Masamichi Inoue

Currents through Torres Strait

Abstract A five-month field study of the circulation in the Torres Strait was carried out. Baroclinic effects were negligible. The Arafura Sea and the Coral Sea forced a different tide on either side of Torres Strait, resulting in fluctuations of sea level difference of up to 6 m on either side of the Strait. The tidal dynamics in the Strait were controlled by a local balance between the acceleration, the sea level slope, and the bottom friction. Only 30% of the semidiurnal tidal wave was transmitted through Torres Strait. There were also fluctuations of the high-frequency sea level residuals (up to 0.8 m peak to trough) which appeared to be related to complex flows both through the Strait and across the Strait. Low-frequency sea level fluctuations were incoherent on either side of the Strait, and resulted in fluctuations of the low-frequency sea level differences on either side of the Strait of typically 0.3 m. These sea level gradients and the local wind forcing generated low-frequency current fluctuati...

Loop Current rings and the deep circulation in the Gulf of Mexico

A detailed examination of the three-dimensional circulation associated with Loop Current rings in the Gulf of Mexico has been made using the Modular Ocean Model with 15 levels in the vertical and 1/8° horizontal grid spacing. Monthly mean wind stress and a seasonal boundary condition on temperature and salinity fields are applied at the surface. The vertical shear and geostrophic transport of the Yucatan Current also vary seasonally. The upper layer seasonal circulation, and the formation, structure, and westward migration of Loop Current rings in the model compare favorably with observations. An anticyclone-cyclone pair develops in the deep layer beneath the Loop Current as a ring is forming in the eastern Gulf. The model circulation beneath the Loop Current reverses from anticyclonic to cyclonic because the anticyclone leads the pair in the deep layer as the ring separates and migrates westward in the surface layer. The deep anticyclone-cyclone pairs are guided by the bottom bathymetry as they migrate westward in tandem with the rings in the surface layer. The deep anticyclone decays more quickly than the cyclone in the western Gulf, and the cyclone dominates the deep circulation beneath the ring. Cyclonic flow in the deep Gulf of Mexico has been observed using current meters, inferred from hydrographic data, and produced in other numerical and theoretical models. Although the formation and westward migration of deep anticyclone-cyclone pairs in conjunction with rings has not been directly observed, the results of this modeling study agree with other published reports on the deep circulation in the Gulf of Mexico.

Modeling Seasonal Variability in the Wind-driven Upper-Layer Circulation in the Indo–Pacific Region

Abstract A basin-scale fine-resolution primitive equation reduced-gravity model forced by the climatological monthly wind of Hellerman and Rosenstein is used to study seasonal variability of the wind-driven upper-layer circulation in the Indo–Pacific region. The model domain is limited to the tropical Pacific Ocean and the eastern Indian Ocean. The use of the open boundary conditions allows the model to account for a net transport of mass from the Pacific to the Indian Ocean. An active eddy field is modeled east of Mindanao in the strong shear zone formed between the North Equatorial Current and the North Equatorial Countercurrent. This eddy field gives rise to the energetic shorter time scale variations in the western Pacific and appears to be responsible for considerable variability in surface currents noted previously. A distinct current bifurcation at the southern coast of New Britain in the Solomon Sea is modeled. The western branch of the resulting flow exits through Vitiaz Strait, while the eastern...

Hindcast/forecast of ENSO events based upon the redistribution of observed and model heat content in the Western Tropical Pacific, 1964-86

Anomalous sea level, anomalous observed dynamic height (0/400 db) and anomalous model dynamic height are examined at the locations of 13 island sea level stations in the tropical Pacific for each bimonth of the four year period 1979 to 1982. Starting in 1981, the anomalous dynamic height data show off-equatorial Rossby waves propagated toward the W boundary of the Pacific basin. At the W boundary, the model Rossby wave activity was found to have excited coastally trapped Kelvin-Munk waves which transmitted the anomalous dynamic height equatorward. At the equator, coastally trapped wave activity excited eastward propagating equatorial Kelvin waves, yielding a pair of anomalous peaks in dynamic height variability in the E equatorial Pacific associated with the 1982–1983 ENSO event. The evolution of the peaks in dynamic height associated with the Rossby and Kelvin wave activity reflects the redistribution of observed upper-ocean heat content in the W tropical Pacific, providing a qualitative hindcast for the 1982–1983 ENSO event.

Bimodal Distribution of Tropical Cyclogenesis in the Caribbean: Characteristics and Environmental Factors

Abstract Tropical cyclogenesis critically depends on the presence of warm water at the sea surface. For the North Atlantic basin as a whole, the tropical storm season starts in May, peaks in September, and then declines, generally following the seasonal warming and cooling of sea surface temperature. In the Caribbean, in contrast, there is a distinct bimodal distribution in the number of tropical storms formed, with peaks in June and October separated by a significant minimum in July. The timing of the observed minimum in tropical cyclogenesis appears to be related to the strengthening of the easterly trade winds over the Caribbean associated with the onset of the so-called veranillo, or midsummer drought (MSD), previously recognized over south-central Mexico, Central America, and parts of the Caribbean. It appears that the observed minimum in cyclogenesis is caused by a combination of environmental factors related to the strengthening of the easterly trade winds across the Caribbean Basin. The strengthen...

A high-resolution integrated hydrology-hydrodynamic model of the Barataria Basin system

An attempt was made to build a model that can simulate salinity variations in Barataria Basin, and can ultimately be used for managing day-to-day operation of freshwater diversion aimed to rebuild coastal wetland in the surrounding area near the Mississippi River delta. A high-resolution (O (100m)) integrated hydrology-hydrodynamic model of the Barataria Basin has been developed to simulate the local hydrological cycle over the surrounding drainage basin and hydrodynamics within the basin. A hydrological model of local runoff from the surrounding drainage basin is coupled to a two-dimensional depth-integrated hydrodynamic model of the basin. The integrated model is forced by observed tides coming from the Gulf of Mexico, local wind, rainfall and evaporation over the model domain. The model can be used to simulate salinity changes in response to a variety of climactic conditions including drought and flood. For management purposes, the integrated model can be useful in simulating salinity alterations associated with the introduction of freshwater diversions.

Coastal land loss and hypoxia: the 'outwelling' hypothesis revisited

It is generally believed that interannual variability in the areal extent of the Gulf of Mexico hypoxia is driven primarily by the magnitude of the Mississippi River freshwater and nutrient fluxes. It has recently been proposed that outwelling of carbon from deteriorating coastal wetlands into the surrounding Gulf of Mexico could be an important mechanism promoting the development of hypoxia. We used a coupled hydrology?hydrodynamics model of the Barataria estuary, a site of massive wetland loss, to calculate the fluxes of nitrogen, chlorophyll a and carbon at the estuary?ocean interface. The hydrology model calculates runoff from rainfall and evaporation data, and then feeds it into the high-resolution (100?m ? 100?m grid, 1.3 million elements), two-dimensional depth-integrated hydrodynamic model. Model results show substantial outwelling of total organic carbon (TOC, 110 ? 106?kg?yr ? 1), dissolved organic carbon (DOC, 94.3 ? 106?kg?yr ? 1), particulate organic carbon (POC, 15.7 ? 106?kg?yr ? 1) and chlorophyll a (Chl a, 0.3 ? 106?kg?yr ? 1) from the estuary to the coastal waters and an import of nitrate (N?NO3, 6.9 ? 106?kg?yr ? 1) from the nutrient-rich coastal waters into the estuary. Estuarine fluxes of TOC, DOC, POC, Chl a and N?NO3, account for 2.8%, 2.7%, 3.4%, 7.5% and 1%, respectively, of the annual fluxes carried by the lower Mississippi River. The flux of total nitrogen was not statistically significant. Overall, this study supports the conclusion of the previous modeling study (Das et al 2010 Ecol. Modeling 221 978?85), suggesting that the Barataria estuary supplies a relatively small amount of the carbon consumed in the Gulfs hypoxic zone. Importantly, our results indicate that import of nitrate from the coastal waters and its assimilation within the estuary could account for 38% and 208%, respectively, of the calculated TOC and Chl a exports, demonstrating the pervasive control of the Mississippi River on the productivity of this shelf.

Predictability of the decay of the 1982/83 El Niño

Abstract A dynamical forecast model which has been applied to the onset of the 1982/83 El Nino is applied to the decay of this event. The timing of the decay is well predicted, illustrating the flexibility of the dynamical forecast model which could handle an unusual El Nino, i.e., the 1982/83 event with significant wind changes outside a well-recognized site for usual El Nino related wind changes. The results suggest the need to include zonal winds from the entire equatorial Pacific. It appears that the dynamical forecast model based on a linear numerical model forced by ship winds can be used to forecast the timing of the onset and decay of a major El Nino. The evolution of the 1982/83 El Nino is described using the dynamical model forced by the observed wind. The equatorial Pacific Ocean response during this event is basically that to an eastward translating zonal band of westerly wind anomalies. The observed double peaks in the sea-level record in the eastern Pacific in early 1983 appear to be due to ...