Re: Sistema Topograph 98 Se.epub
Latrisha Adan
A regional model combination (WRF+ROMS+WW3+SWAN), identified as SPNOA (Numeric Ocean-Atmosphere Forecasting System), was applied for coastal flood forecast in Cuban coastal zones. A module to predict sea level rise by wave setup was added. Nested domains were used, covering the Inter-American Seas, Cuban surrounding waters and shore areas. Several hurricanes were considered as study cases in the experimental work to test the system effectiveness. The following procedures were utilized to evaluate the obtained results: A) WRF output circulation patterns were compared with NOAA re-analyses, and hurricane trajectories with NHC best tracks. B) The records of meteorological stations and buoys were compared with punctual model outputs. C) Storm tide forecast, given by ROMS and wave setup modules at the shore line, were evaluated in comparison with tide gauge records at some points of the Cuba coastal zone, near or located in the flooding areas. Some local testimonies about flooding intensity were also analyzed. It was concluded that SPNOA system is efficient in terms of up to 72 hours for the representation and prediction of wind waves and sea level rise, under the influence of hurricanes; therefore, its use in the Cuban meteorological service is recommended.
Se presenta la aplicacin de los modelos combinados (WRF+ROMS+WW3+SWAN) dentro del Sistema SPNOA (Sistema de Pronsticos Numricos Ocano-Atmsfera), en la representacin y prediccin de las inundaciones costeras en Cuba, para uso del servicio meteorolgico nacional. Se aade un mdulo para el clculo del aumento de nivel por rompiente de oleaje (wave setup). Se utilizan dominios anidados que cubren los mares Interamericanos, las aguas aledaas y las costas cubanas. Para comprobar la efectividad del sistema en la representacin y pronstico de las inundaciones, se analizan varios estudios de caso de huracanes. Se comparan los patrones de circulacin de salida de WRF con los re-anlisis NOAA y las trayectorias de los huracanes con las mejores trayectorias (Best track) de NHC. Posteriormente, se comparan los registros de estaciones meteorolgicas y de boyas, de las variables viento, presin atmosfrica y elementos de ola, con las salidas de WRF, WW3 y SWAN. Las salidas de sobreelevacin del nivel del mar, dadas por ROMS+wave setup, se evalan en comparacin con registros de maregrafos en algunos puntos de las costas de Cuba, cercanos o localizados en las reas de inundacin. Se concluye que el sistema SPNOA es eficiente en plazos de hasta 72 horas para la representacin y prediccin de oleaje y sobreelevacin del nivel del mar, al paso de huracanes, por lo que se recomienda su uso en el servicio meteorolgico cubano.
Cuban Archipelago is frequently affected by coastal floods, generated by tropical cyclones. To mitigate the possible damages, it is necessary to increase the quality and anticipation of weather, wind wave and sea level rise forecasts, which is efficiently achieved using numerical models.
SPNOA system (Numeric Ocean-Atmosphere Forecasting System) was created by Prez Bello et al. (2013 b) and consists of a combination of atmospheric, wind wave and ocean circulation models, which allows obtaining in a fully automated way the space-temporal representation and forecast of atmospheric circulation, oceanic circulation, wind waves and sea level increase in Cuban coastal areas and adjacent seas. These characteristics make it a very practical tool, to increase the quality of coastal flood forecast; but it is necessary to assess the possibilities and limitations of the system.
The general objective of the present work is to develop weather, wind wave and sea level increase forecasts in presence of hurricanes on Cuban territory and surrounding waters, as generators of coastal flooding, using high-resolution atmospheric and marine models. The following actions are necessary to achieve this objective: a) Application of a combination of numerical models for weather and sea surface state forecast, in presence of tropical cyclones. b) Addition of a wave setup calculation module to the model system used. c) Verification of the model outputs, in comparison with synoptic re-analyses and records of meteorological stations, oceanographic buoys and tide gauges.
The SPNOA system, developed by Prez et al. (2013), includes the combination of the numerical models WRF, ROMS, WW3 and SWAN. The wave setup calculation module (WST) was added, following the recommendations of CEM (2006). The incorporation of a wind setup module was not considered necessary, since this calculation is included in ROMS model. Figures 1.1 a, b show the work domains and SPNOA model chain scheme.
A variant of WRF 3.5.1 (Weather Research and Forecast model, version 3.5.1) was applied, according to the description and recommendations of WRF User Page (WRF, 2008-2012) and taking into account the national experiences on the application of MM5V3 and WRF in previous research (Mitrani et al., 2011; 2012 a, b). Two nested domains were used, covering the area of interest for Cuban meteorological service at regional and local scale. The model was developed on LINUX support and run on a cluster of personal computers, which allows faster data assimilation and appropriate graphic presentation graphic outputs for users. The working language is FORTRAN-90/95 and graphic outputs are produced in Grads.
Taking into account the physical - geographical characteristics of Cuba and its position in the central zone of the Inter-American Seas, as well as previous Cuban experiences (Mitrani et al., 2011), two nested domains were defined in Lambert projection, with central coordinates at 22 N and 80 W. This point is approximately towards the center of the area, so that meridian 80 practically divides the island in half, as defined by Lecha et al. (1994). The outer domain covers the Inter-American Seas with a total of 26257 mesh points (217x121) and with space steps of 18 km. The inner domain occupies Cuban Archipelago and surrounding waters, with steps of 6 km and a total of 40600 mesh points (280x145). In both domains, 30 vertical levels were used (Fig. 3.1).
GFS (Global Forecast System) outputs, with space resolution of 0.25 degrees (approximately 28 km), available on the website , were used every 6 hours as input to the atmospheric model WRF (Weather Research and Forecast system) The meteorological variables were: sea level pressure, air temperature, relative humidity and wind components, from the surface, 1000, 850, 700, 500, 400, 300, 200, 150 and 100 hPa levels; as well as the geopotential heights. Sea surface temperature was determined from the input data at the initial moment, remaining constant throughout the forecast period.
Version 2.22 of the wind wave model Wave Watch III (Tolman, 2002; 2006) was assimilated, which is freely available on INTERNET (the later variant requires a license by now). It has a 6-km space step and a total of 176368 mesh points (604x292) over the second WRF domain. This domain was chosen, because it covers the entire area of the Inter-American Seas, where a predominance of natural land borders reduces the use of simulated borders over the sea.
Tolman (2002) recommends not to use WW3 in areas where the main limiting factor for wind wave development is sea depth. In addition, the space step should not be less than ten kilometers. These recommendations, confirmed at the model website (WW3, 2010), exits because local details of the coastal zone are not well treated inside the model algorithm. Therefore, fine-tuning the resolution may be unnecessary, because it does not provide better results. For this reason, WW3 should be combined with a coastal model that takes into account all the details of bathymetry, bottom relief, coastal configuration and land use, such as the SWAN model.
To preserve WW3 mathematical stability, it must be satisfied the condition that Cg = (δt/δs) < 1 must be satisfied, where Cg is the wave group speed and the expression (δt/δs) refers to the relationship between the spatial and temporal steps of model integration. According to the classic trochoidal wind wave representation, the ratio between wave length and period is taking as λ= 1.56 τ2/g, but the wind wave length can be greater than 100 m under the action of hurricane winds, with a period over 10 s, so the relationship between the temporal and spatial steps in the model integration must be quite less than 0.1. For this reason, the appropriate integration time step was 300 seconds in the current work.
As WW3 input data, WRF wind outputs every three hours were used, and a bathymetry matrix in combination with the coastal topography and inclusion of small islands, with a mesh size of 6 km. These data were taken from GEBCO Atlas (2003), for the area that is observed in Figure (1.2). Wind and bathymetry meshes were made to coincide by linear interpolation. At the end, WW3 outputs were available every one hour with a space step of 6 km.
JONSWAP spectrum of limited fetch. It was selected for the spectral approximation of sea surface state. It was considered the most appropriate due to the peculiarity of the study area, which is enclosed by land in three of its borders, so that fetch is effectively limited by geographical conditions.
Propagation scheme described by Tolman (2002). It is used because it includes techniques that soften the "sprinkler" effect of the wind, which when overestimated produces excessive deformation in the direction of wave propagation, especially when it is generated by hurricane winds.
The dissipative term parametrization of Tolman-Chalikov (1994, 1996), improved by Tolman (2002). This parameterization represents in detail the swell formation, propagation and mitigation in time and space. This detail is important, given the frequency of flooding in the northwestern part of Cuba by a combination of sea and swell surface states, with predominance of swell.
ROMS (Regional Oceanic Modeling System) is a three-dimensional numerical model for ocean circulation, as it is described by Shchepetkin and McWilliams (2005). This model has been specially designed to improve the precision of simulations in regional ocean systems. The tidal data used to run the model were obtained from the global model TPXO7 (Egbert and Erofeeva, 2002), of Oregon State University, with 0.25 degrees of spatial resolution. In the present work, an space resolution of 3 km is used, with a total of 139264 mesh points (544x256) and 16 vertical levels, from surface to the seabed.
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