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Diagnostic analysis of the evolution mechanism for a vortex over the Tibetan Plateau in June 2008 总被引：2，自引：0，他引：2
Based on the final analyses data (FNL) of the Global Forecasting System of the NCEP and the obser- vational radiosonde data, the evolution mechanism of an eastward-moving low-level vortex over the Tibetan Plateau in June 2008 was analyzed. The results show that the formation of the vortex was related to the convergence between the northwesterly over the central Tibetan Plateau from the westerly zone and the southerly from the Bay of Bengal at 500 hPa, and also to the divergence associated with the entrance re- gion of the upper westerly jet at 200 hPa. Their dynamic effects were favorable for ascending motion and forming the vortex over the Tibetan Plateau. Furthermore, the effect of the atmospheric heat source (Q1) is discussed based on a transformed potential vorticity (PV) tendency equation. By calculating the PV budgets, we showed that Q1 had a great inffuence on the intensity and moving direction of the vortex. In the developing stage of the vortex, the heating of the vertically integrated Q1 was centered to the east of the vortex center at 500 hPa, increasing PV tendency to the east of the vortex. As a result, the vortex strengthened and moved eastward through the vertically uneven distribution of Q1. In the decaying stage, the horizontally uneven heating of Q1 at 500 hPa weakened the vortex through causing the vortex tubes around the vortex to slant and redistributing the vertical vorticity field. 相似文献
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针对区域分级不能在CorelDRAW中自动实现的问题,本文把ActiveX Automation技术和ADO数据库访问技术在VB编程环境下结合起来,对CorelDRAW X6进行二次开发,实现了对区域进行自动分级的功能,其中包括常用的三种分级模型,最后通过实例验证了其可行性。 相似文献
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近百年来中国冰川变化及其对气候变化的敏感性研究进展 总被引：18，自引：3，他引：15
冰川变化是气候变化的产物,也是气候变化的指示器.在全球变暖的背景下,近百年来我国冰川消融强烈,以退缩为主.本文对近百年来我国冰川末端退缩、物质平衡变化和冰川面积变化方面的研究成果进行了综合分析.从时间和空间两方面探讨了我国冰川变化对气候变化响应的敏感性.结果表明,我国冰川末端变化对气候变化的响应在时间上要滞后10～20年,冰川末端退缩、物质平衡变化和面积变化的幅度在青藏高原边缘和周边地区要大于高原内部,对气候变化响应的敏感性也由内部向边缘增强.最后指出了我国冰川变化研究中存在的主要问题及今后发展趋势. 相似文献
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珠穆朗玛峰地区雪冰中重金属浓度与季节变化 总被引：2，自引：0，他引：2
The concentrations of heavy metals Ba, Pb, Cu, Zn and Co in snow pit collected in September, 2005 from the accumulation area
of the East Rongbuk Glacier (6523 m a.s.l.), which lies on the northern slope of Mt. Qomolangma, were determined by inductively
coupled plasma mass spectrometry (ICP-MS). Concentrations (pg/ml) of heavy metals are Ba2-227, Co2.8-15.7, Cu10-120, Zn29-4948
and Pb14-142, respectively. The δ18O was determined by MAT-252. The time period of the snow pit spans from autumn 2005 to summer 2004. Seasonal variations of
the concentrations and δ18O are observed, of which Pb, Cu, Zn and Co are much lower in summer monsoon season than that in non summer monsoon season,
suggesting that different sources of heavy metals contributed to the site. EFc (crustal enrichment factors) is Co3.6, Cu27, Pb33 and Zn180, respectively. Higher EFc values of Pb, Cu and Zn suggest that Pb, Cu especially Zn are mainly contributed by anthropogenic sources.
Foundation: National Natural Science Foundation of China, No.40501014; No.40871058
Author: Duan Jianping (1981–), Ph.D. Candidate, specialized in climate and environmental change. 相似文献
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基于长偏移距瞬变电磁法一维正演研究,计算层参数和偏移距变化时的模型响应,对比分析视电阻率曲线变化规律和分辨系数。结果表明,对低阻目标层的分辨能力主要由纵向电导所决定,纵向电导越大越易分辨,低阻目标层纵向电导与覆盖层纵向电导比值越高,越易对低阻层分辨;在高阻层厚/覆盖层厚(V2)1时,对高阻层的分辨能力随厚度的增大而提高,而电阻率在一定范围内变化对其几乎无影响,在V21时,视电阻率曲线在一定范围内存在T等值原理。该方法对低阻层的分辨能力要远大于高阻层,偏移距的变化对分辨能力影响甚微。 相似文献
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大地电磁(MT)数值模拟中通常使用有限单元法,通过伽辽金(Galerkin)法将微分方程转化为与其等价的泛函形式,对泛函求取极值并在单元上定义插值基函数,得到节点上电磁场值的线性方程组,最终形成大型复对称稀疏矩阵。要达到较高的有限元计算精度,一般采用密集的网格或高次插值的方法,这样做大大的减慢了正演的速度。结合两者的优点利用三次插值和h-型自适应相结合的有限元法来实现MT的正演算法。首先从一个粗网格出发并利用三次插值,通过后验误差估计方法局部加密网格,在计算量较小的情况获得较高的计算精度。这种方法可以针对目标区域和介质分界面发生突变处进行网格加密,不需要全局加密网格。最后通过对国际标准模型COMMEMI-2D1的模拟,分别比较二次插值与三次插值的自适应网格数量和数值模拟结果,证明了三次插值自适应有限元算法的可行性。 相似文献
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一、有助于土地承包经营制度的有效实施
近些年来,我国农村许多地方弃耕、抛荒或毁田、滥占农地建房等破坏地力、改变土地用途的现象的出现固然是农地经济效益的低下造成的,但土地承包金的约定不明,承包人责任不清显然也是一个重要的原因。规定适当的土地承包金对土地承包人起着一定的“刺激”作用,它意味着如果土地承包人不积极行使土地权利获得较大收益的话, 相似文献