Erosion processes in karst landscapes of the Russian plain northern taiga,based on digital elevation modeling     

Elena Polyakova  Mikhail Gofarov  Yuriy Kutinov  Vladimir Beljaev  Zinaida Chistova  Nikolay Neverov  Vadim Staritsyn  Alexandr Mineev  Sergey Durynin 《山地科学学报》2016,13(4):569-580

This paper considers the problems of the potential development of erosion processes in the natural landscapes of northern taiga in the Russian plain. It is considered that in forest ecosystems, erosion processes are slow and are weakly reflected in the terrain. However, the situation changes radically if the vegetation cover integrity is violated, which is inevitable with the modern methods of developing northern territories. Furthermore, global changes in average annual temperatures and the occurrence of karst processes may be the reason behind the development of erosion processes. The authors suggest a method for determining territories with a varying occurrence probability of erosional processes, based on digital elevation modelling. The territory of the Pinezhsky Nature Reserve (Arkhangelsk region) was chosen as the test plot. Direct field studies were previously used to detect exogenous geological processes in this territory. The authors were the first to suggest digital elevation modelling as a method that allows determining the potential danger of erosion in karst landscapes of the northern taiga. The geomorphometric studies resulted in the determination of areas with the greatest and lowest occurrence probability of erosion processes in the Pinezhsky Nature Reserve. It was established that the most significant erosion type was linear erosion, represented by incised river valleys and karst ravines. Sheet erosion is less significant and occurs as sinkholes, local declines, and chasms over the valleys of subterranean rivers.  相似文献   

Carbonate karst and its relationship with geodynamic conditions of the Odessa city (Ukraine)     

Olena Dragomyretska  Oleksandr Dragomyretskyy  Mikhail Skipa 《Environmental Earth Sciences》2016,75(7):569

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Long Term Evolution of Solar Meridional Circulation and Phase Synchronization Viewed Through a Symmetrical Kuramoto Model     

Elena Blanter  Jean-Louis Le Mouël  Mikhail Shnirman  Vincent Courtillot 《Solar physics》2018,293(10):134

The solar-cycle oscillations of the toroidal and poloidal components of the solar magnetic field in the northern solar hemisphere have a persistent phase difference of about \(\pi \). We propose a symmetrical Kuramoto model with three coupled oscillators as a simple way to understand this anti-synchronization. We solve an inverse problem and reconstruct natural frequencies of the top and bottom oscillators under the conditions of a constant coupling strength and a non-delayed coupling. These natural frequencies are associated with angular velocities of the meridional flow circulation near the solar surface and in the deep layer of the solar convection zone. A relationship between our reconstructions of the shallow and the deep meridional flow speed during recent Solar Cycles 21?–?23 is in agreement with estimates obtained in helioseismology and flux-transport dynamo modeling. The reconstructed top oscillator speed presents significant solar-cycle like variations that agree with recent helioseismical reconstructions. The evolution of reconstructed natural frequencies strongly depends on the coupling strength. We find two stable regimes in the case of strong coupling with a change of regime during anomalous solar cycles. We see the onset of a new transition in Solar Cycle 24. We estimate the admitted range of coupling values and find evidence of cross-equatorial coupling between solar hemispheres not accounted for by the model.  相似文献   

Sunspot Positions and Areas from Observations by Pierre Gassendi     

Mikhail Vokhmyanin  Nadezhda Zolotova 《Solar physics》2018,293(11):150

Solar activity behaviour on the eve of the Maunder minimum may provide important information on the period of further suppression of sunspot population. We analyse sunspot positions and areas in the 1630s extracted from rare drawings published by Pierre Gassendi in Opera Omnia. This work was published in two different editions, the first in Lyon and the second almost 70 years later in Florence. The drawings published in Lyon are found to be slightly different from those published in Florence, which produces a discrepancy in the position of spots of a few degrees, while sunspot group areas may differ by a factor of two. We reveal that the orientation of the drawings in the book is not always the same as might be seen in the telescope. We conjecture that the time of Gassendi’s observations covers the beginning of a new Schwabe cycle in the southern hemisphere. The differential rotation rate in the 1630s is also assessed and discussed.  相似文献   

Stabilization versus decomposition in alpine ecosystems of the Northwestern Caucasus: The results of a tea bag burial experiment     

Tatiana G. Elumeeva  Vladimir G. Onipchenko  Asem A. Akhmetzhanova  Mikhail I. Makarov  Joost A. Keuskamp 《山地科学学报》2018,15(8):1633-1641

Mountainous areas exhibit highly variable decomposition rates as a result of strong local differences in climate and vegetation type. This paper describes the effect of these factors on two major determinants of the local carbon cycle: litter decomposition and carbon stabilization. In order to adequately reflect local heterogeneity, we have sampled 12 typical plant communities of the Russian Caucasus. In order to minimize confounding effects and encourage comparative studies, we have adapted the widely used tea bag index (TBI) that is typically used in areas with low decomposition. By incubating standardized tea litter for a year, we investigated whether (1) initial litter decomposition rate (k) is negatively correlated with litter stabilization (S) and (2) whether k or S exhibit correlations with altitude and other environmental conditions. Our results show that S and k are not correlated. Altitude, pH, and water content significantly influenced the stabilization factor S, while soil-freezing had no influence. In contrast, none of these factors predicted the decomposition rate k. Based on our data, we argue that collection of decomposition rates alone, as is now common practice, is not sufficient to understand carbon input to soils and can potentially lead to misleading results. Our data on community-specific decomposition and stabilization rates further constrain estimates of litter accumulation in subalpine communities and the potential effects of climate change.  相似文献   

Increasing Accuracy of the GLONASS Time Service     

Mikhail Medvedev  Nikolai Shienok 《GPS Solutions》2001,4(3):11-15

GLONASS time is the reference for all time scales aboard GLONASS satellites. It is derived from the Central Synchronizer (CS), which consists of an ensemble of hydrogen clocks (HC) having a instability of (1...3) × 10⁻¹⁴ (averaging interval 24 hours). The CS time is compared to UTC(SU) in a differential mode using a TV channel of the Technical TV Center. Presently the error of GLONASS time is within 20...150 ns; however, there is a potential to decrease this value to 15 to 50 ns (3σ). The paper discusses the possible benefits of mutual phase comparisons between the HCs to determine the grouped frequency standard. These comparisons are averaged daily. The approach yields an accuracy of better than 10 ns (3σ) for CS, bringing the expected GLONASS time accuracy to the level of 15 to 50 ns (3σ). ? 2001 John Wiley & Sons, Inc.  相似文献   

Oceanic upper mantle structure from experimental scaling of V_S and density at different depths     

Mikhail K. Kaban  Peter Schwintzer 《Geophysical Journal International》2001,147(1):199-214

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Analyzing ice dynamics using Sentinel-1 data at the Solheimajoküll Glacier,Iceland     

Diego Gómez  Pablo Salvador  Julia Sanz  Mikhail Urbazaev  José Luis Casanova 《地理信息系统科学与遥感》2020,57(6):813-829

ABSTRACT

The climate in southern Iceland has warmed over the last 70 years, resulting in accelerated glacier dynamics at the Solheimajoküll glacier. In this study, we compare glacier terminus locations from 1973 to 2018, to changes in climate across the study area, and we derive ice-surface velocities (2015–2018) from satellite remote-sensing imagery (Sentinel-1) using the offset-tracking method. There have been two regional temperature trends in the study period: cooling (1973–1979) and warming (1980–2018). Our results indicate a time lag of about 20 years between the onset of glacier retreat (?53 m/year since 2000) and the inception of the warming period. Seasonally, the velocity time series suggest acceleration during the summer melt season since 2016, whereas glacier velocities during accumulation months were constant. The highest velocities were observed at high elevations where the ice-surface slope is the steepest. We tested several scenarios to assess the hydrological time response to glacier accelerations, with the highest correlations being found between one and 30 days after the velocity estimates. Monthly correlation analyses indicated inter-annual and intra-annual variability in the glacier dynamics. Additionally, we investigate the linkage between glacier velocities and meltwater outflow parameters as they provide useful information about internal processes in the glacier. Velocity estimates positively correlate with water level and negatively correlate with water conductivity between April and August. There is also a disruption in the correlation trend between water conductivity and ice velocity in June, potentially due to a seasonal release of geothermal water.  相似文献   

Spectral photometry of selected areas of the lunar surface during maximum solar activity     

Joseph Sidky Mikhail  Nabil Shoukry Awadalla  Imam Ibrahem Ahmed 《Earth, Moon, and Planets》1976,15(3-4):353-402

Photoelectric observations have been carried out during maximum solar activity in order to investigate the variation of the brightness of the lunar surface with the solar cycle and to detect the possiblity of existing colour anomaly. The brightness data, using a wide-passband filter, do not show any evidence of variation with the solar cycle. No colour anomaly is found for the investigated lunar regions, and the doubt that has been felt by some investigators about the nonexistence of certain colour indices' variation with phase is not confirmed.  相似文献   

Magma fragmentation dynamics: experiments with analogue porous low-strength material     

Mikhail Alidibirov  Vsevolod Panov 《Bulletin of Volcanology》1998,59(7):481-489

 Experiments were conducted on the fragmentation of analogue low-strength porous material (plastiprin) by rapid decompression in a shock-tube-type apparatus. The porous samples (length=365 mm, cross-section dimensions 40×40 mm) pressurized by air to pressures up to 0.9 MPa, were rapidly decompressed to 0.1 MPa. Rapid decompression of samples caused fragmentation and ejection of the fragmentation products into a large volume tank. The process of analogue material fragmentation was documented using high-speed cinematography and dynamic pressure measurements. The duration of the fragmentation event is significantly shorter than that of the ejection event. The fragmentation of material precedes the acceleration of fragments. As a result of fragmentation, sub-parallel fractures are generated. The characteristic fragment size decreases as the initial pressure differential increases. The ejected fragments obtain velocities of 60 m/s. The mechanisms of material fragmentation during unloading and fragmentation wave propagation are discussed. The experimental results provide insight into the fragmentation dynamics of highly viscous magmas in which brittle failure at high strain rate is possible. Received: 23 July 1997 / Accepted: 23 November 1997  相似文献