Stability Analysis of the Climate-Vegetation System in the Northern High Latitudes

The stability of the climate-vegetation system in the northern high latitudesis analysed with three climate system models of different complexity: A comprehensive 3-dimensional model of the climate system, GENESIS-IBIS, and two Earth system models of intermediate complexity (EMICs), CLIMBER-2 andMoBidiC. The biogeophysical feedback in the latitudinal belt 60–70° N, although positive, is not strong enough to support multiple steady states: A unique equilibriumin the climate-vegetation system is simulated by all the models on a zonal scale for present-day climate and doubled CO₂ climate.EMIC simulations with decreased insolation also reveal a unique steady state. However, the climate sensitivity to tree cover, T_F, exhibits non-linear behaviour within the models. For GENESIS-IBIS and CLIMBER-2, T_F islower for doubled CO₂ climate than for present-day climate due to a shorter snow season and increased relative significance ofthe hydrological effect of forest cover. For the EMICs, T_F is higher for low tree fraction than for high treefraction, mainly due to a time shift in spring snow melt in response to changes in tree cover. The climate sensitivity to tree coveris reduced when thermohaline circulation feedbacks are accounted for in the EMIC simulations. Simpler parameterizations of oceanic processes have opposite effects on T_F: T_F is lower in simulations with fixed SSTs and higher in simulations with mixed layer oceans. Experiments with transient CO₂ forcing show climate and vegetation not in equilibrium in the northern high latitudes at the end of the 20thcentury. The delayed response of vegetation and accelerated global warming lead to rather abrupt changes in northern vegetation cover in the first halfof the 21st century, when vegetation cover changes at double the present day rate.     

Features of the long-term transformation of the Krasnodar reservoir,near the mouth of the Kuban River,Russia

The article considers the long-term(1941–2018) transformation of the Krasnodar valley reservoir, the largest in the North Caucasus. The main functions of the Krasnodar reservoir are irrigation of rice systems and flood protection of land in the Krasnodar reservoir region and the Republic of Adygea. According to topographic maps, Landsat satellite images(1974–2018) and field observations(2016–2018), four stages of transformation of the floodplain reservoir are identified. The selected stages are characterized by both natural causes(the transformation of the filling deltas into the extended deltas, etc.) and man-made causes(runoff diversions in the delta areas, etc.). The key factor of transformation is the formation of deltas of rivers flowing into the reservoir. Each of the selected stages, against the background of a gradual reduction in the area and volume of the reservoir, is characterized by the peculiarities of the formation of river deltas with the formation of genetically homogeneous sections of delta regions. During the period of operation of the reservoir, the delta of the main Kuban River moved up to 32.4 km and took away an area of 35.4 km~2 of the reservoir. During the formation of the deltas of the Kuban and Belaya rivers, a bridge was formed on the Krasnodar reservoir. The evolution of the delta regions led to the division of the reservoir into two autonomous reservoirs. The total area of the delta regions was 85.9 km~2 by 2018, i.e., 21% of the initial area of the reservoir. The transformation of the Krasnodar reservoir leads to a decrease in its regulated volume and gradual degradation.     

Mesoscale dynamics and walleye pollock catches in the Navarin Canyon area of the Bering Sea

Large canyons incise the shelf break of the eastern Bering Sea to be preferred sites of the cross-shelf exchange. The mesoscale eddy activity is particularly strong near the shelf-break canyons. To study the mesoscale dynamics in the Navarin Canyon area of the Bering Sea, the time series of velocities derived from AVISO satellite altimetry between 1993 and 2015, drifters, Argo buoys, and ship-borne data are analyzed. We demonstrate that the strength of anticyclonic eddies along the shelf edge in spring and summer is determined by the wind stress in March–April. The increased southward wind stress in the central Bering Sea forced a supply of low-temperature and low-salinity outer shelf water to the deep basin and formation of the anticyclonic mesoscale circulation seaward of the Navarin Canyon. Enhanced northwestward advection of the Bering Slope Current water leads to increase in an ice-free area in March and April and increased bottom-layer temperature at the outer shelf. The strong (weak) northwestward advection of the eastern Bering Sea waters, determined by eastern winds in spring, creates favorable (unfavorable) conditions for the pollock abundance in the western Navarin Canyon area in summer.     

Water dynamics in the western Bering Sea and its impact on chlorophyll a concentration

Ocean Dynamics - To study the water dynamics in the western Bering Sea, the time series of geostrophic velocities derived from satellite altimetry, Global total current (Copernicus Globcurrent)...     

On the role of diffractions in velocity model building: a full-waveform inversion example

Studia Geophysica et Geodaetica - Imaging of small-scale heterogeneities is important for the geological exploration in complex environments. It requires a processing sequence tuned to...     

Mesoscale circulation along the Sakhalin Island eastern coast

The seasonal and interannual variability of mesoscale circulation along the eastern coast of the Sakhalin Island in the Okhotsk Sea is investigated using the AVISO velocity field and oceanographic data for the period from 1993 to 2016. It is found that mesoscale cyclones with the horizontal dimension of about 100 km occur there predominantly during summer, whereas anticyclones occur predominantly during fall and winter. The cyclones are generated due to a coastal upwelling forced by northward winds and the positive wind stress curl along the Sakhalin coast. The anticyclones are formed due to an inflow of low-salinity Amur River waters from the Sakhalin Gulf intensified by southward winds and the negative wind stress curl in the cold season. The mesoscale cyclones support the high biological productivity at the eastern Sakhalin shelf in July– August.     

Study of variable stars associated with maser sources: G025.65+1.05

We report variation of K-band infrared(IR) emission in the vicinity of the G025.65+1.05 water and methanol maser source. New observational data were obtained with the 2.5 m telescope at the Caucasian Mountain Observatory(CMO) of Moscow State University on 2017–09–21 during a strong water maser flare. We found that the IR source situated close to the maser position had decreased brightness in comparison to archive data. This source is associated with a massive young stellar object(MYSO) corresponding to the compact IR source IRAS 18316–0602(RAFGL 7009 S). A similar decrease in K-brightness of the IR source close to the maser position was observed in March 2011 when the water maser experienced a period of increased activity. The dips in MYSO brightness can be related to the maser flare phases. Maser flares that are concurrent with dips in the IR emission can be explained if the lower IR radiation field enables a more efficient sink for the pumping cycle by allowing IR photons to escape the maser region.     

Spectroscopic and photometric observations of symbiotic nova PU Vul during 2009–2016

A new set of low-resolution spectral and UBVJHKL-photometric observations of the symbiotic nova PU Vul is presented. The binary has been evolving after its symbiotic nova outburst in 1977 and now it is in the nebular stage. It is found that the third orbital cycle(after 1977) was characterized by great changes in associated light curves. Now, PU Vul exhibits a sine-wave shape in all the light curves(with an amplitude in the U band of about 0.7 mag), which is typical for symbiotic stars in the quiescent state. Brightness variability due to pulsations of the cool component is now clearly visible in the VRI light curves. The amplitude of the pulsations increases from 0.5 mag in the V band to 0.8 mag in the I band. These two types of variability, as well as a very slow change in the physical parameters of the hot component due to evolution after the outburst of 1977, influence the spectral energy distribution(SED)of the system. The variability of emission lines is highly complex. Only hydrogen line fluxes vary with orbital phase. An important feature of the third orbital cycle is the first emergence of the OVI, 6828  Raman scattering line. We determine the temperature of the hot component by means of the Zanstra method applied to the He II, 4686  line. Our estimate is about 150 000 K for the spectrum obtained near orbital maximum in 2014. The VO spectral index derived near pulsation minimum corresponds to M6 spectral class for the cool component of PU Vul.