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Optimizing Fungicide Timing for the Control of Rhizoctonia Crown and Root Rot of Sugar Beet Using Soil Temperature and Plant Growth Stages  

Microsoft Academic Search

Kirk, W. W., Wharton, P. S., Schafer, R. L., Tumbalam, P., Poindexter, S., Guza, C., Fogg, R., Schlatter, T., Stewart, J., Hubbell, L., and Ruppal, D. 2008. Optimizing fungicide timing for the control of Rhizoctonia crown and root rot of sugar beet using soil temperature and plant growth stages. Plant Dis. 92:1091-1098. Azoxystrobin is applied early in the sugar beet

W. W. Kirk; P. S. Wharton; R. L. Schafer; P. Tumbalam; S. Poindexter; C. Guza; R. Fogg; T. Schlatter; J. Stewart; L. Hubbell; D. Ruppal



Low frequency noise generated by ocean waves: a consistent theory from surface gravity waves to seismic Rayleigh and waves.  

NASA Astrophysics Data System (ADS)

Both oceanic observations, even in very deep water, and seismic observations, anywhere on Earth, contain low frequency noise that can be related to ocean waves. Most of the recorded noise has been explained by a nonlinear wave-wave interaction mecanism. This noise can take the form of surface gravity (Herbers and Guza 1994), acoustic (Lloyd 1981) or seismic waves (Longuet-Higgins 1950), that can be free to propagate outside of their generation area, or forced to follow their forcing wave groups. All previous theoretical work on seismic waves has been related to Rayleigh modes, while acoustic studies have only considered an ocean of infinite depth. Here we show how all types of waves: seismic waves (including Rayleigh and body waves), acoustic waves in the ocean, and surface gravity waves can be produced and estimated from directional wave spectra, using one single theory. This theory gives the known and well-verified gravity wave result, derived for incompressible motions, when taking the limit of short wave numbers. This consistent approach makes it possible to reconcile noise measurements at sea with land-based seismic data, as illustrated with data acquired in 2010 in the the southern Indian Ocean. In particular, this new dataset shows very well the presence of at least the first 4 vertical modes in a water layer of 4500 m over a uniform solid half-space, as expected from the theory by Stoneley (1926). Based on this understanding, it is possible to validate the noise sources predicted by a numerical wave model (Ardhuin et al. 2011, Schimmel et al. 2011) using locally forced gravity modes, measured with pressure sensors at depths from 10 to 300 m (Herbers and Guza 1994). Because seismic waves are caused by this same noise source, but now integrated spatially, this better knowledge of the source can be used to focus on uncertainties in the noise propagation and attenuation. In particular, there is a clear evidence from seismic stations on land, that the seismic attenuation must vary spatially.

Ardhuin, F.; Herbers, T. H. C.; Marié, L.; Royer, J. Y.; Obrebski, M.; Stutzmann, E.; Schimmel, M.



Canyon Effects on Nearshore Infragravity Waves During NCEX  

NASA Astrophysics Data System (ADS)

Infragravity waves become increasingly important as the water depth gets shallower and wind generated waves become saturated due to wave breaking. Infragravity wave energy is composed of wave-group forced long waves and reflected leaky waves and trapped edge waves. Typically conditions on a approximately alongshore uniform beach are consisdered (e.g. Herbers et al., 1994, van Dongeren et al., 2003). Here we examine the alongshore variability in the infragravity conditions induced by nearby canyons utilizing a 2D-surfbeat model (Reniers et al., 2004). The model simulates the propagation of both leaky and trapped infragravity waves that are generated by directionally spread wave groups. Model computations are used to examine the potential reflection (Inman et al., 1976, Huntley et al., 1981) of shore-trapped edge waves from the canyon walls by considering various model-scenarios with and without the canyons. Computational results will be compared with observations of infragravity conditons obtained from an alongshore array of pressure and velocity meters situated just north of the canyon (MacMahan et al., 2004, this conference). References Herbers, T.H.C., Steve Elgar and R.T. Guza, 1994: Infragravity-frequency (0.005 0.05 Hz) motions on the shelf. Part 1: Forced waves. J. Phys. Oc., 25, 1063-1079. Huntley, D. A., R. T. Guza and E. B. Thornton, 1981, "Field Observations of Surf Beat: Part I, Progressive Edge Waves", J. Geophys. Res., 86, 6451-6466. Inman, D.L., C.E. Nordstrom and R.E. Flick, 1976: Currents in sub-marine canyons: An air-sea-land interaction, Ann. Rev. Fluid Mech., 8, 275-310. MacMahan, J., E.B. Thornton, A. Reniers and T.P. Stanton, 2004, The Torrey Pines Rip-currents, this conference. Reniers, A.J.H.M., E.B. Thornton and J.A. Roelvink, 2004: Morphodynamic modeling of an embayed beach under wave-group forcing, J. Geophys. Res., 109, C01030, doi:10.1029/2002JC001586. Van Dongeren, A.R., A.J.H.M. Reniers, J.A. Battjes and I.A. Svendsen, 2003, "Numerical modeling of infragravity wave response during Delilah." J. Geoph. Res, 108 (C9), 4-1-19

Reniers, A.; Macmahan, J.; Thornton, E.; Stanton, T.



Wave Dissipation Formulations in Frequency Domain Models  

NASA Astrophysics Data System (ADS)

Incorporation of wave dissipation due to breaking in both time-domain and frequency domain models have long been a subject of study. Until recently, the formulation of wave breaking in frequency domain models have been based on lumped-parameter dissipation models based on a Rayleigh distribution function for the wave heights in the surf zone (Battjes and Janssen, 1978; Thornton and Guza, 1983). Modifications to improve the dissipation model include allowing for nonlinear energy transfer (Mase and Kirby, 1992), which leads to improvements in predictions of the skewness and asymmetry. Bredmose (2004) show how time- domain wave breaking models can be included in a frequency domain version of the Boussinesq model using a time-domain inversion of the roller model. However, frequency domain versions of the Boussinesq model tend to perform poorly until the waves are close to breaking. In this study, we will show how time-domain wave breaking models can be included in frequency domain models that are based on the mild-slope formulation. We will then compare the results of using such a breaking model to the empirical bulk-dissipation formulation. Comparisons will include wave height distributions, skewness, and asymmetry. We will also discuss implications of using different breaking models on sediment transport.

Veeramony, J.; Kaihatu, J. M.



A new 3D fully wave-current model MARS-WAVEWATCH : development, validation and application to the rip currents  

NASA Astrophysics Data System (ADS)

The interaction of waves with three-dimensional current structure is investigated using a two-way coupled modelling system combining MARS3D (Lazure and Dumas 2008) with WAVEWATCH III (Tolman 2008, Ardhuin et al. 2009) , a wave model (NOAA/NCEP, Tolman 2008). After a basic validation in two dimensions, the flow model MARS3D was adapted with three options that solve for the total momentum (Mellor 2003, 2008) or the quasi-Eulerian momentum (Ardhuin et al. 2008b). Adiabatic model results show that, as expected from theory (Ardhuin et al. 2008a), the total momentum fluxes parameterized by Mellor are not self-consistent and can lead to very large errors (Bennis and Ardhuin 2010). We thus use the model option to solve for the quasi-Eulerian momentum, including sources of momentum and turbulent kinetic energy (TKE). The influence of these TKE sources is investigated in the case of the NSTS experiment (Thornton and Guza, 1986). The feedback of the currents on the waves is negligible in this case. The sources of TKE from wave breaking and wave bottom friction are found to have strong influence on the bottom friction, in a way consistent with the parameterizations by Longuet-Higgins (1970) and Mellor (2002). The complete model is then applied to a real case of a large rip current on the South-West coast of France (Bruneau et al., Cont. Shelf Res. 2009). The breaking of waves on the opposed current generates a strong coupling on the rip current that partially controls the strength of the current and it three-dimensional shape.

Bennis, A.; Ardhuin, F.; Dumas, F.; Bonneton, P.



Modeling of depth-induced wave breaking under finite depth wave growth conditions  

NASA Astrophysics Data System (ADS)

Recent studies have shown that the spectral wind wave model SWAN (Simulating Waves Nearshore) underestimates wave heights and periods in situations of finite depth wave growth. In this study, this inaccuracy is addressed through a rescaling of the Battjes and Janssen (1978) bore-based model for depth-induced breaking, considering both sloping bed surf zone situations and finite depth wave growth conditions. It is found that the variation of the model error with the breaker index ?BJ in this formulation differs significantly between the two types of conditions. For surf zones, clear optimal values are found for the breaker index. By contrast, under finite depth wave growth conditions, model errors asymptotically decrease with increasing values of the breaker index (weaker dissipation). Under both the surf zone and finite depth wave growth conditions, optimal calibration settings of ?BJ were found to correlate with the dimensionless depth kpd (where kp is the spectral peak wave number and d is the water depth) and the local mean wave steepness. Subsequently, a new breaker index, based on the local shallow water nonlinearity, expressed in terms of the biphase of the self-interactions of the spectral peak, is proposed. Implemented in the bore-based breaker model of Thornton and Guza (1983), this breaker index accurately predicts the large difference in dissipation magnitudes found between surf zone conditions and finite depth growth situations. Hence, the proposed expression yields a significant improvement in model accuracy over the default Battjes and Janssen (1978) model for finite depth growth situations, while retaining good performance for sloping bed surf zones.

van der Westhuysen, André J.



Parametric Wave Transformation Models on Natural Beaches  

NASA Astrophysics Data System (ADS)

Seven parametric models for wave height transformation across the surf zone [e.g., Thornton and Guza, 1983] are tested with observations collected between the shoreline and about 5-m water depth during 2 experiments on a barred beach near Duck, NC, and between the shoreline and about 3.5-m water depth during 2 experiments on unbarred beaches near La Jolla, CA. Offshore wave heights ranged from about 0.1 to 3.0 m. Beach profiles were surveyed approximately every other day. The models predict the observations well. Root-mean-square errors between observed and simulated wave heights are small in water depths h > 2 m (average rms errors < 10%), and increase with decreasing depth for h < 2 m (average rms errors > 20%). The lowest rms errors (i.e., the most accurate predictions) are achieved by tuning a free parameter, ?, in each model. To tune the models accurately to the data considered here, observations are required at 3 to 5 locations, and must span the surf zone. No tuned or untuned model provides the best predictions for all data records in any one experiment. The best fit ?'s for each model-experiment pair are represented well with an empirical hyperbolic tangent curve based on the inverse Iribarren number. In 3 of the 4 data sets, estimating ? for each model using an average curve based on the predictions and observations from all 4 experiments typically improves model-data agreement relative to using a constant or previously determined empirical ?. The best fit ?'s at the 4th experiment (conducted off La Jolla, CA) are roughly 20% smaller than the ?'s for the other 3 experiments, and thus using the experiment-averaged curve increases prediction errors. Possible causes for the smaller ?'s at the 4th experiment will be discussed. Funded by ONR and NSF.

Apotsos, A. A.; Raubenheimer, B.; Elgar, S.; Guza, R. T.