Anatomy of Ursa Majoris

A nearby friable cloud in Ursa Majoris contains 270 galaxies with radial velocities 500 < VLG < 1500 km s^-1 inside the area of RA= [11h; 13h] and DEC= [+40deg; +60deg]. At present, 97 galaxies of them have individual distance estimates. We use these data to clarify the structure and kinematics of the UMa complex. According to Makarov & Karachentsev (2011), most of the UMa galaxies belong to seven bound groups, which have the following median parameters: velocity dispersion of 58 km s^-1, harmonic projected radius of 300 kpc, virial mass of 2.10^12 Msol, and virial- mass-to-K-band-luminosity of 27Msol/Lsol. Almost a half of the UMa cloud population are gas-rich dwarfs (Ir, Im, BCD) with active star formation seen in the GALEX UV-survey. The UMa groups reside within 15-19 Mpc from us, being just at the same distance as Virgo cluster. The total virial mass of the UMa groups is 4.10^13 Msol, yielding the average density of dark matter in the UMa cloud to be Omega_m = 0.08, i.e. a factor three lower than the cosmic average. This is despite the fact that the UMa cloud resides in a region of the Universe that is an apparent overdensity. A possible explanation for this is that most mass in the Universe lies in the empty space between clusters. Herewith, the mean distances and velocities of the UMa groups follow nearly undisturbed Hubble flow without a sign of the 'Z-wave" effect caused by infall toward a massive attractor. This constrains the total amount of dark matter between the UMa groups within the cloud volume.Comment: correction of a typo in the abstract, 18 pages, 2 figures. accepted for MNRAS, nov 26, 201

Large-basin hydrological response to climate model outputs: uncertainty caused by internal atmospheric variability

An approach is proposed to assess hydrological simulation uncertainty originating from internal atmospheric variability. The latter is one of three major factors contributing to uncertainty of simulated climate change projections (along with so-called "forcing" and "climate model" uncertainties). Importantly, the role of internal atmospheric variability is most visible over spatio-temporal scales of water management in large river basins. Internal atmospheric variability is represented by large ensemble simulations (45 members) with the ECHAM5 atmospheric general circulation model. Ensemble simulations are performed using identical prescribed lower boundary conditions (observed sea surface temperature, SST, and sea ice concentration, SIC, for 1979–2012) and constant external forcing parameters but different initial conditions of the atmosphere. The ensemble of bias-corrected ECHAM5 outputs and ensemble averaged ECHAM5 output are used as a distributed input for the ECOMAG and SWAP hydrological models. The corresponding ensembles of runoff hydrographs are calculated for two large rivers of the Arctic basin: the Lena and Northern Dvina rivers. A number of runoff statistics including the mean and the standard deviation of annual, monthly and daily runoff, as well as annual runoff trend, are assessed. Uncertainties of runoff statistics caused by internal atmospheric variability are estimated. It is found that uncertainty of the mean and the standard deviation of runoff has a significant seasonal dependence on the maximum during the periods of spring–summer snowmelt and summer–autumn rainfall floods. Noticeable nonlinearity of the hydrological models' results in the ensemble ECHAM5 output is found most strongly expressed for the Northern Dvina River basin. It is shown that the averaging over ensemble members effectively filters the stochastic term related to internal atmospheric variability. Simulated discharge trends are close to normally distributed around the ensemble mean value, which fits well to empirical estimates and, for the Lena River, indicates that a considerable portion of the observed trend can be externally driven

Расчёты формирования снежного покрова на основе модели взаимодействия поверхности суши с атмосферой SWAP

In framework of the project «The Earth system Models – Snow Models Intercomparison Project» (ESMSnowMIP), calculations of snow storages were carried out on ten experimental sites organized for longterm monitoring of the snow cover variability in various regions of the globe. The calculation method is based on the physical and mathematical description of heat and moisture exchange processes occurring within the system «ground water – soil – vegetation cover/snow cover – surface layer of the atmosphere», and it is implemented in the form of the model of interaction between the land surface and the atmosphere (SWAP). The model was developed at the Institute of water problems (IWP) of Russian Academy of Sciences. The model makes possible to calculate components of water and heat balances and different characteristics of the hydrological regime of terrestrial ecosystems and river basins having different spatial scales and located in different natural conditions. Good quality of reproduction of the snow storages variability on all considered sites is reached that allows consideration of the SWAP model as one of the best models of the snow cover formation. Thus, the SWAP model has a sufficiently optimal degree of complexity of the algorithm for reproducing the dynamics of snow cover, which is necessary and sufficient in global and regional hydrological models describing formation of the water balance of the land in the cold regions of the planet, and can be used to create scenario forecasts of snow dynamics (as the important part of the cryosphere). This conclusion is verified by the results of using the SWAP model to reproduce long-term variability of snow storages in basins of the River Lena and the River Ob (with its tributary Irtysh) which are the two largest rivers of the Russian Federation. The calculated and measured characteristics of snow cover dynamics for these basins are shown to be in good agreement.Расчёты снегозапасов на десяти экспериментальных площадках в разных районах земного шара показали, что модель SWAP входит в число лучших мировых моделей формирования снежного покрова. Расчёты по этой модели многолетней динамики снегозапасов в бассейнах рек Лены и Оби (с её притоком р. Иртыш) подтвердили вывод о способности модели SWAP адекватно воспроизводить формирование снегозапасов в крупных речных бассейнах.

Blueshifted galaxies in the Virgo Cluster

We examine a sample of 65 galaxies in the Virgo cluster with negative radial velocities relative to the Local Group. Some features of this sample are pointed out. All of these objects are positioned compactly within a virial zone of radius 6{\deg} in the cluster, but their centroid is displaced relative to the dynamic center of the cluster, M87, by 1.1{\deg} to the northwest. The dwarf galaxies in this sample are clumped on a scale of ~10' (50 kpc). The observed asymmetry in the distribution of the blueshifted galaxies may be caused by infall of a group of galaxies around M86 onto the main body of the cluster. We offer another attempt to explain this phenomenon, assuming a mutual tangential velocity of ~300 km/s between the Local Group and the Virgo cluster owing to their being repelled from the local cosmological void.Comment: 10 pages, 4 figures, 1 table. Published in Astrophysics, Vol. 53, No. 1, pp. 32-41, 201

The observed infall of galaxies towards the Virgo cluster

We examine the velocity field of galaxies around the Virgo cluster induced by its overdensity. A sample of 1792 galaxies with distances from the Tip of the Red Giant Branch, the Cepheid luminosity, the SNIa luminosity, the surface brightness fluctuation method, and the Tully-Fisher relation has been used to study the velocity-distance relation in the Virgocentric coordinates. Attention was paid to some observational biases affected the Hubble flow around Virgo. We estimate the radius of the zero-velocity surface for the Virgo cluster to be within (5.0 - 7.5) Mpc corresponding to (17 - 26)^\circ at the mean cluster distance of 17.0 Mpc. In the case of spherical symmetry with cosmological parameter \Omega_m=0.24 and the age of the Universe T_0= 13.7 Gyr, it yields the total mass of the Virgo cluster to be within M_T=(2.7 - 8.9) * 10^{14} M_\sun in reasonable agreement with the existing virial mass estimates for the cluster.Comment: 22 pages, 11 figures, 2 tables. Accepted for publication in MNRA

On the kinematics of the Local cosmic void

We collected the existing data on the distances and radial velocities of galaxies around the Local Void in the Aquila/Hercules to examine the peculiar velocity field induced by its underdensity. A sample of 1056 galaxies with distances measured from the Tip of the Red Giant Branch, the Cepheid luminosity, the SNIa luminosity, the surface brightness fluctuation method, and the Tully-Fisher relation has been used for this purpose. The amplitude of outflow is found to be ~300 km/s. The galaxies located within the void produce the mean intra-void number density about 1/5 of the mean external number density of galaxies. The void's population has a lower luminosity and a later morphological type with the medians: M_B = -15.7^m and T = 8 (Sdm), respectively.Comment: Version 1. 14 pages, 8 figures, 2 tables. Accepted to Astrophysics, Volume 54, Issue

Оценки современных изменений снегозапасов в бассейне Северной Двины по данным наблюдений и моделирования

The variability of snow accumulation in the Northern Dvina River basin at the end of March 1980-2016 was studied using data on the snow water equivalent of (SWE) obtained from archives of the Russian Institute of HydroMeteorological Information-World Data Center (RIHMI-WCD) as well as calculated by models of the local heat and moisture exchange SWAP and SPONSOR using the WATCH reanalysis (WFDEI) as input data. A possibility to use the SWE data from these sources to describe long-term variability of the SWE values, including trend, high-frequency component, quasi-decadal fluctuations, and spatial distribution, is evaluated. When describing the structure of the SWE variability, in particular, the contribution of trend and quasi-decadal fluctuations, as well as spatial characteristics, uncertainty remains associated with both the capabilities of the models under consideration and the imperfection of the observation network (insufficient density, measurement errors, etc.). Taking into account these uncertainties, the following conclusions can be made: the SWE variability in the Northern Dvina basin at the end of March has a low-frequency component (trend), as well as high-frequency, two- and five-year quasi-periodicities and quasi-decadal fluctuations. Long-lasting SWE anomalies in 1989–1995 and 1999–2005 and the absolute minimum in 1996 associated with quasi-decadal fluctuations are almost synchronously reflected in spring runoff anomalies. The informativeness of the considered data was also investigated from the point of view of the influence of SWE on the anomalies of the spring runoff of the Northern Dvina. The results of regression estimates and calculations of predictive values point to the advantage of the model SWE data for describing anomalies of spring river discharge compared to observations, which is primarily due to the high resolution of the model data. All the considered data sources indicate a long period of SWE deficits, starting from 2005 – 15-20%. Estimates of trend parameters are in a wide range. Depending on the data source, the rate of the SWE decrease over the basin, can vary from 4 mm per 10 years according to observations and up to 10 mm per 10 years according to calculations using the SPONSOR model.Изменчивость снегозапасов в бассейне р. Северная Двина (1980–2016 гг.) исследуется на основе данных о водном эквиваленте снега (ВЭС), полученных из станционных наблюдений и в результате расчётов на моделях тепло- и влагообмена. Обсуждаются оценки параметров тренда и вклада высокочастотных и квазидесятилетних колебаний, а также особенности пространственного распределения изменчивости ВЭС, полученные по сведениям из разных источников. В качестве критерия информативности наблюдений и модельных расчётов рассматриваются оценки вклада изменчивости ВЭС в конце марта в аномалии весеннего стока