Statistical study on the local equilibrium between wind and wind waves by using data from ocean data buoy stations

The local equilibrium between the wind and wind waves, which is defined by a range of the coefficient of the 3/2-power law between the non-dimensional significant wave height and period, is statistically investigated by using wind and wave data obtained at four ocean data buoy stations in the seas near Japan. The friction velocity is calculated from the wind speed measured at one height together with the significant wave period by using formulas of the wave dependent drag coefficient proposed by Tobaet al. (1990). The data for small waves or for weak winds indicate that the waves do not satisfy the criterion for the local equilibrium, because they may be affected by changing winds or remotely generated swells. In the seas near Japan, the data which satisfy the local equilibrium are about 6% through a year. Otherwise swells are dominant in most situations. Changing winds also cause deviations from the local equilibrium. The degree of satisfaction of the local equilibrium can be classified by ranges of the significant wave height. As the significant wave height exceeds 4 m, the local equilibrium is more frequently satisfied.     

In situ measurement of incoming solar radiation by voluntary ships in the western Pacific

We have been performingin situ measurement of downward short wave radiation (solar radiation) in the western Pacific Ocean in cooperation with voluntary ships since autumn 1990 in order to obtain much more precise knowledge of downward short wave radiation at the sea's surface than before. Preliminary result of the observation from autumn 1990 through spring 1992 is shown in this paper. The comparison of observed daily mean downward short wave radiation with that estimated from observed cloudiness by using Reed (1977) formula is also presented to show the necessity ofin situ measurement in the study of the downward short wave radiation at the sea's surface.     

Comparison of sea surface heights observed by TOPEX altimeter with sea level data at Chichijima

The sea surface heights (SSHs) observed by the TOPEX altimeter are compared with tide gauge data at Chichijima in Ogasawara (Bonin) Islands and hydrographic data taken around the islands, in order to quantitatively verify the altimeter observations and oceanic tide corrections by three tide models proposed by Cartwright and Ray (1991), Rayet al. (1994), and Maet al. (1994). First, performance of the new tide models is assessed by comparing tidal variations consisting of diurnal and semi-diurnal constituents with the tide gauge data at Chichijima. The tide model proposed by Rayet al. gives the smallest root-mean-squared (rms) difference of 2.61 cm. Errors in amplitude and phase in each tide model are evaluated by spectral analysis. The TOPEX SSHs corrected by the tide models are compared with sea level data at Chichijima. A long-term variation of a period of about 1 year is found in the residual between the SSHs and the Chichijima sea levels. This variation is also found in the difference between the dynamic height anomalies calculated from hydrographic data around the island and the Chichijima sea levels. By subtracting the long-term variation, the rms difference between the TOPEX SSHs and the Chichijima sea levels is reduced to about 4 cm and the slope of the regression line is improved to unity. The residual shows variations related to aliasing caused by incompleteness of the ocean tide correction with the repeat cycle of the altimeter observation.     

Trajectory of Mesoscale Eddies in the Kuroshio Recirculation Region

Trajectories of mesoscale eddies in the Kuroshio recirculation region were investigated by using sea surface height (SSH) anomaly observed by the TOPEX/POSEIDON and ERS altimeters. Cyclonic and anticyclonic eddies have been traced on maps of the filtered SSH anomaly fields composed from the altimeter observations every ten days. Both the cyclonic and anticyclonic eddies propagate westward in the Kuroshio recirculation region from a region south of the Kuroshio Extension. The propagation speed of these eddies has been estimated as about 7 cm s⁻¹, which is much faster than the phase speed theoretically estimated for the baroclinic first-mode Rossby wave in the study area. It was also found that in the Izu-Ogasawara Ridge region, most of eddies pass through the gap between the Hachijojima Island and Ogasawara (Bonin) Islands, and some of the eddies decay around the Izu-Ogasawara Ridge. It seems that the trajectory of the eddies is crucially affected by the bottom topography. In the region south of Shikoku and east of Kyushu, some of the eddies coalesce with the Kuroshio. It is also suggested that this coalescence may trigger the path variation of the Kuroshio in the sea south of Japan. This revised version was published online in August 2006 with corrections to the Cover Date.     

Statistical properties of microwave backscattering from laboratory wind-wave surfaces

The microwave backscattering from wind-wave surfaces is observed in a windwave tunnel under various conditions of the wind and wind waves, and its statistical features are investigated. The dependence of the backscattered power on the wind speed and the incident angle shows similar features to those predicted by models proposed previously. However, the dependence of the backscattered power on the incident angles also corresponds to the asymmetrical feature of the wind-wave surfaces with respect to the wind direction. The spectral analyses of time series of the backscattered intensity show that the propagating speed of fine structures of the wind-wave surface contributing to the backscattering at large incident angles does not coincide with the phase speed of the freely propagating Braggwaves. Atupwind incidence, the surface structures of wind waves contributing to the backscattering propagates with the dominant waves at their phase speed. This result is inconsistent with the two-scale model in which the Bragg waves are simply superimposed on longer waves, but is consistent with the results of optical observation by Ebuchiet al. (1987). At downwind incidence, the propagating speed is slower than the phase speed of the dominant waves.     

The transition zone chlorophyll front, a dynamic global feature defining migration and forage habitat for marine resources

Pelagic ecosystem dynamics on all temporal scales may be driven by the dynamics of very specialized oceanic habitats. One such habitat is the basin-wide chlorophyll front located at the boundary between the low chlorophyll subtropical gyres and the high chlorophyll subarctic gyres. Global satellite maps of surface chlorophyll clearly show this feature in all oceans. In the North Pacific, the front is over 8000 km long and seasonally migrates north and south about 1000 km. In the winter this front is located at about 30–35°N latitude and in the summer at about 40–45°N. It is a zone of surface convergence where cool, vertically mixed, high chlorophyll, surface water on the north side sinks beneath warm, stratified, low chlorophyll water on the south side. Satellite telemetry data on movements of loggerhead turtles and detailed fisheries data for albacore tuna show that both apex predators travel along this front as they migrate across the North Pacific. The front is easily monitored with ocean color satellite remote sensing. A change in the position of the TZCF between 1997 and 1998 appears to have altered the spatial distribution of loggerhead turtles. The position and dynamics of the front varied substantially between the 1998 El Niño and the 1999 La Niña. For example, from May to July 1999 the transition zone chlorophyll front (TZCF) remained between about 35°N and 40°N latitude showing very little meandering, whereas in 1998, during the same period, the TZCF exhibited considerable meandering and greater monthly latitudinal movement. Catch rates for albacore were considerably higher in 1998 than in 1999, and we hypothesize that a meandering TZCF creates regions of convergence, which enhances the foraging habitat for apex predators along the front.     

Farm income,inequality, and poverty among farm families of a flood-prone area in Bangladesh: climate change vulnerability assessment

GeoJournal - This paper examines the farm income differences, income inequality of farm households, parameters of income variability that ascertain vulnerability levels, and cost-income variability...     

Effect of translate speed of typhoon on wind waves

Natural Hazards - Quantitative assessments on the effect of translate speed of typhoons on wind waves were carried out. A WRF-SWAN coupled model that used observed meteorological data was applied...