Improvements

Improvements to the operational Marine

Core Service (MyOcean) model for the

Northwest European shelf seas

COSS-TT workshop Lecce, Italy Feb 2013

© Crown copyright Met Office

Enda O'Dea, John Siddorn, Rachel Furner (Met Office) , Jason Holt (NOC), and

Chris Jenkins (INSTAAR)

Overview

Quick Review of NWS MFC and AMM7

On Going Developments

of AMM7 Physics

Future AMM60


A review of the MyOcean Monitoring and

Forecasting Centre for the North West European

Continental Shelf (NWS MFC)

• One of the operational production centres of the GMES FP7 MyOcean

project

• Aims to provide the fully validated ocean hindcast,nowcast and forecast

products, free of charge at the point of delivery

• Services are in four areas of use: maritime safety; marine resources;

coastal and marine environment; and weather, seasonal forecasting &

climate

• The MyOcean NWS MFC has built upon the NOOS (North West Shelf

Operational Oceanography System )collaboration and cooperation to

deliver improved products, systems and services for users of the Marine

Core Services in the NOOS region


NWS MFC Service Provision

• Provided by the operational meteorological centres of

the UK and Norway (the Met Office and met.no), with

the nominal service being provided by the Met Office

and a backup forecast being available to operational

users from met.no.

• The hindcast products are provided by the Institute of

Marine Research, Bergen (IMR) and the National

Oceanography Centre, Liverpool (NOC).

• The dissemination of products is from operationally

supported servers maintained at the Met Office and

met.no, with full redundancy in the production.


AMM7 ≈ NEMO + FOAM + ERSEM :

An operational shelf seas forecast

system

• Atlantic Margin Model (~7km Horizontal Resolution)

O'Dea EJ et al (2012)

• Nucleus for European Modelling of the Ocean

Madec G (2008)

• Forecast Ocean Assimilation Model

Martin et al (2007) + Storkey et al (2010)

• European Regional Seas Ecosystem Model

Blackford et al (2004) + Edwards KP et al (2012)


AMM7 and the Northwest

European Shelf


So that's the review, what’s New?

Developments under way for AMM7

Physics

• New Vertical Stretching Function for Terrain Following

Coordinates

• New Baltic boundary Conditions from Baltic MFC

• New Rivers from Ehype

• 2D varying Light Attenuation

• 2D varying Bed Friction


New Vertical Stretching

Function John Siddorn & Rachel

Furner

• Why redesign the vertical coordinate

• What are the critical features a vertical coordinate

needs

• Introducing the “gamma” coordinate

• Results for Seamount test case and initial AMM7

results


Why redesign the coordinate

system in NEMO

Z-coordinate (deep ocean model) problems

• Deep ocean models struggle to represent overflows

• Unless you use large number of cells, Z-coords cannot

resolve shelf and deep

S-coordinate (shelf model) problems

• AMM cannot resolve surface (i.e. SST) in deep water -> no

diurnal cycle

• AMM cannot sustain water-masses from Baltic through to

Norwegian Trench

• Vertical coordinate at boundary between Z-coord deep

models and S-coord shelf models inconsistent



system in NEMO

Winter observations show

surface low temperature

and salinity consistent with

plume from Baltic

stabilising surface and

allowing heat loss


Model doesn’t

Poor air-sea exchange,

and/or diffuse inputs from

Baltic??

What are the desirable

features a coordinate needs

• A constant (or user controllable) bottom resolution without steps to allow

flows along and over topography

• It must not require a large number of vertical levels

• It can converge on sigma or Z-coordinates in shallow water

• It can be made to match Z-coordinates in deep water for nesting to Z-

coordinate models

• It must be constrained to a monotonically increasing solution

• The rate of change of cell depths must be constrained to limit numerical

noise

• A constant surface resolution to allow coupling and resolution of the

diurnal cycle



A step in that direction

User Control Of Coordinate

Potential criticism is user definition of it is constrained BUT here

the user has a good deal of control.

Extent and position of stretching is a function of α:

• α = 1 => No stretching except as required by definition of

Zs and Zb

• α < 1 => More stretching towards the surface

• α > 1 => More stretching towards the bed

Thus pure sigma can be created in the special case that Zs and

Zb are both H/(n-1)

Will work for all depths, BUT will not produce sensible

stretching if not applied carefully.



SH94 Solid Lines Vs L50 contoured surfaces Vs

gamma coordinates –Dashed(bathy 5500m (left)

to 50m(right) upper 100m shown

Quantifying the Coordinate Slope

Hydrostatic consistency parameter (Haney 1991):

x,k denote values adjacent to the side and below S is the coord

in computational space try to minimize r

Slope Factor:

This slope factor, Beckmann and Haidvogel (1993), is a

measure of the resolution compared to the bathymetric

variability and its range is 0 < s < 1. 0 means no slope, 1

means depth change is entire depth of ocean


The depth mean hydrostatic consistency, r, for

the gamma and SH94 stretching for the AMM7

Gamma Coordinate r value

SH94 r value



Seamount test case depth mean s values solid, r

values dashed SH94 Black, gamma grey

Depth mean current speeds (m/s) after 48 hours

for the SH94 stretching (left)

and gamma stretching (right).


An idealised experiment with a seamount testcase following Beckmann and

Haidvogel (1993), Constant S profile and tanh T profile initially at rest

AMM7 experiment with initial T tanh profile:

Forcing: daily-averaged shortwave-radiation diurnal

cycle, A constant 400 Wm^−2 of downward longwaveradiation

background windspeed and a constant air

temp of 16C.

SST range large in gamma Midnight temperature larger in gamma Mixed Layer Depth Shallower in gamma


E-Hype River Data


E-HYPE: High resolution pan-European

water model

The E-HYPE model

calculates hydrological

variables on a daily timestep

at a high subbasin

resolution (1000 km2)

simultaneously for the

entire continent. The

hydrological variables

calculated for all of Europe

include water balance, daily

discharge, and the dynamic

variations of variables such

as soil moisture and snow

cover.


SMHI through E-HYPE working with Met Office to

understand impact of using real-time hydro-model vs

river climatology

....


BAL MFC Boundary Condition


DMI and MyOcean BAL MFC provide data and

expertise to improve flow through Belts

Significant improvements to Norwegian Trench can be

expected

Current AMM Baltic inflow uses 'rivers'

Replaced with Higher resolution boundary

condition from BAL MFC mode.


Full AMM model run with BAL boundaries yet to be

done but sample validation of BAL models in this area

is good..

Salinity Validation

Temperature Validation


2D-Light Attenuation from MEECE

dataset

With Thanks to Tim Smyth at PML and Patrick Hyder at MO


Currently Light Penetration in AMM in based on a

simple assumption of penetration depth (single band)

based on the water depth, crude though better than

uniform Chlorophyll everywhere in the ocean!

Places where this

approximation fails badly

are deep areas with

short extinction

coefficients. e.g. the

Norwegian Trench


This could be improved by using Chlorophyll data,

even annual would be better than what is currently

used. Below is 1/kd490 Based on SeaWifs (Annual)

Note relatively short extinction depths in Norwegian Trench



Even Better, monthly, or even near real time for many

wave bands. MEECE (Marine Ecosystem Evolution in

a Changing Environment) Inherent Optical Property

Dataset may be a good starting point


January doesn't have much data, but then there isn't

much light in January..

If using Multi Band Approach care is required on what

percentage of incoming light goes into the bands of

interest and the non-penetrating bands..

Top of the Atmosphere radiation 0 -

2000nm

Top of the Atmosphere radiation over

'Ocean Penetrating' Wave bands


If using Multi Band Approach care is required on what

percentage of incoming light goes into the bands of

interest and the non-penetrating bands..

Rough Approximation

of typical percentage

contribution of each

MEECE 'waveband' to

TOA radiation in the

penetrating range.


Variable Bottom Roughness for NWS

(Chris Jenkins, INSTAAR, University of

Colorado Boulder


Z0 from SeaFloor Database

Databases dealing with seafloor materials, features and

properties can be used to estimate z0 – the bottom

roughness scale for flows. Here we applied the dbSEABED

database to the problem for the North Sea Region.



Methods

Acquire a database of suitably integrated seafloor observations, taking care to

have a comprehensive and unbiased collection (sampling types, word &

numerical data).

Integrate the contributions to z0:

Background (default) z0

Sediment granular roughness – Nikuradse (1950) scaling, adjusted to local

sediment types

z0 assigned per facies – sediment type, rock areas, coral and shell banks

Scattered feature roughness, boulder fields – e.g. Schlichting (1936) method

Evolving feature roughness: bedform predictors based on wave climate, bed

texture (Soulsby & Whitehouse 2005; Wiberg & Harris 1994)


Next Steps

• improve the underlying database – seafloor properties

• improve evolving bedform roughness under waves

• z0 contributions from saltation, shear flattening, timedegradation

• validation tests – incl. NW Europe, Chesapeake Bay

• interface with flow dynamics - numerical circulation

models

Nikuradse, J. 1950. Stromungsgesetze in rauhen rohren, VDI-Forschungsheft, 361, 1933, see English Translation NACA

TM 1292.

Wiberg, P. L. and Harris, C. K. 1994. Ripple geometry in wave dominated environments. J. Geophys. Res., Oceans,

99C1, 775–89.

Schlichting H. 1936. Experimentelle untersuchung zum auhigkeitsproblem. Ingenieur-Archiv 7 (Band, 1. Heft): 1D34.

Soulsby, R. & Whitehouse, R. (2005b), Prediction of ripple properties in shelf seas: Mark 2, predictor for time evolution,

Technical Report TR 154, HR Wallingford, Wallingford, UK.


Beyond AMM7... AMM60?

Higher resolution model to be initially developed as part of

the Fastnet Shelf Break Project.

Nominally 1/60th Degree resolution with rotated grid


Questions and answers



Extras...


system in NEMO

Geopotential Coordinates:

• Constant thin boxes near the surface are good for resolving

surface mixing and upper ocean dynamics.

• But does not allow for a good representation of varying

topography (staircase at bottom = > inaccurate bottom

boundary layer (Gerdes 1993)

• Inaccurate bottom torques (Bell 1999, Hughes and de

Cuevas 2001, Song and Wright 1998)

• Bad for flows over sills and deep water formation

somewhat improved by shaved cells.



system in NEMO

Terrain Following Coordinates:

• Transform real space into dimensionless computational domain

bounded by sea surface and seabed.

• Sigma-coordinate when evenly spread, S-Coordinate when stretched

• Usually used for shelf or coastal applications

• Good for bottom boundary conditions (follows topography)

But not independent of local depth => large variation of bottom

means large variation of grid =>

• Horizontal Pressure gradient Errors

• Hydrostatic inconsistency

• Inconsistent for air sea flux due to varying surface box dimension

(bad for Coupled models)....


Constraining the solution for

shallow water

In shallow water if the prescribed surface/bottom cell sizes become large relative to

H/n the resolution will increase away from the surface/bed.

=> for water depths below some critical depth Hc treat the coordinate differently

Z|H

Constraining the solution for

shallow water

Requirement of gradual transition from shallow to deep => Hc should be

approximately n[Zs + Zb]/2

To prevent sharp changes in the coordinate smoothing must be applied around Hc

as a function of H-Hc

Can achieve this by requiring for H ≥ Hc

where e is a transition length scale.

NOTE: Surface and bottom resolutions will differ from the prescribed values close to

Hc


Further Constraints

Additional criteria still need to be satisfied.

Solution thus far does not guarantee monotonically increasing

values of in all cases

Does not guarantee gradually varying cell size in vertical nor

horizontal in all cases.

Thus require that:

Monotonically increasing everywhere

Increase is less than a certain tolerance


Exploring parameter space

subject to constraints

The above criteria are not straightforward to apply analytically, but can be used to

define the range of acceptable input values for the user controlled parameters.

In practice the value for n will be computationally limited and Zs will be expected to

be some constant suitable for air-sea exchange.

=> explore the acceptable parameter ranges for Zb and α, given the constraints on

monotonicity and rates of change given above .

Selecting Zb and α within these ranges leaves all criteria met except the stipulation

that the stretching minimises the rate of change of the coordinate for adjacent cells in

the horizontal.



Current speeds (m/s) for a SH94 (black) and gamma

(grey).Domain mean currents solid lines, domain

maximum speeds broken lines.

Improvements

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