Meteotsunamis in the Balearic Sea Renault L., Vizoso G., Wilkin J., Tintore J.

Introduction : The Balearic Sea

Introduction : The Ciutadella Harbor, a peaceful natural harbor Jansa et al., 2007

Introduction : Introduction : 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 Introduction : A Rissaga happens !

-MeteoTsunami ! >7mb! Vilibic et al., : 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 ???

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 ROMS Aim : 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 ? An atmospheric remote forcing SLP 850Hpa wind and temp 500Hpa geopot and temp 300Hpa geopot ECMWF

mbars Wave propagation  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, ~ km.  Form: semi-circle Jansa (p.c.) Origen of the Rissagas ? An atmospheric remote forcing WRF

h L U C=√gh h 3. A resonant amplification in a harbour/inlet : Incoming wave with a maximum energy on the harbour eigenfrequencies A large amplification factor T=4L/√gh, ~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 ? Three main conditions

Presentation plan I.Introduction II.Origen of the Rissaga III.Ideal cases IV. Realistic cases

Ideal cases Idealized pressure with idealized bathymetries. THE RESPONSE OF SEA LEVEL TO TRAVELLING PRESSURE DISTURBANCES: 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 Idealized pressure with idealized bathymetries. Vibilic, I. Numerical simulations of the Proudman resonance, Continental Shelf Research, Mercer D et al. Barotropic waves generated by rapidly moving storms, Journal of Geophysical Research, Gill, A. E., Atmosphere-Ocean Dynamics. Academic press Deep waters: static barometric response 2.Shelf: resonant response Solution (Proudman, 1929) for sea level when an atmospheric pressure disturbance is travelling over a channel of uniforme depth (Vibilic, 2008) “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 U/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 U/c >1

Resonant case. Transition from elliptic to hyperbolic behavior In our case, the typical speed of the perturbation is about m/s. So the resonant case corresponds to depth m Ideal cases U/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 ? Ocean response

Ideal cases Real 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 Harbor resonance Harbor : bath=5m Constant bathymetry: 100m Shelf: bathymetry: 100  10m Shelf  X=DY=1k m  X=DY=20 m Ideal Bathmetry One way nesting Atmospheric forcing : Gaussian pressure Proudman Shelf amp 1000 m. 100 m 5m

Ideal cases Harbor resonance  ROMS is able to reproduce the oceanic response to a pressure oscillation from deep water to inside the inlet mn 10 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 ? Sum-up

Ideal cases Sum-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 The 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 ? 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 1997 Oceanic 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 1997 Inlet 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 Africa Greece Japan Kuril island British Columbia

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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 2006 Convective Rissaga Realisitic Case 2: June 2006 Convective 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 2006 Extrapolated mesured pressure Realistic case 2: June 2006 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