1. Multi-nest high-resolution model of submesoscale circulation features in the Gulf of Taranto
F. Trotta, N.Pinardi, E. Fenu, A. Grandi
EGU General Assembly 27/04/ Session CL5.08/AS1.3/OS4.10 Downscaling: methods and applications

2. ONE–WAY–NESTED MODELLING APPROACH
NESTED-GRID OCEAN CIRCULATION MODELLING SYSTEM
Parent Domain
Dl, Dj, Dz
NEST1
Dl, Dj, Dz
NEST2
Lateral BC
Dl, Dj, Dz
SURF provides a numerical
plataform for short-time forecast
at high spatial and temporal resolution.
NEST3
ONE–WAY–NESTED MODELLING APPROACH
Lateral BC
Dl, Dj, Dz
It is based on NEMO code: 3D Finite Difference Hydrodynamic (FDH) model which solve the primitive equations on an Arakawa C-grid with free surface.
Lateral BC
It can be easily and quickly deployed in any region of a large-scale
Ocean Forecasting System via nesting procedure(one-way nesting approach)
The plataform include multiple nesting capability.
For each nesting, the coarse-grid (parent) model provides initial and lateral boundary condition to the fine-grid (child) model.
We can increase the model resolution in a sub-domain and resolve a wider range of scale, not only the mesoscale flow field (10-100km) but also the submesoscale flow field (100m-10km)

3. CASE STUDY: THE GULF OF TARANTO
LS1
LS2 CS t
01Oct
02Oct
03Oct
04Oct
05Oct
06Oct
07Oct
08Oct
09Oct
10Oct
11Oct
12Oct
Oceanographic cruise (MREA14) in Taranto Gulf was carried out in October 2014 on Galatea (Italian Navy Hydrographic Institute)
GULF OF
TARANTO
Mar Grande
Costal Scale
A multi-scale CTD data collection
(from 1 to 11 October 2014)
Large Scale: LS1 &LS2 with resolution 16km
Coastal Scale: CS with resolution 5km
Mar Grande : MG with resolution of 1km
Large Scale

4. MODEL SET-UP LS1 LS2 CS t MFS NEST1 NEST2 NEST3 01Oct 02Oct 03Oct
Spin-up
NEST2
Spin-up
NEST3
Spin-up
MFS
NEST1
NEST2
NEST3
TIME
Start Date -
2014/10/05
(00:00)
2014/10/06
2014/10/07
nDay 8 7 6
Time Step
200s
150s
72s
36s
SPATIAL GRID
Horizzontal Grid (spherical coordinate system)
N° of points
Grid resolution
821x253
1/16
6114m
94x79
1/48
2038m
230x160
1/144
680m
220X200
1/432
227m
Vertical Grid (z-coord with partial step)
N° of levels
Grid res 1° layer
Maximu Depth 72
2.8m
2000m
120
PHYSICS
Horizontal Subgrid-scale physics (bilaplacian operator)
Viscosity coeff
Diffusivity coeff
-1e+09
-6e+08
-1.2e+07
-7.4e+06
-91449
-1881
-1129
Vert Subgrid-scale physics (PP mixing parametrization)
EVD Max coeff
1.2e-05
1.2e-06 10
MFS
6km
NEST1
2km
NEST2
680m
NEST3
227m
INITIAL CONITION
MFS-field (T,S,u,v and SSH)
with LS1-CTD data assimilated
BOUNDARY CONITION
Surface BC (MFS Bulk formulae using ECMWF data )
Lateral close BC (No-slip condition)
Lateral open BC (Flather and Flow Relaxation scheme)
Bottom BC (Non linear friction)
SPECIFIC NUMERIC FORMUL.
Moment Adevection (EEN scheme)
Tracer Adevection (MUSCL scheme)
Bottom BC (Non linear friction)

5. SUBMESOSCALE STRUCUTREs
MFS
6000m
NEST1
2038m
Horiz. section of Temp + Current at 10m
(October :00)
MFS VS
1NEST
Large scale anticyclonic rim current with intesified jets and additional features emerged in the higher resolution nests.
A submesoscale cyclonic vortex with diameter of 4 km was found. To generate this eddy a 200m resolution was required
This eddy was confirmed by observa- tional data collected in the study area.
NEST1
2038m
NEST2
680m
1NEST VS
2NEST
NEST2
680m
NEST3
227m
Pinardi et all. 2016
2NEST VS
3NEST

6. EVOLUTION OF SUBMESOSCALE STRUCTUREs
Horizontal section of Temperature + Current at 10m (October from 00:00 to 24:00) t
01Oct
02Oct
03Oct
04Oct
05Oct
06Oct
07Oct
08Oct
09Oct
10Oct
11Oct
12Oct
Oct10–00:00
Oct10–06:00
Oct10–12:00
Oct10–18:00
Oct10–24:00
Formation of a meander.
Eddy formation process accours in severa hours over a space scale of few ten km

7. EVOLUTION OF SUBMESOSCALE STRUCTUREs
Horizontal section of Relative Vorticity at 10m (October from 00:00 to 24:00) t
01Oct
02Oct
03Oct
04Oct
05Oct
06Oct
07Oct
08Oct
09Oct
10Oct
11Oct
12Oct
Oct10–00:00
Oct10–06:00
Oct10–12:00
Oct10–18:00
Oct10–24:00
Formation of a meander.
Eddy formation process accours in severa hours over a space scale of few ten km

8. SURFACE MIXED-LAYER
Zonal section of Vertical Velocity Field (October from 00:00 to 24:00) t
01Oct
02Oct
03Oct
04Oct
05Oct
06Oct
07Oct
08Oct
09Oct
10Oct
11Oct
12Oct
Oct10–00:00
Increasing resolution was accompanied by an increase of vertical velocity (from few m/day (NEST1) up to 100 m/day (NEST3) near the surface.

9. SURFACE MIXED-LAYER
Zonal section of Vertical Velocity Field (October from 00:00 to 24:00) t
01Oct
02Oct
03Oct
04Oct
05Oct
06Oct
07Oct
08Oct
09Oct
10Oct
11Oct
12Oct
Oct10–06:00
Increasing resolution was accompanied by an increase of vertical velocity (from few m/day (NEST1) up to 100 m/day (NEST3) near the surface.

10. SURFACE MIXED-LAYER
Zonal section of Vertical Velocity Field (October from 00:00 to 24:00) t
01Oct
02Oct
03Oct
04Oct
05Oct
06Oct
07Oct
08Oct
09Oct
10Oct
11Oct
12Oct
Oct10–12:00
Increasing resolution was accompanied by an increase of vertical velocity (from few m/day (NEST1) up to 100 m/day (NEST3) near the surface.

11. SURFACE MIXED-LAYER
Zonal section of Vertical Velocity Field (October from 00:00 to 24:00) t
01Oct
02Oct
03Oct
04Oct
05Oct
06Oct
07Oct
08Oct
09Oct
10Oct
11Oct
12Oct
Oct10–18:00
Increasing resolution was accompanied by an increase of vertical velocity (from few m/day (NEST1) up to 100 m/day (NEST3) near the surface.
Starting with a weakly stratified ML, we observed, in higher resolution nests, a faster restratification (increase in the restratification rate)

12. CONCLUSIONs
We implemented a triple-nested model using the new relocatable ocean platform “SURF” from the coarser resolution (6000m) MFS model to the NEST1 (2000m), NEST2 (700m) and NEST3 (200m) models in order to explicitly resolve the submesoscale in the Gulf of Taranto.
The flow field showed large-scale anticyclonic rim current with intensified jets and additional small-scale features emerging in higher resolution nests.
A submesoscale cyclonic vortex with diameter of 4 km was found in the northwest region of the central anticyclonic gyre. To generate submesoscale eddies, it was found that ∼200 m resolution was required.
This eddy was confirmed by observational data collected in the study area.
Increasing resolution was accompanied by an increase in the vertical velocity field in the upper ocean (up to 100 m/day).
As horizontal resolution increased, we obseved an increase in the restratification rate in the Mixed Layer.

13. END