, KMA has operated the wave (RWAM : Regional Wave Model) and storm surges/tide prediction system (RTSM : Regional Tide/Storm Surges Model) for ocean forecasting. The RWAM is WAVEWATCH III which is a third generation wave model developed by Tolman (1989). The RTSM is based on POM (Princeton Ocean Model, Blumberg and Mellor, 1987). The RWAM and RTSM cover the northwestern Pacific Ocean from 115¢®¨¡E to 150¢®¨¡E and from 20¢®¨¡N to 52¢®¨¡N. The horizontal grid intervals are 1/12¢®¨¡ in both latitudinal and longitudinal directions. The development, testing and application of a coupling module in which wave-tide-storm surges are incorporated within the frame of KMA Ocean prediction system, has been considered as a step forward in respect of ocean forecasting. In addition, advanced wave prediction model will be applicable to the effect of ocean in the weather forecasting system. The main purpose of this study is to show how the coupling module developed and to report on a series of experiments dealing with the sensitivities and real case prediction of coupling wave-tide-storm surges prediction system.
OS41B-1221
A study on the optimization of the Wind Wave models
The wind wave models have been widely applied to the wave forecast. This paper, in view of the single SWAN model, the WAM model, the NWW III model and the WAM/SWAN nest model, discusses these models¡¦ calculation ability. Because each model has different value methods, parameter values and empirical equation, the computed results also can be various. Through simulate calculation in spent time, different mesh analysis, and time ranges, the relation between correlation coefficient and absolute error in simulate results and actual values is discussed. The result shows that the WAM/SWAN nest model has higher accuracy than the other models in the wave height simulation. The WAM model compared with the other three models in the cyclical simulation has the best simulate result. NWW III model takes the shortest time in simulation. In the research, when typhoons coming, the mesh of WAM/SWAN nest-shaped pattern can describe the water depth change in nearshore better, so it can simulate a more accurate wave height peak value This paper also discusses the Cs of different parameters in the SWAN pattern. Comparing the computed result with actual material, when Cs is close to 2.36¡Ñe-5, its simulate result can be closer to the actual value.
OS41B-1222
An EMD based Neural Network method for Wind Wave Prediction
Monsoon and storm/Hurricane events affect the wave climate in the West Pacific Ocean. Northeast monsoons often bring strong and persistent wind between the coming October and March of the following year. For wind speeds above 10 degree Beaufort scale (or ~24.5-28.4 m/s), the wave perturbation caused by the northeast monsoon is comparable to storm/Hurricane waves. We use the Neural Network(NN) and Empirical Mode Decomposition (EMD) methods to analyze sea wave variations. Unlike traditional Fourier filtering method, the EMD decomposition does not assume that the waves are stationary. Therefore, the EMD is more robust for time series analysis. The method decomposes a time series into a set of orthogonal modes. The near surface wind, which is crucial for wave activation, is taken from the ECMWF reanalysis (ERA40). We first use the EMD to decompose the time series of the reanalysis wind and then feed the decomposed time series into the NN model for training. The model is constrained by the wave height measurements taken in 2002 in Hualien, Taiwan. The optimized configuration obtained from the NN model is then applied to make the wave height prediction in 2003. We find that the prediction is improved by more than a factor of 2, compared with that by the NOAA WaveWatch III model.
OS41B-1223
Accurate ocean tide modeling in southeast Alaska and large tidal dissipation around Glacier Bay
An accurate prediction of ocean tides in southeast Alaska is achieved using a regional, barotropic ocean model with a finite difference scheme. The model skill is verified by the observational tidal harmonics in southeast Alaska including Glacier Bay. The result is particularly improved in Glacier Bay compared to the previous model of Foreman et al. (2000). We re-estimate tidal energy dissipation in the Alaska Panhandle, and suggest the tidal energy dissipation of 3.5 GW associated with the M2 constituent that is 1.5 times as much as the estimation of Foreman et al. (2000). Large portion of the M2 energy budget entering through Chatham Strait is dissipated in the vicinity of Glacier Bay.
OS41B-1224
Structure of Downwelling on the Oregon Continental Shelf
Winter downwelling on the Oregon shelf leads to surface-to-bottom gravitationally unstable regions at mid-
shelf (10 - 15 km offshore / 80 - 110 m depth). The location of this mixed region is determined by the
thermohaline structure of shelf waters, which is comprised of three distinct water masses: fresh surface water
(SW), saltier intermediate water (IW) and cold, salty near bottom water (BW). Downwelling results in a
rearrangement from vertical to horizontal layering. SW is forced onshore; after a few days of downwelling it is
found nowhere seaward of the 70 m isobath. Simultaneously, BW is forced offshore and is absent inshore of
the 120 m isobath after several days of downwelling. The midshelf region becomes laterally stratified such
that continued downwelling-induced cross-shelf Ekman transport causes decreasing vertical stratification,
eventually resulting in surface-to-bottom convection.
Winter bottom boundary layers are on average thinner than in summer. Over the period of our observations
40% of observed winter boundary layers were less than 1 m thick. Boundary layer height distributions are
strongly skewed and broader (greater variability) in winter, ranging to the total depth of the water column.
http://mixing.coas.oregonstate.edu/research
OS41B-1225
A numerical modeling study of the upwelling source waters along the Oregon coast during 2005
Year 2005 was an anomalous year in terms of the spring transition (and hence the start of the upwelling season), which occurred over one month later than average, and of the temperature, which was ~6°C above the average. Here we study numerically the source of the upwelling waters along the Oregon coast during 2005. The model presents a spring transition and a near-shore temperature anomaly similar to those reported in the literature, and comparisons with observations show that the model reproduces most of the features observed in the sea level and velocity. The contribution to central Oregon alongshore velocity and sea level variability from remote forcing, south of the model's southern boundary, is explored using coastal-trapped wave theory. Preliminary lagrangian analysis of the path of upwelling source waters shows that part of the water parcels come from northern locations beyond the model's northern boundary, from depths below 200 m.
OS41B-1226
Applications of Remote Sensing in Detecting Mesoscale Features in the Gulf of Alaska
Fisheries managers today are tasked with utilizing stock assessment models to evaluate current conditions of fish populations. Currently, remote sensing technologies are evaluated with a decision matrix scenario for potential incorporation into stock assessments. Knowing which remote sensing instruments work best for fisheries management is imperative. For example, Synthetic Aperture Radar is the forefront of accurately detecting mesoscale oceanic features such as eddies and prevailing current systems without the interference of atmospheric anomalies. Here, various satellite products are tested to assess the presence of mesoscale oceanographic features that may influence the distribution of larval groundfish and hence recruitment in the Alaskan fisheries. This study champions a qualitative method for evaluating coastal eddy systems and their correlation to various recorded locations of highly valuable commercial groundfish species.
OS41B-1227
Progress in Observing the Coastal Zone by Radar Altimetry
Seventeen years after the launch of ERS-1 and TOPEX/POSEIDON, substantial progress has been achieved
in all the components of Radar Altimetry bringing its accuracy over the open ocean to the centimeter level. In
the coastal ocean the radar altimeter and radiometer measurements are degraded by the presence of land,
the global ocean tide models do not properly account for local tidal effects and other geophysical corrections
are affected by local effects such as the inverted barometer and the sea state bias. It is recognized by the
community that progress can be made in Coastal Zone Radar altimetry by tackling each of these difficulties.
The European Space Agency and the French Space Agency, CNES, have launched a research initiative
focused on developing a special Radar Altimetry Coastal Zone User Product.
The interim outcome of this initiative, among other international and national activities, will be delivered at
the 2nd Coastal Altimetry Workshop to be held in Pisa on 6 and 7 November 2008. The objectives of this
event is to review and acknowledge the important progress recently made in Coastal Zone Radar Altimetry
retrieval algorithms, characterise the difficulties, learn from the ones overcome, focus on the unresolved
issues and identify future required actions.
The development and validation of novel Coastal Zone Radar Altimetry retrieval algorithms and a new user
data product will not only supply user with current Altimetry data in the Coastal Zone but also will permit the
reprocessing of data since the launch of ERS-1 and offer to the non-specialist of Altimetry a Coastal Zone
sea level, wave height and wind speed time series up to 17 years long, globally. Furthermore with the advent
of operational Oceanography and the next launches of Sentinel-3 and Jason-3 an operational Coastal Zone
Radar Altimetry product is under development and requirements for the future altimetric missions are
scheduled to be presented and discussed in a special session followed by a round table session. A
Summary of the findings of the 2nd Coastal Altimetry Workshop will be provided in San Francisco.
http://www.coastalt.eu/pisaworkshop08
OS41B-1228
Comparison of δ18O of Dissolved Oxygen (O2) in Three Basins of the East/Japan Sea
The East/Japan Sea is a marginal sea enclosed by Korea, Japan, and Russia, but it has some oceanic characteristics, therefore, it is called "Miniature Ocean". It has three basins deeper than 2000 m, which are Japan Basin (JB), Ulleung Basin (UB), and Yamato Basin (YB). The concentration and δ18O of O2 in seawater is controlled by photosynthesis, respiration, and air-sea gas exchange near the surface. Respiration reduces O2 concentration and enriches 18O, while photosynthesis brings the opposite result. For this reason, δ18O of O2 is used a tracer for biological and chemical processes in the ocean interior. To compare the distribution of δ18O of O2 in three basins of the East/Japan Sea, the vertical samples were collected through three expeditions in May and October, 2007. Seawater was injected to the pre-evacuated glass bottles, and the dissolved gases were extracted instantly. The molecular oxygen was separated, and the 18O/16O ratio was determined by GC-MS. The concentration of O2 was 220-340 μmol/kg in the surface, and reached the maximum at about 50 m, and decreased as the depth increased, 200 μmol/kg in the bottom. The δ18O values in the surface were 22-24 ‰ (vs. SMOW), which was slightly lower than the atmospheric equilibrium value (24.2 ‰) at sea surface temperature, and the values in the bottom were 29-31 ‰, strongly enriched in 18O. The δ18O values increased from JB to UB and YB below 1000 m. Possible reasons for higher δ18O in UB and YB may be 1) higher oxygen utilization rate (OUR) or 2) older water mass with the same OUR. As considerable differences in OUR among three basins could hardly be found in previous studies, the same OUR can be applied to all basins. The age difference between basins in the East/Japan Sea estimated from the distribution of δ18O will be discussed.
OS41B-1229
Turbulence and mixing generated by internal waves shoaling on a barrier reef.
Results are presented from an observational study of the turbulent bottom boundary layer on the outer Southeast Florida shelf in July and August 2005. ADCPs and ADVs deployed at 15 m on Conch Reef measured mean and turbulent velocities. Turbulence in the reef bottom boundary layer is highly variable in time and is modified by near bed flow, shear, and stratification driven by shoaling internal waves. In the absence of internal waves on the shelf, currents from 1 to 5 meters above the bed are well described by a logarithmic profile and turbulent dissipation measured 0.6 to 3.0 meters above the bed agrees with classic bottom boundary layer scaling. We examine turbulence in the bottom boundary layer during a typical internal wave event and show that internal waves can induce significant increases in near-bed flow speed, shear, dissipation, and turbulent scalar diffusivity, Kρ. Estimates of flux Richardson number, calculated directly from measurements of dissipation and buoyancy flux, support the dependence of Rf on Frt and on turbulent intensity, ε/νN2, relationships that have been previously shown in laboratory and numerical work. Results from this study suggest that for reef communities exposed to continental shelf and slope processes, internal waves may play an important role in mass transfer to benthic organisms. In addition to the episodic onshore transport of cool, subthermocline water masses, with elevated nutrient concentrations, we have shown that the bottom-intensified currents from shoaling internal waves can increase turbulent dissipation and mixing in the reef bottom boundary layer.
OS41B-1230
Calculating Reynolds stresses from ADCP measurements in the presence of surface gravity waves using the cospectra fit method.
Recently, the velocity observations obtained by acoustic Doppler current profilers (ADCPs) have been used to successfully estimate vertical profiles of Reynolds stresses in estuaries or tidal channels. However, current methods for calculating stresses from ADCPs in the presence of surface-gravity waves, which can significantly bias stress estimates, have been unable to achieve results that correspond closely with estimates of boundary stresses. This work describes and tests a new method, the cospectra-fit method, which provides a superior way to calculate Reynolds stresses in the presence of surface gravity waves from ADCP observations. Stress results are dynamically consistent at levels below the estimated uncertainties, and thus able to quantify the turbulent transfer of momentum during both tidal dynamics and significant sub- tidal wind events. Using the method, the aliasing of turbulent energy by waves is a more significant obstacle to providing valid, unbiased stress estimates than are instrument biases due to bin size or orientation. Mean bias errors due to instrument orientation can be accounted for if the horizontal turbulent length scales, estimated by the method, are long relative to the horizontal separation of the bottom sampling bin. Thus, this work shows that measuring coastal ocean stresses in the presence of waves using typical instrument configurations is possible under certain conditions.
OS41B-1231
Observations of Active Submarine Groundwater Discharge on a Shallow Coastal Sea in Yucatan, Mexico
This contribution presents detailed measurements of fresh water fluxes from an energetic submarine groundwater discharge (SGD) located on the coastal ocean on Dzilam Bravo, Yucatan, Mexico. Due to the geologic characteristics of the site (karstic geology), inland groundwater flows through karstic conduits and exits at sea. Time series of fluxes measured by an acoustic velocimeter (VECTOR), temperature and salinity are correlated to the variability imposed by tides, currents, waves and rainfall. The contribution of SGD is a determining factor in the dynamics of marine ecosystems because it provides fresh water, nutrients, contaminants and other solutes. For this reason it is important to increase the knowledge about its dynamics and mixing processes that take place in these kind of environments. To study the spacial variability of thermohaline conditions, an area of 1 by 1 km (which includes five freshwater springs) was measured with a vessel towed CTD during drough and rainfall seasons. The results reveal that the flow conditions for the main spring (X'buya–Ha) is controlled by sea level variations, which include tides and weather effects. The outflow velocity is about 0.5 m/s during dry season when the discharge is weak, and about 3 m/s during periods of intense rainfall, when the discharge is strong. Also, it was noted that outflow direction changes as a result of high and low tides along a day. Results will be presented on the spatial influence as well, showing that the effect of the springs is very localised during high tide, but expands considerably during low tides.
OS41B-1232
Seasonal Variability at the Mesoscale in the Southern California Current System Revealed by Glider Surveys
The California Current System is rich in mesoscale variability. Since late 2006 we have used Spray gliders to measure temperature, salinity and chlorophyll fluorescence to 500 m depth along CalCOFI Lines 80 and 90 in the Southern California Bight. Measurements at horizontal resolutions of 3 km over two years now allow us to examine seasonality at the mesoscale in this region. Geostrophic velocities referenced to measured vertically-averaged currents show the equatorward California Current offshore, the poleward California Undercurrent along the shelf, and a second poleward undercurrent further offshore. This offshore undercurrent is strongest in summer at Line 90 and in fall at Line 80 where it reaches the surface off Point Conception. Multiple fronts are apparent on both Lines 80 and 90 after averaging seasonally and over all surveys, especially near the low salinity California Current. We investigate the horizontal variability along level surfaces and isopycnals within the mixed layer, near the mixed layer base and within the thermocline using horizontal structure functions. Variability of temperature and salinity are generally greatest near the base of the mixed layer and in summer. A concentration of energy at scales of 100-200 km is apparent in many cases. Chlorophyll fluorescence shows somewhat shorter scales with greatest variability in spring.
OS41B-1233
Seasonal Climatology of Wind-Driven Circulation on the NJ Shelf
The mean and subtidal surface circulation in the central region of MAB are characterized using six years of CODAR Long Range HF Radar data. The mean surface flow is 3-7 cm/s downshelf and offshore to the southwest. Subtidal variability on the NJ Shelf is on the order of the mean offshore but several times that of the mean inshore. The response of the surface current to wind depends on the stratification and exhibits significant seasonal patterns. The flow tends to be either along-shelf or cross-shelf dominated. The seasonal climatology of the wind driven circulation for the NJ Shelf shows that the alongshore wind is correlated with cross-shelf current in the summer time, the cross-shore wind is correlated with cross-shelf current in the winter time, and the along-shore wind is correlated with along-shelf current in the transition seasons of spring and autumn. Cross-shore NW wind drives cross-shelf offshore flow in the unstratified winter season. Along-shore SW wind drives cross-shelf offshore flow in the stratified summer season. NE wind, often associated with storm events in the spring and fall, drives downshelf alongshelf flow. The Hudson Shelf Valley acts as a dynamical boundary between the northern and southern NJ Shelf with the north consistently showing weaker flow than the south. Analysis of virtual Lagrangian surface drifters show that the residence time of surface material ranges from 1 week to 8 weeks. The transport pathways are either cross- shelf or along-shelf dominated. Interannual variability in seasonal wind affects the mean winter flow; the strength of the winter cross-shore wind is correlated with the intensity of cross-shelf flow. Summer upwelling wind has little effect on the mean summer flow.
OS41B-1234
HF Radar Performance on a Low Energy Environment as Found Using CODAR SeaSonde on the West Florida Shelf
A network of three CODAR (Coastal Ocean Dynamics Application Radar) SeaSonde HF radars operating at 4.925 MHz has operated on the West Florida Shelf since 2003. HF Radar performance is evaluated in terms of percentage of data returns and RMS differences between the HF radar radial currents and an array of velocity measurements by moored acoustic Doppler current profilers (ADCP). Temporal variation of the radial current coverage is described and possible factors affecting the HF radar observations on this low energy (current and wave) shelf are discussed. Despite the challenge of achieving more backscatter from this low energy shelf, the data quality is good when the acquired HF radial currents are compared with the ADCP top bins. The RMS difference is in the range of 6 - 11 cm/s for hourly and 3 - 6 cm/s for 36-hour low-pass filtered radial currents, respectively.
OS41B-1235
A REAL TIME OCEAN OBSERVING SYSTEM FOR THE LOUISIANA COAST
WAVCIS is an ocean observation program implemented for coastal Louisiana. It measures met-ocean processes and sea state information for offshore Louisiana, Mississippi and Florida Panhandle. The data measured from offshore stations are transmitted on a real time basis to the Laboratory and posted on the World Wide Web (www.wavcis.lsu.edu). As of September 2008, there are six operational stations and several stations have been planned for future deployment. WAVCIS has played an important role in the past several years in providing the valuable information for educational institute, scientific research communities, and industrial companies. A very clear overview of offshore conditions using the web GIS can be shown when users interact with the real time measurement information and different scaled maps. This provides seamless, multiple data sources with different resolutions and spatial extents for the needs of different user groups within one interface. A major benefit of a real time oceanographic data collection program is that it provides a first order check on the data quality and sensor operation thereby preventing a long time period of data. WAVCIS is maintained by Coastal Studies Institute, Louisiana State University with strong coastal dynamics, oceanographic expertise and information technology expertise along with a well experienced field support engineering personnel. The data also have social significance and management uses, where the information provided by the system is especially critical during hurricane events like recent power storms like Gustav and Ike. The observational data from WAVCIS coastal stations are further used for the skill assessment and for further fine tuning of hydrodynamic models like MIKE21,WAM, SWAN, WAVEWATCH III, HYCOM. We validate these models by the comparison of the hind cast data and WAVCIS observation data during 60 hours period.