According to the glacial landforms and deposits with the optically stimulated luminescence （OSL）dating results, two glacial stages of the last glacial cycle （LGC） and Late Glacial were identified. The Late Glacial...According to the glacial landforms and deposits with the optically stimulated luminescence （OSL）dating results, two glacial stages of the last glacial cycle （LGC） and Late Glacial were identified. The Late Glacial stage （Meteorological Station glacier advance） took place about 11 ka （11.3±1.2 ka）, and the last glacial maximum （LGM）, named Black Wind Mouth glacier advance, occurred at 20 ka （20.0±2.1 ka）. Based on the Ohmura＇s formula in which there is a relationship between summer （JJA） atmospheric temperature （T） and the annual precipitation （P） at ELA, the present theoretical equilibrium line altitude （ELAt） in Changbai Mountains was 3380±100 m. Six methods of accumulation-area ratio （AAR）, maximum elevation of lateral moraines （MELM）, toe-to headwall altitude ratios （THAR）, the terminal to summit altitudinal （TSAM）, the altitude of cirque floor （CF）, and the terminal to average elevation of the catchment area （Hofer） were used for calculation of the former ELAs in different stages. These methods provided the ELA for a range of 2250-2383 m with an average value of 2320±20 m during the LGM, which is 200 m higher than the value of previous investigation. The snowlines during the Late Glacial are 2490 m on northern slope, and 2440 m on western slope. The results show that the snowline on northern slope is 50 m higher than that on western slope during the Late Glacial, and the average snowline is 2465m. The/kElP, values were more than 1000 m during the LGM, and about 920 m lower than now during the Late Glacial stage respectively. Compared with Taiwan Residents and Japanese mountains in East Asia during the LGM, the effect of the uplift on ELA in Changbai Mountains during the glaciations （i.e. 20 m uplift in the LGM and 11 m in the Late Glacial） is not obvious.展开更多
Glacier variation is one of the best indicators of climate change in mountainous environment. In French Alps, many temporal data are acquired by glaciologists at glaciers scale: geometrical parameters (surface area, t...Glacier variation is one of the best indicators of climate change in mountainous environment. In French Alps, many temporal data are acquired by glaciologists at glaciers scale: geometrical parameters (surface area, thickness, length and front altitude) are surveyed since the end of the 19th century. Those parameters are necessary to estimate the mass-balance of glaciers and, then, an accurate temporal signal of glacier variation. However, the time-response of the glaciers can be highly variable because of the topoclimate, and more generally the local settings of the glaciers. Moreover, climatologists and hydrologists are requiring estimation of glacier variations at regional scale and not only at local scale. In this paper, we highlight that the Equilibrium Line Altitude (ELA) is a parameter prone to spatio-temporal reconstructions at regional scale. ELA can indeed be interpolated at a region scale from local data: for instance, many geographers have reconstructed spatial trends during 1980s. Here, we try to interpolate ELA from multi-dimensionnal regression analysis: ELA is explained by many local parameters (Incoming solar radiation, topographic indexes, snow-redistribution by wind, etc.). Regression model was adjusted from a spatio-temporal database of 50 glaciers, located in the Massif des écrins. ELA was estimated for each glacier thanks to the Accumulation Area Ratio (ratio = 0.65) at two stages: LIA maximum and at present. Results first show that the multiple regression analysis is efficient to interpolate ELA through space: the adjusted r2 is about 0.49 for the reconstruction during the LIA, and 0.47 at present. Moreover, the RMSE error is about 50 meters for the LIA period, 55 meters at present. Finally, a high spatial variability (standard deviation of about 150 meters) is highlighted: incoming solar radiation and snow redistribution by wind mostly explain the observed differences. We can also assess a rise of the ELA of about 250 meters during the 20th century.展开更多
Based on numerical experiments undertaken with nine climate models, the glacier equilibrium line altitudes(ELAs)in western China during the last glacial maximum(LGM) are investigated to deepen our understanding of the...Based on numerical experiments undertaken with nine climate models, the glacier equilibrium line altitudes(ELAs)in western China during the last glacial maximum(LGM) are investigated to deepen our understanding of the surface environment on the Tibetan Plateau. Relative to the preindustrial period, the summer surface air temperatures decrease by 4–8°C while the annual precipitation decreases by an average of 25% across the Tibetan Plateau during the LGM. Under the joint effects of reductions in summer temperature and annual precipitation, the LGM ELAs in western China are lowered by magnitudes that vary with regions. The ELAs in the southern margin and northwestern Tibetan Plateau decline by approximately 1100 m;the central hinterland, by 650–800 m;and the eastern part, by 550–800 m, with a downward trend from southwest to northeast. The reduction in ELAs is no more than 650 m in the Tian Shan Mountains within China and approximately 500–600 m in the Qilian Mountains and Altai Mountains. The high-resolution models to reproduce the low values of no more than 500 m in ELA reductions in the central Tibetan Plateau, which are consistent with the proxy records from glacier remains. The accumulation zones of the Tibetan Plateau glaciers are mainly located in the marginal mountains during the LGM and have areas 2–5 times larger than those of the modern glaciers but still do not reach the central part.展开更多
In this paper, we have studied several classes of planar piecewise Hamiltonian systems with three zones separated by two parallel straight lines. Firstly, we give the maximal number of limit cycles in these classes of...In this paper, we have studied several classes of planar piecewise Hamiltonian systems with three zones separated by two parallel straight lines. Firstly, we give the maximal number of limit cycles in these classes of systems with a center in two zones and without equilibrium points in the other zone (or with a center in one zone and without equilibrium points in the other zones). In addition, we also give examples to illustrate that it can reach the maximal number.展开更多
Delineation of the grounding line(GL) is necessary for calculating the mass balance of Antarctica, but GL measurements for most of the continent remain at a relatively coarse level. We used Sentinel-1 constellation da...Delineation of the grounding line(GL) is necessary for calculating the mass balance of Antarctica, but GL measurements for most of the continent remain at a relatively coarse level. We used Sentinel-1 constellation data to map the GL of the Amery Ice Shelf(AIS) using double-differential synthetic aperture radar interferometry. The ice thickness anomaly deduced from hydrostatic equilibrium and existing Antarctic GL products is compared with our result. With this new and very accurate GL, we detected new ice rises in the north of the AIS. Our new measurement shows no major change of the AIS GL, particularly in the southernmost part.展开更多
基金National Natural Science Foundation of China,No.40571016
文摘According to the glacial landforms and deposits with the optically stimulated luminescence （OSL）dating results, two glacial stages of the last glacial cycle （LGC） and Late Glacial were identified. The Late Glacial stage （Meteorological Station glacier advance） took place about 11 ka （11.3±1.2 ka）, and the last glacial maximum （LGM）, named Black Wind Mouth glacier advance, occurred at 20 ka （20.0±2.1 ka）. Based on the Ohmura＇s formula in which there is a relationship between summer （JJA） atmospheric temperature （T） and the annual precipitation （P） at ELA, the present theoretical equilibrium line altitude （ELAt） in Changbai Mountains was 3380±100 m. Six methods of accumulation-area ratio （AAR）, maximum elevation of lateral moraines （MELM）, toe-to headwall altitude ratios （THAR）, the terminal to summit altitudinal （TSAM）, the altitude of cirque floor （CF）, and the terminal to average elevation of the catchment area （Hofer） were used for calculation of the former ELAs in different stages. These methods provided the ELA for a range of 2250-2383 m with an average value of 2320±20 m during the LGM, which is 200 m higher than the value of previous investigation. The snowlines during the Late Glacial are 2490 m on northern slope, and 2440 m on western slope. The results show that the snowline on northern slope is 50 m higher than that on western slope during the Late Glacial, and the average snowline is 2465m. The/kElP, values were more than 1000 m during the LGM, and about 920 m lower than now during the Late Glacial stage respectively. Compared with Taiwan Residents and Japanese mountains in East Asia during the LGM, the effect of the uplift on ELA in Changbai Mountains during the glaciations （i.e. 20 m uplift in the LGM and 11 m in the Late Glacial） is not obvious.
文摘Glacier variation is one of the best indicators of climate change in mountainous environment. In French Alps, many temporal data are acquired by glaciologists at glaciers scale: geometrical parameters (surface area, thickness, length and front altitude) are surveyed since the end of the 19th century. Those parameters are necessary to estimate the mass-balance of glaciers and, then, an accurate temporal signal of glacier variation. However, the time-response of the glaciers can be highly variable because of the topoclimate, and more generally the local settings of the glaciers. Moreover, climatologists and hydrologists are requiring estimation of glacier variations at regional scale and not only at local scale. In this paper, we highlight that the Equilibrium Line Altitude (ELA) is a parameter prone to spatio-temporal reconstructions at regional scale. ELA can indeed be interpolated at a region scale from local data: for instance, many geographers have reconstructed spatial trends during 1980s. Here, we try to interpolate ELA from multi-dimensionnal regression analysis: ELA is explained by many local parameters (Incoming solar radiation, topographic indexes, snow-redistribution by wind, etc.). Regression model was adjusted from a spatio-temporal database of 50 glaciers, located in the Massif des écrins. ELA was estimated for each glacier thanks to the Accumulation Area Ratio (ratio = 0.65) at two stages: LIA maximum and at present. Results first show that the multiple regression analysis is efficient to interpolate ELA through space: the adjusted r2 is about 0.49 for the reconstruction during the LIA, and 0.47 at present. Moreover, the RMSE error is about 50 meters for the LIA period, 55 meters at present. Finally, a high spatial variability (standard deviation of about 150 meters) is highlighted: incoming solar radiation and snow redistribution by wind mostly explain the observed differences. We can also assess a rise of the ELA of about 250 meters during the 20th century.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA20070103)the National Natural Science Foundation of China (Grant Nos. 41625018 & 41421004)
文摘Based on numerical experiments undertaken with nine climate models, the glacier equilibrium line altitudes(ELAs)in western China during the last glacial maximum(LGM) are investigated to deepen our understanding of the surface environment on the Tibetan Plateau. Relative to the preindustrial period, the summer surface air temperatures decrease by 4–8°C while the annual precipitation decreases by an average of 25% across the Tibetan Plateau during the LGM. Under the joint effects of reductions in summer temperature and annual precipitation, the LGM ELAs in western China are lowered by magnitudes that vary with regions. The ELAs in the southern margin and northwestern Tibetan Plateau decline by approximately 1100 m;the central hinterland, by 650–800 m;and the eastern part, by 550–800 m, with a downward trend from southwest to northeast. The reduction in ELAs is no more than 650 m in the Tian Shan Mountains within China and approximately 500–600 m in the Qilian Mountains and Altai Mountains. The high-resolution models to reproduce the low values of no more than 500 m in ELA reductions in the central Tibetan Plateau, which are consistent with the proxy records from glacier remains. The accumulation zones of the Tibetan Plateau glaciers are mainly located in the marginal mountains during the LGM and have areas 2–5 times larger than those of the modern glaciers but still do not reach the central part.
文摘In this paper, we have studied several classes of planar piecewise Hamiltonian systems with three zones separated by two parallel straight lines. Firstly, we give the maximal number of limit cycles in these classes of systems with a center in two zones and without equilibrium points in the other zone (or with a center in one zone and without equilibrium points in the other zones). In addition, we also give examples to illustrate that it can reach the maximal number.
基金supported by National Program on Key Basic Research Project (Program 973, Grant no. 2013CBA01804)National Natural Science Foundation of China (Grant nos. 41531069 and 41376187)Chinese Polar Environment Comprehensive Investigation & Assessment Program (Grant no. CHINARE2016-02-04)
文摘Delineation of the grounding line(GL) is necessary for calculating the mass balance of Antarctica, but GL measurements for most of the continent remain at a relatively coarse level. We used Sentinel-1 constellation data to map the GL of the Amery Ice Shelf(AIS) using double-differential synthetic aperture radar interferometry. The ice thickness anomaly deduced from hydrostatic equilibrium and existing Antarctic GL products is compared with our result. With this new and very accurate GL, we detected new ice rises in the north of the AIS. Our new measurement shows no major change of the AIS GL, particularly in the southernmost part.
