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IntroductionIntroduction::The Balearic SeaThe Balearic Sea
Introduction: The Ciutadella Harbor, a peaceful natural harbor
Jansa et al., 2007
IntroductionIntroduction::But, sometimes ...
Seiche : Wave heigth can reach up to 4 meters !
They dammage boats and the ciutadella harbor !
They cause flood
Millions of Euros of Dammage !
Jansa et al., 2007
IntroductionIntroduction::A Rissaga happens !A Rissaga happens !
-MeteoTsunami !
>7mb!
Vilibic et al., 2008
2006 : wave up to 4 meters into the inlet ! More than 10 Millions $ of dammage !
-Meteorit ??
-Earthquake ??
-Storm surge ??
‘Meteotsunamis’ are generated by traveling air-pressure disturbances over a shallow region through resonant processes
WHY ???WHY ???
Problematic• Some studies, mostly theorical or based on observations, only a few numericals
They don’t allow us to predict the Rissagas intensity.
•Some atmospheric studies, without ocean response ... Are they realistic ?
• Signifiant rissaga (~1 meter) occur a few times per year (summer)Only small floods
• Destructive rissaga (>2 meters) occurs every 4-5 years
To avoid these dramatic Rissagas effect, need to predict both Rissagas occurences and intensities.Mesoscale phenomenon, use both oceanic and atmospheric modeling with high temporal and spatial res. WRF and ROMSAim : Reproduce Rissaga,both atmospheric and oceanic part
Document the sensitivity of this ocean/atmosphere coupling
Presentation plan
I. Introduction
II.Origin of the Rissaga
III.Ideal cases
IV.Realistic cases
Gravity waves (and/or convection) appear in the layer (3), the vertical oscillations are transmitted to the inversion layer, resulting in pressure oscillations at surface
Jansa et al., 2007 (1) low level Mediterranean air, with a weak surface depression
(2) warmer African air blowing above,around 850 hPa,
Separated by an inversion layer
3) a poorly stable or a conditionally unstable layer between the African air and colder air in the upper levels, with a marked vertical wind shear across this layer (Ramis and Jansa (1983), Monserrat et al., 1991a, b).
Origen of the Rissagas ?Origen of the Rissagas ? An atmospheric remote forcingAn atmospheric remote forcing
SLP 850Hpa wind and temp
500Hpa geopot and temp
300Hpa geopot
ECMWF
mbars
Wav
e pr
opag
ation
Oscillations, can be due to:
atmospheric gravity waves (Ramis and Jansa, 1983; Monserrat et al., 1991a, b) and/or to convective pressure jumps (Jansa, 1986).
Long surface waves in the ocean which in turn produce an amplified “seiche” whithin the inlet (Tintoré et al.,1988; Gomis et al., 1993; Garcies et al., 1996).
Renault et al., 2010, in preparation
Dimensiones: Small convective core : ~20 km Structure more synoptical: with wave train, ~100-150 km.Form: semi-circle
Jansa (p.c.)
Origen of the Rissagas ?Origen of the Rissagas ? An atmospheric remote forcingAn atmospheric remote forcing
WRF
hh
LL
UU
C=C=√gh√gh
hh
3. A resonant amplification in a harbour/inlet :
• Incoming wave with a maximum energy on the harbour eigenfrequencies
• A large amplification factor
T=4L/T=4L/√gh, √gh, ~10mn~10mn
same mecanism for any tsunami amplification !!
1. A traveling air-pressure disturbance
2. A resonant transfert of energy from the atmosphere to the sea Proudman resonance (Proudman, 1929)
Origen of the Rissagas ?Origen of the Rissagas ? Three main conditionsThree main conditions
Presentation plan
I. Introduction
II.Origen of the Rissaga
III.Ideal cases
IV. Realistic cases
Ideal cases Ideal cases Idealized pressure with idealized bathymetries.Idealized pressure with idealized bathymetries.
THE RESPONSE OF SEA LEVEL TO TRAVELLING PRESSURE DISTURBANCES:
patm x,y, t p0 pexp x x pert t 2 y y pert t 2
2
• Rectangular ocean basin (100m depth) on a f plane centered at N39.5º
• Dimension : 500km x 150km
• Initial condition: a state of rest with uniform and flat ocean
• DP = 7HPa
Ideal cases Ideal cases Idealized pressure with idealized bathymetries.Idealized pressure with idealized bathymetries.
Vibilic, I. Numerical simulations of the Proudman resonance, Continental Shelf Research, 28. 2008Mercer D et al. Barotropic waves generated by rapidly moving storms, Journal of Geophysical Research, 107. 2002Gill, A. E., Atmosphere-Ocean Dynamics. Academic press. 1982
1. Deep waters: static barometric response2. Shelf: resonant response
Solution (Proudman, 1929) for sea level when an atmospheric pressure disturbance is travelling over a channel of uniforme depth (Vibilic, 2008)
1
1 Fr2x Ut 1
2 1 Fr P x ct 1
2 1Fr P x ct
Fr U
cU
gH
“forced wave” Free bar. waves
Based on the work of Vibilic, Mercer, Gill, etc …, we will try to reproduce the physical ocean response using ROMS
When U<<c, elliptic solution, as is the case of deep waters (or very slow storms), the response to the perturbation will be isostatic (inverse barometer). No resonant amplification
Ideal cases Ideal cases U/c <1U/c <1
20 mn 100 mn 160 mn
Hyperbolic solution. The perturbation generates a wake behind, analogous to the wake generated by a ship
Ideal cases Ideal cases U/c >1U/c >1
Resonant case. Transition from elliptic to hyperbolic behaviorIn our case, the typical speed of the perturbation is about 25-28 m/s. So the resonant case corresponds to depth 80-100 m
Ideal cases Ideal cases U/c=1U/c=1
ROMS is able to reproduce the Proudman
resonance, now, we will use a realistic bathymetry
If Fr=1 Proudman maximal Strong Proudman resonance along the shelf
Fr=U/c
Origen of the Rissagas ?Origen of the Rissagas ? Ocean responseOcean response
Ideal cases Ideal cases Real bathymetryReal bathymetry
Threre is a strong non-isostatic response when the perturbation moves near the local gravity wave speed.Strong Proudman resonance and also shallowing effect ! Frequencies are in good agreement with the obs and
litterature.
Fr<1 Fr~1
Ideal cases Ideal cases Harbor resonanceHarbor resonance
Harbor : bath=5m
Constant bathymetry:
100m
Shelf: bathymetry: 10010m
Shelf
X=DY=1km X=DY=20
m
• Ideal Bathmetry
• One way nesting
• Atmospheric forcing : Gaussian pressure
ProudmanShelf amp
1000
m.
100
m5m
Ideal cases Ideal cases Harbor resonanceHarbor resonance
ROMS is able to reproduce the oceanic response to a pressure oscillation from deep
water to inside the inlet
0.4
-0.4
1
-1
5
-5
1
25mn10 mn
• Harbor resonance !
• Amplification factor ~5
• Frequencies comparable with the reality :
•25 mn: Shelf mode, 20mn oscillation multiple of the harbor eigenfreq.
•10 mn: Harbor mode
20mn
2006 Strong event
Vilibic et al., 2008
Origen of the Rissagas ?Origen of the Rissagas ? Sum-upSum-up
Ideal cases Ideal cases Sum-upSum-up
• Results are consistents with other studies and with observations.
• Very sensitive system :
Froud number ( wave velocity)
Intensity
Orientation
• Resonance exitation of the harbor very important due to the linecoast and bathymetrie.
•Based on our hypotesis, ROMS is able to reproduce an ocean response similar to the observed
Presentation plan
I. Introduction
II.Origen of the Rissaga
III.Ideal cases
IV.Realistic cases
WRF is able to reproduce a rissaga event, but some problems with the mean position To Study the ocean response, we translate the slp oscillation over
the shelf
• Consistent with observations
• July 1997 Rissaga is due to an atmospheric wave train
• Lengthscale ~30-40km
• V~=25-28m/s and dP~=3-5mbar
Realistic case 1: July 1997 Realistic case 1: July 1997 The atmospheric perturbationThe atmospheric perturbation
5mbar
Wave train!
Renault et al., 2010, in preparation
The Rissaga event outside the harbor is well simulated by the model. What about the inlet ?
20-25 min.
50cm.
Proudman
- Good agreement with the observations, both in intensity than in frequency
-The shelf frequency is reproduced
-Proudman + shelf amp ~4-5cm 50cm!
Realistic case 2:July 1997Realistic case 2:July 1997OceanicOceanic response over the shelf response over the shelf
Renault et al., 2010, in preparation
The model is able to reproduce the July 97 Rissaga event, both outside the inlet than inside. The fundamental period is pretty
well reproduced.
-Good agreement with the observations and vilibic et al., 2008: wave >1 meter !
-The simulated inlet fundamnental period is similar than the oberved : ~ 10 minutes (Helmholds period)
-Current ~1meter/s !
- Amplification harbor > 2
10 mn
24mn
>1 meter!
10mn
Realistic case 1: July 1997Realistic case 1: July 1997Inlet responseInlet response
Max current
20mn
Renault et al., 2010, in preparation
Conclusions and perspectives (1)• Numerical regional model are able to reproduce some Rissagas ! But problems with wave orientation and intensity
• Resonant phenomenon simulated are consistants with the observed and the litterature (Mercer, Gill, ...)• Frequencies simulated have a good agrement with the observed (10mn and 24mn mainly)• Intensities of the generated wave comparable with other studies (i.e. Vilibic et al., 2008) and obs.
• From a low resolution atmospheric forcing, we are able to reproduce traveling pressure disturbance
• Wave train during the July 1997 Rissaga• dP=3-5mb, V=25-28m/s, angle~45º, wavelength : ~30-40km• Some problems with the 2006 complex strong rissaga (convective case), on work ....
Conclusions and perspectives (2)
• Impact of the trapped wave on the oceanic response ??
•Meteotsunami occurs not only in the Balearic sea but around the world ! i.e: ‘rissaga’ ‘milghuba’ , ‘marrubio’, ‘abiki’
• Mostly a barotropic response, but stratification impact (Cushman-roisin et al., 2004) ? What it the orden of the baroclinic response ? Wind efect ?
• Toward an operational forecasting of the Rissaga
• How to improve the atmospheric wave simuation ?? Boundaries conditions ? Physics ? Data assimilation ?
Great Lakes
Ciutadella Sicillia
Vela Luka Bay
South AfricaGreece
Japan
Kuril islandBritish Columbia
Thank you !
Add on
Fig. 3: The WRF model configuration
WRF domains
• Three embedded domains, two way nesting
• 30km 6km ( 1.5km)
• SST forcing by medinspiron
Main phsyics option
Realisitic Case 2: June 2006Realisitic Case 2: June 2006Convective RissagaConvective Rissaga
• WRF simulate an atmospheric pressure jump, but problems :
1. Location
2. Intensity : only 3-4mb
• Ocean response too weak:
1. Only ~40cm entrance
WEAK ENERGY
1. Frequencies are not multiple of the harbor frequencies WEAK HARBOR RESONANCE
Problem to simulate the 2006 event with various WRF configuration. It was a strong particular event, with convective
atmospheric effect. Data assimilation ? Boundaries conditions ?
Realistic case 2: June 2006Realistic case 2: June 2006Extrapolated mesured pressure Extrapolated mesured pressure
• Realistic response ! Why ? Stronger atmospheric signal stronger energy.
•Ocean respond violently generating strong eigenoscillation insite both coastline.
•Into the harbor, wave up to 2 meters, weaker than the testimomies but stronger than the one simulated in Vilibic et al., 2008
• currents about -2 2 m/s
• Same metodology than Vibilic et al., 2008 : propagation of the observed pressure : 25ms and 45º, wavelength ~130km
2006 event pretty well reproduced by ROMS. Main diff. between observed and simulated atmospheric pressure: pressure
gradient
~1h30
