Robert E. Jensen

A High-Resolution Coupled Riverine Flow, Tide, Wind, Wind Wave, and Storm Surge Model for Southern Louisiana and Mississippi. Part I: Model Development and Validation

Abstract A coupled system of wind, wind wave, and coastal circulation models has been implemented for southern Louisiana and Mississippi to simulate riverine flows, tides, wind waves, and hurricane storm surge in the region. The system combines the NOAA Hurricane Research Division Wind Analysis System (H*WIND) and the Interactive Objective Kinematic Analysis (IOKA) kinematic wind analyses, the Wave Model (WAM) offshore and Steady-State Irregular Wave (STWAVE) nearshore wind wave models, and the Advanced Circulation (ADCIRC) basin to channel-scale unstructured grid circulation model. The system emphasizes a high-resolution (down to 50 m) representation of the geometry, bathymetry, and topography; nonlinear coupling of all processes including wind wave radiation stress-induced set up; and objective specification of frictional parameters based on land-cover databases and commonly used parameters. Riverine flows and tides are validated for no storm conditions, while winds, wind waves, hydrographs, and high wa...

A High-Resolution Coupled Riverine Flow, Tide, Wind, Wind Wave, and Storm Surge Model for Southern Louisiana and Mississippi. Part II: Synoptic Description and Analysis of Hurricanes Katrina and Rita

Abstract Hurricanes Katrina and Rita were powerful storms that impacted southern Louisiana and Mississippi during the 2005 hurricane season. In Part I, the authors describe and validate a high-resolution coupled riverine flow, tide, wind, wave, and storm surge model for this region. Herein, the model is used to examine the evolution of these hurricanes in more detail. Synoptic histories show how storm tracks, winds, and waves interacted with the topography, the protruding Mississippi River delta, east–west shorelines, manmade structures, and low-lying marshes to develop and propagate storm surge. Perturbations of the model, in which the waves are not included, show the proportional importance of the wave radiation stress gradient induced setup.

Evaluation of Contemporary Ocean Wave Models in Rare Extreme Events: The “Halloween Storm” of October 1991 and the “Storm of the Century” of March 1993

Abstract Two recent severe extratropical storms, the “Halloween storm” of October 26–November 2 1991 (HOS) and the “storm of the century” (SOC) of March 12–15 1993, are characterized by measurements of sea states of unprecedented magnitude off the east coast of North America. A Canadian buoy moored in deep water south of Nova Scotia recorded peak significant wave heights (HS) exceeding 16 m in both storms. In SOC, a NOAA buoy moored southeast of Cape Hatteras recorded a peak HS of 15.7 m, a record high for NOAA buoys. These extreme storm seas (ESS) exceed existing estimates of the 100-yr estimated design wave in these regions by about 50%. The extensive wave measurements made in both storms from buoys moored in deep water provide a rare opportunity to validate modern ocean wave models in wave regimes far more severe than those used for model tuning. In this study, four widely applied spectral wave models (OWI1G, Resio2G, WAM4, and OWI3G) are adapted to the western North Atlantic basin on fine mesh grids a...

Swell and Slanting-Fetch Effects on Wind Wave Growth

Abstract Wind-sea generation was observed during two experiments off the coast of North Carolina. One event with offshore winds of 9–11 m s−1 directed 20° from shore normal was observed with eight directional stations recording simultaneously and spanning a fetch from 4 to 83 km. An opposing swell of 1-m height and 10-s period was also present. The wind-sea part of the wave spectrum conforms to established growth curves for significant wave height and peak period, except at inner-shelf stations where a large alongshore wind-sea component was observed. At these short fetches, the mean wave direction θm was observed to change abruptly across the wind-sea spectral peak, from alongshore at lower frequencies to downwind at higher frequencies. Waves from another event with offshore winds of 6–14 m s−1 directed 20°–30° from shore normal were observed with two instrument arrays. A significant amount of low-frequency wave energy was observed to propagate alongshore from the region where the wind was strongest. The...

Monitoring and Understanding Changes in Extremes: Extratropical Storms, Winds, and Waves

This scientific assessment examines changes in three climate extremes—extratropical storms, winds, and waves—with an emphasis on U.S. coastal regions during the cold season. There is moderate evidence of an increase in both extratropical storm frequency and intensity during the cold season in the Northern Hemisphere since 1950, with suggestive evidence of geographic shifts resulting in slight upward trends in offshore/coastal regions. There is also suggestive evidence of an increase in extreme winds (at least annually) over parts of the ocean since the early to mid-1980s, but the evidence over the U.S. land surface is inconclusive. Finally, there is moderate evidence of an increase in extreme waves in winter along the Pacific coast since the 1950s, but along other U.S. shorelines any tendencies are of modest magnitude compared with historical variability. The data for extratropical cyclones are considered to be of relatively high quality for trend detection, whereas the data for extreme winds and waves ar...

A New Approach to Ocean Wave Parameter Estimates From C-Band ScanSAR Images

Because of their large swath widths of about 400-500 km, the ScanSAR modes of RADARSAT-1 and -2 and of the Advanced SAR (ASAR) system on Envisat have been the preferred modes of operation for hurricane and typhoon observations and similar applications. While C-band ScanSAR images have been demonstrated to be well suitable for wind retrievals, ocean wave retrievals are a more challenging problem: Because of the limited spatial resolution of 100 m (RADARSAT)/150 m (Envisat), only long waves can get imaged directly, and many images of tropical storm scenarios do not exhibit clear signatures of any waves in large areas. The interpretation of wave patterns that exist in an image is difficult because of the imaging mechanisms nonlinearities. We think we have found a promising new technique for wave parameter retrievals from C-band ScanSAR images, which determines peak wavelengths and directions from image spectra where possible but uses an empirically determined relation to estimate significant wave heights (SWHs) from local mean image intensities, which is similar to the method used for wind retrievals. This way, it is possible to obtain SWH estimates for the entire image and to account for the contributions of subresolution-scale waves. We explain how the algorithm works and how the empirical SWH model function has been determined from a set of hurricane images from RADARSAT-1 and reference wave spectra from a numerical wave model. The first independent test with a set of RADARSAT-2 and Envisat images from the 2010 Impact of Typhoons on the Ocean in the Pacific (ITOP) experiment reveals a few weaknesses but essentially confirms the feasibility of the concept.

Wind Speed Scaling in Fully Developed Seas

Abstract Recent tests of all generations of numerical wave models indicate that extreme wave heights are significantly underpredicted by these models. This behavior is consistent with the finding by Ewing and Laing that fully developed wave spectra do not have the universal self-similar form postulated by Pierson and Moskowitz. This paper postulates that it is inappropriate to scale fully developed seas by winds taken from a fixed level above the mean sea surface. Instead, winds should be taken from a dynamically scaled height that is linearly related to the wavelength of the spectral peak. This alternative scaling is consistent with friction-velocity scaling and yields predicted wave heights and periods that are in better agreement with the data collected by Ewing and Laing and appear to explain some of the discrepencies in results from previous studies with numerical wave models in large storms.

Measurements of Ocean Surface Stress Using Aircraft Scatterometers

Abstract Scatterometer model functions that directly estimate friction velocity have been developed and are being tested with radar and in situ data acquired during the Surface Wave Dynamics Experiment (SWADE) of 1991. Ku-band and C-band scatterometers were operated simultaneously for extensive intervals for each of 10 days during SWADE. The model function developed previously from the FASINEX experiment converts the Ku-band normalized radar cross-section (NRCS) measurements into friction velocity estimates. These are compared to in situ estimates of surface wind stress and direction across a wide area both on and off the Gulf Stream (for hourly intervals), which were determined from buoy and meteorological measurements during February and March 1991. This involved the combination of a local, specially derived wind field, with an ocean wave model coupled through a sea-state-dependent drag coefficient. The Ku-band estimates u∗ magnitude are in excellent agreement with the in situ values. The C-band scatter...

Regional Wave Modeling and Evaluation for the North Atlantic Coast Comprehensive Study

AbstractAccurate estimation of storm surge along the coasts subject to extreme storm conditions requires proper wind and pressure forcing and quantification of the wind waves resulting from local and far-field energy sources. This paper summarizes the steps involved in accurately representing the offshore wave climate for the North Atlantic Coast Comprehensive Study (NACCS) domain, defined from the United States–Canadian border in Maine to the Virginia–North Carolina border. The motivation of the regional wave modeling is to provide offshore boundary conditions for the simulation of extreme extratropical and synthetic tropical events to drive the nearshore wave and surge modeling efforts within the NACCS. The offshore wave conditions were estimated using the third-generation WAve Modelling (WAM) model. Value-added wind fields were defined for each of the four wave model grids (North Atlantic Ocean Basin, U.S. Coastal Regional scale, and two subregional-scale grid systems covering the NACCS coastal domain)...

Directional Response of Wind Waves to a Large Wind Shift

Abstract The directional response of a fully arisen sea to a ∼90° wind shift is studied using a combination of airborne radar and in situ directional wave observations. The observations were made in February 1991 as a part of the Surface Wave Dynamics Experiment. Radar and buoy mean wave directions in several frequency bands are polynomial-smoothed in fetch and duration coordinates and analyzed for the directional relaxation parameter b by using finite differences of the gridded, smoothed data in a one-dimensional advection equation for the mean wave direction. The analysis is carried out using several different sets of buoy wind and wave data in an event window of 40 h in duration by 200 km in fetch (100–300 km offshore). For the most well-populated and reliable inverse wave age class in the study, 1.2 ⩽ U/c < 1.6, the authors find b = 3.3(±0.1) × 10−5. The data do not support any inference as to possible wave age dependence other than, perhaps, the null hypothesis, b = const (U/c). Frequencies near the ...