地形对沙尘暴的影响及敏感试验研究   总被引：2，自引：3，他引：2  

沈建国  姜学恭  孙照渤 《高原气象》2007,26(5):1013-1022

在初步探讨地形影响沙尘扬升、传输、沉降等动力过程可能机制的基础上,利用沙尘数值预报模式对一次强沙尘暴过程进行了模拟研究,结果表明:沙尘暴形成阶段沙尘主要来源于阿尔泰—萨彦岭及以东地区,这部分沙尘主要向东扩展,该区域地形对其强度具有重要影响;内蒙古中西部、甘肃、宁夏等地的起沙主要在沙尘暴持续阶段产生影响,之后主要向南输送,青藏高原东侧地形绕流对其强度具有影响。地形影响可以使沙尘的扩展分为两种不同的方式,当上下游地形落差较小时形成整体推进式传输,此时沙尘位于对流层低层,没有上下沙尘层的分离;当上下游地形落差较大时形成分离式传输,沙尘位于对流层中层且在传输过程中沉降很弱,同时与地面附近的沙尘层分离。源于蒙古国、内蒙古等地的沙尘往往产生整体推进式传输;而产生于青藏高原的沙尘常形成分离式传输。  相似文献   

Algorithms to Account for Topographic Shading Effects and Surface Temperature Dependence on Terrain Elevation in Diagnostic Meteorological Models     

R.?BellasioEmail author  G.?Maffeis  J.?S.?Scire  M.?G.?Longoni  R.?Bianconi  N.?Quaranta 《Boundary-Layer Meteorology》2005,114(3):595-614

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地形强迫对大气长波调整的可能影响     

张立凤  余沛龙  黎爱兵  顾明逸 《大气科学》2014,38(4):804-812

地形作为大气的外部强迫,其动力和热力作用对波动结构演变及极端天气出现都有不能忽视的作用。本文通过数值求解考虑地形强迫的β平面正压准地转位势涡度方程,探讨了地形强迫作用对大气长波调整的可能影响,结果表明:同非线性作用和纬向非均匀基流作用一样,无基流情形下具有纬向差异的地形分布影响了大气长波结构的演变,也能强迫出大气长波调整现象。大气长波调整依赖于地形的高度和地形分布,地形越高,长波越容易出现波数的调整;地形波数越大,即地形结构复杂,越不易出现波数变化。大气长波调整还与纬度有关,纬度越高,β越小,地形强迫作用越突出,长波调整容易出现;反之,低纬度以β效应为主的线性波动不易出现波数调整。大气长波调整对波动初始波动的振幅不敏感,但依赖于波动的初始结构。此外,有基流作用时,地形强迫还是诱发定常波的重要因素,且定常波流场结构依赖于地形高度分布,与波动初始结构无关。  相似文献   

Effect of lithology and structure on seismic response of steep slope in a shaking table test   总被引：4，自引：2，他引：2  

LIU Han-xiang  XU Qiang  LI Yan-rong 《山地科学学报》2014,11(2):371-383

Studies on landslides by the 2008 Wenchuan earthquake showed that topography was of great importance in amplifying the seismic shaking, and among other factors, lithology and slope structure controlled the spatial occurrence of slope failures. The present study carried out experiments on four rock slopes with steep angle of 60° by means of a shaking table. The recorded Wenchuan earthquake waves were scaled to excite the model slopes. Measurements from accelerometers installed on free surface of the model slope were analyzed, with much effort on timedomain acceleration responses to horizontal components of seismic shaking. It was found that the amplification factor of peak horizontal acceleration, RPHA, was increasing with elevation of each model slope, though the upper and lower halves of the slope exhibited different increasing patterns. As excitation intensity was increased, the drastic deterioration of the inner structure of each slope caused the sudden increase of RPHA in the upper slope part. In addition, the model simulating the soft rock slope produced the larger RPHA than the model simulating the hard rock slope by a maximum factor of 2.6. The layered model slope also produced the larger RPHA than the homogeneous model slope by a maximum factor of 2.7. The upper half of a slope was influenced more seriously by the effect of lithology, while the lower half was influenced more seriously by the effect of slope structure.  相似文献   

大对流有效位能和条件不稳定下地形降水的三维理想数值研究   总被引：7，自引：3，他引：4  

赵玉春  王叶红  崔春光 《气象学报》2011,69(5):782-798

利用WRF(V3.01)中尺度数值模式,对具有大对流有效位能和条件不稳定层结下中小尺度地形对降水的影响进行了一系列三维理想数值试验,探讨了不同地形高度、尺度、形状(水平形态比)以及环境气流对降水模态和分布的影响.结果发现:在大对流有效位能(2875 J/kg)和条件不稳定(Nw≈0.01 s-1)下,地形重力波破碎触发...  相似文献   

Exploring the relationships between post-fire vegetation regeneration dynamics,topography and burn severity: A case study from the Montane Cordillera Ecozones of Western Canada     

《Applied geography (Sevenoaks, England)》2015

In this study the relationships between vegetation regeneration dynamics to topography and burn severity for a Canadian landscape were investigated using freely available Earth Observation (EO) imagery from Landsat TM sensor. The Okanagan Mountain Park, located in the Montane Cordillera Ecozones of Western Canada at which a fire occurred in 2003, was used as a case study. First, vegetation regeneration dynamics were quantified for a period of 8 years following the fire event based on a chronosequence analysis of the Normalized Difference Vegetation Index (NDVI) and the Regeneration Index (RI). The spatio-temporal patterns of post-fire NDVI from each image date were statistically compared to the pre-fire pattern to determine the extent to which the pre-fire spatial pattern was re-established and also the rate of recovery. Subsequently, the relationships of vegetation regrowth to both topography and burn severity was quantified using a series of additional statistical metrics. Burn severity was derived from the differenced Normalized Burn Ratio (dNBR) index computed from the Landsat TM images. Information on topography properties of the region was obtained from the ASTER global operational product.NDVI and RI analysis indicated a moderate vegetation recovery to pre-fire patterns, with regeneration to over 60% of the pre-fire levels 8-years after the fire. Regression analysis of pre- and post-fire mean NDVI exhibited significant re-growth in the first 3 years after the fire with a more gradual return in later years (an increase of 0.400 in R² by 2006 compared to only an increase of 0.129 for the subsequent 5 years). Re-growth rates appeared to be somewhat higher in north-facing slopes in comparison to south facing ones. As expected, NDVI decline due to fire was positively correlated with burn severity class, whereas negative correlation was found between damage and regeneration ability (recovery after 3 years = low severity 64%/high severity 58%, recovery after 8 years = low severity 72%/high severity 70%). To our knowledge, this study is one of the few attempting to explore the interrelationships of post-fire vegetation regrowth, topography and burn severity, especially in the case of a single large fire. RI based on control plots provides a valuable tool to quantify fire impact and subsequent vegetation regrowth. Furthermore, indication of burn severity is useful for strategically rehabilitating areas of slow or unsuitable post-fire vegetation recovery. This study corroborates the significance of EO technology as a successful and cost-effective solution in providing information related to economic and environmental post-fire regeneration assessment.  相似文献   

青藏高原东部冬季降水对北极涛动异常的响应     

刘胜胜  周顺武  吴萍  孙阳  谢洁宏  李可 《气象学报》2021,79(4):558-569

基于1979—2015年中国区域CN05.1格点降水以及全球降水气候中心（GPCC）降水等数据资料,采用回归、合成分析等方法,分析了青藏高原东部（简称高原）冬季降水的南、北区域性差异及其年际变化对北极涛动（AO）异常的响应。结果表明:（1）高原北部和南部冬季降水都与AO异常存在密切关系,但降水的年际变化并不一致,对AO异常响应的机理也不同。（2）高原北部冬季降水变化主要和东亚冬季风有关,AO正（负）异常时东亚冬季风减弱（增强）,高原北部对流层各层均为东南（西北）风距平,有（不）利于西太平洋的水汽进入高原北部,导致北部降水增加（减弱）。（3）高原南部冬季降水变化主要和南支槽有关,AO正（负）异常时南支槽加强（减弱）,有（不）利于源自孟加拉湾的水汽北上高原,低层辐合（散）高层辐散（合）,上升（下沉）运动增强,导致南部降水增加（减弱）。简言之,AO通过影响东亚冬季风（南支槽）,进而影响高原北（南）部冬季降水,但AO负异常对高原冬季降水的影响比AO正异常的影响更加显著。   相似文献   

Stereo topographic models of Mercury after three MESSENGER flybys     

Frank Preusker  Jürgen Oberst  James W. Head  Thomas R. Watters  Mark S. Robinson  Maria T. Zuber  Sean C. Solomon 《Planetary and Space Science》2011,59(15):1910-1917

From photogrammetric analysis of stereo images of Mercury obtained during three MESSENGER flybys, we have produced three digital terrain models (DTMs) that have a grid spacing of 1 km and together cover 30% of the planet's surface. The terrain models provide a rich source of information on the morphology of Mercury's surface, including details of tectonic scarp systems as well as impact craters and basins. More than 400 craters larger than 15 km in diameter are included in the models. Additionally, the models provide important test cases for the analysis of stereo image data to be collected during MESSENGER's orbital mission phase. Small lateral offsets and differences in trends between stereo DTMs and laser altimeter profiles may be due to remaining errors in spacecraft position, instrument pointing, or Mercury coordinate knowledge. Such errors should be resolved during the orbital mission phase, when more joint analyses of data and detailed orbit modeling will be possible.  相似文献   

Effects of three-dimensionality on seismic response of Gaussian-shaped hills for simple incident pulses     

《Soil Dynamics and Earthquake Engineering》2013

In this paper the boundary element algorithm which uses the time-convoluted traction kernels is applied to a numerical parametric study on the seismic behavior of three-dimensional Gaussian-shaped hills subjected to vertically propagating incident waves. All calculations were executed in the time-domain and the medium was assumed to have a linear elastic constitutive behavior. Results are discussed in both time and frequency domain with respect to the dimensionless parameters. It was shown that wave length and site geometry, including shape and dimension ratios and, to some extent, wave type are the key independent parameters governing hill amplification behavior. Comparing two- and three-dimensional hills with similar shape ratios, two-dimensional hill had greater characteristic periods, where the three-dimensional hill had greater maximum amplification potential. Three-dimensionality has a strong effect on the seismic responses of the hill; however the rate of seismic response variation with the three-dimensionality factor depends on the shape ratio. It was shown that two-dimensional behavior was dominant in low height three-dimensional hills, however, as the shape ratio increased, three-dimensionality effects appeared and the seismic response of the hill tends toward the axisymmetric three-dimensional hill.  相似文献   

Ecological constraints on and consequences of land use heterogeneity: A case study of the Mongolian Gobi     

《Journal of Arid Environments》2013

Mongolian herders are transhumant and therefore follow a specific land use pattern. To understand their movements through a case study, we mapped and superimposed their seasonal camps on a vegetation map and a digital elevation model. We also questioned them about the reasons justifying the locations of their camps, and how they use the surrounding land. It appears that vegetation quality may play a role only in summer, whereas topography is a key driver during 3 seasons. In winter, herders seek shelter against cold winds in rugged places exposed to the south, while in spring and summer, they seek flat places. In spring, to have a clear view of their newborns and in summer, to allow wind to reduce the insect discomfort. Moreover, most of the livestock species stay within a certain distance of the camps depending on the season, but which never exceeds 5.1 km. This leads to a land use pattern where livestock is restrained to specific areas according to the season. Interestingly, during the growing season, when plants are most sensitive to defoliation, most livestock is concentrated on 30.92% of the site surface. Such information is important for range scientists working on grazing impacts at large scales.  相似文献