Delft Software Days, November 5th 2014

Global tide and storm-surge modelwith Delft3D Flexible Mesh

Martin.verlaan@deltares.nl

DSD November 5th 2014

Outline

• Motivation

• Grid development

• Required physical processes

• Calibration

• Some results

• Ongoing work and challenges

3

New surge & tide model – DCSMv6

DCSM-v5 DCSM-v6

1/8º x 1/12º 1/40º x 1/60º

Includes tidal potential

Zijl et. Al. 2013 & Slobbe et. al. 2013

4

Effect of sealevel rise on tides

Effect of 2 meter rise of MSL on M2 amplitude

Pickering et. al. 2013

OTIS-MPI

DSD November 5th 2014

Existing global tide models

M2

DSD November 5th 2014

First attempt of grid in Delft3D

→ Lack of resolution near coasts.

DSD November 5th 2014

Grid in Dflow-FM

Unstructured approach - step 1: grid thinning at high latitudes

8

Grid in Dflow-FM

This Dflow-FM grid uses triangles and rectangles for local grid refinement. Resolution is based on Courant number.

Unstructured approach - step 2: grid refinement in shallow areas

First results in Dflow-FM

DSD November 5th 2014

Necessary improvements

• Self attraction and loading

• Tides modify the gravity potential as well

• Computation is very time-consuming

• Start wit simple approximation

• Internal tides

• Tides create internal tidewhere there is stratificationand steep bathymetry

• This creates dissipation (roughly ¼ of total tidaldissipation on global scale)

f x=βg∂ h∂ x

N=√−gρ0

∂ρ

∂ zDepends on stratification

DSD November 5th 2014

Modified equations

r

αR

e

R

Conservation of momentum

∂u∂ t

+u∂u∂ x

+v∂ u∂ y

+g∂h−ζ−βh

∂ x−f v+

gu √u2+v2

C2 H+

α κ N d2 √ω2−f 2

2ω Hu=0

∂ v∂ t

+u∂ v∂ x

+v∂ v∂ y

+ g∂ h−ζ−βh

∂ y+ f u+

g v √u2+v2

C2 H+

α κ N d2 √ω2−f 2

2ω Hv=0

ζ

1. tidal forcing2. SAL3. dissipation by internal tides

Gravity potential

DSD November 5th 2014

Calibration of the Model

FES2012

Altimeter observations:- assimilated FES2012 gridded data- very accurate on deep water

Calibration parameters: - Depth & Friction- 7 regions

Automated calibration:- 21 parameters- deep water series Jan2007

DSD November 5th 2014

Calibration results for deep water

Region Before After

Arctic 5.1 cm 3.2 cm

N. Atlantic 9.4 7.4

S. Atlantic 12.1 8.4

N. Pacific 8.1 6.2

S. Pacific 11.2 7.3

Indian Ocean 11.7 8.2

S. Ocean 12.4 10.2

Total 10.2 7.4

DSD November 5th 2014

Sample deep water station

Before calibration

DSD November 5th 2014

Sample deep water station

After calibration

DSD November 5th 2014

Sample coastal time-series

Tide

Surge

Cordova Honolulu

DSD November 5th 2014

Ongoing work and challenges

• Ongoing work:

• Operational global storm-surge model (ID-Lab)

• Climate impact studies (cooperation with VU and EU-RISES)

• Modeling Self-Attraction and Loading

• Challenges:

• Further improve dissipation by internal tides

• Improve computational performance with parallel computing

• Link to real-time observations

• Hurricane forecasts

• Improve open-boundary conditions for regional models

Questions?

Grid Arctic

Grid North America

Grid South-East Asia

Grid Northern Europe