A Numerical Study of the Mechanism for the Effect of Northern Winter Arctic Ice Cover on the Global Short-Range Climate Evolution

By using a nine-layer global spectral model involving fuller parameterization of physical processes, with a rhomboidal truncation at wavenumber 15, experiments are performed in terms of two numerical schemes, one with long-term mean coverage of Arctic ice (Exp.1), the other without the ice (Exp.2). Results indicate that the Arctic region is a heat source in Exp.2 relative to the case in Exp.1. Under the influence of the polar heat source simulated, there still exist stationary wavetrains that produce WA-EUP and weak PNA patterns in Northern winter. That either the Arctic or the tropical heat source can cause identical climatic effects is due to the fact that the anomaly of the Arctic ice cover will directly induce a south-propagating wavetrain, and bring about the redistribution of the tropical heat source / sink. The redistribution is responsible for new wavetrains that will exert impact on the global climate. The simulation results bear out further that the polar region in Exp.2 as a heat source, can produce, by local forcing, a pair of positive and negative difference centers, which circle the Arctic moving eastwards. Observed in the Northern Hemisphere extratropics is a 40-50 day oscillation in relation to the moving pair, both having the same period.

Altitudinal seasonality as a potential driver of morphological diversification in rear-edge bird populations

Populations at the low latitude limits of a species range(rear-edge populations)are often considered more vulnerable to climate change.However,their ability to track different environmental settings at a regional scale has been widely overlooked,although this may be relevant to accurately assess their adaptive capacity to cope with ongoing changes.Here we tested whether the endemic African Chaffinch(Fringilla coelebs africana)tracks environmental changes(e.g.decreasing temperatures,snow cover)by rearranging their numbers between seasons(spring vs.winter)along the altitude gradients of its northwestern African range.We additionally tested whether these seasonal changes in abundance were paralleled by morphological variation,suggesting a process of population diversification.We assessed African Chaffinch abundance in tree covered farmland and woodland sites distributed along an altitude gradient in spring and winter.In addition,we captured and measured chaffinches within the study gradient to explore the patterns of morphological variation.Our results showed that chaffinches shifted to lowlands from snow covered highlands during winter.In addition,highland individuals showed longer and more concave wings than their lowland counterparts.These morphological traits are usually related to flight efficiency in migratory birds,which suggest the presence of altitudinal movements aimed to track the environmental seasonality caused by orography.These results suggest a potential role of altitudinal seasonality as a driver of regional diversification within the African Chaffinch populations,which could be occurring in other North African avian species given their relatively high endemicity in the region.The evolutionary and conservation implications of these displacements have been often overlooked despite they can shape the adaptive capacity of rear-edge bird populations to face the ongoing environmental changes in this peripheral area of the Palearctic.

Country-scale spatio-temporal monitoring of soil erosion in Iran using the G2 model

The aim of this study was the spatial and temporal monitoring of soil erosion patterns in Iran.The G2 model was used,as an appropriate tool to provide the required month-time step country-wide soil loss maps and statistical outputs.The input parameters were derived with field surveys and remote sensing imagery(MODIS,SRTM,SPOT,and Sentinel-2 scenes).An innovation for G2 was the consideration of the snow cover effect on the rainfall erosivity.It was also the first time G2 was used to map such a big country like Iran on a country scale.The mean annual soil erosion in Iran was found to be 16.5 t ha−1,which is equal to about 2.7 billion tons of soil loss.In spatial terms,the highest soil loss values were found in the north,west and southwest part of Iran,in the steep slopes in Alborz and Zagros mountains.In temporal terms,the highest and lowest monthly erosion values of 3.2 and 0.09 t ha−1 correspond to January and July,respectively.

Study on the force chain characteristics with coal dust layer and the three-body contact stiffness

To explore the influence of the meso-mechanical behaviors of the wet coal dust layers on the contact stiffness of mechanical bonding surfaces,a three-body contact model incorporating an interface with wet coal dust was constructed based on breakage theory.The model considered the mechanical surface morphology and contact characteristics of the wet coal dust.The force chain evolution laws of the wet coal dust layer were elucidated under the effects of gap filling and the cover layer,and the bearing characteristics of the three-body contact bonding surfaces were revealed by quantitative analyses of the number,length,collimation coefficient,and coordination number of the force chains within the wet coal dust layer.Finally,the three-body normal contact stiffness under various preload forces was computed and experimentally validated.The results demonstrate that the external load transfer path of the three-body contact bonding surfaces was from mechanical surface(macroscopic stress)to wet coal dust layer(mesoscopic force chains)and then to mechanical surface(peaks and valleys).The interactions among these three elements contributed to transforming the distributions of the macroscopic stresses and mesoscopic force chains to the locations at the peaks and valleys of the mechanical surface.Among them,the proportion of short force chains in the wet coal dust layer increased from approximately 0.8%–91%,while the proportion of long force chains exhibited an opposite changing trend.The force chain collimation coefficient initially increased and subsequently stabilized,reaching a maximum value of 0.93.A large number of broken,small particles in the wet coal dust layer mainly served to fill the gaps among large particles.The maximum relative error between the experimental and simulated values on the three-body contact stiffness is 7.26%,indicating that the simulation results can be an approximate substitute for the experimental results with a certain degree of accuracy and practicality.The research results are of great significance for understanding the contact characteristics of mechanical surfaces containing particulate media.