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11.
本文利用数值模拟的诊断分析结果对出现在江苏地区冬季的一次强对流风暴的成因进行了研究,结果表明,在河套气旋缓慢东移过程中,冷锋前暖区较长时期的大雾天气及下湿上干的湿度分布为强风暴的产生准备了大气层结不稳定的条件,中尺度辐合流场对强风暴的产生起了触发作用。对流云的下沉辐散气流是雷暴向前传播的重要机制。 相似文献
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湘西北地区发育寒武系下统牛蹄塘组、志留系下统龙马溪组两套富有机质黑色页岩。通过合成地震记录和已知地质特征推断反射层位的方法,对两套含烃黑色页岩层的地震地质特征、波组层位识别、波组特征进行了分析对比,总结出湘西北地区页岩层地震反射波所具有的典型特征:龙马溪组存在3~4个强相位,主频集中在30Hz左右;牛蹄塘组存在3个强反射界面,因深度加大,其主频集中在20Hz左右。由于龙马溪组和牛蹄塘组二组地层间距达2 500~3 000m,因此在湘西北地区将二组地层的反射波视作一个波系,其二维地震剖面存在3个波组4个反射层位或3个波组3个反射层位,三个波组分别为龙马溪组,中寒武底界及牛蹄塘组。另外因龙马溪组砂质泥岩段具有低速、低密度、低电阻率、高放射性等特征,其界面波阻抗差异较大,可作为本区的地震波标志层位。 相似文献
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活动造山带基岩河流地貌研究,目前已成为构造地貌学研究的前沿和热点。河道宽度形态的调整变化是基岩河流响应构造、岩性和气候等扰动的重要方式之一。通过研究祁连山北部地区6个重点流域基岩河道的宽度形态发现:河道宽度总体上呈现出东西向和南北向的变化特征,河道向下游增宽的速率,东段地区显著高于中段地区,低山带显著高于高山带;对比河道宽度的变化特征与构造抬升速率及岩性抗蚀性的变化,可以推断:在祁连山北部地区,基岩河道宽度响应构造抬升和岩性抗蚀性的变化进行了系统地调整,构造抬升控制了流域河道宽度变化的总体趋势,而岩性抗蚀性变化则导致了流域内部局部河段河道宽度的大幅波动。在祁连山北部地区开展的基岩河道宽度形态研究,为利用基岩河道形态研究造山带的构造变形奠定了基础,对于探索构造抬升背景下地貌的发育过程具有十分重要的意义。
相似文献15.
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Risk assessment of maize drought disaster in southwest China using the Environmental Policy Integrated Climate model 总被引:2,自引:0,他引:2
The East Asian monsoon has a tremendous impact on agricultural production in China. An assessment of the risk of drought disaster in maize-producing regions is therefore important in ensuring a reduction in such disasters and an increase in food security. A risk assessment model, EPIC(Environmental Policy Integrated Climate) model, for maize drought disasters based on the Erosion Productivity Impact Calculator crop model is proposed for areas with the topographic characteristics of the mountainous karst region in southwest China. This region has one of the highest levels of environmental degradation in China. The results showed that the hazard risk level for the maize zone of southwest China is generally high. Most hazard index values were between 0.4 and 0.5,accounting for 47.32% of total study area. However,the risk level for drought loss was low. Most of the loss rate was 0.1, accounting for 96.24% of the total study area. The three high-risk areas were mainlydistributed in the parallel ridge–valley areas in the east of Sichuan Province, the West Mountain area of Guizhou Province, and the south of Yunnan Province.These results provide a scientific basis and support for the reduction of agricultural drought disasters and an increase in food security in the southwest China maize zone. 相似文献
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Soft-shell clams (Mya arenaria) can serve important ecological roles in intertidal mudflats and are an important economic and recreational resource in the northwestern Atlantic. However, environmental factors affecting newly-settled and juvenile clam abundances within a given settlement season remain uncertain. We conducted a field study assessing relationships between juvenile soft-shell clam abundance and spatial, temporal, and environmental variables in coastal mudflats of the northern shore of the Bay of Fundy. Sediment pH and low-tide water temperature (tide pools) were monitored in situ on a biweekly–monthly basis over the course of the M. arenaria settlement season in 2012 at four study sites to quantify diel variation in sediment pH and temperature. Core samples were also collected to quantify M. arenaria (<6 mm) abundance. Sea-surface and air temperature, and in situ sediment pH and water temperature were then used to predict clam abundance. Sediment pH was spatially and temporally variable, while in situ temperature was stable and declined over the sampling season. Akaike’s information criterion model selection indicated that models incorporating site, date, and air temperature best predicted 2012 recruitment patterns in linear models when all variables were included. When only environmental variables were included, the best linear model included minimum air temperature and sediment pH. When data were averaged across dates for each site to remove potential temporal effects, mean clam abundance displayed a significant positive relationship with sediment pH and sediment grain size, but not minimum air temperature. The results of this study suggest that sediment pH and/or sediment grain size may influence within-season juvenile soft-shell clam abundances across mudflats in the Bay of Fundy. Field experiments at the same (or similar) sites are now needed to confirm the mechanism driving the observed relationships. 相似文献
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GPS Solutions - The EUREF Permanent Network (EPN) is a network of continuously operating GNSS stations installed throughout the European continent. The EPN Central Bureau (CB) performs the... 相似文献
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Nannochloropsis oculata CS179, a unicellular marine microalga, is rich in long-chain polyunsaturated fatty acids (LCPUFAs). Elongase and desaturase
play a key role in the biosynthesis of PUFAs. A new elongase gene, which encodes 322 amino acids, was identified via RT-PCR and 5′ and 3′ RACE. The sequence of the elongase gene was blast-searched in the NCBI GenBank and showed a similarity
to those of the cryptosporidium. But the NJ-tree revealed that the N. oculata CS179 elongase clustered with those of the microalgae Phaeodactylum tricornutum, Ostreococcus tauri and Thalassiosira pseudonana. 相似文献