The effect of radiative heat loss on steady cellular convection

Summary In the atmosphere there may be layers undergoing cellular convection with a much larger heat flux through the base of the layer than through the top. This may be either because there is a steady loss of heat by radiation from the body of the fluid or because the temperature is everywhere rising. In this latter case the temperature gradients could remain constant so that the mechanics would be the same as if the heat were being lost and the temperature kept steady. The fluid is considered incompressible as in the classical theory of cellular convection, and we determine the critical Rayleigh number for the onset of convection and the width to height ratio of the cells as functions of the heat loss. The problem, is in some respects analogous to that of the motion of a viscous fluid between rotating cylinders but in this case there are two non-dimensional-numbers-the Rayleigh number (g h ⁴/K v) and a number representing the ratio of the heat loss by radiation to the heat flux. It is found that the critical Rayleigh number is decreased and the cells widened as had already been found for the case of a fluid with transfer coefficients having a spatial variation, with free boundaries, but the cells are made more narrow if the boundaries are rigid.     

Infrared Spectroscopy of V4334 Sgr (Sakurai's Object)

IR spectroscopy and photometry in the 0.8–2.4 and 3–14 mregions are reported for seven dates between March 21 1998 and July20 2000 UT. The shorter wavelength region displays a smooth continuum increasing to longerwavelengths that is indicative of the Wien tail of a Planck function. Only theHe I 1.0830 line is present early and it shows a P-Cygni profile which laterdisappears. The long wave spectra show a smooth continuum between 3 and 13m that was well fit by a gray body at 1000 K. A weak, unidentifiedemission feature appears between 8 and 10 m.     

Flow and sediment dynamics in migrating salinity intrusions: Fraser River estuary, Canada

The salinity intrusion in the Fraser estuary, Canada, migrates landward during the rising tide and is flushed downstream on the falling tide. Suspended sediment concentrations are higher during unstratified flows than during stratified conditions. Mixing between the upper layer and the salinity intrusion is restricted by a strong density interface on the rising tide but enhanced mixing occurs across a weak salinity gradient on the falling tide. A weakly-developed estuarine turbidity maximum (ETM) and positive internal waves occur at the tip of the salinity intrusion as it migrates seaward. Spectral analyses of optical backscatter probe time series indicate that sediment movement from the upper layer is restricted by the density interface on the rising tide. During the falling tide, sediment mixing is enhanced by internal waves at the surface of the ETM. Internal waves generated at the density interface have a higher frequency during the rising tide than the falling tide.     

Geodetic sensitivity to surface meteorological data: 24-h and 6-h observing sessions

Tests have been performed to assess the utility of surface meteorological measurements for improved geodetic performance. Three types of a priori met data are considered: a default global, seasonal model; local met measurements collected at a subset of the test network; output values from a NOAA Forecast Systems Lab assimilation model. A variety of configurations for handling tropospheric parameters in the geodetic solutions is also considered. We find no geodetic advantage in using the measured met data under any test scenario. Differences among the three types of a priori information are generally insignificant, although biases can be introduced when some troposphere parameters are not adjusted. Even when using only a relatively small network (<100 km) the differences remain minor. When observing sessions are reduced from 24 h to 6 h the increased error due to measurement noise obscures all other effects except for the shortest baselines where some advantage may be achieved by not adjusting troposphere parameters for very close station pairs.     

The Pitman Canyon paleoseismic record: A re-evaluation of southern San Andreas Fault segmentation

Correlation of three well-resolved paleoseismic records, including the Pitman Canyon site with its emerging record, presents a new possibility to understand fault segmentation. To be a useful concept, fault segment boundaries must be relatively stationary over multiple seismic cycles and must appear frequently in limiting the rupture extent of earthquakes; thus, sites on the same segment should share more paleoseismic events than those on different segments. A conclusive event correlation between sites is difficult or impossible due to dating uncertainties. However, often the data are adequate to preclude correlation and thus provide firm limits on rupture extent for those events. Thus clear non-correlations provide more information about segmentation than do unprovable potential correlations.The southern end of the most recent rupture in 1857, between Wrightwood and Pitman Canyon, is often used to define a segment boundary. However, there is an absence of significant non-correlation between the previous five Pitman Canyon events and the Wrightwood events. While both Pallett Creek and Wrightwood ruptured in 1857, only two of the previous five Wrightwood events can correlate with Pallett Creek events, which may or may not indicate that they actually do. These paleoseismic records do not support the existence of a segment boundary between Wrightwood and Pitman Canyon as defined by the 1857 rupture extent, suggesting a reevaluation of southern San Andreas Fault segmentation, and using historic ruptures to define segments in general.     

Effect of lethal concentrations of copper on Mystus bleekeri (day)

In the batch test with daily exchange of medium the effect of copper ions at 2.4 mmol/l (Ca²⁺ + Mg²⁺) over 10 d of exposure is investigated. The LT₅₀ values and 95% confidence limits at 3.7, 2.1 and 1.0 ppm of Cu were 26.7 (23.6… 29.9), 47.5 (39.6… 57.0) and 101.5 (78.5… 130.7) h, respectively. The LC₅₀ values of copper in ppm were 4.05 (24 h), 1.69 (48 h), 0.829 (9.96 and 0.776 (240 h).     

Subduction of the Daiichi Kashima Seamount in the Japan Trench

In 1984–1985, the Kaiko consortium collected Seabeam, single-channel seismic and submersible sampling data in the vicinity of the Daiichi-Kashima seamount and the southern Japan trench. We performed a prestack migration of a Shell multichannel seismic profile, that crosses this area, and examined it in the light of this unusually diverse Kaiko dataset. Unlike the frontal structure of the northern Japan trench, where mass-wasting appears to be the dominant tectonic process, the margin in front of the Daiichi-Kashima shows indentation, imbrication, uplift and erosion. Emplacement of the front one-third of the seamount beneath the margin front occurs without accretion. We conclude that the Daiichi-Kashima seamount exemplifies an intermediate stage between the initial collision and subduction of a seamount at a continental margin.