Testing long-term summer temperature reconstruction based on maximum density chronologies obtained by reanalysis of tree-ring data sets from northernmost Sweden and Finland

Here we analyse the maximum latewood density (MXD) chronologies of two published tree-ring data sets: one from Torneträsk region in northernmost Sweden (TORN; Melvin et al., 2013) and one from northern Fennoscandia (FENN; Esper et al., 2012). We paid particular attention to the MXD low-frequency variations to reconstruct summer (June–August, JJA) long-term temperature history. We used published methods of tree-ring standardization: regional curve standardization (RCS) combined with signal-free implementation. Comparisons with RCS chronologies produced using single and multiple (non-climatic) ageing curves (to be removed from the initial MXD series) were also carried out. We develop a novel method of standardization, the correction implementation of signal-free standardization, tailored for detection of pure low-frequency signal in tree-ring chronologies. In this method, the error in RCS chronology with signal-free implementation is analytically assessed and extracted to produce an advanced chronology. The importance of correction becomes obvious at lower frequencies as smoothed chronologies become progressively more correlative with correction implementation. Subsampling the FENN data to mimic the lower chronology sample size of TORN data shows that the chronologies bifurcate during the 7th, 9th, 17th and 20th centuries. We used the two MXD data sets to reconstruct summer temperature variations over the period 8 BC through AD 2010. Our new reconstruction shows multi-decadal to multi-centennial variability with changes in the amplitude of the summer temperature of 2.2 °C on average during the Common Era. Although the MXD data provide palaeoclimate research with a highly reliable summer temperature proxy, the bifurcating dendroclimatic signals identified in the two data sets imply that future research should aim at a more advanced understanding of MXD data on distinct issues: (1) influence of past population density variations on MXD production, (2) potential biases when calibrating differently produced MXD data to produce one proxy record, (3) influence of the biological age of MXD data when introducing young trees into the chronology over the most recent past and (4) possible role of waterlogging in MXD production when analysing tree-ring data of riparian trees

The intensity of the climatic signal in the dynamics of the inсrement of Scots pine (Pinus silvestris L.) of the Khrenovskii forest (Voronezh region, Russia)

Our research was carried out in the center of the Voronezh Region, Russia, in the pine forest "Khrenovskoy forest", located in the forest steppe zone of the Russian Plain. The samples for dendrochronological analysis were collected from 30 trees (1 core per tree). The climatic characteristics are taken from the data of the weather stations "Khrenovskoy forest", for the period 1936-1996 and Voronezh for the period 1862-2015. In accordance with the goal of the research, we identified high correlation coefficients (up to 0.42) and dispersion (up to 0.66) between the radial increment of Scots pine and the climatic limiting growth factors (sum of atmospheric precipitation, hydrothermal coefficient Selyaninova

Optimization of end mills periphery milling

Розроблена математична модель для оптимізації процесу периферійного фрезерування, яка містить чисельний метод визначення сили різання, а також рівняння, що зв'язують обмеження з керованими параметрами режиму різання: частотою обертання шпинделя і подачею. Доведено, що шорсткість поверхні не залежить від геометричної складової профілю, що утворюється при переміщенні зубів фрези за траєкторією квазітрохоїди, а визначається максимальною амплітудою і частотою спектру сили різання, а також частотними характеристиками технологічної оброблювальної системи. Оптимальний режим різання формується в області допустимих значень фазового простору «частота обертання – подача» в основному двома обмеженнями: за стійкістю інструменту і за шорсткістю. Створена прикладна програма для автоматизованого визначення оптимального режиму різання при периферійному фрезеруванні сталей, чавунів та легких сплавів на основі алюмінію.A mathematical model is developed for optimization of process of the peripheral milling, which contains the digital method of determination of cutting force, and also equalizations relating limitations with the guided parameters of the cutting mode: by frequency of rotation of spindle and feed-rate. It is well-proven that the roughness of surface does not depend on the geometrical constituent of type, appearing at moving of points milling cutter on a cvasytrohoid, and determined maximal amplitude and frequency of spectrum of cutting force, and also by frequency descriptions of the technological processing system. The optimum mode of cutting is formed in area of legitimate values of phase space «frequency of rotation – feed-rate» mainly by two limitations: on firmness of instrument and on a roughness. The application program is created for the automated determination of the optimum mode of cutting at the peripheral milling of steels, cast-irons and easy alloys on the basis of aluminum.Разработана математическая модель для оптимизации процесса периферийного фрезерования, которая содержит численный метод определения силы резания, а также уравнения связывающие ограничения с управляемыми параметрами режима резания: частотой вращения шпинделя и подачей. Доказано, что шероховатость поверхности не зависит от геометрической составляющей профиля, образующейся при перемещении зубьев фрезы по квазитрохоиде, а определяется максимальной амплитудой и частотой спектра силы резания, а также частотными характеристиками технологической обрабатывающей системы. Оптимальный режим резания формируется в области допустимых значений фазового пространства «частота вращения – подача» в основном двумя ограничениями: по стойкости инструмента и по шероховатости. Создана прикладная программа для автоматизированного определения оптимального режима резания при периферийном фрезеровании сталей, чугунов и легких сплавов на основе алюминия

Simulation of end mills milling

Розроблена математична модель і алгоритм моделювання фрезерування контуру кінцевими фрезами. Математична модель ураховує повну геометричну конфігурацію інструмента, а саме, забезпечує можливість зміни кута нахилу спіральної канавки, кількості зубів, можливість використання довільних контурів деталі і заготовки. Створене програмне забезпечення дозволяє не тільки моделювати процес фрезерування, а й визначати управління подачею для стабілізації сили різання. Результати моделювання підтверджені експериментами на верстаті VF-3 фірми HAAS.A mathematical model and algorithm of simulation of contour milling by end mills is developed. A mathematical model takes into account complete geometrical configuration of instrument, namely, provides possibility of change of angle of slope of spiral ditch, amounts of points, possibility of the use of arbitrary contours of detail and workpiece. The created software allows not only to simulate a milling process but also determine a control of feed for stabilizing of cutting force. Design results are confirmed experiments on the CNC-machine VF-3 HAAS.Разработана математическая модель и алгоритм моделирования фрезерования контура концевыми фрезами. Математическая модель учитывает полную геометрическую конфигурацию инструмента, а именно, обеспечивает возможность изменения угла наклона спиральной канавки, количества зубьев, возможность использования произвольных контуров детали и заготовки. Созданное программное обеспечение позволяет не только моделировать процесс фрезерования, но и определять управление подачей для стабилизации силы резания. Результаты моделирования подтверждены экспериментами на станке VF-3 фирмы HAAS

Recurrent transitions to Little Ice Age-like climatic regimes over the Holocene

Holocene climate variability is punctuated by episodic climatic events such as the Little Ice Age (LIA) predating the industrial-era warming. Their dating and forcing mechanisms have however remained controversial. Even more crucially, it is uncertain whether earlier events represent climatic regimes similar to the LIA. Here we produce and analyse a new 7500-year long palaeoclimate record tailored to detect LIA-like climatic regimes from northern European tree-ring data. In addition to the actual LIA, we identify LIA-like ca. 100-800 year periods with cold temperatures combined with clear sky conditions from 540 CE, 1670 BCE, 3240 BCE and 5450 BCE onwards, these LIA-like regimes covering 20% of the study period. Consistent with climate modelling, the LIA-like regimes originate from a coupled atmosphere-ocean-sea ice North Atlantic-Arctic system and were amplified by volcanic activity (multiple eruptions closely spaced in time), tree-ring evidence pointing to similarly enhanced LIA-like regimes starting after the eruptions recorded in 1627 BCE, 536/540 CE and 1809/1815 CE. Conversely, the ongoing decline in Arctic sea-ice extent is mirrored in our data which shows reversal of the LIA-like conditions since the late nineteenth century, our record also correlating highly with the instrumentally recorded Northern Hemisphere and global temperatures over the same period. Our results bridge the gaps between low- and high-resolution, precisely dated proxies and demonstrate the efficacy of slow and fast components of the climate system to generate LIA-like climate regimes.Peer reviewe

Об оценке объёма льда горных ледников

Volume (V) − area (S) scaling approach (V = kSp, where V and S are obtained from direct measurements) is widely used for ice storage assessments in glacier-mountain systems. Accuracy of this approach was tested using surface area and volume dataset for 121 glaciers of different morphological type and sizes in Altay Mountains. It is shown that to increase total volume estimation accuracy, the coefficients k and p should be calculated for dominant morphological glacier types in the given region. Volume assessments for individual glaciers can be done using limited ice thickness data along the longitudinal profile. For two glaciers in Caucasus volume was calculated using parabolic and Topo to Raster approximation for cross section profiles of their surface and bedrock with acceptable accuracy (from 1 to 33%). It is also shown that ice-thickness data for 10–15 glaciers of dominant morphological type is enough for adequate estimation of the total ice storage in given mountain system with error less than 20%.Имеющиеся данные по измерению толщины и объёма горных ледников, а также существующие расчётные методы не позволяют достаточно точно установить запасы льда в горно-ледниковых системах. Обсуждаются существующие методы определения объёма горных ледников и запасов льда в горно-ледниковых системах, а также способы их более точной оценки на основе ограниченных данных о толщине и объёме отдельных ледников. Оценивается ошибка определения объёма отдельных ледников при ограниченном числе измерений

Last millennium northern hemisphere summer temperatures from tree rings: Part I: The long term context

Large-scale millennial length Northern Hemisphere (NH) temperature reconstructions have been progressively improved over the last 20 years as new datasets have been developed. This paper, and its companion (Part II, Anchukaitis et al. in prep), details the latest tree-ring (TR) based NH land air temperature reconstruction from a temporal and spatial perspective. This work is the first product of a consortium called N-TREND (Northern Hemisphere Tree-Ring Network Development) which brings together dendroclimatologists to identify a collective strategy for improving large-scale summer temperature reconstructions. The new reconstruction, N-TREND2015, utilises 54 records, a significant expansion compared with previous TR studies, and yields an improved reconstruction with stronger statistical calibration metrics. N-TREND2015 is relatively insensitive to the compositing method and spatial weighting used and validation metrics indicate that the new record portrays reasonable coherence with large scale summer temperatures and is robust at all time-scales from 918 to 2004 where at least 3 TR records exist from each major continental mass. N-TREND2015 indicates a longer and warmer medieval period (∼900–1170) than portrayed by previous TR NH reconstructions and by the CMIP5 model ensemble, but with better overall agreement between records for the last 600 years. Future dendroclimatic projects should focus on developing new long records from data-sparse regions such as North America and eastern Eurasia as well as ensuring the measurement of parameters related to latewood density to complement ring-width records which can improve local based calibration substantially

Сравнение гидротермической структуры двух ледников Шпицбергена и Тянь-Шаня по данным радиозондирования

The distribution of cold and temperate ice and water in polythermal glaciers significantly affects their dynamics, thermal and hydrological regime. Radar techniques are an effective remote method of their studies that allows one to determine a glacier thickness by the delay time and to estimate the water content in temperate ice and at bedrock by the intensity of reflections from the interface between cold and temperate ice and the glacier bed. In case study of Austre Grønfjordbreen in Spitsbergen and Central Tuyksu glacier in Tien Shan we consider the features of their hydrothermal structure in spring and summer periods using the data of ground-based radio-­echo sounding at frequency of 20 MHz. To estimate the relative water content, we used data from measurements of relative power reflections from the cold-temperate ice interface, at the bedrock, and from the temperate ice body. In these glaciers (Austre Grønfjordbreen and Central Tuyksu), the average thickness of cold and temperate ice is, respectively, 61 ± 6 and 27 ± 2 m, and 39 ± 4 and 20 ± 2 m, the volume of cold ice is 0.466 ± 0.005 km3 and 0.044 ± 0.002 km3, and volume of temperate ice is 0.104 ± 0.001 and 0.034 ± 0.001 km3. Warm ice contains 2080 × 103 and 680 × 103 m3 of water, respectively, with an average content of 2%. Measurements along the longitudinal profiles of these glaciers showed that in some parts on Austre Grønfjordbreen in the spring period the average intensity of reflections from the cold­temperate ice interface and the bedrock is −0.02 – −26.3 and −6.0 – −11.8 dB, respectively, and at the whole profile this is −13.36 dB. At Central Tuyuksu glacier the spring values are −14.5 – −32.4 and −29.6 dB, respectively. We attribute such differences of glaciers to the different water content in the temperate ice below and above these boundaries, to the specific distribution of the ice facies zones and glacial nourishment, to the different intensity of surface melting in the spring and summer periods, and to the different crevassing and velocity of glaciers.Рассмотрены особенности распределения толщины холодного и тёплого льда и воды в политермических ледниках на Шпицбергене (Земле Норденшельда) и Тянь-Шане (Заилийский Алатау) по данным наземных радиолокационных измерений на частоте 20 МГц, выполненных соответственно весной 2010 и 2019 гг. и летом 2013 г. По времени запаздывания и интенсивности отражений от поверхности раздела холодного и тёплого льда из толщи тёплого льда и от ложа определены толщина и объём холодного и тёплого льда, оценено содержание воды в тёплом льду и показана связь этих характеристик с особенностями строения и режима ледников в весенний и летний периоды, до и после начала таяния

Запасы льда в ледниках на Земле Норденшельда (Шпицберген) и их изменения за последние десятилетия

Data on thickness and area of 16 glaciers on the Nordenskiöld Land (Svalbard) were obtained in 1999 and 2010–2013. These data were used to determine volume of the glaciers and to establish statistical local relationship between the volume V and the area A (V–A scaling) in the form of the power function V = cAγ, and then to calculate the total ice volume of all 202 glaciers in this area and its changes during the period since 1936 to 2002–2008. The total area of 16 glaciers was 129.9±0.35 km2, 14 of which had areas from 0.2 to 8.1 km2. The two largest ones, the Fridtjof and the West Grenfjord, had the areas 17.5 and 47.3 km2, respectively, and thus occupied about 50% (64.8 km2) of the total area of 16 glaciers. These two glaciers account for 67% of the total measured volume (10,034 km3) of the 16 glaciers. A nonlinear least-squares method was used to estimate ice reserves in all 202 glaciers from data on the volume and area of 16 glaciers. The relation between volume V and area A of the  glaciers (V–A scaling) was obtained as the ratio V = 0.03637A1,283 with 95%‑th confidence intervals of the coefficients с and γ, (0.02303–0,4971) and (1.184–1.381), respectively. This made possible to calculate total volume of 202 glaciers as of 2002-2008 state using data from RGI v.6.0, and that prove to be equal to 32.89 (16.75–56.63) km3. To verify this estimation, we applied the bootstrapping method for chosen 43 glaciers and calculated the volume by means of sequential use of data for large and smaller glaciers. According to this estimate, the total volume of 202 glaciers amounted to 30.34 km3 with a 95% confidence interval of 15.42–44.27 km3, that turned out to be slightly smaller than the volume calculated by nonlinear least squares method basing on measurements on 16 glaciers. Despite the large error (on the average, from −49% to +84%) in estimating the total volume of 202 glaciers in the Nordenskiöld Land, the data obtained were used for assessment of relative changes in the total volume of glaciers in this area over different time intervals. During the period from 1936 to1990 (54 years), the total area of all glaciers reduced from 738.1 to 546.7 km2, and the total volume decreased from 49,205 to 34,857 km3. Similar results for the period 1990–2002–2008 (~15 years) are the total area changes from 546.7 to 507.9 km2 and their total volume - from 34.857 to 32.890 km3. The rate of decrease of the volume for the period 1936–1990 was equal to −0.266 km3/year, for the period 1990–2002–2008 – minus 0.131 km3/year, and as a whole for the studied period (since 1936 to 2002–2008) – minus  0.236 km3/year. The average mass balance in the first period was equal to −0.372 m w.e./year, in the second one −0.224 m w.e./year, and for the whole time −0.342 m w.e./year. Приведены результаты наземных радиолокационных измерений в 1999 и 2010–2013 гг. толщины и объёма 16 ледников на Земле Норденшельда (Шпицберген) с применением статистической связи между объёмом и площадью ледников. Оценены запасы льда во всех 202 ледниках этого района и их изменения за последние десятилетия с использованием данных о площади ледников по состоянию на 1936, 1990, 2002–2008 гг. и на годы радиолокационных измерений

Реконструкция баланса массы ледника Гарабаши (1800–2005 гг.) по дендрохронологическим данным

The exploration whether tree-ring data can be effectually applied for the mass balance reconstruction in Caucasus was the main goal of this research. Tree-ring width and maximum density chronologies of pine (Pinus sylvestris L.) at seven high-elevation sites in Northern Caucasus were explored for this purpose. As well as in other places of the temperate zone tree- ring width has complex climate signal controlled both temperature and precipitation. Instrumental mass balance records of Garabashi Gglacier started at 1983s. It is well known that Caucasus glaciers intensively retreat in the last decades and according to instrumental data mass balance variations are mostly controlled by the ablation, i.e. summer temperature variations. Maximum density chronology has statistically significant correlation with mass balance due to summer temperature sensitivity and great input of ablation to total mass balance variations. To include in our reconstruction different climatically sensitive parameters, stepwise multiple regression model was used. The strongest relation (r = 0.88; r2 = 0.78; p < 0.05) between two ring-width and one maximum density chronologies was identified. Cross-validation test (r = 0.79; r2 = 0.62; p < 0.05) confirmed model adequacy and it allowed to reconstruct Garabashi Glacier mass balance for 1800–2005ss. Reconstructed and instrumental mass balance values coincide well except the most recent period in 2000s, when the reconstructed mass balance slightly underestimated the real values. However even in this period it remained negative as well as the instrumental records. The bias can be explained by the weak sensitivity of the chronologies to winter precipitation (i.e. accumulation). The tree-ring based mass balance reconstruction was compared with one based on meteorological data (since 1905s). Both reconstructions have good interannual agreement (r = 0.53; p < 0.05) particularly for the period between 1975 and 2005. According to the reconstruction two distinct periods of positive mass balance occurred in 1830s and 1860s. They agree well with early historical data and the tree-ring of moraines of Kashkatash Glacier in Central Caucasus. Выполнена первая реконструкции баланса массы ледника Гарабаши по дендрохронологическим данным с 1800 по 2005 г. Лучше всего модель воспроизводит изменчивость годового баланса ледника при использовании хронологий по ширине годичных колец и по максимальной плотности поздней древесины. Изучен вклад каждой древесно-кольцевой хронологии в модель и её климатический отклик. Установлена высокая согласованность реконструкции баланса массы ледника по дендрохронологическим данным с реконструкциями, полученными ранее по метеорологическим рядам