Meteotsunami

Las personas están familiarizadas con las olas generadas por el viento y con las mareas, cuyos periodos de oscilación son del orden de segundos y horas, respectivamente. Este libro trata sobre el seiche costero, un evento de oscilación estacionaria que manifiesta un periodo de oscilación intermedio, mayor que el de las olas por viento y menor que el de la marea. El seiche costero es poco conocido por las personas que visitan o residen en la costa. Su carácter intermitente o episódico, lo hace más difícil de ser observado. La costa suroeste de Puerto Rico es uno de esos lugares donde se manifiesta con fuerza este fenómeno físico. La primera sección del libro trata sobre los seiches costeros forzados por olas solitarias internas (solitones internos). La segunda sección trata sobre los meteotsunamis. Ambos fenómenos físicos son responsables en excitar seiches costeros grandes o extremos en Puerto Rico.

Early in a Sunday morning on January 17 2016 at 11:04 GMT a moderate meteotsunami hit the Naples Coast in West Florida. The event was recorded by a tsunami capable tide station NOAA/NOS/CO-OPS/8725110 located at Naples Pier, 26° 7.9' N, 81° 48.5' W. A 2.9 millibars (mb) atmospheric pressure jump travelled East at 52.5 MPH (1.42 km/min) across the West Florida Shelf (WFS) putting energy into a 21 cm amplitude wave propagating 247 km to East at this same speed. This wave tripled its amplitude when reached the Naples Coast Pier. After removing the tidal and subtidal components from the water levels, it was revealed that the actual amplitude of the meteotsunami was only 63.75 cm. The superposition of the high amplitudes from the eight-diurnal (18.58 cm), semi-diurnal (39.47 cm), and diurnal (30.10 cm) tidal constituents, combined with subtidal motions (84.78 cm) and the meteotsunami summed a total water height of 2.37 m above MLLW. This case is a perfect example of how a moderate size meteotsunami (< 1 m) in perfect synchronization with high tides and mean high water (MHW) levels can become a natural hazard for coastal communities. HHT analysis was applied to the one-minute water level data. The results revealed a shift in frequency from 14.5 CPD to 35.2 CPD during the event.

En el periodo 2011-2014, el mareógrafo localizado en el Puerto de Fajardo, Puerto Rico ha detectado 6 meteotsunamis con amplitudes entre 9.3 cm hasta 19.4 cm. Los eventos fueron generados por pulsos en la presión atmosférica (0.4 mb a 1.6 mb) que acompañaban la llegada de ondas tropicales fuertes al Este de Puerto Rico.

This study presents the first observation of a tsunami induced by an atmospheric disturbance, this phenomenon is known in the literature as a meteotsunami. The meteotsunami was small scale and no damage was reported in the ports. On August 16, 2011 between 12:24 and 21:18 AST, the NOAA tide gauges registered a marked increase in the height of the coastal seiches in several ports and bays along 120 miles of the Caribbean coast in Puerto Rico; in the following locations: Puerto de Yabucoa, Santa Isabel, Magueyes Island, Salinas Bay, Puerto Real, Puerto de Mayagüez and in the west of Mona Island. The seiches with the highest height were recorded in Bahía Salinas and in Puerto Real with heights of 0.61 ft (18.5 cm) and 0.48 ft (14.6 cm), respectively. The amplitudes of meteotsunami in these two places were 0.305 ft (9.3 cm) and 0.24 ft (7.3 cm), surpassing by some 9 and 11 times the RMS amplitude of these localities. Even in Bahia Salinas the height of the wave exceeded the vertical range of the tide. The meteotsunami was excited by a pulse at atmospheric pressure of 0.7 mb and 2 ½ hours later by a second pulse of 1.4 mb. Increases in atmospheric pressure were immediately followed by a line of strong winds in gusts, which reached up to 37 knots (42.6 MPH). These events are associated with the passage of an extensive tropical wave over the waters south of Puerto Rico. According to the National Hurricane Center in Miami, the tropical wave was moving westward at about 20 MPH. Meteorological stations along the coast recorded the passage of pulses, which moved westward at an average speed of 35.5 MPH (15.8 m s-1). The tide gauges recorded the excitement of the seiches after the passage of the first pulse in the barometric pressure on each of the locations. The pulses excited seiches progressively throughout each station, making it possible to calculate the propagation speed between 28.6 MPH (12.7 m s-1) and 35.3 MPH (15.7 m s-1), equivalent to the local velocities of a long wave propagating in waters with depths between 16.5 m and 25.1 m. Assuming that the local longwave velocity is on average 32 MPH (14.2 m s-1), the mathematical ratio between the velocity of the atmospheric pulse (0.7 mb) and the long wave velocity is equivalent to a Froude number (Fr) equal to 1.11. This value suggests Proudman resonance between the atmospheric disturbance and the long wave when they travel on the waters of the insular platform, amplifying the first wave by 3 cm and the second wave by 6 cm. The final amplitude of the meteotsunami suggests that there was amplification due to resonance in the harbor or bay. Immediately after the passage of the second pulse, the currents increased their magnitude by 20 cm s-1 towards the west at a depth of 1 m and 4 m.

The oceanic forced wave beneath a moving atmospheric disturbance is amplified by Proudman resonance. When modified by the Earth's rotation this classical resonance only occurs if the disturbance time scale is smaller than the inertial period. With or without Coriolis effects, free transients generated by storm forced waves obliquely crossing step changes in water depth at particular angles are shown to resonate by exciting a range of long barotropic free waves. Rotationally influenced slow atmospherically forced waves crossing a vertical coast at a critical angle lead to a form of subcritical resonance, which occurs only when the component of the disturbances' phase velocities along the coast matches that of a free Kelvin wave (KW). In a rotating ocean, transients generated by disturbances crossing a step at a particular angle are shown to excite a free double Kelvin wave (DKW). This new type of resonance only occurs for sufficiently large steps and disturbances with time scale greater than the inertial period. A storm crossing a step shelf can result in the excitation of an infinite set of edge waves, a single KW, a unique DKW and a first-mode continental shelf wave, depending on the topography and the disturbance time scale, translation speed and incident angle. The study of resonances and wave mode excitations generated by storms crossing a coast or a continental shelf may contribute to understanding how a particular combination of the storm characteristics can result in destructive coastal events with time scales encompassing the typical meteotsunami period band (tens of minutes) and storm surges with periods of several hours or days

On June 13 2013, a pressure disturbance caused a tsunami-like wave along the East Coast of the United States. It is not clear the exact origin point of this oceanic long wave. But at 1705 GMT was detected by the DART II Buoy (see Figure 1), NDBC Station 44402, located at Southeast Block Canyon - 130 NM SE of Fire Island, NY. The station’s water depth was 2443 m.  Long waves speed is a function of water depth. Assuming this location as the Meteotsunami’s departure point, it was possible to calculate the distance and travel time of the long wave to various tsunami capable tide stations. These tidal stations are separated from the Dart Buoy by  a long distance (> 1400 miles) and deep waters (> 3000 m), allowing us to easily calculate the Meteotsunami’s deep water speed. The 1-minuted sampled data was provided by the NOAA/NOS/CO-OPS website and the DART II Buoy data was obtained from the NDBC website. This valuable data allowed us to calculate for the first time the transatlantic Meteotsunami’s long wave speed.

The term “tide-gauge” is inadequate to describe or contain all the current applications of this kind of oceanographic instrument. A more proper name should be a Water Level Gauge (WLG), because it measures changes or oscillations in water levels due to a myriad of oceanographic and atmospheric phenomena. A WLG station measures simultaneously oceanic and meteorological parameters with a high time-resolution (1 to 6 min). But an array of these stations can characterize the spatial coverage of any physical phenomena. Increasing the space resolution and assuring a better analysis of the ocean’s phenomena. Let’s see some recent discoveries made possible by the WLG’s array. • In the Seiche Band o 2011-Discovery of the Magueyes Cycle of extreme seiche activity (T= 6202.2 ± 1.3 days, 16.98 years) o 2011-Discovery of Meteotsunamis generated by pressure jumps associated with the arrival of strong tropical waves o 2013-First measurements of a Transatlantic Meteotsunami • In the Meteorological-Oceanic Band o 2011-Discovery of Edge Waves trapped on the Cabo Rojo-Mayaguez Shelf, about 30 hours after the passage of Hurricane Irene over Puerto Rico • In the Long-Term Band o 2012-Two stations confirm a positive trend of Sea Level Rise around Puerto Rico.

This study is focused to determine amplification (or topographic response) in 12 harbors (bays) of the Puerto Rican Archipelago. On August 16 2011, a meteotsunami was detected by 12 NOS water-level stations. This singular event presents us with the unique opportunity to analyze high quality water-level data; that allow us to calculate the harbor's amplification for many harbors in Puerto Rico. It is important to know the topographic response of the harbors (bays) of Puerto Rico; this way we can identify those locations where their oscillations (coastal seiches) will be larger or last longer. In these harbors marine activities will be affected the most.

Three hurricanes went through a rapid intensification process (Irma, Maria, Michael) and generated small amplitude meteotsunamis about 12 hours before they hit the coast as major hurricanes category 4-5. We suggest in this study that meteotsunamis can be used as a diagnosis tool of the rapid intensification of a hurricane. This novel technique, together with the existing ones, can provide a confirmation of the strengthening of the hurricane at least 12 hours prior to its impact on the coast.

El 8 de Agosto del 2014 a las 12:53 LST (Hora Local) ocurrió un meteotsunami con una altura de 29.9 cm (0.98 ft) en el Puerto de Fajardo, Puerto Rico. Este es el evento de mayor altura registrado hasta el día de hoy (vea Tabla 1). El evento está asociado al paso de una onda tropical por el área de Puerto Rico. Fue generado por un pulso en la presión atmosférica de 0.4 mb.  El pulso se desplazó a 35 MPH desde el ESE, discurrió unos 50.8 km en un trayecto a lo largo de la plataforma insular entre Vieques y Fajardo. El acoplamiento entre el pulso atmosférico y la ola larga barotrópica facilitó que durante el trayecto la resonancia de Proudman (1929) incrementara la amplitud de la ola, desde -0.4 cm hasta 1.8 cm. Luego en el Puerto de Fajardo, nuevamente la amplitud del meteotsunami aumentó 13.15 cm debido a la segunda resonancia con el Puerto de Fajardo. Para alcanzar una amplitud final igual a 14.95 cm.

Proudman resonance amplifies the oceanic forced wave beneath moving atmospheric pressure disturbances. The amplification varies with water depth; consequently, the forced wave beneath a disturbance crossing topography radiates transient free waves. Transients are shown to magnify the effects of Proudman resonance for disturbances crossing the coast or shelf at particular angles. A Snell like reflection law gives rise to a type of resonance for relatively slow moving disturbances crossing a coast in an otherwise flat-bottomed ocean. This occurs for translation speeds less than the shallow water wave speed for disturbances approaching the coast at a critical angle given by the inverse sine of the Froude number of the disturbance. A disturbance crossing the shelf at particular angles can also excite seiche modes of the shelf via generation of a transient at the continental slope. Beyond a typically small angle of incidence, transients generated by a disturbance crossing the continental slope and coast will be trapped on the shelf by internal reflection. The refraction law for a fast-moving forced wave crossing an ocean ridge at greater than a small angle of incidence also results in trapped free-wave transients with tsunami-like periods propagating along the ridge. The subcritical resonance, excitation of shelf modes and trapping of the transients may have implications for storm surges and the generation of destructive meteotsunami.

Tres huracanes que pasaron por un proceso de
intensificación rápida (Irma, María, Michael) generaron
meteotsunamis de poca altura unas 12 horas antes de que estos impactaran la costa como huracanes  categoría 4-5. Sugerimos en este estudio que los meteotsunamis se pueden utilizar como herramienta diagnóstica de la rápida intensificación de un huracán. Esta técnica novel, junto a las ya existentes pueden proveer una confirmación del fortalecimiento del huracán al menos 12 h previo a su impacto en la costa.

Wavelet and cross-wavelet power spectra of sea level records from tide gauges along the Atlantic coast of Canada showed a low-frequency barotropic response after Hurricane Florence crossed the Newfoundland shelf in September 2006. In comparison with two other storms, the results showed that Florence was the only one that excited a propagating sea level disturbance with a period range similar to the passage time of the storm over the shelf (26-30 h) and phase shifts consistent with a barotropic continental shelf wave (CSW). The high amplitude of the oscillations generated by Florence along the shore diminished from approximately 45 to 12 cm as the CSW propagated from the south coast of Newfoundland to the southern Nova Scotia seaboard. This paper presents the first direct measurement of a remarkably high alongshore group speed (11.4±5.9 m s-1), in the manner of free-barotropic CSW, by examination of sea level wavelet power spectra at different locations. Furthermore, using cross-wavelet analysis of pairs of stations, an exceptional phase speed of 16.0±5.1 m s-1 has been found, greater than had been previously observed for a free CSW. The results were consistent with dispersion curves for the first-mode barotropic CSW.