Simulation of severe storms of tornadic intensity over Indo-Bangla region

Many severe thunderstorms of tornadic intensity were reported in the northwestern parts of Bangladesh during 30 August to 14 September, 2008. Two among them occurred at Nilphamari and Kurigram districts on 30th August, and at Nilphamari district on 3rd September. The tornadic storms are studied based on a field survey, surface data, radar and satellite observations and model simulations. Low level moisture influx by southerly flow from the Bay of Bengal coupled with an upper level westerly jet stream causing intense instability and shear in the wind fields triggered a series of storms for two weeks. The exact time and locations of the storms are investigated by using the hourly precipitation data retrieved from a S-band radar of Bangladesh Meteorological Department (BMD) located at Dhaka. Subsequently, the storms are simulated by using the WRF-ARW model on double nested domains at 9 and 3 km horizontal resolutions based on 6 hourly FNL analyses and boundary conditions of NCEP. Among the typical characteristics of the storms, the CAPE, Storm-Relative Environment Helicity (SREH), Bulk Richardson Number Shear (BRNSHR), dew point depression, and potential vorticity are studied. Results show that while there are differences of 2-3 hours between the observed and simulated time of the storms, the distances between observed and simulated locations of the storms are several tens of kilometers. The maximum CAPE is generally above 2400 J kg-1. The maximum amount of vorticity transferred by directional shear in the storm updraft (helicity) due to convective motion simulated by the model is 766 m2 sec-2, and the highest value of BRNSHR that define the region in which low-level mesocyclogenesis is more likely is 168 m2 sec-2 among the 2 cases, which is generally supposed to produce rotating storms according to the prescribed range.

MHD Heat and Mass Transfer Steady Flow of a Convective Fluid Through a Porous Plate in The Presence of Diffusion Thermo and Aligned Magnetic Field

In the presence of a diffusion thermal and coupled magnet field effect, this manuscript seeks continuous free convective motion by a viscous, incompressible fluid that conducts electrically past a sloping platform via a porous medium. The free flow speed may be compatible with the exponentially tiny disrupting law. Two-term harmonic and non-harmonic functions solve dimensional-less control equations analytically. Detailed graphs are used to determine the budgets for tempo, temperature, and concentration for various limit calculations. Also, the numbers of Nusselt and Sherwood are given and evaluated with the graphs. Its sketches illustrate that the velocity profiles get reduced by the increase of aligned magnetic field parameter (α) and inclined angle parameter (ξ). Temperature profile is accelerated by rising heat absorption, Dufour number and concentration distribution is decelerated by enhancing the chemical reaction and Schmidt number. Heat and mass transfer frequently occurs in chemically processed industries, distribution of temperature and moisture over agricultural fields, dispersion of fog and environment pollution and polymer production. Free convection flow of coupled heat and mass transfer occurs due to the temperature and concentration differences in the fluid as a result of driving forces. For example, in atmospheric flows, thermal convection resulting from heating of the earth by sunlight is affected differences in water vapour concentration.

The role of urban development in the formation of a “heat island”

Для оценки роли городской застройки в формировании “острова тепла” и исследования его влияния на распространение загрязняющих веществ разработана микромасштабная математическая модель городской среды. В качестве модельной задачи рассматривалось локальное влияние городской застройки микрорайона г. Красноярска. Установлено, что наибольший вклад в формирование “острова тепла” вносят наружные стены зданий и их верхние конструкции - крыши. При учете теплообмена наблюдаются рост средней скорости воздушного потока внутри квартала и уменьшение низкоскоростных областей более чем на 0.5 м/с. Также выявлено, что при учете теплообмена наблюдается заброс загрязняющих веществ, поступающих от дороги, на б´ольшую высоту, чем без него. Разработанная математическая модель позволяет комплексно подойти к исследованию гидродинамики и прогнозированию экологической обстановки урбанизированных территорий Introduction. The configuration of modern micro districts leads to the formation of zones with low velocity, in which the accumulation of pollutants occurs. On the other hand, during the construction of cities, the surface of the Earth is covered with materials that actively absorb solar radiation, which leads to the formation of an urban heat island. Our work is devoted to the study of the local influence of urban development on the spread of pollutants, which takes into account the above mentioned factors. Mathematical model. For solving our problems we developed the microscale mathematical model based on the Reynolds-averaged Navier-Stokes equations for incompressible flows with variable density. For the correct calculation of the temperature on the surface of buildings, we used a model of conjugate heat transfer with a one-dimensional equation of thermal conductivity. As a model problem, we considered the Krasnoyarsk area with dense development and the presence of a highrise building for two seasons: winter and summer. The source of emission of pollutants was traffic. Results. The results of the calculations show a significant decrease in velocity around buildings. On the contrary, solar radiation leads to the intensification of free convective motion, especially in the surface area. That can double the near-surface velocity compared to the solution that does not account for the heat transfer. Conclusions. The developed mathematical model allows a comprehensive approach to solving hydrodynamic problems of prediction the ecological situation of cities

Global 3D radiation hydrodynamic simulations of proto-Jupiter’s convective envelope

The core accretion model of giant planet formation has been challenged by the discovery of recycling flows between the planetary envelope and the disc that can slow or stall envelope accretion. We carry out 3D radiation hydrodynamic simulations with an updated opacity compilation to model the proto-Jupiter’s envelope. To isolate the 3D effects of convection and recycling, we simulate both isolated spherical envelopes and envelopes embedded in discs. The envelopes are heated at given rates to achieve steady states, enabling comparisons with 1D models. We vary envelope properties to obtain both radiative and convective solutions. Using a passive scalar, we observe significant mass recycling on the orbital timescale. For a radiative envelope, recycling can only penetrate from the disc surface until ∼0.1-0.2 planetary Hill radii, while for a convective envelope, the convective motion can ‘dredge up’ the deeper part of the envelope so that the entire convective envelope is recycled efficiently. This recycling, however, has only limited effects on the envelopes’ thermal structure. The radiative envelope embedded in the disc has identical structure as the isolated envelope. The convective envelope has a slightly higher density when it is embedded in the disc. We introduce a modified 1D approach which can fully reproduce our 3D simulations. With our updated opacity and 1D model, we recompute Jupiter’s envelope accretion with a 10 M⊕ core, and the timescale to runaway accretion is shorter than the disc lifetime as in prior studies. Finally, we discuss the implications of the efficient recycling on the observed chemical abundances of the planetary atmosphere (especially for super-Earths and mini-Neptunes).

THE INFLUENCE OF EXTERNAL FORCES ON THE CHARACTERISTICS OF HARDENING AND THE CHARACTER OF CONVECTIVE FLOWS DURING THE CURING OF INGOTS

The paper describes the influence of external influences on the features and nature of convective flows during the solidification of ingots. It is shown that topping up the profitable part of the ingot with hot portions of the melt changes the nature of the convective motion of the melt in the body of the model ingot. Laminar movement is observed before refilling, after turbulent. The change in the nature of the movement of the liquid in the body of the ingot contributes to an increase in the speed of the front of the solid phase, as evidenced by the results of calculating the rate of solidification throughout the solidification process of the model ingot. The analysis of the structural zones showed an increase in the zone of columnar crystals from 58.6% to 72.3% and the zone of the deposition cone, from 6.5% to 9.1% in refilled ingots compared to the classic ingot. There is also a decrease in the zone of differently oriented crystals from 26.8 to 13.7% and the crustal zone from 5.9% to 2.8%. The length of the axial zone increased from 36 to 54%, with a decrease in its diameter from 6.5 to 5.1%.

Modeling of the mechanism of heterogeneous inhibition of the active flame centers of a jet burning system by fire extinguishing powder particles

The relevance of the work is due to the lack of a physical interpretation of the process of extinguishing jet burning systems with fire extinguishing powders, which is important for ensuring effective fire extinguishing at gas and oil complexes and hazardous chemical industries. A mathematical model of the reaction kinetics of heterogeneous inhibition of active flame centers of a jet burning system by fire extinguishing powder particles in an unsteady mode is considered in the approximation of a purely molecular transfer of matter in the reaction zone. The regularities of the mechanism of heterogeneous inhibition of the active flame centers by the particles of the extinguishing powder under conditions when the active particles of the combustion products participate not only in diffuse, but also in convective transport are established. It is shown, that the convective motion of the active flame centers increases the reaction rate of heterogeneous inhibition of their particles of the extinguishing agent. The results obtained allow us to optimize the conditions for the supply of fire extinguishing powder to the jet burning medium for effective flame suppression.

A globally fragmented and mobile lithosphere on Venus

Venus has been thought to possess a globally continuous lithosphere, in contrast to the mosaic of mobile tectonic plates that characterizes Earth. However, the Venus surface has been extensively deformed, and convection of the underlying mantle, possibly acting in concert with a low-strength lower crust, has been suggested as a source of some surface horizontal strains. The extent of surface mobility on Venus driven by mantle convection, however, and the style and scale of its tectonic expression have been unclear. We report a globally distributed set of crustal blocks in the Venus lowlands that show evidence for having rotated and/or moved laterally relative to one another, akin to jostling pack ice. At least some of this deformation on Venus postdates the emplacement of the locally youngest plains materials. Lithospheric stresses calculated from interior viscous flow models consistent with long-wavelength gravity and topography are sufficient to drive brittle failure in the upper Venus crust in all areas where these blocks are present, confirming that interior convective motion can provide a mechanism for driving deformation at the surface. The limited but widespread lithospheric mobility of Venus, in marked contrast to the tectonic styles indicative of a static lithosphere on Mercury, the Moon, and Mars, may offer parallels to interior–surface coupling on the early Earth, when global heat flux was substantially higher, and the lithosphere generally thinner, than today.