Tropical Basin Research Articles

Estimating Amplitudes of Fifth-Order Sea Level Fluctuations from Peritidal Through Basinal Carbonate Deposits, Lower Mississippian, Wyoming-Montana: ABSTRACT

Three types of 1-10-m upward-shallowing cycles are observed in the Lower Mississippian Lodgepole and lower Madison formations of Wyoming and Montana. Typical peritidal cycles have pellet grainstone bases overlain by algal laminites, which are rarely capped by paleosol/regolith horizons. Shallow ramp cycles have burrowed pellet-skeletal wackestone bases overlain by cross-bedded ooid/crinoid grainstone caps. Deep ramp cycles are characterized by sub-wave base limestone/argillite, storm-deposited limestone, overlain by hummocky stratified grainstone caps. Average cycle periods range from 17-155 k.y. This, rhythmically bedded limestone/argillite deposits of basinal facies do not contain shallowing-upward cycles, but do contain 2-4 k.y. limestone/argillite rhythms. These sub-wave base deposit are associated with Waulsortian-type mud mounds which have >50 m synoptic relief. This relief provides minimum water depth estimates for the deposits, and implies storm-wave base was less than 50 m. Two-dimensional computer modeling of cyclic platform through noncyclic basinal deposits allows for bracketing of fifth-order sea level fluctuation amplitudes, thought responsible for cycle formation. Computer models using fifth-order amplitudes less than 20 m do not produce cycles on the deep ramp (assuming a 25-30 m storm-wave base). Amplitudes >30 m produce water depths on the inner ramp that are too deep, and disconformities extend too far into themore » basin. The absence of meter-scale cycles in the basin suggests water depths were too great to record the effects of sea level oscillations occurring on the platform, or climatic fluctuation, associated with glacio-eustatic sea level oscillations, were not sufficient to affect hemipelagic depositional patterns in the tropical basin environment.« less

Some marine geochemical aspects of kau bay: A tropical fjord-like anoxic basin

Some marine geochemical aspects of kau bay: A tropical fjord-like anoxic basin

Vacillations in a Coupled Ocean–Atmosphere Model

Results are presented from a 35-year integration of a coupled ocean-atmosphere model. Both ocean and atmosphere are two-level, nonlinear primitive equation models. The global atmospheric model is forced by a steady, zonally symmetric Newtonian heating. The ocean model is solved in a rectangular tropical basin. Heat fluxes between ocean and atmosphere are linear in air-sea temperature differences, and the interfacial stress is proportional to lower-level atmospheric winds. The coupled models produce ENSO-like variability on time scales of 3 to 5 years. Since there is no external time-dependent forcing, these are self-sustained vacillations of the nonlinear system. It is argued that the energetics of the vacillations is that of unstable coupled modes and that the time scale is crucially dependent on the effects of ocean waves propagating in a closed basin.

Principal Modes of Atmospheric Variability in Model Atmospheres with and without Anomalous Sea Surface Temperature Forcing in the Tropical Pacific

Abstract Principal modes of low-frequency atmospheric variability and the influence of sea surface temperature anomalies on such modes are investigated by examining the output from two general circulation model experiments. In the first experiment (the “control run”), all boundary forcings were constrained to evolve through 15 identical annual cycles. In the second experiment (the “SST runs”), the sea surface temperature conditions in the tropical Pacific Basin were prescribed to follow the actual month-to-month changes observed during the period 1962–76, which encompasses several El Nino events. The analysis tools employed here include empirical orthogonal functions, teleconnections and composite charts. Two prominent modes of variability have been identified in the wintertime Northern Hemisphere eddy streamfunction of the SST experiment. The first mode bears a strong spatial resemblance to the observed characteristic circulation pattern over the North Pacific–North American sector. It is demonstrated th...

Suspended sediment production in a suburban tropical basin (Lubumbashi, Zaire)

ABSTRACT A study of suspended sediment transport in the 8.5 km2 River Lubwe catchment was carried out during the wet season 1983–1984. The suspended sediment yield was estimated using the suspended-sediment rating curve technique and detailed observations of 10 runoff events. The River Lubwe is characterized by periodic high magnitude floods, during which the bulk of the load is transported. The total suspended load for the hydrological year 1983–1984 is estimated at 108 t, representing a sediment yield of 12.7 t km−2 year−1.

Tropical Cyclone Forecast Errors and the Multimodal Bivariate Normal Distribution

Abstract This study focuses on the use of the bivariate normal distribution model to describe spatial distributions of tropical cyclone forecast errors. In this connection, it is found that forecast errors from the entire Atlantic tropical cyclone basin (Gulf of Mexico, Caribbean and North Atlantic) are multimodal and the fitting of these collective data to the usual unimodal bivariate normal distribution will be judged invalid by the usual statistical goodness-of-fit tests. While this is a recognized pitfall in classical statistics, it is often overlooked in meteorological application. The isolation of the clusters (components) and their statistical characteristics permit the issuance of forecast positions accompanied by more representative error ellipses. The study continues with a bivariate clustering analysis of a set of 979 tropical cyclone 24 h forecast errors for the Gulf of Mexico, Caribbean and North Atlantic. These errors were collected from the entire tropical cyclone basin without regard to se...

Trends in Forecasting the Tracks of Atlantic Tropical Cyclones

Errors in official 24 h forecasts of tropical cyclone motion over the Atlantic for the period 1954–80 are examined for the purpose of isolating any long-term trends in the data. It is shown that the magnitude of a forecast error has been primarily a function of forecast difficulty, i.e., how well storm motion adheres to climatology and persistence. Another contributing factor (in the negative partial correlation sense) is shown to be the storm's initial longitude—a measure of the adequacy of initial analyses. After adjusting 24 h forecast error for these two factors, it is shown that errors have declined gradually over the 27 years from near 124 n mi in 1954 to near 107 n mi in 1980—a 13.7% reduction. Most of the decline since the mid-1960s is attributed to better specification of initial storm motion through satellite imagery. Although the decline of forecast errors is encouraging, a disturbing aspect is that the rate of decline appears to have slowed in recent years. This leveling-off is attributed to a loss in the ability to assess environmental steering through mid-level analysis deficiencies that have been compounding since 1965 and, more recently, to a plateauing in the ability to obtain still better storm initial-motion vectors. To assure a continued monotonic decline in 24 h forecast errors, mid-level initial analysis (500 mb) over the essentially data-void tropical cyclone basins must be improved.

A storm rainfall pattern above the Central African Plateau / Vue d'ensemble de la répartition de pluie sur le Plateau Central Africain

Abstract The spatial and temporal distribution of tropical rainfall above a small tropical basin on the Central African Plateau was studied by using a dense network of rainfall recorders. The results indicate a high variability of the rainfall pattern within a small area of less than 5 km2. Formulae for the calculation of the rainfall rate and depth-area-duration relationship are presented for the purpose of network construction and engineering design in tropical Africa.

TESTING THE EFFICIENCY OF ALGORITHMS AND STRATEGIES FOR AUTOMATIC CALIBRATION OF RAINFALL-RUNOFF MODELS / Essais de l'efficacité des algorithms et des stratégies pour l'étalonnage des modèles pluie-écoulement

Abstract This paper examines the efficiency of various methods of calibrating a rainfall-runoff model. The model used is a 12 parameter version of the Boughton model which has been developed for large tropical basins. Attempts were made to improve the efficiency of calibration in three areas: selection of the best nonlinear programming algorithms; reduction of the number of objective functions required for calibration; and simplification of the model structure. The best algorithms were found to be those of Powell, Rosenbrock, and the simplex method of Nelder and Mead. The Davidon method did not perform well. The number of objective function evaluations can be reduced by performing a sensitivity analysis on the model and selecting a small group of parameters which are not interdependent and which the objective function is sensitive to. This may yield a substantial reduction in the computer time required to calibrate the model. Simplification of the model structure can also yield substantial savings, especi...

Organic and inorganic geochemistry of some coastal plain rivers of the southeastern United States

In a comprehensive study of the distribution of organic and inorganic constituents in natural waters, the chemical compositions of several rivers flowing through the Coastal Plain of southeast Georgia (the Satilla River, in particular) have been investigated. These streams are generally characterized by low suspended load, low ionic strength, low pH values, and a predominance of organic over inorganic constituents. The dominance of sodium and chloride among inorganic ions indicates that rainfall is a major factor in determining the distribution of major elements in these waters. The low pH values and the relatively high concentrations of iron and aluminum appear to result from the high concentrations of organic matter. Chemical analysis (total acidity, carboxyl groups, amino acid residues, and CHN analysis) and spectroscopic analysis (i.r. and NMR) indicate that river water organic matter is chemically similar to soil fulvic acids. The dominance of organic matter over inorganic constituents and the resultant low pH values of these waters are in direct contrast with the chemical compositions of most of the rivers of the world which have been previously studied. Many large tributaries draining from the low relief tropical basins of the Amazon and other tropical rivers are expected to show similar characteristics; however, none of these has been studied extensively.