Effect of snow cover on pan-Arctic permafrost thermal regimes     

Hotaek Park  Alexander N. Fedorov  Mikhail N. Zheleznyak  Pavel Y. Konstantinov  John E. Walsh 《Climate Dynamics》2015,44(9-10):2873-2895

This study quantitatively evaluated how insulation by snow depth (SND) affected the soil thermal regime and permafrost degradation in the pan-Arctic area, and more generally defined the characteristics of soil temperature (T_SOIL) and SND from 1901 to 2009. This was achieved through experiments performed with the land surface model CHANGE to assess sensitivity to winter precipitation as well as air temperature. Simulated T_SOIL, active layer thickness (ALT), SND, and snow density were generally comparable with in situ or satellite observations at large scales and over long periods. Northernmost regions had snow that remained relatively stable and in a thicker state during the past four decades, generating greater increases in T_SOIL. Changes in snow cover have led to changes in the thermal state of the underlying soil, which is strongly dependent on both the magnitude and the timing of changes in snowfall. Simulations of the period 2001–2009 revealed significant differences in the extent of near-surface permafrost, reflecting differences in the model’s treatment of meteorology and the soil bottom boundary. Permafrost loss was greater when SND increased in autumn rather than in winter, due to insulation of the soil resulting from early cooling. Simulations revealed that T_SOIL tended to increase over most of the pan-Arctic from 1901 to 2009, and that this increase was significant in northern regions, especially in northeastern Siberia where SND is responsible for 50 % or more of the changes in T_SOIL at a depth of 3.6 m. In the same region, ALT also increased at a rate of approximately 2.3 cm per decade. The most sensitive response of ALT to changes in SND appeared in the southern boundary regions of permafrost, in contrast to permafrost temperatures within the 60°N–80°N region, which were more sensitive to changes in snow cover. Finally, our model suggests that snow cover contributes to the warming of permafrost in northern regions and could play a more important role under conditions of future Arctic warming.  相似文献   

Some remarks on the estimation of geothermal topocorrections     

Jan Šafanda  Reviewer C. Matyska 《Studia Geophysica et Geodaetica》1987,31(3):284-300

Summary The paper deals with some problems connected with the evaluation of the temperature gradient topocorrections for the purposes of the Earth's heat flow measurements. Some errors, occurring in the routine use of the method, suggested by Jeffreys and Bullard (JB method), are discussed. An example of simple topographic features is used to compare this method with the results obtained by a numerical solution of the heat conduction equation (NS method) by means of the finite difference method. The calculations have shown that the NS method is more precise, but its results are very sensitive to the approximation of the surface used. A stepwise approximation of the surface used in a 3-D model of a real mountainous region causes artificial oscillations of the surface values of the topocorrections, and the accuracy of the obtained results is comparable with that of the JB method. Thus, we are faced with the problem of a more appropriate approximation of the relief without the mentioned negative consequences to the superficial values of the topocorrections.

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Transient hysteresis of near-surface permafrost response to external forcing     

Alexey V. Eliseev  Pavel F. Demchenko  Maxim M. Arzhanov  Igor I. Mokhov 《Climate Dynamics》2014,42(5-6):1203-1215

Estimates of changes in near-surface permafrost (NSP) area S _p relative to change in globally averaged surface air temperature T _g are made by using the global climate model developed at the A.M. Obukhov Institute of Atmospheric Physics RAS (IAP RAS CM). For ensemble of runs forced by scenarios constructed as return-to-preindustrial continuations of the RCP (Representative Concentration Pathways) scenarios family, a possibility of transient hysteresis in dependence of S _p versus T _g is exhibited: in some temperature range which depends on imposed scenario of external forcing, NSP area is larger, at the same global mean surface air temperature, in a warming climate than in a cooling climate. This hysteresis is visible more clearly for scenarios with higher concentration of greenhouse gases in the atmosphere in comparison to those in which this concentration is lower. Hysteresis details are not sensitive to the type of the prescribed continuation path which is used to return the climate to the preindustrial state. The multiple-valued dependence of S _p on T _g arises due to dependence of soil state in the regions of extra-tropical wetlands and near the contemporary NSP boundaries on sign of external climatic forcing. To study the dependence of permafrost hysteresis on amplitude and temporal scale of external forcing, additional model runs are performed. These runs are forced by idealised scenarios of atmospheric CO₂ content varying, depending on run, with periods from 100 to 1,000 year and with different amplitudes. It is shown that the above-mentioned hysteresis is related to the impact of phase transitions of soil water on apparent inertia of the system as well as to the impact of soil state on atmospheric hydrological cycle and radiation transfer in the atmosphere.  相似文献   

Comparison of response of moss,lichens and attic dust to geology and atmospheric pollution from copper mine     

B. Balabanova  T. Stafilov  R. Šajn  K. Bačeva 《International Journal of Environmental Science and Technology》2014,11(2):517-528

Different sampling media (moss, lichen and attic dust) were used for monitoring the distribution of 15 elements, including certain trace elements, in the vicinity of an intensively exploited copper mine in the east of the Republic of Macedonia. Moss species (Hypnum cupressiforme and Campothecium lutescens), epiphytic lichens (Hypogymnia physodes and Evernia prunastri) and attic dust were collected for comparative analysis for monitoring air pollution. In both cases (lithological and anthropogenic affected areas) for the distribution of elements, the sampling media follows the expression capabilities: attic dust > moss > lichens. Enrichment factors M/L—moss vs. lichen, for plant response to elements distribution and D/L—attic dust vs. lichen, for historical response of elements distribution were significant for Cu and Ni, which were singled out as the main markers for anthropogenic and geogenic distribution. The factor analysis highlighted geogenic (F1: Ni-Cr-Cd-Fe-Al-K-Mn-Zn) and anthropogenic (F2: As-Cu-Pb) association of elements from three types of media samples. For anthropogenic affected areas, T value and F value for Cu content were significant at p < 0.05 and higher enrichment factors were obtained for lichen, moss and attic dust media (3.8, 5.0 and 5.7, respectively). Spatial distribution for element deposition (with emphasis on Cu and Ni) is not disturbed by the significant differences in the sampling media matrix. Treated sample materials (attic dust, moss, lichen) are shown to be useful in determining an anthropogenic impact, as well as the chemical properties or geological background on orographic diverse terrain in the presence of complex geological structure.  相似文献   

Deciphering petrogenic processes using Pb isotope ratios from time-series samples at Bezymianny and Klyuchevskoy volcanoes,Central Kamchatka Depression     

Theresa?M.?KayzarEmail author  Bruce?K.?Nelson  Olivier?Bachmann  Ann?M.?Bauer  Pavel?E.?Izbekov 《Contributions to Mineralogy and Petrology》2014,168(4):1067

The Klyuchevskoy group of volcanoes in the Kamchatka arc erupts compositionally diverse magmas (high-Mg basalts to dacites) over small spatial scales. New high-precision Pb isotope data from modern juvenile (1956–present) erupted products and hosted enclaves and xenoliths from Bezymianny volcano reveal that Bezymianny and Klyuchevskoy volcanoes, separated by only 9 km, undergo varying degrees of crustal processing through independent crustal columns. Lead isotope compositions of Klyuchevskoy basalts–basaltic andesites are more radiogenic than Bezymianny andesites (²⁰⁸Pb/²⁰⁴Pb = 37.850–37.903, ²⁰⁷Pb/²⁰⁴Pb = 15.468–15.480, and ²⁰⁶Pb/²⁰⁴Pb = 18.249–18.278 at Bezymianny; ²⁰⁸Pb/²⁰⁴Pb = 37.907–37.949, ²⁰⁷Pb/²⁰⁴Pb = 15.478–15.487, and ²⁰⁶Pb/²⁰⁴Pb = 18.289–18.305 at Klyuchevskoy). A mid-crustal xenolith with a crystallization pressure of 5.2 ± 0.6 kbars inferred from two-pyroxene geobarometry and basaltic andesite enclaves from Bezymianny record less radiogenic Pb isotope compositions than their host magmas. Hence, assimilation of such lithologies in the middle or lower crust can explain the Pb isotope data in Bezymianny andesites, although a component of magma mixing with less radiogenic mafic recharge magmas and possible mantle heterogeneity cannot be excluded. Lead isotope compositions for the Klyuchevskoy Group are less radiogenic than other arc segments (Karymsky—Eastern Volcanic Zone; Shiveluch—Northern Central Kamchatka Depression), which indicate increased lower-crustal assimilation beneath the Klyuchevskoy Group. Decadal timescale Pb isotope variations at Klyuchevskoy demonstrate rapid changes in the magnitude of assimilation at a volcanic center. Lead isotope data coupled with trace element data reflect the influence of crustal processes on magma compositions even in thin mafic volcanic arcs.  相似文献   

Integral transformations of gradiometric data onto a GRACE type of observable     

Michal Šprlák  Pavel Novák 《Journal of Geodesy》2014,88(4):377-390

Integral transformations of gravitational gradients onto a Gravity Recovery And Climate Experiment (GRACE) type of observable are derived in this article. The gravitational gradients represent components of the gravitational tensor in the local north-oriented frame. The GRACE type of observable corresponds to a difference between two gravitational vectors as projected onto the line of sight between the two GRACE satellites. In total, three integral transformations relating vertical–vertical, vertical–horizontal and horizontal–horizontal gravitational gradients with the GRACE type of observable are provided. Spectral and closed forms of corresponding isotropic kernels are derived for each transformation. Special cases show that the integral transformations are general and relate gravitational gradients to many other quantities of the gravitational field, such as the gravitational vector, and its radial and tangential components. Correctness of the mathematical derivations is validated in a closed-loop simulation using synthetic data.  相似文献   

Direct detection of the secondary spectrum of the interacting eclipsing binary TX UMa     

J. Grygar  L. Hřič  R. Komžík  Z. Šíma 《Astrophysics and Space Science》1991,185(2):189-193

Eclipsing binary TX UMa was observed with the D.A.O. high-dispersion spectrographs in 1969–1970, with emphasis on the detailed coverage of the primary minimum. One spectrum was taken exclusively within totality, thus exhibiting an uncontaminated spectrum of the secondary component. This leads to spectral reclassification of the secondary (F6 IV). The narrowing of the line profile of the H-line in totality is interpreted in terms of synchronous rotation of the secondary (v sini80 km s^–1) while the primary rotates faster (v sini130 km s^–1) than synchronously (v sini50 km s^–1). Although the secondary does not fill in its Roche lobe fully, the system exhibits pronounced indications of rather strong physical interaction. This is now supported also by the profound changes of the line profiles of the H-line with phase.  相似文献   

Assess hydrological responses to a warming climate at the Lysina Critical Zone Observatory in Central Europe     

Wenjuan Zheng  Anna Lamačová  Xuan Yu  Pavel Krám  Jakub Hruška  Pavel Zahradníček  Petr Štěpánek  Aleš Farda 《水文研究》2021,35(9):e14281

Climate warming is having profound effects on the hydrological cycle by increasing atmospheric demand, changing water availability, and snow seasonality. Europe suffered three distinct heat waves in 2019, and 11 of the 12 hottest years ever recorded took place in the past two decades, which will potentially change seasonal streamflow patterns and long-term trends. Central Europe exhibited six dry years in a row since 2014. This study uses data from a well-documented headwater catchment in Central Europe (Lysina) to explore hydrological responses to a warming climate. We applied a lumped parameter hydrologic model Brook90 and a distributed model Penn State Integrated Hydrologic Model (PIHM) to simulate long-term hydrological change under future climate scenarios. Both models performed well on historic streamflow and in agreement with each other according to the catchment water budget. In addition, PIHM was able to simulate lateral groundwater redistribution within the catchment validated by the groundwater table dynamics. The long-term trends in runoff and low flow were captured by PIHM only. We applied different EURO-CORDEX models with two emission scenarios (Representative Concentration Pathways RCP 4.5, 8.5) and found significant impacts on runoff and evapotranspiration (ET) for the period of 2071–2100. Results from both models suggested reduced runoff and increased ET, while the monthly distribution of runoff was different. We used this catchment study to understand the importance of subsurface processes in projection of hydrologic response to a warming climate.  相似文献   

Some Aspects of Meteoric Head Echo Velocity Determination     

ŠIMEK  Miloš  Přidal  Petr  Pecina  Petr  Boček  Jaroslav 《Earth, Moon, and Planets》1997,77(1):1-17

Velocity determination of 131 head echoes recorded during Perseid meteor shower observations by the Canadian 2 MW radar, has been performed under the assumption of either their constant velocity or of its linear change with time. Even though the constant velocities concentrated at 60 km s-1 generally accepted for the Perseids, a substantial number of echoes had velocities either lower than 60 km s-1 or greater than this value. The inclusion of variable velocity into considerations led to surprising result that a great portion of the head echoes accelerated (3 possibly decelerating echoes in comparison with 33 accelerating cases on the level of relative standard deviations of output parameters not exceeding 10%). It seems that the allocation of the ionization responsible for the head echo is not entirely identical with the instantaneous meteoroid position. As a consequence, the velocity derived from the measured head echo coordinates can differ from the velocity of parent body. We are not able to explain this finding at present. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

钻井液类型对南极冰层取心钻进工作的影响          下载免费PDF全文

宋佳宇  徐会文  韩丽丽  刘宁  张楠  Pavel Talalay 《探矿工程》2015,42(9):13-17

钻井液的类型与性能对于提高极地冰层取心钻进的效率与保证钻孔稳定性具有重要的影响。在分析铠装电动机械钻具工作原理与钻井液循环方式的基础上,较为详细地分析了升降钻具的速度与钻井液粘度与密度之间的关系;分析了现有钻井液类型和所存在的问题;以二元脂肪酸二醇酯、低分子量饱和脂肪酸酯与甲基硅油的试验测试数据为基础,确定了可用于极地冰层取心钻进的钻井液类型及其性能要求。  相似文献