Wind-generated waves in Hurricane Juan

We present numerical simulations of the ocean surface waves generated by hurricane Juan in 2003 as it reached its mature stage (travelling from deep waters off Bermuda to Nova Scotia and making landfall near Halifax) using SWAN (v.40.31) nested within WAVEWATCH-III (v.2.22; denoted WW3) wave models, implemented on multiple-nested domains. As for all storm-wave simulations, spectral wave development is highly dependent on accurate simulations of storm winds during its life cycle. Due to Juan’s rapid translation speed (accelerating from 2.28 m s⁻¹ on 27 September, 1200 UTC to 20 m s⁻¹ on 29 September, 1200 UTC), an interpolation method is developed to blend observed hurricane winds with numerical weather prediction (NWP) model winds accurately. Wave model results are compared to in situ surface buoys and ADCP wave data along Juan’s track. At landfall, Juan’s maximum waves are mainly swell-dominated and peak waves lag the occurrence of the maximum winds. We explore the influence of surface waves on the wind and show that the accuracy of the wave simulation is enhanced by introducing swell and Stokes drift feedback mechanisms to modify the winds, and by limiting the peak drag coefficient under high wind conditions, in accordance with recent theoretical and experimental results.     

Recent environmental change in an upland reservoir catchment: a palaeoecological perspective

Reservoirs provide important water resources and require careful management, through ecological monitoring, to identify and mitigate changes in water quality. Long-term data on vegetation changes and the impacts of human activities on reservoir water chemistry, however, are often limited. Setting restoration targets can therefore be problematic. Palaeoenvironmental research has made little use of reservoir sediments and there is great potential for palaeoecological data to be incorporated into management planning. Diatoms and pollen were analysed in sediment cores from Venford Reservoir, southwest England, to infer pH and land-use changes, respectively, over the last century. Diatom-inferred (DI) pH indicates that reservoir pH declined from ~pH 6.0 in the early part of the record and reached a low between AD 1920 and 1940 (~pH 5.6), which was likely associated with fossil fuel combustion and acid deposition. DI-pH then increased, but values remained relatively low, even in the most recent sediments (~pH 5.7), and the magnitude of inferred pH change over time was small. Land-use changes, such as increased grazing intensity and erosion, and establishment of pine plantations, also likely influenced reservoir water chemistry changes over time. Understanding the impacts of such factors on water chemistry has implications for future catchment land-use planning, which is essential for managing water resources. The pollen record indicates a shift from heather-dominated to grass-dominated vegetation since ~AD 1935–1950, which could be related to increased grazing intensity. The palaeoecological dataset is valuable as a long-term record against which short-term monitoring datasets and future changes can be assessed.     

Wide-band feedback seismometers

The effects of feedback in seismometers are summarised and the responsivities and detectivities of various open-and closed-loop instruments are compared and discussed. It is concluded that the most satisfactory system is displacement force-feedback employing a capacitive displacement transducer.Details are given of a Willmore Mk III(a) short-period seismometer which has been converted to a wide-band force-feedback instrument by the addition of a capacitive transducer. It provides a wide-band response flat to acceleration from d.c. to 25 Hz, with a theoretical detection level of 10^?10 m s^?2$\text{Hz}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}$ and a dynamic range of 140 dB. Wide-band velocity, long-period narrow-band or short-period responses are easily obtained by filters outside the loop. The instrument has been compared with standard seismometers over a period of several months, and found to compare satisfactorily when enclosed in a small pressure vessel.     

Nonlinear wave-wave interactions and wedge waves

A tetrad mechanism for exciting long waves, for example edge waves, is described based on nonlinear resonant wave-wave interactions. In this mechanism, resonant interactions pass energy to an edge wave,from the three participating gravity waves. The estimated action flux into the edge wave can be orders of magnitude greater than the transfer fluxes derived from other competing mechanisms, such as triad interactions. Moreover, the numerical results show that the actual transfer rates into the edge wave from the three participating gravity waves are two- to three- orders of magnitude greater than bottom friction.     

The 2dF Galaxy Redshift Survey: galaxy luminosity functions per spectral type

We calculate the optical b _J luminosity function (LF) of the 2dF Galaxy Redshift Survey (2dFGRS) for different subsets defined by their spectral properties. These spectrally selected subsets are defined using a new parameter, η , which is a linear combination of the first two projections derived from a Principal Component Analysis. This parameter η identifies the average emission- and absorption-line strength in the galaxy rest frame spectrum, and hence is a useful indicator of the present star formation. We use a total of 75 000 galaxies in our calculations, chosen from a sample of high signal-to-noise ratio, low-redshift galaxies observed before 2001 January. We find that there is a systematic steepening of the faint-end slope ( α ) as one moves from passive  ( α =-0.54)  to active  ( α =-1.50)  star-forming galaxies, and that there is also a corresponding faintening of the rest frame characteristic magnitude   M *-5 log₁₀( h )  (from −19.6 to −19.2). We also show that the Schechter function provides a poor fit to the quiescent (Type 1) LF for very faint galaxies  [ M _{b J}-5 log₁₀( h )  fainter than −16.0], perhaps suggesting the presence of a significant dwarf population. The LFs presented here give a precise confirmation of the trends seen previously in a much smaller preliminary 2dFGRS sample, and in other surveys. We also present a new procedure for determining self-consistent k -corrections, and investigate possible fibre-aperture biases.     

Electrical conductivity measurements on synthetic olivines and on olivine,enstatite and diopside from Dreiser Weiher,Eifel (Germany) under defined thermodynamic activities as a function of temperature and pressure

Results of electrical conductivity measurments on synthetic olivines of the system Mg₂SiO₄Fe₂SiO₄ and on minerals of Dreiser Weiher peridotite nodule Ib-8 (Eifel, Germany) are discussed in relation to the measuring procedure and to the variation of thermodynamic parameters.The measurements were performed in solid state high-pressure vessels between 340 and 1100°C and at a pressure of 10 kbar. It is shown that for ternary olivines and for pyroxenes, the control of two further variables, like the chemical activities of the components, is needed besides temperature and pressure control. The experimental set-up for the control of chemical activities and oxygen partial pressure is shown. From the slopes of the lines of log σ against 1/T the activation energies were calculated. Though in most cases the same oxygen fugacity ?_O2 is applied, the results reveal different values for synthetic and natural samples since the chemical activities of SiO₂ are different.     

Influence of oxygen partial pressure on the Mg/Fe distribution in olivines

The dependence of Mg/Fe ordering on oxygen partial pressure in natural olivine crystals of volcanic origin has been studied by X-ray diffraction. Two natural crystals with 10% and 12% fayalite have been investigated and the atomic positions, anisotropic temperature factors, extinction coefficients and site occupancies have been refined, reaching R-values of 2.2%. After subjecting the crystals to oxygen partial pressures of 10^?16 bar and 10^?21 bar the crystals were studied again. In total six crystals were studied and the distribution coefficients K _D determined. The natural untreated crystals had K _D=1.09 and 1.06, e.g., a slight preference of Fe in (M1). p(O₂) of 10^?16 bar increased the ordering of Fe in (M1) to K _D=1.2, while p(O₂)=10^?21 bar reversed K _D to 0.8 with ordering of Fe in (M2). These experiments suggest that Mg/Fe ordering in olivines is primarily determined by the prevailing oxygen partial pressure.