Análisis de mareas por el método de la descomposición en armonicos

En este artículo se presenta la aplicación del software Gnotide desarrollado para la descomposición de señales de marea en sus constituyentes armónicos, se presenta de manera condensada las ecuaciones que gobiernan dicho fenómeno. Del software desarrollado se presentan los módulos que componen la herramienta de análisis: Módulo de análisis de calidad de la información (“open”), el módulo de graficar la serie (“plot”), el módulo de la transformada de Fourier ( “Fourier”), el módulo de la transformada de onditas (“wavelet”), el módulo de ajuste mínimo cuadrático (“fit”), y el módulo de predicción (“predict”). Se presenta una aplicación a una señal de mareas medida en Cartagena de Indias

Plan de ordenación y manejo de la cuenca del río Aburra -Antioquia, Colombia.

La formulación del POMCA, se desarrolló siguiendo la metodología propuesta en la Guía técnico científica desarrolla por el IDEAM, la cual comprende las fases de Aprestamiento, Diagnóstico, Prospectiva, Formulación, Seguimiento y Control. La conexión entre la situación ambiental actual y los escenarios de futuro se construye en la fase de Formulación por medio de Lineamientos de política, líneas estratégicas, Programas y Proyectos, los cuales serán implementados y vigilados por las autoridades ambientales

Implicaciones metodológicas e inconsistencias de la Tercera Comunicación Nacional sobre Cambio Climático de Colombia

Las Comunicaciones Nacionales sobre Cambio Climático (CNCC) son un mecanismo para que los países informen sus avances en mitigación y adaptación, y constituyen uno de los elementos de base para la política sobre cambio climático a escala nacional. Colombia ha emitido tres CNCC. La tercera plantea un escenario que considera las proyecciones de diversos modelos incluidos en la quinta fase del Proyecto de Comparación de Modelos Acoplados (Coupled Model Intercomparison Project, CMIP), el cual se estima como el promedio de las proyecciones correspondientes a las cuatro trayectorias de concentración representativa (Representative Concentration Pathways,RCP) presentadas en el quinto reporte de evaluación del Panel Intergubernamental sobre Cambio Climático. Cada una de estas RCP representa una trayectoria de concentración de gases de efecto invernadero (GEI) para un escenario particular de crecimiento poblacional, económico y tecnológico que conduce a una posible trayectoria de evolución del sistema climático. En este estudio se comparan las proyecciones presentadas en la Tercera CNCC con las obtenidas directamente de los modelos empleados. Nuestros resultados demuestran que al utilizarse un promedio de RCP se pierden escenarios alternos que podrían ser importantes a la hora de considerar posibles futuros diferentes y anulan la utilidad de plantear diversas trayectorias de emisiones de GEI. Más aun, una comparación entre la Segunda y la Tercera CNCC muestra proyecciones de precipitación opuestas para diferentes regiones del país, lo cual es de particular importancia, pues el escenario de cambio climático planteado en la Tercera CNCC sirve de referencia para la toma de decisiones en materia de cambio climático a nivel nacional

Enhanced vertical mixing within mesoscale eddies due to high frequency winds in the south China sea

The South China Sea is a marginal basin with a complex circulation influenced by the East Asian Monsoon, river discharge and intricate bathymetry. As a result, both the mesoscale eddy field and the near-inertial energy distribution display large spatial variability and they strongly influence the oceanic transport and mixing. With an ensemble of numerical integrations using a regional ocean model, this work investigates how the temporal resolution of the atmospheric forcing fields modifies the horizontal and vertical velocity patterns and impacts the transport properties in the basin. The response of the mesoscale circulation in the South China Sea is investigated under three different forcing conditions: monthly, daily and six-hourly momentum and heat fluxes. While the horizontal circulation does not display significant differences, the representation of the vertical velocity field displays high sensitivity to the frequency of the wind forcing. If the wind field contains energy at the inertial frequency or higher (daily and six-hourly cases), then Vortex Rossby waves and near inertial waves are excited as ageostrophic expression of the vigorous eddy field. Those waves dominate the vertical velocity field in the mixed layer (vortex Rossby waves) and below the first hundred meters (near inertial waves) and they are responsible for the differences in the vertical transport properties under the various forcing fields as quantified by frequency spectra, vertical velocity profiles and vertical dispersion of Lagrangian tracers.MSCommittee Chair: Bracco, Annalisa; Committee Member: Deng, Yi; Committee Member: Emanuele Di Lorenz

Mesoscale variability in the Gulf of Mexico, its impact and predictability

The circulation of the Gulf of Mexico is controlled by presence of large mesoscale structures (10-500 km). We investigate its variability and predictability from interannual to intraseasonal time scales, and the dynamical interactions between physical circulation and biological productivity. We do so by analyzing an ensemble of numerical integrations using the Regional Ocean Modeling System and hydrographic and biogeochemistry observations collected during summer field campaigns in 2010, 2011, and 2012. First, we explore the potential relationships and linkages between Mississippi-Atchafalaya River runoff, nutrient loads, and ocean dynamics from our field data. A negative correlation between nutrient concentration and salinity was confirmed at the surface and in the upper 60m of the water column for nitrite, nitrate, phosphate and silicate. No major changes in the nutrient concentrations were found between our data and previous measurements from twenty years ago. The biological activity in the stations sampled (northern Gulf) is nitrogen limited in 79% of them and phosphorus limited in 8%. Besides the direct input of nutrients from river discharges, the distribution of nutrients in intermediate and high salinity waters in the euphotic layer is influenced by dynamical processes at the ocean mesoscales such as eddies, coastal upwelling events and Loop Current (LC) intrusions. Then, using an ensemble of four model integrations we investigate how mesoscale motions dominate the variability of the Gulf of Mexico circulation both at the surface and in deep waters on intraseasonal time scales. We focus on its predictability by exploring the impact of small variations in the initial conditions and the role of the boundary conditions in the circulation evolution. In all runs, the model provides a good representation of the mean circulation features. However, the shedding of the Loop Current Eddies (LCE) differs in each run considered, and our analysis shows that the detachment of the LCE is a stochastic process. We show that the interannual variability at the model boundaries affects the representation of the LC strength and of the Yucatan Channel transport. On the other hand, the circulation in the LATEX Shelf, TAVE Shelf, and Bay of Campeche is insensitive to the details of the model boundaries, is not affected by the LC, but depends only on the wind variability, and it is therefore predictable if the atmospheric conditions are known. On the contrary, the circulation in the central basin is affected by the LC extension and by the Rings, and dominated by mesoscale features. In most of the basin, mesoscale features are coherent in the top ~ 1000 m of the water column, and below it, but not correlated between the surface and the deep layer. Coherency throughout the whole water column is attributed to particular topographic features such as the south-west corner of the Sigsbee Deep. The chaotic behavior associated with the propagation of the LCE and the elevated mesoscale activity restricts the predictability of the system at intra-seasonal scales to the coastal areas. In consequence, assimilation of continuous in-situ measurements is necessary to insure good hindcasts and forecasts at surface and below 1000 m depth. Finally, since mesoscale activity is key to understand the horizontal and vertical dynamics in the Gulf, we further analyze the model representation of mesoscale circulation under low (monthly) and high (6 hourly) frequency atmospheric forcing. The temporal scale variation from monthly to 6-hourly in the wind forcing impacts the timing of horizontal dynamics, but not the strength. However, high frequency winds impact the model representation of vertical transport that increases as the temporal resolution of the forcing increases. Vertical velocities in the simulation forced by 6-hourly winds are ten times greater than the one obtained using monthly averaged winds. The energy injected by the winds into the ocean is transported in the water column by mesoscale eddies and near-inertial oscillations. If the forcing used by the model does not resolve the inertial frequency (1.4 days in the Gulf), then vertical transport processes are underestimated. Those processes are particularly important for the model representation of biological activity in the ocean upper layers, since they contribute to the input of nutrients into the euphotic zone.Ph.D

Mixing mechanisms at the strongly-stratified Magdalena River's estuary and plume

International audienceThis study analyzed the hydrodynamic structure of the estuary and plume of a large, tropical, and strongly-stratified river, the Magdalena. The Magdalena River is the largest source of fresh water and sediment of the Caribbean Sea and drastically impacts the morphodynamics and ecosystems along the Colombian coast. The analyses are based on the results of a calibrated and validated numerical model. Three scenarios of low, mid, and high freshwater discharge were analyzed to consider the seasonal variability of the mixing processes. The relative importance of three mixing mechanisms in the system is investigated, and the estuary and plume are subdivided into sectors depending on the dominant hydrodynamic processes at each sector. The results show that mixing in this system is mainly controlled by turbulence at the pycnocline, especially at the lift-off point in the transition between the estuary and the plume's near-field. A hydraulic jump occurs in the transition between the near- and mid-fields of the plume, but the mixing produced here is comparatively low since the plume has been mostly diluted already in the estuary and the near-field. During low and mid discharge scenarios, saline intrusion in the river channel forms a strongly stratified estuary where bottom propagated turbulence generates instabilities producing minor mixing. Meanwhile, the saltwater is flushed out of the river during the high discharge scenario, and pycnocline instabilities produce mixing at least one order of magnitude larger than during low discharge conditions. Coriolis acceleration does not seem to be a relevant driver of the plume behavior, despite the larger extension of the plume during high discharges, given the low latitude of the system

Modelación de tsunamis en la costa pacífica colombiana: caso Bahía de Tumaco.

Los tsunamis son fenómenos naturales que se desarrollan en el océano y afectan las zonas costeras a través de diferentes manifestaciones como inundación, modificaciones geomorfológicas de la costa y del lecho marino. Las costas del Pacífico colombiano han sido afectado de manera significativa en cuatro oportunidades en el último siglo por este tipo de fenómeno. Ahora, una de las principales responsabilidades de los organismos de socorro y de quienes planean el territorio en esta porción del país es el conocer claramente la amenazas a la que están expuestas las comunidades. Mediante la modelación matemática de estos fenómenos, se pueden evaluar la inundación producida por un tsunami para diferentes eventos generadores. Adicionalmente, se pueden determinar aspectos que inciden en una correcta planificación del territorio como lo son la posición geográfica más desfavorable de las comunidades asentadas en la zona de influencia del tsunami y el tiempo de arribo de las ondas de tsunami. En este artículo se presenta la metodología y la aplicación de un modelo matemático para la simulación de ondas de tsunami con aplicación a la Bahía de Tumaco. Se presentan los criterios utilizados para la escogencia del sismo generador de tsunami, la escogencia de la marea relevante y los resultados de la simulación en mapas de inundación y de campo de velocidades de la onda de tsunami

Potential Connectivity of Coldwater Black Coral Communities in the Northern Gulf of Mexico

<div><p>The black coral <i>Leiopathes glaberrima</i> is a foundation species of deep-sea benthic communities but little is known of the longevity of its larvae and the timing of spawning because it inhabits environments deeper than 50 m that are logistically challenging to observe. Here, the potential connectivity of <i>L</i>. <i>glaberrima</i> in the northern Gulf of Mexico was investigated using a genetic and a physical dispersal model. The genetic analysis focused on data collected at four sites distributed to the east and west of Mississippi Canyon, provided information integrated over many (~10,000) generations and revealed low but detectable realized connectivity. The physical dispersal model simulated the circulation in the northern Gulf at a 1km horizontal resolution with transport-tracking capabilities; virtual larvae were deployed 12 times over the course of 3 years and followed over intervals of 40 days. Connectivity between sites to the east and west of the canyon was hampered by the complex bathymetry, by differences in mean circulation to the east and west of the Mississippi Canyon, and by flow instabilities at scales of a few kilometers. Further, the interannual variability of the flow field surpassed seasonal changes. Together, these results suggest that a) dispersal among sites is limited, b) any recovery in the event of a large perturbation will depend on local larvae produced by surviving individuals, and c) a competency period longer than a month is required for the simulated potential connectivity to match the connectivity from multi-locus genetic data under the hypothesis that connectivity has not changed significantly over the past 10,000 generations.</p></div