On the stability of a slow deflagration front at the surface of a degenerate star

On the surface of a degerate star, a slow nuclear combustion process with a wake of escaping matter can exist. The evolution of this process has been studied by solving the nonadiabatic, time-dependent hydrodynamic equations. It has been found that this flow is almost stationary and is stable against small spherical symmetric perturbations.     

What should be observed on the sun

Three problems are emphasized in particular: the preflare magnetic field configuration, velocity fields, and the nature of acceleration processes in flares. It is concluded that what we need most urgently are high-resolution hard X-ray, soft X-ray, and EUV-pictures, coronal spectra, and magnetograms with high resolution both in space and time. A space-shuttle equipped with instrumentation of this kind would contribute significantly to our knowledge of the flare process.     

Imperfect fluid Friedmannian cosmology

The bulk viscosity is introduced into the frame of ordinary Friedmannian cosmology (under highly idealized assumption of the constant coefficient of bulk viscosity). Explicit solutions are given for the viscous flat universe filled with the dust-substratum and for the viscous radiative universe. The problem, how does the introduction of viscosity affect the appearance of singularity, is briefly discussed.     

Modification Of The Standard ∈-Equation For The Stable Abl Through Enforced Consistency With Monin–Obukhov Similarity Theory

A condition is derived for consistency of the standard-equation with Monin–Obukhov (MO) similarity theory of thestably-stratified surface layer. The condition is derivedby extending the procedure used to derive the analogous condition forneutral theory to stable stratification. It is shown that consistencywith MO theory requires a function of flux Richardson number, Ri_f, to be absorbed into either of two closure parameters, c ₁ or c ₂.Inconsistency, on the other hand, results if constant values of these are maintained for all Ri_f, as is done in standardapplication of the equation, and the large overpredictions ofturbulence found in such application to the one-dimensionalstable atmospheric boundary layer (1D-SBL) are traced to thisinconsistency. Guided by this, we formulate a MO-consistent-equation by absorbing the aforementioned function intoc ₁, and combine this with a Level-2.5 second-orderclosure model for vertical eddy viscosity and diffusivities.Numerical predictions of the 1D-SBL by the modified model converge to a quasi-steady state, rectifying the predictive failure of the standard -equation for the case.Quasi-steady predictions of non-dimensional variables agree stronglywith Nieuwstadt's theory. Qualitative accuracy of predictionsis inferred from comparisons to field data, large-eddy simulationresults and Rossby-number similarity relationships.     

A 1600-year history of the Labrador Current off Nova Scotia

A multicore from Emerald Basin, on the continental margin off Nova Scotia, has a modern ¹⁴C age at the top, and other ¹⁴C dates indicate a linear sedimentation rate of ~30 cm/ka to 1600 calendar years BP. This rate is great enough to record century-to-millennial scale changes in the surface and deep (~250 m) waters in the basin that are influenced by the Labrador Current. We applied five proxies for seawater temperature changes to the sediments of Emerald Basin, including the percent abundance and the oxygen isotope ratio (d ¹⁸O) of the polar planktonic foraminifer N. pachyderma (s.), the unsaturation ratio of alkenones (U ^k' ₃₇) produced by prymnesiophyte phytoplankton, and the d ¹⁸O and Mg/Ca of benthic foraminifera. All five proxies indicate the ocean warmed suddenly sometime in the past 150 years or so. The exact timing of this event is uncertain because ¹⁴C dating is inaccurate in recent centuries, but this abrupt warming probably correlates with widespread evidence for warming in the Arctic in the nineteenth century. Because the Canadian Archipelago is one of the two main sources for the Labrador Current, warming and melting of ice caps in that region may have affected Labrador Current properties. Before this recent warming, sea surface temperature was continually lower by 1–2 °C, and bottom water was colder by about 6 °C in Emerald Basin. These results suggest that there was no Medieval Warm Period in the coastal waters off Nova Scotia. Because there is also no evidence of medieval warming in the Canadian archipelago, it seems likely that coastal waters from Baffin Bay to at least as far south as Nova Scotia were continually cold for ~1500 of the past 1600 years.     

Feedbacks affecting the response of the thermohaline circulation to increasing CO2: a study with a model of intermediate complexity

A three-dimensional ocean model with an idealized geometry and coarse resolution coupled to a two-dimensional (zonally averaged) statistical-dynamical atmospheric model is used to simulate the response of the thermohaline circulation to increasing CO ₂ concentration in the atmosphere. The relative roles of different factors in the slowing down and recovery of the thermohaline circulation were studied by performing simulations with ocean only and partially coupled models. The computational efficiency of the model allows an extensive and thorough study of the causes of changes in the strength of the thermohaline circulation, through a large number of extended runs. The evolution of the atmosphere-to-ocean surface heat fluxes is shown to be the dominant factor in causing the weakening of the circulation in response to an increasing external forcing as well as in controlling the subsequent recovery. The feedback between heat flux and the sea surface temperature is necessary for the ocean circulation to recover. The rate of the recovery, however, is not sensitive to the magnitude of the feedback, and changes in the atmosphere, while contributing to the recovery, play a secondary role. In the case of very strong feedback, substantial changes in the SST structure are shown not to be a necessary condition for the recovery of the circulation. Subsurface changes in the density structure accompany recovery despite nearly fixed SST in one of the uncoupled experiments. Changes in the zonal distribution of heat fluxes serve as a positive feedback for both decrease and recovery of the meridional overturning, and are as important as changes in the zonal-mean values of heat fluxes. The secondary role of the moisture fluxes is explained by a smaller magnitude of their contribution to the surface buoyancy flux. Imposing amplified changes in the moisture fluxes leads to a significant slow down of the circulation, accompanied, however, by changes in the heat flux. The changed heat flux, in its turn, makes a significant contribution to the future slow down. This feedback complicates the evaluation of the relative roles of the different fluxes.     

A multiple linear statistical model for estimating the mean maximum urban heat island

Summary ¶This study examines the spatial and quantitative influence of urban factors on the surface air temperature field of the medium-sized of Szeged, Hungary, using mobile measurements under different weather conditions in the periods of March 1999–February 2000 and April–October 2002. Efforts have been concentrated on the development of the urban heat island (UHI) in its peak development during the diurnal cycle. Tasks included: (1) determination of spatial distribution of mean maximum UHI intensity and some urban surface parameters (built-up and water surface ratios, sky view factor, building height) using the standard Kriging procedure, as well as (2) development of a statistical model in the so-called heating and non-heating seasons using the above mentioned parameters and their areal extensions. In both seasons the spatial distribution of the mean maximum UHI intensity fields had a concentric shape with some local irregularities. The intensity reaches more than 2.1°C (heating season) and 3.1°C (non-heating season) in the centre of the city. For both seasons statistical model equations were determined by means of stepwise multiple linear regression analysis. As the measured and calculated mean maximum UHI intensity patterns show, there is a clear connection between the spatial distribution of the urban thermal excess and the examined land-use parameters, so these parameters play an important role in the evolution of the strong UHI intensity field. From the above mentioned parameters the sky-view factor and the building height were the most determining factors which are in line with the urban surface energy balance. Therefore in the future, using our model it will be possible to predict mean maximum UHI intensity in other cities, which have land-use features similar to Szeged.Received September 26, 2002; revised February 25, 2003; accepted March 22, 2003 Published online July 30, 2003     

Volumetric characteristics of lava flows from interferometric radar and multispectral satellite data: the 1995 Fernandina and 1998 Cerro Azul eruptions in the western Galápagos

We have used a suite of remotely sensed data, numerical lava flow modeling, and field observations to determine quantitative characteristics of the 1995 Fernandina and 1998 Cerro Azul eruptions in the western Galápagos Islands. Flank lava flow areas, volumes, instantaneous effusion rates, and average effusion rates were all determined for these two eruptions, for which only limited syn-eruptive field observations are available. Using data from SPOT, TOPSAR, ERS-1, and ERS-2, we determined that the 1995 Fernandina flow covers a subaerial area of 6.5×10⁶ m² and has a subaerial dense rock equivalent (DRE) volume of 42×10⁶ m³. Field observations, ATSR satellite data, and the FLOWGO numerical model allow us to determine that the effusion rate declined exponentially from a high of ~60–200 m³ s^-1 during the first few hours to <5 m³ s^-1 prior to ceasing after 73 days, with a mean effusion rate of 4–16 m³ s^-1. Integrating the ATSR-derived, exponentially declining effusion rate over the eruption duration produces a total (subaerial + submarine) DRE volume of between 27 and 100×10⁶ m³, the range in values being due to differing assumptions about heat loss characteristics; only values in the higher part of this range are consistent with the independently derived subaerial volume. Using SPOT, TOPSAR, ERS-1, and ERS-2 data, we determine that the 1998 Cerro Azul flow is 16 km long, covers 16 km², and has a DRE volume of 54×10⁶ m³. FLOWGO produces at-vent velocity and effusion rate values of 11 m s^-1 and ~600 m³ s^-1, respectively. The velocity value agrees well with the 12 m s^-1 estimated in the field. The mean effusion rate (total DRE volume/duration) was 7–47 m³ s^-1. Dike dimensions, fissure lengths, and pressure gradients along the conduit based on magma chamber depth estimates of 3–5 km produce mean effusion rates for the two eruptions that range over nearly four orders of magnitude, the range being due to uncertainty in the magma viscosity, dike dimensions, and pressure gradient between magma chamber and vent. Although somewhat consistent with mean effusion rates from other techniques, their wide range makes them less useful. The exponentially declining effusion rates during both eruptions are consistent with release of elastic strain being the driving mechanism of the eruptions. Our results provide independent input parameters for previously published theoretical relationships between magma chamber pressurization and eruption rates that constrain chamber volumes and increases in volume prior to eruption, as well as time constants of exponential decay during the eruption. The results and theoretical relationships combine to indicate that at both volcanoes probably 25–30% of the volumetric increase in the magma chamber erupted as lava onto the surface. In both eruptions the lava flow volumes are less than 1% of the magma chamber volume.