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A total of 12 indices of temperature extremes and 11 indices of precipitation ex-tremes at 111 stations in southwestern China at altitudes of 285-4700 m were examined for the period 1961-2008. Significant correlations of temperature extremes and elevation in-cluded the trends of diurnal temperature range, frost days, ice days, cold night frequency and cold day frequency. Regional trends of growing season length, warm night frequency, coldest night and warmest night displayed a statistically significant positive correlation with altitude. These characteristics indicated the obvious warming with altitude. For precipitation extreme indices, only the trends of consecutive dry days, consecutive wet days, wet day precipitation and the number of heavy precipitation days had significant correlations with increasing alti-tude owing to the complex influence of atmospheric circulation. It also indicated the increased precipitation mainly at higher altitude areas, whereas the increase of extreme precipitation events mainly at lowers altitude. In addition, the clearly local influences are also crucial on climate extremes. The analysis revealed an enhanced sensitivity of climate extremes to ele-vation in southwestern China in the context of recent warming. 相似文献
194.
京津唐地区的深部挤压带轴线沿宁河、香河、昌平一线呈南东—北西走向,在通过该带的北东向M和C面上均有一向北西弯曲的弧形。地壳下部和上地幔顶部层位呈透镜状增厚,浅部的北东向断裂也向北西弯曲。应力测量表明现今该带的应力场为向北西挤压。深部挤压作用是由渤海底部的扩张所产生的。该挤压带控制着地震的发生,特别其北东侧是一个强地震区 相似文献
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冷暖事件对大气能量循环和纬向平均环流影响的模拟研究 总被引:1,自引:0,他引:1
利用中国科学院大气物理研究所大气科学与地球流体力学数值模拟国家重点实验室新发展的GOALS 5全球海 陆 气耦合模式研究了暖事件 (ElNi no)和冷事件 (LaNina)对大气能量循环和纬向平均环流的影响 ,并用观测资料进行了对比分析。结果表明 :对于纬向平均资料来说 ,冷、暖事件在热带和副热带地区的大气环流相关量的反相变化特征非常清晰 ,中高纬度地区并不明显。此外 ,还发现 ,暖事件时定常涡动的经向热通量的变化是北半球对流层热带外地区温度异常的主要原因 ,而瞬变波的影响则起抵消作用。冷事件时定常波和瞬变波相互抵消的局地特征也依然存在 ,但瞬变波的影响有所增强。 相似文献
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Multi-conjugate adaptive optics(MCAO),consisting of several deformable mirrors(DMs),can significantly increase the adaptive optics(AO)correction field of view.Current MCAO can be realized by either star-oriented or layer-oriented approaches.For solar AO,ground-layer adaptive optics(GLAO)can be viewed as an extreme case of layer-oriented MCAO in which the DM is conjugated to the ground,while solar tomography adaptive optics(TAO)that we proposed recently can be viewed as star-oriented MCAO with only one DM.Solar GLAO and TAO use the same hardware as conventional solar AO,and therefore it will be important to see which method can deliver better performance.In this article,we compare the performance of solar GLAO and TAO by using end-to-end numerical simulation software.Numerical simulations of TAO and GLAO with different numbers of guide stars are conducted.Our results show that TAO and GLAO produce the same performance if the DM is conjugated to the ground,but TAO can only generate better performance when the DM is conjugated to the best height.This result has important application in existing one-DM solar AO systems. 相似文献
198.
A suction caisson can be extracted by applying reverse pumping water,which cannot be regarded as the reverse process of installation because of the dramatically different soil?structure interaction behavior.Model tests were first carried out in this study to investigate the extraction behavior of the modified suction caisson(MSC)and the regular suction caisson(RSC)in sand by reverse pumping water.The effects of the installation ways(suction-assisted or jacking installation)and the reverse pumping rate on the variations of the over-pressure resulting form reverse pumping water were investigated.It was found that neither the RSC nor the MSC can be fully extracted from sand.When the maximum extraction displacement is obtained,the hydraulic gradient of the sand in the suction caisson reaches the critical value,leading to seepage failure.In addition,the maximum extraction displacement decreases with the increasing reverse pumping rate.Under the same reverse pumping rate,the final extraction displacements for the RSC and MSC installed by suction are lower than those for the RSC and MSC installed by jacking.The final extraction displacement of MSC is almost equal to that of the RSC with the same internal compartment length.Based on the force equilibrium,a method of estimating the maximum extraction displacement is proposed.It has been proved that the proposed method can rationally predict the maximum extraction displacement and the corresponding over-pressure. 相似文献
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