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# AliDispersionControl

Dynamic Water Level Correction is a process by which modeled water levels are dynamically adjusted by use of a forcing term. The correction can be applied as constant or varying in space and/or time. The correction is applied as a forcing term in the momentum equations whose mathematical form is equivalent to that of an atmospheric pressure term. This means that, for gradually-varying corrections, corrected water levels should closely follow the input correction, though these may deviate if a correction is applied very quickly or to an area that has a very weak connection to an open boundary through which water can flow. Further discussion is below in the FAQ.

Overviews and examples of this capability have been provided in multiple presentations (Luettich et al. 2017[1], Asher et al. 2018[2]) and a journal article (Asher et al. 2019[3]) with details and an application to Hurricane Matthew. Users looking for ways to generate water level correction surfaces can look to that same article and this digital publication/data repository[4], which holds the code base used in the aforementioned paper.

## Version

 ADCIRC version: ≥ 55: Technical Preview

This is considered a technical preview in version 55. Theoretical work is still ongoing.

## Controlling Dispersive Behavior

The feature is triggered by the presence of the &AliDispersionControl namelist at the bottom of the fort.15 file. Here is an example of how this line is used (the following floats are the default values):
`&AliDispersionControl CAliDisp=T, Cs=1500.0, Ad = 0.0050189, Bd = 0.23394/`

• `CAliDisp` logical flag to turn Ali's dispersion correction on (F=false by default).
• `Cs` is the speed of sound in water [m/s] for the Mach number based dispersive correction. Set Cs to a negative value to turn the Mach number based correction off.
• `Ad` the power law constant.
• `Bd` the power law exponent.
1. Luettich, R.L., T.G. Asher, B.O. Blanton, J.G. Fleming. Representing Low Frequency, Spatially Varying Water Level Anomalies in Storm Surge Computations. 2017 American Meteorological Society Annual Meeting. Link to talk
2. Asher, T.G., R.L. Luettich, J.G. Fleming, B.O.Blanton. Assimilation of Observed Water Levels into Storm Surge Model Predictions. 2018 American Meteorological Society Annual Meeting. Link to talk
3. Asher, T.G., Luettich Jr., R.A., Fleming, J.G., Blanton, B.O., 2019. Low frequency water level correction in storm surge models using data assimilation. Ocean Modelling 144, 101483. https://doi.org/10.1016/j.ocemod.2019.101483
4. Asher, T., 2019. Hurricane Matthew (2016) Storm Surge and Wave Simulations with Data Assimilation. https://doi.org/10.17603/2Z8H-7K90