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821.
东亚副热带西风急流位置变化及其对中国东部夏季降水异常分布的影响 总被引:29,自引:13,他引:16
利用1951~2004年美国国家环境预报中心 (NCAR/NCEP) 再分析候平均资料和同期中国740站日降水资料, 分析了东亚副热带西风急流轴位置的变化趋势及其对中国东部夏季降水分布的影响, 结果表明: (1) 夏季7~8月东亚副热带西风急流位置和形态在1975~1980年间出现转折, 1980年后西风急流中心逐渐向西移动的同时伴随有西风急流向南偏移。 (2) 在1980年以后华北地区降水量减少和降水强度减弱, 雨季开始时间推迟、 雨季变短, 而长江中下游地区入梅提前、 梅雨期变长, 降水量增加, 从而形成南涝北旱的降水分布形势。 (3) 1957~1964年华北典型多雨时期, 西风急流呈纬向分布, 在华北地区有高低空急流耦合, 强辐合上升区正好位于华北, 并有充足的水汽条件供应, 使得华北降水偏多。而1980~1987年和1997~2002年华北地区为典型少雨时期, 1980~1987年西风急流中心位置偏南和1997~2002年急流位置显著偏西, 在华北地区均无高低空急流耦合的环流形势, 水汽辐合区位于长江流域, 强辐合上升区位置在30°N以南区域, 有利于江南地区降水增加而华北地区少雨, 这表明西风急流位置变化导致环流调整对中国东部降水分布有显著影响。因而, 在讨论东亚副热带西风急流位置与中国东部地区降水异常的关系时, 不仅要考虑西风急流南北位置变化, 还需要综合分析西风急流的东西位置和形态的变化。 相似文献
822.
823.
2008年河南黄淮地区暴雨过程个例分析 总被引:7,自引:4,他引:3
利用常规气象资料和NCEP资料对2008年7月22日河南黄淮地区的暴雨过程进行了分析.结果表明:这次过程是在500 hPa槽前西南气流引导下,高低空急流耦合区内西南涡沿切变线移出,弱冷空气侵入暖倒槽触发不稳定能量释放造成的.垂直螺旋度计算结果显示:中低层正垂直螺旋度中心与降水落区有很好的对应关系,大暴雨中心位于正垂直螺旋度中心附近.湿位涡演变分析发现,这次过程有"干侵入"发生,暴雨区中低层对流不稳定和对称不稳定共存,有利于降水增幅.水汽条件分析表明:这次过程的水汽源地在孟加拉湾和南海,主要是低层和近地层的水汽辐合. 相似文献
824.
Jason Cosford Hairuo Qing Yin Lin Bruce Eglington Dave Mattey Yue Gau Chen Meiliang Zhang Hai Cheng 《Quaternary Research》2010,73(3):541-549
Stalagmite J1 from Jintanwan Cave, Hunan, China, provides a precisely dated, decadally resolved δ18O proxy record of paleoclimatic changes associated with the East Asian monsoon from ∼29.5 to 14.7 ka and from ∼12.9 to 11.0 ka. At the time of the last glacial maximum (LGM), the East Asian summer monsoon weakened and then strengthened in response to changes in Northern Hemisphere insolation. As the ice sheets retreated the East Asian summer monsoon weakened, especially during Heinrich event H1, when atmospheric and oceanic teleconnections transferred the climatic changes around the North Atlantic to the monsoonal regions of Eastern Asia. A depositional hiatus between ∼14.7 and 12.9 ka leaves the deglacial record incomplete, but an abrupt shift in δ18O values at ∼11.5 ka marks the end of the Younger Dryas and the transition into the Holocene. Comparisons of the J1 record to other Chinese speleothem records indicate synchronous climatic changes throughout monsoonal China. Further comparisons to a speleothem record from western Asia (Socotra Island) and to Greenland ice cores support hemispherical-scale paleoclimatic change. Spectral and wavelet analyses reveal centennial- and decadal-scale periodicities that correspond to solar frequencies and to oscillations in atmospheric and oceanic circulation. 相似文献
825.
826.
Taking into account reconstructed precipitation time series in Huashan mountain area of China on the one hand and sunspot numbers observations on the other hand, the authors used here continuous wavelet transform and cross wavelet transform to investigate possible connection between the two sets of indicators. The analysis was performed over the last 300 years: it is found that solar activity influences precipitation in that geographical area of China to some extent, with an excess of 5% statistical significance level red noise over the 11-year solar activity cycle. 相似文献
827.
828.
根据极限分析上限理论,基于Davis等人提出的隧道垮落模型,提出了剪切区参数α等于1时的新的隧道垮落模型。由不可压缩性条件和速度连续性条件求出了剪切区速度和间断线表达式,计算了该模型间断线上能量耗损、剪切区能量耗损和总外力所做的功。利用功能原理,求出了稳定率的表达式,并计算了相应的稳定率。从求解结果来看,所得上限解小于Davis等人的结果,因而该上限解将更接近真实解。从与实验结果比较来看,该上限解位于实验值附近,能与实验结果比较好地吻合,从而说明该模型更加接近真实隧道垮落情形。该上限解可为隧道支护提供理论依据。 相似文献
829.
The Daenam mine, which produced over 9250 tons of iron oxide ore from 1958 to 1962, is situated in the Early Cretaceous Yeongyang subbasin of the Gyeongsang basin. It consists of two lens-shaped, hematite-bearing quartz veins that occur along faults in Cretaceous leucocratic granite. The hematite-bearing quartz veins are mainly composed of massive and euhedral quartz and hematite with minor amounts of pyrite, pyrrhotite, mica, feldspar and chlorite.Fluid inclusions in quartz can be divided into three main types: CO2-rich, CO2–H2O, and H2O-rich. Hydrothermal fluids related to the formation of hematite are composed of either H2O–CO2–NaCl ± CH4 (homogenization temperature: 262–455 °C, salinity <7 eq. wt.% NaCl) or H2O–NaCl (homogenization temperature: 182–266 °C, and salinity <5.1 eq. wt.% NaCl), both of which evolved by mixing with deeply circulating meteoric water. Hematite from the quartz veins in the Daenam mine was mainly deposited by unmixing of H2O–CO2–NaCl ± CH4 fluids with loss of the CO2 + CH4 vapor phase and mixing with downward percolating meteoric water providing oxidizing conditions. 相似文献
830.
Genming Luo Junhuang Huang Shucheng Xie Paul B. Wignall Xinyan Tang Xianyu Huang Hongfu Yin 《International Journal of Earth Sciences》2010,99(4):775-784
This paper investigates kerogen carbon isotopes, the difference between carbonate and kerogen carbon isotopes (Δ13Ccarb-kero = δ
13Ccarb − δ
13Ckero) and the difference between carbonate and n-C19 alkane compound-specific carbon isotopes (Δ13Ccarb-n-C19 = δ
13Ccarb − δ
13C
n-C19) during the Permian–Triassic transition at Meishan, South China. The results show that kerogen carbon isotopes underwent
both gradual and sharp shifts in beds 23–25 and 26–29, respectively. The differences between carbonate and organic carbon
isotopes, both the Δ13Ccarb-kero and Δ13Ccarb-n-C19, which are mainly affected by CO2-fixing enzyme and pCO2, oscillated frequently during the Permian–Triassic transition. Both the variations of Δ13Ccarb-n-C19 and Δ13Ccarb-kero coupled with the alternation between cyanobacteria and green sulfur bacteria indicated by biomarkers. The episodic low values
of Δ13Ccarb-n-C19 corresponded to episodic blooms of green sulfur bacteria, while the episodic high values of Δ13Ccarb-n-C19 corresponded to episodic blooms of cyanobacteria. The relationships between the variation of carbon isotopes and biota show
that the microbes which flourished after the extinction of macroorganism affected the carbon isotope fractionation greatly.
Combining the carbon isotope compositions and the pattern of size variation of the conodont Neogondolella, this paper supposes that anoxia of the photic zone at bed 24 was episodic and it would be caused by the degradation of terrigenous
organic matters by sulfate reducing bacteria in the upper water column. Considered together with results from previous research,
the high resolution variation of the biogeochemistry presents the sequence of the important geo-events during the Permian–Triassic
crisis. 相似文献