Modification of Two-Equation Models to Account for Plant Drag

A modification of the most popular two-equation (E–φ) models, taking into account the plant drag, is proposed. Here E is the turbulent kinetic energy (TKE) and φ is any of the following variables: El (product of E and the mixing length l), (dissipation rate of TKE), and ω (specific dissipation of TKE, ). The proposed modification is due to the fact that the model constants estimated experimentally for ‘free-air’ flow do not allow for adequate reconstruction of the ratio between the production and dissipation rates of TKE in the vegetation canopy and have to be adjusted. The modification is universal, i.e. of the same type for all E–φ models considered. The numerical experiments carried out for both homogeneous and heterogeneous plant canopies with E–φ models (and with the E–l model taken as a kind of reference) show that the modification performs well. They also suggest that E– and E–ω schemes are more promising than the E–El scheme for canopy flow simulation since they are not limited by the need to use a wall function.In addition, a new parameterization for enhanced dissipation within the plant canopy is derived. It minimizes the model sensitivity to C _μ, the key parameter for two-equation schemes, and whose estimates unfortunately vary considerably from experiment to experiment. The comparison of results of new modified E– and E –ω models with observations from both field and wind-tunnel experiments shows that the proposed parameterization is quite robust. However, because of uncertainties with the turbulence Prandtl and Schmidt numbers for the E– model within the canopy, the E–ω model is recommended for future implementation, with the suggested modifications.     

WSO-UV progress and expectations

The World Space Observatory Ultraviolet (WSO-UV) is the space mission that will grant access to the ultraviolet (UV) range in the post Hubble epoch. WSO-UV is equipped with instrumentation for imaging and spectroscopy and it is fully devoted to UV astronomy. In this article, we outline the WSO-UV mission model and present the current status of the project.     

A Quantitative Study on Magnetic Configuration for Active Regions

As compared with the Mount Wilson Magnetic Classification (MWMC), effective distance (d _E) is a useful parameter because it gives a quantitative measure of magnetic configuration in active regions. We have analyzed magnetograms of 24 active regions of different types with MWMC. We have studied the evolution of magnetic fields of five active regions using d _E, total flux (F _t) and tilt angle (Tilt) quantitatively. Furthermore, 43 flare-associated and 25 CME-associated active regions have been studied to investigate and quantify the statistical correlation between flares/CMEs and the three parameters. The main results are as follows: (1) There is a basic agreement between d _E and MWMC. (2) The evolution of magnetic fields can be described in three aspects quantitatively and accurately by the three parameters, in particular by d _E on the analysis of δ-type active regions. (3) The high correlation between d _E and flares/CMEs means that d _E could be a promising measure to predict the flare-CME activity of active regions.     

Deuterated water: partition functions and equilibrium constants

HDO and D₂O are thought to be present in significant quantities in the coldest regions of the Universe. Partition functions are calculated for these species and used to calculate temperature dependent equilibrium constants for the most important fractionation reactions involving water. HDO may also be a key indicator of the absence of deuterium burning in very low mass stars. The HDO partition function calculation is extended to high  ( T ≤ 6000 K)  temperatures for this purpose.     

Maximum feedback and dark matter profiles of dwarf galaxies

The observed rotation curves of dark matter-dominated dwarf galaxies indicate low-density cores, contrary to the predictions of CDM models. A possible solution of this problem involves stellar feedback. A strong baryonic wind driven by vigorous star formation can remove a large fraction of the gas, causing the dark matter to expand. Using both numerical and analytical techniques, we explore the maximum effect of the feedback with an instantaneous removal of the gaseous disc. The energy input depends on the compactness of the disc, hence the specific angular momentum of the disc. For the plausible cosmological parameters and a wide range of the disc angular momenta, the feedback is insufficient to destroy the central halo cusp, while the inner density is lowered only by a modest factor of 2 to 6. Any realistic modelling of the feedback would have even lesser impact on dark matter. We find that no star formation effect can resolve the problems of CDM cusps.     

Development of the ElarmS methodology for earthquake early warning: Realtime application in California and offline testing in Japan

In July 2009, the California Integrated Seismic Network concluded a three-year study of earthquake early warning systems in California. Three algorithms were expanded and examined during the study. Here we discuss the history, methodology, and performance of one of the algorithms, ElarmS. Earthquake Alarm Systems, or ElarmS, uses peak displacement and maximum predominant frequency of the P-wave to detect earthquakes and quantify their hazard in the seconds after rupture begins. ElarmS was developed for Northern and Southern California, and now processes waveforms in realtime from 603 seismic sensors across the state. We outline the methodology as currently implemented, present several example events from different regions of California, and summarize the performance in terms of false and missed alarms. ElarmS was also tested offline with a dataset of 84 large magnitude earthquakes from Japan. The results from the Japan dataset were used to create a statistical error model for the algorithm. The model can be used to provide realtime uncertainty estimates at any stage in processing. In August 2009 the CISN embarked on a second three-year study of earthquake early warning. As part of this ongoing research, we identify the technological and methodological challenges facing ElarmS. Telemetry latencies and false alarm rates are two key opportunities for improvement.     

Do organic ligands affect calcite dissolution rates?

Steady state Iceland-spar calcite dissolution rates were measured at 25 °C in aqueous solutions containing 0.1 M NaCl and up to 0.05 M dissolved bicarbonate at pH from 7.9 to 9.1 in the presence of 13 distinct dissolved organic ligands in mixed-flow reactors. The organic ligands considered in this study include those most likely to be present in either (1) aquifers at the conditions pertinent to CO₂ sequestration or (2) soil/early diagenetic environments: acetate, phthalate, citrate, EDTA⁴⁻, succinate, d-glucosaminate, l-glutamate, d-gluconate, 2,4-dihydroxybenzoate, 3,4-dihydroxybenzoate, fumarate, malonate, and gallate. Results show that the presence of <0.05 mol/kg of these organic anions changes calcite dissolution rates by less than a factor of 2.5 with the exception of citrate and EDTA⁴⁻. The presence of 0.05 mol/kg citrate and EDTA⁴⁻ increases calcite dissolution rates by as much as a factor of 35 and 500, respectively, compared to rates in organic anion-free solutions. Further calcite dissolution experiments were performed in the presence of organic polymers similar to bacterial exudates, cell exopolysaccharides, and analogs of microbial cell envelopes: alginate, lichen extract, humic acid, pectin, and gum xanthan. In no case did the presence of <100 ppm of these organics change calcite dissolution rates by more than a factor of 2.5. Results obtained in this study suggest that the presence of aqueous organic anions negligibly affects calcite forward dissolution rates in most natural environments. Some effect on calcite reactivity may be observed, however, by the presence of organic anions if they change substantially the chemical affinity of the fluid with respect to calcite.     

Using Mg Isotopes to Trace Cyanobacterially Mediated Magnesium Carbonate Precipitation in Alkaline Lakes

This study assesses the potential use of Mg isotopes to trace Mg carbonate precipitation in natural waters. Salda Lake (SW Turkey) was chosen for this study because it is one of the few modern environments where hydrous Mg carbonates are the dominant precipitating minerals. Stromatolites, consisting mainly of hydromagnesite, are abundant in this lake. The Mg isotope composition of incoming streams, groundwaters, lake waters, stromatolites, and hydromagnesite-rich sediments were measured. Because Salda Lake is located in a closed basin, mass balance requires that the Mg isotopic offset between Lake Salda water and precipitated hydromagnesite be comparable to the corresponding offset between Salda Lake and its water inputs. This is consistent with observations; a ??²⁶Mg offset of 0.8?C1.4??? is observed between Salda Lake water and it is the incoming streams and groundwaters, and precipitated hydromagnesite has a ??²⁶Mg 0.9?C1.1??? more negative than its corresponding fluid phase. This isotopic offset also matches closely that measured in the laboratory during both biotic and abiotic hydrous Mg carbonate precipitation by cyanobacteria (Mavromatis, V., Pearce, C., Shirokova, L. S., Bundeleva, I. A., Pokrovsky, O. S., Benezeth, P. and Oelkers, E.H.: Magnesium isotope fractionation during inorganic and cyanobacteria-induced hydrous magnesium carbonate precipitation, Geochim. Cosmochim. Acta, 2012a. 76, 161?C174). Batch reactor experiments performed in the presence of Salda Lake cyanobacteria and stromatolites resulted in the precipitation of dypingite (Mg₅(CO₃)₄(OH)₂·5(H₂O)) and hydromagnesite (Mg₅(CO₃)₄(OH)₂·4H₂O) with morphological features similar to those of natural samples. Concurrent abiotic control experiments did not exhibit carbonate precipitation demonstrating the critical role of cyanobacteria in the precipitation process.     

Sequentially sampled gas hydrate water,coupled with pore water and bottom water isotopic and ionic signatures at the Kukuy mud volcano,Lake Baikal: ambiguous deep-rooted source of hydrate-forming water

The isotopic and ionic composition of pure gas hydrate (GH) water was examined for GHs recovered in three gravity cores (165–193 cm length) from the Kukuy K-9 mud volcano (MV) in Lake Baikal. A massive GH sample from core St6GC4 (143–165 cm core depth interval) was dissociated progressively over 6 h in a closed glass chamber, and 11 sequentially collected fractions of dissociated GH water analyzed. Their hydrogen and oxygen isotopic compositions, and the concentrations of Cl^– and HCO₃ ^– remained essentially constant over time, except that the fraction collected during the first 50 minutes deviated partly from this pattern. Fraction #1 had a substantially higher Cl^– concentration, similar to that of pore water sampled immediately above (135–142 cm core depth) the main GH-bearing interval in that core. Like the subsequent fractions, however, the HCO₃ ^– concentration was markedly lower than that of pore water. For the GH water fractions #2 to #11, an essentially constant HCO₃ ^–/Cl^– ratio of 305 differed markedly from downcore pore water HCO₃ ^–/Cl^– ratios of 63–99. Evidently, contamination of the extracted GH water by ambient pore water probably adhered to the massive GH sample was satisfactorily restricted to the initial phase of GH dissociation. The hydrogen and oxygen isotopic composition of hydrate-forming water was estimated using the measured isotopic composition of extracted GH water combined with known isotopic fractionation factors between GH and GH-forming water. Estimated δD of ?126 to ?133‰ and δ¹⁸O of ?15.7 to ?16.7‰ differed partly from the corresponding signatures of ambient pore water (δD of ?123‰, δ¹⁸O of ?15.6‰) and of lake bottom water (δD of ?121‰, δ¹⁸O of ?15.8‰) at the St6GC4 coring site, suggesting that the GH was not formed from those waters. Observations of breccias in that core point to a possible deep-rooted water source, consistent with published thermal measurements for the neighboring Kukuy K-2 MV. By contrast, the pore waters of core St6GC4 and also of the neighboring cores GC2 and GC3 from the Kukuy K-9 MV show neither isotopic nor ionic evidence of such a source (e.g., elevated sulfate concentration). These findings constrain GH formation to earlier times, but a deep-rooted source of hydrate-forming water remains ambiguous. A possible long-term dampening of key deep-water source signatures deserves further attention, notably in terms of diffusion and/or advection, as well as anaerobic oxidation of methane.     

On the Transfer of Microbubbles by Surface Waves

Izvestiya, Atmospheric and Oceanic Physics - Direct numerical simulation (DNS) is performed and the dynamics of a near-surface water layer populated by air bubbles in the presence of a stationary...