Relation between the Celestial Reference System and the Terrestrial Reference System of a rigid Earth

A relation between the Celestial Reference System (CRS) and the Terrestrial Reference System is established theoretically by solving the equations of motion of a rigid Earth under the influence of the Sun and the Moon up to the second order perturbation. The solutions include not only nutation including Oppolzer terms but also the right ascension of the dynamical departure point (DP), as well as the wobble matrix.We have found that the kinematical definition of the Non-Rotating Origin NRO (for which our term is DP) given by Capitaine, Guinot and Souchay (1987) is not entirely equivalent to that included in the solutions of the equations of motion but shows perturbation, in particular when this is taken on the instantaneous equator. Besides this serious fault, we feel little merit in taking the DP as reference: (1) Unnecessary spurious mixed secular terms appear which come from the geometrical configuration that the DP leaves far and far from the ecliptic. (2) the DP moves secularly as well as oscillating with respect to space; this literally contradicts the term NRO, or is at least misleading. (3) It does not free us from the precession uncertainty to adopt DP as reference, since we cannot avoid virtual proper motions in terms of the current CRS. (4) No terms ignored hitherto are introduced, even if we take the DP properly chosen, i.e., on the equator of the celestial ephemeris pole. The transformation is only mathematical. There is no sufficient reason to take it instead of the equinox, which is observable in principle, as reference at the cost of the labor of changing all the textbooks, ephemerides, data and computer software now existing.     

Impact of mercury emissions from incineration of automobile shredder residue in Japan

Mercury emissions from the incineration of automobile shredder residues (ASRs) were investigated. Continuous monitoring of elemental and reactive gaseous Hg in flue gas was performed in lab-scale and plant-scale ASR incineration. Results of continuous monitoring agreed with those obtained using the JIS K0222 method and Ontario-Hydro method. Before cleaning by air pollutant control devices (APCDs), reactive Hg was the dominant form of that element in both lab-scale and plant-scale results. Emission factors of reactive Hg before APCDs estimated from monitoring results showed large differences between plant-scale and lab-scale emissions. The emission factor in the plant scale was more than 10 times larger than that in the lab-scale, which is explainable by the different Hg contents of ASR. Based on plant-scale monitoring at the stack, emission factors after APCDs were estimated as 0.79 mg-Hg/Mg-ASR for elemental Hg and 6.8 mg-Hg/Mg-ASR for reactive Hg. Using these emission factors, total Hg emissions from ASR incineration were estimated as 2.2 kg/a. An ASR incineration plant investigated in this study used highly effective APCDs. Consequently, these emission factors might result in underestimation of national Hg emissions from ASR incineration. Emission factors estimated from lab-scale monitoring at a fabric filter outlet side might be more appropriate. However, even if emission factors calculated from plant-scale or the lab-scale monitoring are used, estimated emissions are still less than 1.0% of total Hg emissions in Japan. Therefore, Hg emissions from ASR incineration can be evaluated as insignificant. Unless Hg contents of ASR increase extremely, ASR incineration would be a minor source of Hg atmospheric emission in Japan, even if all ASRs were incinerated.     

Sio Guyot: A complex volcanic edifice in the western Mid-Pacific Mountains

Sio Guyot, in the westernmost edge of the Mid-Pacific Mountains, is a large, complex volcanic edifice rising to more than 1200 m below sea level. The summit is divided into two flat-topped areas by a WNW-trending sediment-filled trough. Seismic reflection profiles reveal three acoustic units: an upper transparent layer (pelagic cap), a lower opaque layer (reef- and lagoon-derived sediments), and an acoustic (volcanic) basement. Free-air gravity anomalies indicate three eruptive centers or conduits within the main edifice, which apparently was constructed during late Cretaceous time on a broad basement swell or plateau that today is more than 3400 m below sea level (1500 m above regional abyssal depths).     

Seasonal and Spatial Variations of Iceberg Drift off Dronning Maud Land, Antarctica, Detected by Satellite Scatterometers

Seasonal and spatial variations of iceberg drift were studied using continuous satellite scatterometer images off Dronning Maud Land, East Antarctica. Generally, iceberg drift speed showed a westward increase to the Greenwich Meridian. Seasonal variations of the drift speed were high in autumn—early winter and low in spring, and their magnitudes also increased westward. Seasonal variations of the drift speed were significantly correlated with variations of sea levels at Syowa and Mawson Stations, and hence qualitatively consistent with geostrophic current variations. Thus, the scatterometer data are demonstrated to be useful in monitoring iceberg trajectory and oceanic current variations. This revised version was published online in July 2006 with corrections to the Cover Date.     

Convection induced by cooling at one side wall in two-dimensional non-rotating fluid —applicability to the deep Pacific circulation—

In recognition that similarity in the density balance leads to resemblance in circulation between the two-dimensional non-rotating and three-dimensional rotating systems which have similar density stratification, we investigate convection induced by cooling at one side wall and heating at the sea surface by using a two-dimensional non-rotating model as idealized representation for the deep Pacific circulation. In the model, various vertical profiles are taken for the side wall cooling, which are assumed to correspond to the density structure of the Anatarctic Circumpolar Current. In a small diffusivity range, two important features are found to be robust against change in the vertical profile of the side wall cooling. One is that the density stratification is horizontally almost uniform. The other is that the balance in the density equation between the vertical advection and the vertical diffusion holds in the interior. Consequently, the vertical density balance, together with the equation of continuity, determines the circulation pattern for the prescribed vertical profile of the side wall cooling. The multi-layered meridional flow, which is expected to exist in the deep Pacific, is shown to form for certain vertical profiles of the side wall cooling.     

Branching and joining of the Tsushima Current around the Oki Islands

We discussed the branching and joining of the Tsushima Current around the Oki Islands, based on ADCP and CTD measurements carried out in June 1990 by the quadrireciprocal method (Katoh, 1988). The volume transport of the northeastward current northwest of the Izumo Coast was about 2 Sv. The triple-branch structure of the Tsushima Current was obscure there. This northeastward current divided into the eastward and northward currents, with volume transports of 0.5 Sv and 1.5 Sv, respectively, at the west entrance of the Oki Strait. Most of the first branch of the Tsushima Current seemed to be separated again from the other confluent branches and to pass through the Oki Strait as this eastward current. The northward current was composed of the second and the third branches of the Tsushima Current. It detoured the Oki Islands, and almost all of it returned south to the Tajima Coast. In the vicinity of the Tajima Coast, the eastward current was abruptly strengthened through the confluence of the southward one which was originated from the northward current west of the Oki Islands. This showed that the first branch finally joined the compound of the second and the third branches detouring the Oki Islands. Between the Oki Strait and the Tajima Coast, the two-layer structure of currents was clearly found.     

Numerical study of the summer temperature decrease induced by the enhancement of estuarine circulation in Fukuoka Bay

The Princeton Ocean Model with realistic bottom topography has been used to investigate the summer temperature decrease in the past 25 years in Fukuoka Bay. The vertical mixing of the model is expressed by a scheme that effectively includes the influences of interannual variations of tidal currents and wind. The results show that the historical temperature decrease in summer has been caused by tidal currents and wind weakening in the past 25 years in Fukuoka Bay. The weakening of tidal currents and wind gives rise to weakening of the vertical mixing, and to enhancement of the estuarine circulation in the bay. The enhancement of the estuarine circulation activates the inflow of open-ocean water toward Fukuoka Bay. Coastal water in summer has therefore tended to be colder and more saline in the past 25 years. This interannual variation in coastal waters is called “open-oceanization” in this study. On the basis of the numerical model, it is anticipated that the temperature will decrease by 0.2°C in the next 25 years in Fukuoka Bay if the tide and wind weaken persistently as in the present bay.     

Bachelor-modon type eddies and isolated eddies near the coast on anf-plane

The behavior of isolated meso-scale eddies near the coastal boundary is studied by numerical experiments based on the quasi-geostrophic equation in a basin on an f-plane. First, Bachelor-modon type eddies are investigated as an idealized model of isolated eddies close to the wall. The first-mode Bachelor-modon type eddy is found to be robust enough to recover its original form even after it turns a corner of the basin. In contrast, the second mode is unstable; it tends to move away from the wall and finally splits into two eddies proceeding in opposite directions along the wall. An initially Gaussian eddy a little distant from the boundary interacts with a Bachelor-modon type eddy translating along the boundary, sometimes resulting in vortex merging and pairing just as in the head-on collision of two modons on a beta-plane. It is found that an initially Gaussian eddy located moderately close to the coast rapidly settles down to a steadily translating eddy, which can be approximated remarkably well by a first-mode Bachelor-modon type eddy not only in appearance but also in translation velocity within an error of about 20%.