NUMERICAL WAVE MODELS

COMPARISON OF GULF OF MEXICO WAVE INFORMATION STUDIES (WIS) 2-G HINDCAST WITH 3-G HINDCASTING

GULF LEVEL 2 COMPARISONS

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for the Level 2 Gulf hindcast and interpolated to the

sites in 1995; Table 2 lists the available Level 2 1995

1/12-deg grid for the Level 3 hindcast.

measurement sites. Both tables give location

information, depth of site, and months available.

The 1 deg Atlantic wind fields for Level 1 were taken

from the AES40 Atlantic wind product (Swail, et al.,

Table 1. Level 3 Measurement Sites

2000), which was developed by Oceanweather for the

Meteorological Service of Canada (formerly called

Atmospheric Environment Service). This wind

product was derived from the 6-hr NCEP/NCAR

reanalysis wind fields. Oceanweather's website

(www.oceanweather.com) is available for more details

42016

-88.17

30.08 19

May

and references on wind analysis.

42039

-86.00

28.75 300

Dec

42036

-84.50

28.50 51

Jan-Dec

4. NUMERICAL WAVE MODELS

Wave models used in this study include WISWAVE,

WAM, and WAVEWATCH III (version 2.22). These

Table 2. Level 2 Measurement Sites

wave models solve the action balance equation:

NDBC

Lon.

Lat.

Dep.(m)

Months

∂N

+ C g ⋅ ∇N = ∑ S i

(1)

42001

-89.75

26.00 3165

Jan-Dec

∂t

42002

-93.50

26.00 3123

Jan-Dec

i=1

where N is action density, t is time, Cg group speed,

42003

-86.00

26.00 3206

Jan-Dec

and Si are source functions consisting of wind input,

dissipation, non-linear wave-wave interactions, and

3. WIND INPUT

bottom effects. Second-generation wave models such

as WISWAVE use a parameterization of the non-

The same input wind fields were used for each of the

linear wave-wave interaction source terms and third-

hindcast applications. The 1990-1999 Gulf wind

generation models like WAM and WAVEWATCH

fields were generated by Oceanweather, Inc., in

use an approximate calculation of this source term.

connection with the WIS mission to develop hindcasts

All wave models strive to represent the physics of

for all the US coastlines. Oceanweather, Inc., has

wave growth, development, dissipation, and

vast experience in both the theoretical and practical

interaction. All the models simulate directional

aspects of wind modeling products. Cox and Cardone

spectra to produce the energy-based significant wave

(2002) gives an overview of Oceanweather's analysis

height and details about the wave spectrum such as

capabilities.

peak wave period and vector mean wave direction for

designated output stations. Brief descriptions of the

The Gulf wind fields (0.25 deg spacing) were

wave models are given with references. All these

developed using National Centers for Environmental

models are well-known to the wave modeling

Prediction (NCEP) wind fields (at 6 hr intervals)

community, and they all have excellent reputations.

available from NOAA. Swail, Ceccacci, and Cox,

2000, describes the NCEP/NCAR reanalysis product

4.1 WISWAVE

which was used for the Gulf wind fields. The NCEP

winds have approximately 1.9 deg spacing.

The WIS hindcasts use the numerical wave hindcast

Oceanweather's process included interpolation from 6

model, WISWAVE, developed by Don Resio for the

hours to 1 hour, applying NCEP wind corrections by

Army Corps of Engineers. WISWAVE has been used

grid point and assimilation of measured wind

extensively in wave hindcasting at U.S. Army Corps

information to create a 1-hr product on a 0.25 deg

of Engineers (USACE) offices and throughout the

grid. Oceanweather is noted for specification of

engineering community. WISWAVE uses the time-

tropical storm wind fields using their Planetary

dependent wave action balance equation to create a

Boundary Layer wind model described in Thompson

directional spectral matrix with twenty frequencies

and Cardone (1996). Cox and Cardone (2000)

and 16 direction bands at each grid point on a land-sea

describes their tropical storm analysis. Tropical storm

mesh derived from a latitude-longitude grid including

winds were assimilated into the final wind field. The

finite depths for each grid point. Wave growth is

final product represents hourly Gulf wind fields

based on the Phillips and Miles mechanism; weak

utilizing all available information and expert

nonlinear wave-wave interaction, equilibrium Jonswap

meteorological analysis. These wind fields were used

and Kitaigorodskii spectral functions, linear refraction,

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