Changes In Active Layer Research Articles

High Arctic Vegetation Communities With a Thick Moss Layer Slow Active Layer Thaw

AbstractSvalbards permafrost is thawing as a direct consequence of climate change. In the Low Arctic, vegetation has been shown to slow down and reduce the active layer thaw, yet it is unknown whether this also applies to High Arctic regions like Svalbard where vegetation is smaller, sparser, and thus likely less able to insulate the soil. Therefore, it remains unknown which components of High Arctic vegetation impact active layer thaw and at which temporal scale this insulation could be effective. Such knowledge is necessary to predict and understand future changes in active layer in a changing Arctic. In this study we used frost tubes placed in study grids located in Svalbard with known vegetation composition, to monitor the progression of active layer thaw and analyze the relationship between vegetation composition, vegetation structure and snow conditions, and active layer thaw early in summer. We found that moss thickness, shrub and forb height, and vascular vegetation cover delayed soil thaw immediately after snow melt. These insulating effects attenuated as thaw progressed, until no effect on thaw depth was present after 8 weeks. High Arctic mosses are expected to decline due to climate change, which could lead to a loss in insulating capacity, potentially accelerating early summer active layer thaw. This may have important repercussions for a wide range of ecosystem functions such as plant phenology and decomposition processes.

A study of thermal modeling parameters and their impact on modelled permafrost responses to climate warming

Climate warming is causing significant changes in the Arctic, leading to increased temperatures and permafrost instability. The active layer has been shown to be affected by climate change, where warmer ground surface temperatures result in progressive permafrost thaw and a deepening active layer. This study assessed the effects of thermal modeling parameters on permafrost ground response to climate warming using the fifth phase of the Coupled Model Intercomparison Project (CMIP5) and TEMP/W software. We analyzed how variations in depth, water content, and soil type affect predictions of future active layer depths and settlement under various climate scenarios using the soil characteristics along Hudson Bay Railway corridor. The results indicate that, for fine-grained soils, the depth of the model is a more significant parameter than for coarse-grained soils. The water content of all soil types is a critical factor in determining the time at which permafrost thaws and the depth at which the active layer is located, as higher water content leads to larger active layer changes and more settlement in most cases. Our findings have important implications for infrastructure and land use management in the Arctic region.

Land surface temperature analysis and active layer changes in Terkh River Valley

In this study, we identified the relationship between Ground Surface Temperature (GST) with the geography and environmental factors in the Terkh River Valley, Mongolia, and explored the possibility of using satellite data to determine active layer thickness and seasonally frozen ground changes. We obtained data from three boreholes for the permafrost monitoring, and ten GST measuring instruments that we installed in the valley. According to the results, the active layer thickness at the three boreholes varied between 2.8 and 6.22 m. In the Terkh Ar borehole, the active layer thickness increased by 5 cm per year, while the seasonally frozen ground depth in the Terkh Uvur borehole decreased by 12 cm during the study period. When comparing mean GST with geographic factors such as elevation, slope, and aspect, the correlation was weak (R2 = 0.026-0.23). However, when comparing mean GST in the summer season with indices such as MSAVI, MNDWI, and NDMI, the correlation was high (R2 = 0.37-0.91). The highest value of the thawing degree days (TDD) was 2708°C and observed at T-10, while the lowest value of the TDD was 1174°C and observed at T-1. The minimum value of freezing degree days (FDD) was -3020°C and observed at the T-n point, while the maximum value of FDD was -1553°C and observed at the T-10 point. The N-factor derived from the FDD and TDD values revealed a high correlation with the MSAVI index (R2 = 0.77). It is indicated that the MSAVI index can be one of the factors modeling the active layer thickness. Тэрхийн голын хөндийн гадаргын температурын анализ болон улирлын хөлдөлт, гэсэлтийн өөрчлөлт ХУРААНГУЙ: Бид энэхүү судалгаагаар Тэрхийн голын хөндийн гадаргын температурын үйл явцыг газарзүй болон байгалийн хүчин зүйлстэй хамаарлыг судлах, мөн ул хөрсний улирлын хөлдөлт гэсэлтийн өөрчлөлтийг мониторинг цооногийн мэдээ ашиглан тогтоох, цаашлаад улирлын хөлдөлт гэсэлтийн загварчлалыг хийхэд хиймэл дагуулын мэдээг ашиглах боломж зэргийг судаллаа. Судалгаанд ашигласан мэдээг энэхүү голын хөндийд байрлах цэвдгийн мониторингийн 3 цэг болон гадаргын температур хэмжигч 10 багажаас авсан. Судалгааны үр дүнгээс үзэхэд улирлын хөлдөлтийн гүн цэвдгийн мониторингийн 3 цэгт 2.8 – 6.22 м-ийн гүнд хэлбэлзэж байсан. Харин улирлын гэсэлтийн гүн Тэрх ар цооногт жилд 5 см-аар нэмэгдэж байсан бол Тэрх ар цооногт улирлын хөлдөлтийн гүн жилд 12 см-аар буурч байна гэсэн үр дүн гарсан. Гадаргын жилийн дундаж температурыг газарзүйн хүчин зүйлс болох өндөршил, зүг зовхис, гадаргын налуу зэрэг хүчин зүйлстэй харьцуулж үзэхэд бага хамааралтай байв (R2 = 0.026-0.23). Харин зуны улирлын гадаргын дундаж температурыг MSAVI, MNDWI, NDMI зэрэг индексүүдтэй харьцуулж үзэхэд хоорондын хамаарал өндөр байна (R2 = 0.37-0.91). Хамгийн өндөр TDD утгыг Т-10 цэгт 2708°С байгаа бол хамгийн бага нь Т-1 дээр 1174°С байна. Хүйтний улирал буюу FDD-ийн хамгийн бага утга нь T-n цэгт -3020°С байсан бол хамгийн их нь Т-10 цэгт -1553°С тус тус байна. Дээрх утгуудаас гаргаж авсан N-факторыг MSAVI индекстэй харьцуулж үзэхэд R2 нь 0.77 буюу сайн гэж гарсан нь цаашид энэхүү индексийг улирлын хөлдөлт гэсэлтийн загварчлалд ашиглах боломжтой гэдгийг харуулж байна. Түлхүүр үгс: N-фактор, Улирлын хөлдөлт, Улирлын гэсэлт, MSAVI, MNDWI, NDMI

Permafrost table temperature and active layer thickness variability on James Ross Island, Antarctic Peninsula, in 2004–2021

Climate change and its impacts on sensitive polar ecosystems are relatively little studied in Antarctic regions. Permafrost and active layer changes over time in periglacial regions of the world are important indicators of climate variability. These changes (e. g. permafrost degradation, increasing of the active layer thickness) can have a significant impact on Antarctic terrestrial ecosystems. The study site (AWS-JGM) is located on the Ulu Peninsula in the north of James Ross Island. Ground temperatures at depths of 5, 50, and 75 cm have been measured at the site since 2011, while air temperature began to be measured in 2004. The main objective is to evaluate the year-to-year variability of the reconstructed temperature of the top of the permafrost table and the active layer thickness (ALT) since 2004 based on air temperature data using TTOP and Stefan models, respectively. The models were verified against direct observations from a reference period 2011/12–2020/21 showing a strong correlation of 0.95 (RMSE = 0.52) and 0.84 (RMSE = 3.54) for TTOP and Stefan models, respectively. The reconstructed average temperature of the permafrost table for the period 2004/05–2020/21 was −5.8 °C with a trend of −0.1 °C/decade, while the average air temperature reached −6.6 °C with a trend of 0.6 °C/decade. Air temperatures did not have an increasing trend throughout the period, but in the first part of the period (2004/05–2010/11) showed a decreasing tendency (−1.3 °C/decade). In the period 2011/12–2020/21, it was a warming of 1.9 °C/decade. The average modelled ALT for the period 2004/05–2020/21 reached a value of 60cm with a trend of −1.6 cm/decade. Both models were found to provide reliable results, and thus they significantly expand the information about the permafrost and ALT, which is necessary for a better understanding of their spatiotemporal variability and the impact of climate change on the cryosphere.

Systematic investigation on stability influence factors for organic solar cells

Degradation of organic solar cells has always hindered the commercialization of organic solar cells (OSCs). In this paper, we fabricate OSCs with a power conversion efficiency (PCE) of 16.20%. The impact of different layers on degradation is studied for the first time by performing accelerated aging test on each layer. The device experiencing accelerated aging process on ITO/ZnO barely decays, indicating the electron transport layer (ETL) ZnO hardly affects the device degradation. The device experiencing accelerated aging process on ITO/ZnO/active layer and the and the device experiencing accelerated aging process on ITO/ZnO/active layer/MoO3 decay fast, manifesting the big impact of active layer and MoO3 on degradation. During the accelerated aging process, the morphology of the active layer changes, hindering light absorption and charge transport. Besides, the work function of hole transport layer (HTL) MoO3 becomes shallower after accelerated aging, making the hole extraction less efficient. Transient absorption spectroscopy (TAS) is recorded to investigate exciton physics change during the accelerated aging process, proving that inefficient charge transfer (CT) state excitons formation and separation account for the PCE decay. The mechanism of the degradation of OSCs is discussed, laying the foundation of their commercialization.

Permafrost dynamics and their hydrologic impacts over the Russian Arctic drainage basin

Permafrost is an important component in hydrological processes because changes in runoff over the Arctic drainage basin cannot be well explained by changes in precipitation-related variables. However, current understanding of the influences of permafrost on hydrological dynamics is insufficient. This study investigated historical variations in permafrost conditions and their potential hydrologic effects over the Russian Arctic drainage basin. The results show that soil temperature (at 0.40 m below surface) has increased about 1.4 °C over the Ob, 1.5 °C over the Yenisei, and 1.8 °C over the Lena River basin from 1936 through 2013, possibly resulted in a significant thawing of permafrost. Rapid active layer changes have occurred since the 1970s. The volume of the active layer increased by 28, 142, and 228 km3 over the Ob, Yenisei, and Lena basins, respectively, since the 1970s. Melting ground ice caused by deepening active layer may be a limited contribution to annual runoff. Runoff during freeze season (October–April) showed significant positive correlations (p < 0.05) to active layer thickness in the Yenisei and Lena basins while negative correlation (p > 0.05) in the Ob basin. These results imply that, in basins with high permafrost coverage, a deeper active layer increased soil water storage capacity and perhaps contribute to an increase in winter runoff.

Quantitative evaluation of characteristic precipitation event (CPE)’s effect on hydro-thermal state of active layer in Beiluhe area

The climate change is significantly changing the hydro-thermal state of active layer at Qinghai–Tibet Plateau (QTP), which endangers permafrost environment. The degradation of permafrost would damage the linear engineering in cold regions; furthermore, the alternation of soil hydro-thermal state in the area of rugged terrain would lead to geo-hazards and then threaten the safety of local people. Global warming is widely accepted as a big threat to the ecological environment of arctic, subarctic and alpine regions, while the changing trend of precipitation around the world is still in dispute. Furthermore, the role of precipitation accompanied with global warming is unknown. Hence, in this study, the localized monitoring data from Beiluhe permafrost monitoring station at QTP, including atmospheric and soil hydro-thermal data, were utilized for further processing and comparative analysis. Firstly, the changing trend of precipitation here was investigated through the atmospheric data from 2003 to 2013. Thereafter, the hydro-thermal change of active layer was analyzed combined with precipitation events during this period. However, the raining pattern in QTP is characterized with continuity, short duration and small amount, basically referring to thawed season. The hydro-thermal change affected by corresponding raining event could be influenced by temporally nearby event in timescale. To differentiate the effect, the characteristic precipitation event (CPE) was selected through an elaborate algorithm. Subsequently, the hydro-thermal changes of active layer were reanalyzed in response to CPEs. Representative outcomes were chosen for the specific analysis under the influence from CPEs. Hence, under the circumstance of global warming, the effect from precipitation on the hydro-thermal properties of active layer was also obtained, and the possible harmful consequence induced by that was also discussed.

Permafrost seasonal surface changes revealed from Sentinel-1 InSAR time-series, Yamal peninsula

Abstract. Widespread thawing of permafrost in the northern Eurasian continent causes severe problems for infrastructure and global climate. We test the potential of Sentinel-1 SAR imagery to enhance detection of permafrost surface changes in the Siberian lowlands of the northern Eurasian continent at the Yamal peninsula site. We used InSAR time-series technique to detect seasonal surface movements related to permafrost active layer changes. The satellite InSAR time-series analysis has detected continuous movements, subsidence in three zones, which have occurred during the time period from 2017 to 2018. Observed subsidence zones show up to 180 mm yr−1 rates of seasonal active layers changes. These seasonal ground displacement patterns align well with lithology and linked to anthropogenic impact on the permafrost surface changes in the area. The results show that Sentinel-1 mission is of great importance for the longer-term monitoring of active layer thickening in permafrost regions. The combined analyses of the obtained InSAR time series with additional field observations may support regular process monitoring as part of a global warming risk assessment.

Reflection and transmission of electromagnetic waves by a multilayered solar cell containing organic materials

Light trapping or absorption is a key concept for design and fabricating solar cells. The propagation of electromagnetic waves through a multilayered solar cell containing organic materials has theoretically investigated. In particular, the reflected, transmitted, and absorbed powers are found and defined. The main parameters of the structure and the required equations for TE polarization are presented in detail. The boundary conditions of the electric and magnetic fields of the incident waves are imposed at each interface and Snell’s law is applied. Expressions for the overall reflection and transmission coefficients are provided by a recursive method. The reflected, transmitted, and absorbed powers are determined using these coefficients. In the numerical results, the mentioned powers are computed and illustrated as a function of the angle of incidence, the wavelength, and the thickness of the active layer when the extinction coefficient of the active layer changes.

Reconciling DLVO and non-DLVO Forces and Their Implications for Ion Rejection by a Polyamide Membrane.

Recognizing the significance of surface interactions for ion rejection and membrane fouling in nanofiltration, we revise the theories of DLVO (named after Derjaguin, Landau, Verwey, and Overbeek) and non-DLVO forces in the context of polyamide active layers. Using an atomic force microscope, surface forces between polyamide active layers and a micrometer-large and smooth silica colloid were measured in electrolyte solutions of representative monovalent and divalent ions. While the analysis of DLVO forces, accounting for surface roughness, provides how surface charge of the active layer changes with electrolyte concentration, scrutiny of non-DLVO hydration forces gives molecular insight into the composition of the membrane-solution interface. Importantly, we report an expansion of the diffuse layer at high ionic strength, consistent with the recent development of the electrical double layer theory, but in contrast to the widely accepted phenomenon of aggregation in the secondary minimum. Further, the enhanced repulsion acting on modified membranes via polyelectrolyte adsorption can be quantitatively predicted by DLVO and non-DLVO forces. This work serves to solve past misunderstandings about the interaction forces acting on nanofiltration membranes, and it provides guidance for future work on the relation between surface properties and rejection mechanisms and fouling.

Efficient Light Trapping in Organic Solar Cell Using a Short-Pitched Hexagonal Array of Metallic Nanocylinders

Plasmonic nanostructures have a great potential for enhancing light absorption of organic solar cells (OSCs). Our previous work has demonstrated that light absorption for OSCs with thin active layer can be significantly increased with a 1-D short-pitched metal grating, but the absorption enhancement is sensitive to the polarization of light and vanishes when the active layer is thicker than 60 nm. In this work, we extend the grating into 2-D space, specifically, with metallic nanocylinders packed in a hexagonal array embossed at the silver cathode. Numerical calculations indicate that the proposed OSC not only possesses polarization insensitivity but outperforms the corresponding equivalent planar device as well when the thickness of the active layer changes over a wide range from 40 to 120 nm. The absorption enhancement factor increases with the decrease of the active layer thickness, reaching 81.5% when the active layer is 40-nm thick. The evident enhancement in absorption is mainly due to the excitation of the strong dipole-like surface plasmon resonance, as well as their mutual coupling between neighboring nanocylinders. The present work could provide a promising route for the development of high-efficiency OSCs.

INTEGRATED SAR TECHNOLOGIES FOR MONITORING THE STABILITY OF MINE SITES: APPLICATION USING TERRASAR-X AND RADARSAT-2 IMAGES

Abstract. The last three decades have seen significant mining development in the northern regions of Canada, where the freeze and thaw cycle of permafrost and corresponding surface subsidence and heave represent a significant challenge at all mining stages, from the design of infrastructures to the monitoring of restored areas. Over the past ten years, SAR interferometry has been widely used to monitor ground surface deformation. With this technique, changes in phase between two SAR acquisitions are used to detect centimetre to millimetre surface displacements over a large area with high spatial resolution. This paper presents the results of a project that aims to develop a SAR solution to provide useful information for environmental monitoring and assessing the stability of mining sites. RADARSAT-2 and TerraSAR-X images acquired during the summer of 2014 were used to measure the displacements of ground surface, infrastructures and stockpiles caused by seasonal changes in permafrost extent. The study area is an open-pit mine located in Nunavut, northern Canada, in the continuous permafrost zone. Results shown that surface displacements calculated from RADARSAT-2 and TerraSAR-X are very similar and in agreement with scientific and terrain knowledge. Significant displacements were observed in loose soil areas while none was detected in bedrock and rock outcrop areas. The areas most affected by active layer changes showed surface subsidence during the thaw settlement period. Thus, InSAR can be used as a tool to guide the siting and design of new infrastructure as well as highlighting risks in areas of unstable terrain.

Modeling the effects of fire severity and climate warming on active layer thickness and soil carbon storage of black spruce forests across the landscape in interior Alaska

There is a substantial amount of carbon stored in the permafrost soils of boreal forest ecosystems, where it is currently protected from decomposition. The surface organic horizons insulate the deeper soil from variations in atmospheric temperature. The removal of these insulating horizons through consumption by fire increases the vulnerability of permafrost to thaw, and the carbon stored in permafrost to decomposition. In this study we ask how warming and fire regime may influence spatial and temporal changes in active layer and carbon dynamics across a boreal forest landscape in interior Alaska. To address this question, we (1) developed and tested a predictive model of the effect of fire severity on soil organic horizons that depends on landscape-level conditions and (2) used this model to evaluate the long-term consequences of warming and changes in fire regime on active layer and soil carbon dynamics of black spruce forests across interior Alaska. The predictive model of fire severity, designed from the analysis of field observations, reproduces the effect of local topography (landform category, the slope angle and aspect and flow accumulation), weather conditions (drought index, soil moisture) and fire characteristics (day of year and size of the fire) on the reduction of the organic layer caused by fire. The integration of the fire severity model into an ecosystem process-based model allowed us to document the relative importance and interactions among local topography, fire regime and climate warming on active layer and soil carbon dynamics. Lowlands were more resistant to severe fires and climate warming, showing smaller increases in active layer thickness and soil carbon loss compared to drier flat uplands and slopes. In simulations that included the effects of both warming and fire at the regional scale, fire was primarily responsible for a reduction in organic layer thickness of 0.06 m on average by 2100 that led to an increase in active layer thickness of 1.1 m on average by 2100. The combination of warming and fire led to a simulated cumulative loss of 9.6 kgC m−2 on average by 2100. Our analysis suggests that ecosystem carbon storage in boreal forests in interior Alaska is particularly vulnerable, primarily due to the combustion of organic layer thickness in fire and the related increase in active layer thickness that exposes previously protected permafrost soil carbon to decomposition.

MODIS-Derived Arctic Land-Surface Temperature Trends

Across the Arctic changes in active layer, melting of glaciers and ground ice, thawing of permafrost and sequestration changes of carbon storage are driven in part by variations of land surface heat absorption, conduction and re-radiation relative to solar irradiance. We investigate Arctic land-surface temperature changes and regional variations derived by the MODIS sensors on NASA Aqua and Terra from March 2000 through July 2012. Over this decadal period we detect increase in the number of days with daytime land-surface temperature above 0℃. There are indications of increasing trends of land-surface temperature change. Regional variations of the changes in land-surface temperature likely arise due to surface material types and topography relative to the daytime variation of solar irradiance.

Periglacial processes and landforms of the Antarctic: a review of recent studies and directions

Abstract The wide range of periglacial environments of the Antarctic, from the wet, mild oceanic sub-Antarctic through to the cold, dry continent, provides not only an extensive modern laboratory, but also one that offers insights into conditions in the Northern Hemisphere at the height of the last glacial, is an analogue for periglacial conditions on other planets, and can be used for monitoring climatic change. Almost the whole known suite of periglacial landforms is present. Recent research directions show strong linkages between the biotic components and the abiotic responses, offering new insights into periglacial synergies and hence landform development. Other new directions are those of using the Antarctic as an analogue for periglacial conditions on Mars, and multinational undertakings monitoring permafrost and active layer changes. During the past three decades there have been a number of reviews of periglacial landforms and processes for both the area as a whole as well as for specific locations or regions. Here information regarding material post-dating the most recent reviews is provided and an attempt is made to highlight new directions and findings. This broad-based review provides a foundation for more detailed accounts on some of the periglacial attributes provided in other papers within these volumes.

Annual soil CO2 efflux in a wet meadow during active layer freeze–thaw changes on the Qinghai-Tibet Plateau

Soil CO2 efflux from an ecosystem responds to the active layer thawing depth (H) significantly. A Li-8100 system was used to monitor the CO2 exchange from a wet meadow ecosystem during a freeze–thaw cycle of the active layer in a permafrost region on the Qinghai-Tibet Plateau. An exponential regression equation ( $$ F_{\text{soil\, flux}} = 1.84e^{0.023H} + 5.06\,R^{2} = 0.96 $$ ) has been established on the basis of observed soil CO2 efflux versus the thawed soil thickness. Using this equation, the total soil CO2 efflux during an annual freeze–thaw cycle has been calculated to be approximately 8.18 × 1010 mg C. The results suggest that freeze–thaw cycles in the active layer play an important role in soil CO2 emissions and that thawed soil thickness is the major factor controlling CO2 fluxes from the wet meadow ecosystem in permafrost regions on the Qinghai-Tibet Plateau. It can be concluded that with active layer thickening due to permafrost degradation, massive amounts of soil carbon would be emitted as greenhouse gases, and the permafrost region would become a carbon source with a positive feedback effect on climate warming. Hence, more attention should be paid to the influences of the active layer changes on soil carbon emission from these permafrost regions.

Hydrochemical and sedimentary responses of paired High Arctic watersheds to unusual climate and permafrost disturbance, Cape Bounty, Melville Island, Canada

AbstractHigh Arctic river responses to changing hydroclimatic and landscape processes are poorly understood. In non‐glacierized basins, snowmelt and rainfall generate river discharge, which provides first order control over fluxes. Further factors include the seasonality of precipitation, seasonal active layer development, and permafrost disturbance. These controls were evaluated in terms of sedimentary and biogeochemical fluxes from paired catchments at Cape Bounty, Melville Island, Nunavut during 2006–2009. Results indicate that the source of runoff can be more important than the amount of runoff for sediment, solutes, and organic yields. Although the snowmelt period is typically the most important time for these yields, heavy late summer precipitation events can create disproportionately large yields. Rainfall increases yields because it hydrologically connects areas otherwise isolated. Inorganic solute yields from late summer rainfall are higher because the thick active layer maximizes hydrologic interactions with mineral soils and generates high solute concentrations. Results also indicate that while the catchments are broadly similar, subtle topographic differences result in important inter‐catchment differences in runoff and suspended and dissolved loads. The East watershed, which had less extensive permafrost disturbance, consistently had higher concentrations of dissolved solids. These higher dissolved fluxes cannot therefore be explained by thermokarst features, but rather by deeper active layer development, due to a greater proportion of south‐facing slopes. Although warm temperatures in 2007 led to extensive active layer disturbance in the West watershed, because the disturbances were largely hydrologically disconnected, the total disturbed area was small, and inter‐annual variability in discharge was high, there was no detectable response in dissolved loads to disturbances. Sediment availability increased after 2007, but yields have largely returned to pre‐disturbance levels. Results indicate that seasonality and frequency‐magnitude characteristics of projected increases in precipitation must be considered along with active layer changes to predict the fluvial sedimentary and biogeochemical response to regional climate change. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Assessing the role of differential frost heave in the origin of non-sorted circles

A. L. Washburn famously proposed and reviewed 19 hypotheses for the origin of patterned ground in periglacial environments over 50 years ago (Washburn, 1956). Of these 19 mechanisms, only a few have been analyzed starting from a fundamental description of the physics to assess their potential contribution to the initiation of patterned ground. Here, differential frost heave (DFH) is investigated as the origin of non-sorted circles in periglacial landscapes. Model results indicating that DFH can spontaneously lead to patterned ground are compared to measurements of patterned ground in the Canadian Arctic Archipelago. The characteristic size of the predicted emerging pattern depends strongly on the maximum depth of freezing but is only weakly dependent on the soil composition. The predicted emerging patterns may also be dramatically different in size with a small change in active layer when a relatively thin (~ 10 cm) insulating snow covers the ground during freezing. The model predicted trends agree with field observations of pattern size and active layer depth at two distinct sites. Although two data points cannot conclusively indicate a trend, this correlation gives support for the possibility of determining some subsurface properties using remote sensing images of surface patterned ground.

Simulation of transient thermal states in layered electronic microstructures

The analysis of dynamic temperature changes in microelectronic layered circuit (especially made in thick-film technology) has been presented in the paper. Such transient states are caused by electric pulse with high energy and short time of duration. It leads to short but the very violent temperature increase and – as result – defects or parameter changes of active layer. The mathematical function which describes the instantaneous temperature changes was presented in this paper in order to provide more accurate analysis of reliability and thermal properties measurement problems. The two-layer structures (with different thermo-physical properties) were the subject of conducted research, especially one of them, namely heat source excited by electric pulse. Such configuration is typical for microcircuits made in hybrid technology such as LTCC (low temperature co-fired ceramic), HTCC (high temperature co-fired ceramic) as well as thick – film technology in which polymer and photoimageable (photosensitive) materials are used.

Effects of local changes in active layer and soil climate on seasonal foliar nitrogen concentrations of three boreal forest shrubs

Caribou Poker Creeks Research Watershed is a boreal forest watershed in Interior Alaska that is susceptible to regional warming and permafrost thaw. We measured seasonal foliar N concentrations of the black spruce understory shrubs, Vaccinium uliginosum L., Vaccinium vitis-idaea L., and Ledum palustre L. on north- and south-facing sides of the watershed. We predicted that the shrubs would respond to small-scale changes in active layer and soil climate, and we expected similar responses according to growth strategy (evergreen or deciduous). Overall, foliar N in shrubs was higher on warmer, drier soils with deep active layers: +7.9% N in V. uliginosum, +11.1% N in V. vitis-idaea, and +9.4% N in L. palustre. Each shrub had species-specific foliar N patterns that could not be categorized by growth strategy and were not well explained by soil climate or active layer. Leaf mineral nutrition is influenced by multiple processes, and foliar N was best explained by the combination of environmental variables operating at the study site. For Caribou Poker Creeks Research Watershed, we can expect increased N status of the black spruce understory along with continued climate warming, but changes cannot be predicted based on growth strategy.