1: storm surge and assumptions

What is ROMS?

Regional Ocean Modeling System

structured grid of quadrilateral cells

What is SCHISM?

Semi-implicit Cross-scale Hydroscience Integrated System Model

follow coastline more

Difference between ROMS and SCHISM?

ROMS (square) resolution is everywhere, so same resolution/cell size offshore vs at a coastline

SCHISM (triangle) follow coastline, islands, channels better - more detailed - can be small where needed but large offshore where not neeeded

>better resolution where needed

ROMS vs SCHISM modelling method?

ROMS = explicit method - calculates next update directly using already known values (incl values at neighbouring cells)

SCHISM = semi-implicit - calculates next update by

1. explicit for some terms (uses already known values) AND

2. implicit for others — aka unknown values we have to solve for:

• pressure-gradient term (caused by sea-level slopes)

• continuity equations

External gravity wave aka surface gravity wave

Wave traveling along the interface or between two media i.e. air and water

Local acceleration

How the current velocity changes over time at a fixed location

Cancel by > Steady state: the current does not change with time.

Advection (transport of momentum) in x direction

Cancel by > depth-averaged current u = 0

Advection (transport of momentum) in y direction

Cancel by > 1D flow v = 0

Coriolis term - effect of Earths rotation

Cancel by > neglect earths rotation

Water-surface Pressure gradient

Caused by sloping water surface

The tilted water surface creates a pressure force that pushes water back against the wind.

Atmospheric pressure gradient

Cancel by > atmospheric pressure is uniform

Wind stress

Bottom stress acceleration

Cancel by > no current = no bottom drag, ideal conditions

Horizontal momentum diffusion

Cancel by > Depth-average current u = 0

Total water depth after change in surface elevation (n)

Why is shallow water prone to storm surge vs deep

Wind interacts with the surface of waves and pushes water down.

Deeper waters = greater mass of water = not as much effect from wind force.

But when shallow waters = less mass of water = greater effect from wind force

• surface rises at one end, starts to tilt, produces storm surge onto coast.

1/h relationship - what does it do if you half the depth? i.e. shallow waters? Q1C

Produces 2x the wind driven setup.

What is the inverse baramoter effect? Q1C

Atmospheric pressure pushes down on the ocean surface.

Low atmospheric pressure reduces the load/weight on the sea surface, so surrounding water flows in and sea level rises