A recently introduced tool for the analysis of turbulence, wavelet bicoherence [B. Ph. van Milligen, C. Hidalgo and E. Sánchez, Phys. Rev. Lett. 16 (1995) 395], is investigated. It is capable of detecting phase coupling-nonlinear interactions of the lowest (quadratic) orderwith time resolution. To demonstrate its potential, it is applied to numerical models of chaos and turbulence and to real measurements. It detected the coupling interaction between two coupled van der Pol oscillators. When applied to a model of drift wave turbulence relevant to plasma physics, it detected a highly localized coherent structure. Analyzing reflectometry measurements made in fusion plasmas, it detected temporal intermittency and a strong increase in nonlinear phase coupling coinciding with the L/H (Low-to-High confinement mode) transition.

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Abstract. In the Large Helical Device (LHD), the volume averaged beta value <β dia > of 5 %, which is the highest value in all of heliotron/stellarators and relevant to the reactor requirement, was achieved by optimizing the magnetic configuration from the viewpoint of magneto-hydrodynamic (MHD) characteristics, transport and heating efficiency of the neutral beam. This beta value was instantaneously obtained by pellet injection and maintained for more than 10τ E , whereas the steady state plasma with a maximum <β dia > of 4.8 % was sustained for 85τ E by the gas-puff fueling. While it is predicted theoretically that stochastization of the peripheral magnetic field structure develops with an increment of <β dia >, no serious degradation of the global confinement has been observed in the present <β dia > range. The several low-order MHD activities located in the periphery were enhanced with the beta value and sometimes affect the local profiles. The amplitude of the mode in the periphery strongly depends on the magnetic Reynolds number, which is close to that of the growth rate and/or the radial mode width of the resistive interchange instability.

Particulate organic carbon flux from the shelf to oceanic waters during upwelling between 19øN and 25øN off Mauritania has been analyzed using coastal zone color scanner (CZCS) imagery. Biomass in the giant filament has been estimated using surface pigment concentration registered by CZCS during time series in December 1983, March 1984, and October 1984. Evidence for active phytoplankton growth in offshore waters is presented. Formatron of the giant filament seems to be favored by the combination of a number of factors perhaps unique to the Mauritanian shelf. The large-scale circulation patterns promote offshore advection,• and the typically long period of wind forcing can move the upwelling center to the shelf break area, thus causing maximal phytoplankton growth rate to be achieved in oceanic waters. The relatively high pigment concentrations registered by CZCS in oceanic waters suggest that nutrients have not been depleted on the shelf and that in situ growth is occurring in deep waters. We have used a baroclinic, hydrodynamic model to estimate cross-slope flux of particulate organic carbon at the 200-m isobath and derive a mean value of about 1 x 105 g C s -1 during each of the CZCS time series. INTRODUCTION Biological export of carbon fixed during photosynthesis on continental shelves has been suggested as a major sink for the global carbon cycle [Deuser, 1979; Walsh et al., 1981; Walsh, 1983, 1989] although the general applicability of this hypothesis has been questioned [Rowe et al., 1986; Falkowski et al., 1988]. Compared with other continental shelf ecosystems, upwelling zones are distinguished by a high input of "new" nutrients and subsequent relatively high fertility. Because of this high fertility the quantity of organic material that can be exported from upwelling areas through loss to shelf sediments [D. J. ,Smith et al., 1983] or adjacent deep waters, or as a fishery yield, is 10 to 100 times higher than other ecosystems can support [Barber and Smith, 1981]. Major coastal upwelling zones occur along eastern oceanic boundaries where large-scale weather patterns produce consistent longshore wind stress inducing Ekman transport of surface waters offshore. The cooler, usually nutrient-rich oceanic waters which are upwelled onto the continental shelf to replace the surface waters promote high local primary production. In contrast to other coastal and oceanic ecosystems, which may be limited to a single major productivity event per year, the period and rate of primarYproduction are significantly greater in upwelling zones. Continental shelves where upwelling occurs are thus potentially important sites for conversion of dissolved inorganic carbon (in the newly upwelled waters as well as "old" shelf waters) to particulate organic form and export from the water column either to the shelf sediment, continental slope, or, by advection and settling processes, beneath the ocean thermocline [Wollast, 1990; McClain et al., 1986]. This last pathway, the so called biological pump, may be critical to the dynamics of...