Relation between the active region magnetic field and solar flares

A weak active region (NOAA 11158) appeared on the solar disk near the eastern limb. This region increased rapidly and, having reached the magnetic flux higher than 10²² Mx, produced an X-class flare. Only weak field variations at individual points were observed during the flare. An analysis of data with a resolution of 45 s did not indicate any characteristic features in the photospheric field dynamics during the flare. When the flux became higher than 3 × 10²² Mx, active region NOAA 10720 produced six X-class flares. The field remained quiet during these flares. An increase in the magnetic flux above ～10²² Mx is a necessary, but not sufficient, condition for the appearance of powerful flares. Simple active regions do not produce flares. A flare originates only when the field distribution in an active region is complex and lines of polarity inversion have a complex shape. Singular lines of the magnetic field can exist only above such active regions. The current sheets, in the magnetic field of which the solar flare energy is accumulated, originate in the vicinity of these lines.     

Effect of snow cover on pan-Arctic permafrost thermal regimes

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.     

基于CoLM模型的根分布对陆-气水热交换的影响研究:以玉米农田为例

利用2007—2008年辽宁锦州玉米农田生态系统野外观测站资料,基于CoLM模型对玉米根分布在陆-气水热通量模拟中的影响进行研究,结果表明:模型模拟性能随年际气象条件的差异而不同,与2007年相比,2008年生长季内降水偏多,感热和潜热模拟精度明显提高;决定根分布形态的50%和95%根总量土层深度(d50和d95)两个参数中,d50比d95敏感;根分布对土壤湿度的影响在极端干旱条件下很小,在一定土壤湿度范围内随土壤湿度及土层深度的增大而减小;在水汽通量各分量中,植物蒸腾受根分布影响最大,其次是土壤蒸发,而叶片蒸发不受影响;根分布对潜热和感热模拟的影响随土壤湿度增大而减小。     

Evaluation of distributed recharge in an upland semi-arid karst system: the West Bank Mountain Aquifer,Middle East

Assessment of recharge in a structurally complex upland karst limestone aquifer situated in a semi-arid environment is difficult. Resort to surrogate indicators such as measurement of spring outflow and borehole discharge, is a common alternative, and attempts to apply conventional soil moisture deficit analysis may not adequately account for the intermittent spate conditions that arise in such environments. A modelling approach has been made using the West Bank Mountain Aquifer system in the Middle East as a trial. The model uses object oriented software which allows various objects to be switched on and off. Each of the main recharge processes identified in the West Bank is incorporated. The model allows either conventional soil moisture deficit analysis calculations or wetting threshold calculations to be made as appropriate, and accommodates both direct recharge and secondary recharge. Daily time steps enable recharge and runoff routing to be calculated for each node. Model runs have enabled a series of simulations for each of the three aquifer basins in the West Bank and for the whole of the West Bank. These provide recharge estimates comparable to those prepared by earlier workers by conventional means. The model is adaptable and has been successfully used in other environments.     

Using Diurnal Temperature Signals to Infer Vertical Groundwater‐Surface Water Exchange

Heat is a powerful tracer to quantify fluid exchange between surface water and groundwater. Temperature time series can be used to estimate pore water fluid flux, and techniques can be employed to extend these estimates to produce detailed plan‐view flux maps. Key advantages of heat tracing include cost‐effective sensors and ease of data collection and interpretation, without the need for expensive and time‐consuming laboratory analyses or induced tracers. While the collection of temperature data in saturated sediments is relatively straightforward, several factors influence the reliability of flux estimates that are based on time series analysis (diurnal signals) of recorded temperatures. Sensor resolution and deployment are particularly important in obtaining robust flux estimates in upwelling conditions. Also, processing temperature time series data involves a sequence of complex steps, including filtering temperature signals, selection of appropriate thermal parameters, and selection of the optimal analytical solution for modeling. This review provides a synthesis of heat tracing using diurnal temperature oscillations, including details on optimal sensor selection and deployment, data processing, model parameterization, and an overview of computing tools available. Recent advances in diurnal temperature methods also provide the opportunity to determine local saturated thermal diffusivity, which can improve the accuracy of fluid flux modeling and sensor spacing, which is related to streambed scour and deposition. These parameters can also be used to determine the reliability of flux estimates from the use of heat as a tracer.     

Vertical circulation in the tropical atmosphere during extreme El Niño-Southern Oscillation events

Scenarios for the development of large-scale vertical circulation anomalies during warm and cold phases of El Niño-Southern Oscillation are generalized based on the NCEP/NCAR reanalysis data for 1958-1998. Composite models of the cells of vertical circulation in the monsoon and trade-wind regions of the tropical Pacific are obtained for the first time for El Niño and La Niña separately. An unprecedented shift of the ascending branch of the zonal Walker circulation from the “maritime continent” of Indonesia to the east, to the central and eastern Pacific, was observed during the warm phase over the tropical Pacific; this shift was accompanied by an abrupt increase in the tropical cyclogenesis activity in the southern Pacific zone of convergence. On the contrary, during the cold phase, the ascending motions in the region of the summer Australian monsoon are subject to abrupt intensification. The reconstruction of the vertical meridional circulation during the warm phase manifested itself in the almost complete disappearance of the Hadley classic circulation over the central Pacific, characteristic of the trade-wind intertropical convergence zone (ITCZ), and in its replacement by the latitudinal monsoon circulation typical of the ITCZ over the Indian Ocean. During a cold phase, the Hadley circulation is both restored and intensified.     

Use of the population potential model for predicting the growth of cities in a region (with reference to Moscow Oblast)

"A modification of the population potential model is used to analyze the structure of the potential of population for cities of the Moscow region, to develop a relationship between population potential and city size, and to use this procedure to forecast future population change in Moscow Oblast cities." Cities in the region with a population of 50,000 or more at the censuses of 1959, 1970, and 1979 are included.     

Calculating surface water PCO2 from foraminiferal organic δC

The δ¹³C of organic matter bound within the crystal lattice of foraminiferal calcite tests may provide a potential tracer of the isotopic composition of the surface water primary photosynthate. Using δ¹³C of the organic matter extracted from the crystal lattice and the calcite test, it is theoretically possible to estimate the paleo-surface water pCO₂. We have tailored this technique initially for the subpolar planktonic foraminifera species Globigerina bulloides. Initial surface water pCO₂ estimates from deep-sea core BOFS 5K (50°41.3′N, 21°51.9′W, water depth 3547 m) indicate that the northeast Atlantic Ocean may have been a greater sink for CO₂ during the last glacial than during the Holocene. Greatly reduced benthic foraminifera abundances, especially phytodetritus feeders, in BOFS 5K during the last glacial indicates low surface productivity. This rules out a productivity-driven CO₂ sink. The enhanced glacial CO₂ sink must, therefore, have results from a southwards shift of the centre of deep water formation.     

Geoarchaeological and Bioarchaeological Studies at Mira,an Early Upper Paleolithic Site in the Lower Dnepr Valley,Ukraine

New geoarchaeological and bioarcheological research was undertaken at the open‐air site of Mira, which is buried in deposits of the Second Terrace of the Dnepr River, roughly 15 km downstream from the city of Zaporozhye in Ukraine. Previous excavation of the site revealed two occupation layers dating to ∼32,000 cal BP. The lower layer (II/2) yielded bladelets similar to those of the early Gravettian, while the upper layer (I) contained traces of an artificial shelter and hundreds of bones and teeth of horse (Equus latipes). Mira represents the only firmly dated early Upper Paleolithic (EUP) site in the Dnepr Basin, and occupies a unique topographic setting for the EUP near the center of the broad floodplain of the Dnepr River. The site was visited during a period of floodplain stability, characterized by overbank deposition and weak soil formation under cool climate conditions. Mira was used as a long‐term camp, but also was the locus of large‐mammal carcass processing associated with a nearby kill of a group of horses (Layer I).     

Seismic earth pressures on rigid and flexible retaining walls

While limiting-equilibrium Mononobe–Okabe type solutions are still widely used in designing rigid gravity and flexible cantilever retaining walls against earthquakes, elasticity-based solutions have been given a new impetus following the analytical work of Veletsos and Younan [23]. The present paper develops a more general finite-element method of solution, the results of which are shown to be in agreement with the available analytical results for the distribution of dynamic earth pressures on rigid and flexible walls. The method is then employed to further investigate parametrically the effects of flexural wall rigidity and the rocking base compliance. Both homogeneous and inhomogeneous retained soil is considered, while a second soil layer is introduced as the foundation of the retaining system. The results confirm the approximate convergence between Mononobe–Okabe and elasticity-based solutions for structurally or rotationally flexible walls. At the same time they show the beneficial effect of soil inhomogeneity and that wave propagation in the underlying foundation layer may have an effect that cannot be simply accounted for with an appropriate rocking spring at the base.