Polygonal Structures in the Gaseous Disk: Numerical Simulations

The results of numerical simulations of a gaseous disk in the potential of a stellar spiral density wave are presented. The conditions under which straightened spiral arm segments (rows) form in the gas component are studied. These features of the spiral structure were identified in a series of works by A.D. Chernin with coauthors. Gas-dynamic simulations have been performed for a wide range of model parameters: the pitch angle of the spiral pattern, the amplitude of the stellar spiral density wave, the disk rotation speed, and the temperature of the gas component. The results of 2D- and 3D-disk simulations are compared. The rows in the numerical simulations are shown to be an essentially nonstationary phenomenon. A statistical analysis of the distribution of geometric parameters for spiral patterns with rows in the observed galaxies and the constructed hydrodynamic models shows good agreement. In particular, the numerical simulations and observations of galaxies give $\simeq 120^\circ$ for the average angles between straight segments.Comment: 22 pages, 10 figure

Gravitational stability and dynamical overheating of stellar disks of galaxies

We use the marginal stability condition for galactic disks and the stellar velocity dispersion data published by different authors to place upper limits on the disk local surface density at two radial scalelengths $R=2h$. Extrapolating these estimates, we constrain the total mass of the disks and compare these estimates to those based on the photometry and color of stellar populations. The comparison reveals that the stellar disks of most of spiral galaxies in our sample cannot be substantially overheated and are therefore unlikely to have experienced a significant merging event in their history. The same conclusion applies to some, but not all of the S0 galaxies we consider. However, a substantial part of the early type galaxies do show the stellar velocity dispersion well in excess of the gravitational stability threshold suggesting a major merger event in the past. We find dynamically overheated disks among both seemingly isolated galaxies and those forming pairs. The ratio of the marginal stability disk mass estimate to the total galaxy mass within four radial scalelengths remains within a range of 0.4---0.8. We see no evidence for a noticeable running of this ratio with either the morphological type or color index.Comment: 25 pages, 5 figures, accepted to Astronomy Letter

Verification of the Regional climate model RegCM v4.5 for the Lower Volga

Представлены результаты верификации региональной климатической модели (РКМ) RegCM 4.5 для территории Нижнего Поволжья с использованием данных реанализа NCEP/NCAR Reanalysis и GHCN + CAMS. Подробно обсуждаются проблемы выбора расчeтной области, параметров численной сетки и их влияние на климатический прогноз. Мы дополнили базовый код RegCM модулем, позволяющим разбивать территорию на произвольное число зон, каждая из которых характеризуется своим набором физических характеристик. Проведено более 100 имитационных расчeтов для изучения чувствительности результатов моделирования климатических состояний от топографии местности, шероховатости поверхности, свойств почвы и растительности. Исследована возможность определения климатической роли крупнейших водохранилищ региона - Волгоградского и Цымлянского, а также Волго-Ахтубинской поймы. The verification results of the regional climate model (RCM) RegCM 4.5 for Lower Volga area using NCEP / NCAR and GHCN + CAMS reanalysis are presented. The choice problems of the computational domain, the numerical grid parameters and the influence of these factors on the climate forecast are discussed in detail. We have made a new module for divide territory into zones for the base RegCM code, which improves the simulations quality. We have competed over 100 simulations to study the sensitivity of our climate modeling results from topography, surface roughness, soil and vegetation properties. The role of the largest reservoirs on the climate in the numerical model is investigated.Исследование выполнено при финансовой поддержке РФФИ и Администрации Волгоградской области в рамках научных проектов № 18-47-340003 р_а, № 18-41-342001 р_мк

Creating a digital elevation model for interfluves

The procedure for constructing a digital elevation model (DEM) of the northern part of the Volga-Akhtuba interfluve (VAI) is described. We take the elevation matrix of SRTM data as the basis for further refining and updating spatial data using satellite imagery, GPS measurements, depth surveys of the Volga and Akhtuba riverbeds. Important sources of high-altitude data for VAI are observations of the shorelines dynamics of small temporary reservoirs (lakes, ducts, water spills), which arise during the spring flood and disappear during the low-flow period. The system of digitized coastlines at different points in time can significantly improve the quality of the DEM. Our method of constructing digital elevation models includes an iterative algorithm that uses the results of the DEM morphostructural analysis and the numerical hydrodynamic simulation of the VAI flooding.Исследование выполнено при финансовой поддержке РФФИ и Администрации Волгоградской области в рамках научных проектов № 18-47-340007 р_а (в части построения актуализированной цифровой модели местности) и № 18-41-342001 р_мк (в части расчета параметров транспортной сети малых русел)