Source localization with broad-band matched-field processing inshallow water

Acoustic source localization using matched-field processing is presented for multitone signals from the Shallow Water Evaluation cell Experiment 3 (SWellEX-3). The experiment was carried out in July 1994 west of Point Loma, CA, in 200 m of water of complex bathymetry. The multitone signal (ten tones between 50 and 200 Hz) was transmitted from an acoustic source towed at various depths over tracks which produced complex propagation paths to a vertical line array receiver. Broad-band and narrow-hand processing, localization, and tracking results are compared with each other and with independent estimates of source position. With narrow-band processing, mismatch between the data and the predicted signal replica of ~1 dB reduced the mainlobe to levels equal to or below the sidelobes. Incoherently averaging the processing output over the multiple tones reduced range/depth sidelobe levels, allowing accurate source localization and tracking     

Abundance and distribution of ichthyoplankton in the upwelling zone off Oregon during anomalous El Niño conditions

The abundance and distribution patterns of nearshore ichthyoplankton were investigated during a year of anomalously high sea temperatures off Oregon. Samples collected from 2 to 18 km offshore from April through September of 1983 showed increased occurrences and higher abundances of taxa usually found at distances offshore of 37 km in other years. The dominant species collected, comprising more than half of the total larval fish abundance, was the northern anchovy (Engraulis mordax). Larval anchovy have rarely been collected inshore in previous studies. Many of the dominant taxa normally found inshore, especially osmerids, were present in reduced numbers in 1983. Changes in the hydrographic conditions associated with onshore surface drift and reduced summer upwelling during the 1983 El Niño could explain the distributional patterns observed. The warm inshore waters apparently provided a substantial spatial and temporal expansion of the spawning habitat for E. mordax.     

The center-to-limb wavelength shift of a number of Fraunhofer lines

The center-to-limb wavelength shifts of the cores of faint, medium and strong Fraunhofer lines are presented: Fei 3767, Caii 3968, Ceii 4222, Cai 4227, Nai 5896, Baii 6497, and Ki 7699.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation.     

‘Intermittent’ solar periodicities

The signal from a stable periodicity can seem to be intermittent when it is partially masked by an unmodelled window function or when the data set is too short to resolve closely spaced periodicities. By taking this into account, short-lived periodicities in solar data can be reinterpreted as evidence for continuously periodic behavior. The periodic sources are located in the solar interior and caused by global oscillation modes. The convective envelope acts as the window for these sources. Recent reports of seven periodicities from 100 to 1000 days are compared with this model. Precise long-term values for the periodicities are predicted and they agree closely with observations. Some elements are suggested that might explain the well-documented 155-day periodicity. Conventional filtering methods to suppress effects of the 11-year cycle are criticized as inadequate.     

Nonlinear meridional scale interaction in baroclinic instability

Baroclinic instability of a zonal flow with latitudinal structure is examined using a nonlinear quasi-geostrophic, two-level β-plane model. An initially small perturbation with the structure of the linearly most unstable mode is allowed to grow to finite amplitude through nonlinear interaction. Because of latitudinal asymmetries of the basic zonal flow, a spectrum of meridional modes is generated in the perturbation. The time evolution of zonal wind and perturbation meridional structures, and their Fourier meridional mode spectra are examined. The radius of deformation is an important meridional scale in both the zonal flow and perturbation. This is especially true during the barotropic decay phase of the baroclinic wave. Time series of energy conversion terms show there is no energy accumulation.     

Vertical cloud structure of Jupiter's Equitorial Plumes

A model for the vertical cloud structure of Jupiter's Equitorial Plumes is deduced based on an analysis of Voyager images of the equitorial region in the 6190Å methane band and the 6000-Å continuum, and ground-based 8900-Å methane band images of Jupiter. A computer code that represents scattering and absorption from aerosol and gas layers was applied to a heirarchy of increasingly complex model aerosol structures to match the observations in the three wavelengths. The observations are consistent with a model for the vertical cloud structure of the equitorial region that consists of four aerosol layers. A high-altitude haze layer (HAL) with optical depth τ = 1 uniformly blankets the equitorial region at an altitude between 100 and 250 mbar. Below that, a middle-level cloud layer between 400 and 800 mbar contains the well-known Equatorial Plumes. The Plume clouds are optically thick (τ ≥ 12), bright clouds with single scattering albedo $\text{ω}\text{= 0.997}$. They are probably composed of ammonia ice. The darker ($\text{ω}\text{= 0.990}$) interplume regions contain optically thinner clouds (2 ≤ τ ≤ 5) at the same altitude as the Plumes. An opaque cloud deck between 4000 and 6000 mbar, which is probably composed of water, forms the lowest model layer. In addition to these three layers, a thin forward scattering haze layer above 100 mbar was included in the models for consistency with previous work (Tomasko et al., 1978). We conclude that the vertical structure of the Equatorial Plume clouds is consistent with the hypothesis (Hunt et al., 1981) that the Plumes are caused by upwelling at the ammonia condensation level produced by bouyancy due to latent heat release from the condensation of water clouds nearly three scale heights below the Plumes.     

High-precision 40Ar/39Ar sanidine geochronology of ignimbrites in the Mogollon-Datil volcanic field,southwestern New Mexico

⁴⁰Ar/³⁹Ar age spectra have been obtained from 85 sanidine separates from 36 ignimbrites and one rhyolitic lava in the latest Eocene-Oligocene Mogollon-Datil volcanic field of southwestern New Mexico. Of the 97 measured age spectra, 94 yield weighted-mean plateau ages each giving single-spectrum 1 precision of±0.25%–0.4% (±0.07–0.14 Ma). Replicate plateau age determinations for eight different samples show within-sample 1 precisions averaging ±0.25%. Plateau ages from multiple (n=3–8) samples of individual ignimbrites show 1 within-unit precision of ±0.1%–0.4% (±0.04–0.13 Ma). This within-unit precision represents a several-fold improvement over published K-Ar data for the same ignimbrites, and is similar to the range of precisions reported from single-crystal laser fusion studies. A further indication of the high precision of unit-mean ⁴⁰Ar/³⁰Ar ages is their close agreement with independently established stratigraphic order. Two samples failed to meet plateau criteria, apparently due to geologic contamination by older feldspars. Effects of minor contamination are shown by six other samples, which yielded slightly anomalous plateau ages. ⁴⁰Ar/³⁹Ar plateau ages permit resolution of units differing in age by 0.5% (0.15 Ma) or less. This high resolution, combined with paleomagnetic studies, has helped to correlate ignimbrites among isolated ranges and has allowed development of an integrated timestratigraphic framework for the volcanic field. Mogollon-Datil ignimbrites range in age from 36.2 to 24.3 Ma. Ignimbrite activity was strongly episodic, being confined to four brief (<2.6 m.y.) eruptive episodes separated by 1–3 m.y. gaps. Ignimbrite activity generally tended to migrate from the southeast toward the north and west.     

Trace-element and Sr,Nd, Pb,and O isotopic composition of Pliocene and Quaternary alkali basalts of the Patagonian Plateau lavas of southernmost South America

The Pliocene and Quaternary Patagonian alkali basalts of southernmost South America can be divided into two groups. The cratonic basalts erupted in areas of Cenozoic plateau volcanism and continental sedimentation and show considerable variation in ⁸⁷Sr/⁸⁶Sr (0.70316 to 0.70512), ¹⁴³Nd/¹⁴⁴Nd (_Nd) and ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb ratios (18.26 to 19.38, 15.53 to 15.68, and 38.30 to 39.23, respectively). These isotopic values are within the range of oceanic island basalts, as are the Ba/La, Ba/Nb, La/Nb, K/Rb, and Cs/Rb ratios of the cratonic basalts. In contrast, the transitional basalts, erupted along the western edge of the outcrop belt of the Pliocene and Quaternary plateau lavas in areas that were the locus of earlier Cenozoic Andean orogenic arc colcanism, have a much more restricted range of isotopic composition which can be approximated by ⁸⁷Sr/⁸⁶Sr=0.7039±0.0004, _Nd, ²⁰⁶Pb/²⁰⁴Pb=18.60±0.08, ²⁰⁷Pb/²⁰⁴Pb=15.60±0.01, and ²⁰⁸Pb/²⁰⁴Pb=38.50±0.10. These isotopic values are similar to those of Andean orogenic are basalts and, compared to the cratonic basalts, are displaced to higher ⁸⁷Sr/⁸⁶Sr at a given ¹⁴³Nd/¹⁴⁴Nd and to higher ²⁰⁷Pb/²⁰⁴Pb at a given ²⁰⁸Pb/²⁰⁴Pb. The transitional basalts also have Ba/La, Ba/Nb, La/Nb, and Cs/Rb ratios higher than the cratonic and oceanic island basalts, although not as high as Andean orogenic are basalts. In contrast to the radiogenic isotopes, ¹⁸O values for both groups of the Patagonian alkali basalts are indistinguishable and are more restricted than the range reported for Andean orogenic are basalts. Whole rock ¹⁸O values calculated from mineral separates for both groups range from 5.3 to 6.5, while measured whole rock ¹⁸O values range from 5.1 to 7.8. The trace element and isotopic data suggest that decreasing degrees of partial melting in association with lessened significance of subducted slabderived components are fundamental factors in the west to east transition from arc to back-arc volcanism in southern South America. The cratonic basalts do not contain the slab-derived components that impart the higher Ba/La, Ba/Nb, La/Nb, Cs/Rb, ⁸⁷Sr/⁸⁶Sr at a given ¹⁴³Nd/¹⁴⁴Nd, ²⁰⁷Pb/²⁰⁴Pb at a given ²⁰⁸Pb/²⁰⁴Pb, and ¹⁸O to Andean orogenic arc basalts. Instead, these basalts are formed by relatively low degrees of partial melting of heterogeneous lower continental lithosphere and/or asthenosphere, probably due to thermal and mechanical pertubation of the mantle in response to subduction of oceanic lithosphere below the western margin of the continent. The transitional basalts do contain components added to their source region by either (1) active input of slab-derived components in amounts smaller than the contribution to the mantle below the arc and/or with lower Ba/La, Ba/Nb, La/Nb, and Cs/Rb ratios than below the arc due to progressive downdip dehydration of the subducted slab; or (2) subarc source region contamination processes which affected the mantle source of the transitional basalts earlier in the Cenozoic.