Vertical motion of the thermocline, nitracline and chlorophyll maximum layers in relation to currents on the Southern California Shelf

A continuous four-day time series of nitrate concentration, temperature, chlorophyll fluorescence, and currents, sampled at fixed depths, revealed that distributions of temperature and nitrate could be accounted for by vertical motions in the water column associated with the semidiurnal internal tide and internal waves. A probable mixing event was observed: the transport of nitrate into the surface-layer associated with shear instabilities generated by internal waves. On temporal scales of less than a few hours, the variation of chlorophyll fluorescence could also be explained by vertical advection. However, on longer scales, swimming behavior of the phytoplankton assemblage (dominated by Ceratium spp.), along with vertical motions in the water column, appears to account for the vertical distribution of chlorophyll. These results indicate that the nitracline maintains a stable relationship with the density structure of the water column on a scale of days, whereas the subsurface chlorophyll maximum can change significantly over several hours

Observations and modeling of coastal internal waves driven by a diurnal sea breeze

During the Internal Waves on the Continental Margin (IWAVES) field experiments of 1996 and 1997 off of Mission Beach, California (32.75° N), we observed energetic, dirunal-band motions across the entire study site in water depths ranging from 15 to 500 m and spanning a cross-shore distance of 15 km. The spectral peak of the currents was at the diurnal frequency (σD₁ = 1 cpd) and was sufficiently well resolved to be clearly separated from the slightly higher local inertial frequency (f = 1.08 cpd). These motions were surface enhanced and clockwise circularly polarized and had an upward phase propagation speed of ~68 m d¯¹, suggesting that the motions were driven predominantly by the diurnal sea breeze. However, the downward energy (upward phase) propagation seems irreconcilable with the subinertial diurnal period, and moreover, the intermittent diurnal current events were not obviously associated with the diurnal sea breeze events. We rationalize these features using a flat-bottomed linear modal sum internal wave model that includes advection and refraction due to subtidal alongshore flow, V(x,t). Fluctuations in V at the observing site can change the “effective” local Coriolis parameter f + Vx by as much 50%, thus making the diurnal motions at different times effectively either subinertial or superinertial. The model is integrated numerically for 200 days at a latitude of 32.75°N under different wind and subtidal flow conditions: purely diurnal winds and no V, purely diurnal winds and a time-independent V, narrow-band diurnal winds and no V, and narrow-band diurnal winds and subtidal, time-dependent V. Model diurnal currents forced by narrow-band diurnal winds and subtidal V show complex offshore structure with realistic intermittency and spectral broadening. This study suggests that continental margins in the vicinity of the 30° latitude (where σD₁ = f) are regions that could potentially produce energetic, sea breeze-driven baroclinic motions and that these motions could be regulated by the vorticity of the local subtidal currents

Observations of the semidiurnal internal tide on the southern California slope and shelf

We give a detailed description of the semidiurnal-band current and temperature variability observed during the Internal Waves on the Continental Margin (IWAVES) field experiments of 1996 and 1997 off of Mission Beach, California. This variability was dominated by the internal tide, and the structure of the internal tide on the slope and shelfbreak region was different from that on the narrow shelf. On the slope and shelfbreak, the internal tide was dominated by alongshore propagating coastal-trapped waves. In this region, semidiurnal-band currents were predominantly oriented in the alongshore direction. In the lower half of the water column at a water depth H of 350 m, current and temperature variability were consonant with a short wavelength (~8 km) bottom trapped wave propagating in the alongshore direction to the north. In the upper 120 m of the water column (above the depth of the shelfbreak), slope and shelfbreak currents were highly coherent with a zero phase lag; that is, there was no phase propagation in the cross-shore direction. On the narrow (~10 km) shelf, cross-shore currents u were much more energetic than on the slope and had the structure of a mode-one internal wave. The alongshore currents v decreased monotonically from the surface to the bottom of the water column with a phase that did not change with depth. The near-bottom u signal propagated toward the coast during all mooring deployments, faster in the summer than in the fall. The near-bottom u and mid-column temperature relative phase was neither consistent with a purely progressive nor a purely standing mode-one internal wave. We conclude that the internal tide on the shelf was partially reflected.Copyrighted by American Geophysical Union.Keywords: continental shelf and slope circulation, internal tide, coastal-trapped wave, internal wave

Statistical aspects of surface drifter observations of circulation in the Santa Barbara Channel

Argos-tracked drifters are used to study the near-surface circulation in the Santa Barbara Channel. The mean consists of a cyclonic cell in the western Santa Barbara Channel with weaker flow in the eastern Channel. Drifter mean velocities agree well with record means from near-surface current meters. At the eastern entrance to the channel, drifter velocities are biased toward outflow (eastward velocity) conditions. Drifter variability at synoptic and seasonal scales shows a tendency for upwelling and eastward flow in spring, a strong cyclonic circulation in summer, poleward relaxation in fall, and weak, variable circulation in winter. Drifter estimates of eddy stress divergence indicate advective terms play a secondary role in the mean surface momentum balance. Lagrangian time and space scales are about 1 day and under 10 km, respectively. The mismatch between Lagrangian and Eulerian timescales indicates advective terms are important to the fluctuating circulation.Copyrighted by American Geophysical Union

Dual-phase argon ionization detector for measurement of coherent elastic neutrino scattering and medium-energy nuclear recoils

We propose to build and deploy a 10-kg dual-phase argon ionization detector for the detection of coherent neutrino-nucleus scattering, which is described by the reaction; (V) + (Z,N) {yields} (v) + (Z,N). Our group would be the first to make this measurement. Its detection would validate (or refute) central tenets of the Standard Model. The existence of this process is also relevant to astrophysics, where coherent neutrino scattering is assumed to impede energy transport within neutron stars. We have built a gas-phase argon ionization detector to determine the feasibility of measuring small recoil energies ({approx}1keV) predicted from coherent neutrino scattering, and to characterize the recoil spectrum of the argon nuclei induced by scattering from medium-energy neutrons. We present calibrations made with 55-Fe, a low energy x-ray source, and describe a planned measurement of the recoil spectra from the 60keV Lithium-target neutron generator at LLNL. A high signal-to-noise measurement of the recoil spectrum will not only serve an important milestone in achieving the sensitivity necessary for measuring coherent neutrino-nucleus scattering, but will break new scientific ground by providing a first ever measurement of low-energy quenching factors in argon. Coherent scattering occurs when the momentum transfer from a neutrino to the nucleus is much smaller than the inverse size of the recoil nucleus. A detection of coherent neutrino-nucleus scattering would verify an unconfirmed Standard Model prediction [1], explore non-standard neutrino-quark interactions, confirm stellar collapse and supernova energy transport and neutrino opacity models, and could be applied to the measurement of the flavor-blind neutrino spectrum from next nearby supernova, or could be used to promote non-intrusive reactor power monitoring [2]. We propose detecting the ionization induced by recoiling argon nuclei using a 10 kg dual-phase argon detector. The principle of dual-phase detection has been described elsewhere [3]. We propose using a 3 GW commercial nuclear reactor as a source of antineutrinos. We have designed and built a gas-phase prototype of the detector with which we have measured the 200-electron equivalent ionization signals from a 6keV Fe-55 source with a signal-to-noise threshold of 50 electrons. This prototype also enables study of scintillation properties of Argon and investigation of electron and nuclear recoils in Argon. We will measure medium energy neutron-nuclear recoils in our prototype detector using the recently-commissioned LLNL compact pulsed neutron source

Paradoxical reaction in non HIV-tuberculosis, a rare case with pancreatic involvement

A 24-year-old young man presents a sudden hepatic cytolysis and cholestasis after two months of isoniazid, rifampin and pyrazinamide therapy for severe lung tuberculosis. Initial data included heroin consumption history, HIV-negative serology, drug sensitivity and a normal abdominal CT

Determining Foreground Contamination in CMB Observations: Diffuse Galactic Emission in the MAXIMA-I Field

Observations of the CMB can be contaminated by diffuse foreground emission from sources such as Galactic dust and synchrotron radiation. In these cases, the morphology of the contaminating source is known from observations at different frequencies, but not its amplitude at the frequency of interest for the CMB. We develop a technique for accounting for the effects of such emission in this case, and for simultaneously estimating the foreground amplitude in the CMB observations. We apply the technique to CMB data from the MAXIMA-1 experiment, using maps of Galactic dust emission from combinations of IRAS and DIRBE observations, as well as compilations of Galactic synchrotron emission observations. The spectrum of the dust emission over the 150--450 GHz observed by MAXIMA is consistent with preferred models but the effect on CMB power spectrum observations is negligible.Comment: 19 pages, 8 figures, accepted for publication in the Astrophysical Journal. Monor changes to match the published versio