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101.
A mathematical relation between deformation and vertical vorticity tendency is built by introducing the frontogenesis function and the complete vertical vorticity equation, which is derived by virtue of moist potential vorticity. From the mathematical relation, it is shown that properly configured atmospheric conditions can make deformation exert a positive contribution to vortex development at rates comparable to other favorable factors. The effect of deformation on vortex development is not only related to the deformation itself, but also depends on the current thermodynamic and dynamic structures of the atmosphere, such as the convective stability, moist baroclinicity and vertical wind shear(or horizontal vorticity). A diagnostic study of a heavy-rainfall case that occurred during 20–22 July 2012 shows that deformation has the most remarkable effect on the increase in vertical vorticity during the rapid development stage of the low vortex during its whole life cycle. This feature is mainly due to the existence of an approximate neutral layer(about 700 h Pa) in the atmosphere where the convective stability tends to be zero. The neutral layer makes the effect of deformation on the vertical vorticity increase significantly during the vortex development stage, and thus drives the vertical vorticity to increase. 相似文献
102.
Both 1981 and 2013 were weak La Niña years with a similar sea surface temperature (SST) anomaly in the tropical Pacific, yet the western Pacific subtropical high (WPSH) during August exhibited an opposite anomaly in the two years. A comparison indicates that, in the absence of a strong SST anomaly in the tropics, the cold advection from Eurasian high latitudes and the convection of the western Pacific warm pool play important roles in influencing the strength and position of the WPSH in August. In August 1981, the spatial pattern of 500 hPa geopotential height was characterized by a meridional circulation with a strong ridge in the Ural Mountains and a deep trough in Siberia, which provided favorable conditions for cold air invading into the lower latitudes. Accordingly, the geopotential height to the north of the WPSH was reduced by the cold advection anomaly from high latitudes, resulting in an eastward retreat of the WPSH. Moreover, an anomalous cyclonic circulation in the subtropical western Pacific, excited by enhanced warm pool convection, also contributed to the eastward retreat of the WPSH. By contrast, the influence from high latitudes was relatively weak in August 2013 due to a zonal circulation pattern over Eurasia, and the anomalous anticyclonic circulation induced by suppressed warm pool convection also facilitated the westward extension of the WPSH. Therefore, the combined effects of the high latitude and tropical circulations may contribute a persistent anomaly of the WPSH in late summer, despite the tropical SST anomaly being weak. 相似文献
103.
利用常规气象观测资料、NCEP 1°×1°逐6h的再分析资料、GPS可降雨资料和地闪定位资料,对2013年7月4—5日山东中南部出现的暴雨到大暴雨天气过程的不同阶段特征和成因进行了分析,结果表明:本次暴雨过程是冷暖切变线所引发,暴雨的水汽源于南海;低空急流的强弱和水汽通量的大小呈正相关;暖切变线暴雨的雨强、影响范围和持续时间明显大于冷切变线暴雨;冷、暖切变线GPS可降雨量表现不同,前者短时间内增幅大,地面强降雨在峰值出现1h后发生,对地面降雨变化反映较敏感,后者强降雨出现前8h可降雨量快速上升,可降雨量峰值对应地面降雨大值,对地面降雨变化反映不敏感;冷切变线对流性更强,地闪频次为暖切变线降雨的2倍,正地闪频次为暖切变线降雨的1/2,负地闪频次为暖切变线降雨的2倍;降雨云团正、负地闪活跃程度呈反相位关系,正、负地闪的变化能很好地反映强降雨的变化;冷、暖切变线动力结构不同,前者物理量场从低层到高层向北倾斜,后者则为垂直分布;冷切变线上升运动区较暖切变线深厚。 相似文献
104.
青藏高原积雪对全球气候变化十分重要,针对已有积雪遥感判识方法中普遍采用的可见光与红外光谱数据易受复杂地形与高海拔影响,导致青藏高原地区积雪判识精度较低的问题,提出了一种基于多光谱遥感与地理信息数据特征级融合的积雪遥感判识方法:以风云三号卫星可见光与红外多光谱遥感资料与多要素地理信息作为数据源,由地面实测雪深数据与现有积雪产品交叉筛选出样本标签,构建并训练基于层叠去噪自编码器(SDAE)的特征融合与分类网络,从而有效辨识青藏高原遥感图像中的云、积雪以及无雪地表。经地面实测雪深数据验证,该方法分类精度显著高于使用相同数据源的FY-3A/MULSS积雪产品,略高于国际主流积雪产品MOD10A1与MYD10A1,并且年均云覆盖率最低。试验结果表明该方法可有效地减少云层对积雪判识的干扰,提升分类精度。 相似文献
105.
低空大比例尺地形图航测生产关键技术 总被引:3,自引:1,他引:2
针对传统航空摄影测量生产工艺在生产过程中遇到的影响大比例尺测图精度的问题,该文探讨了低空航测生产大比例尺地形图的关键技术。通过选用宽角相机、低航高飞行、强化影像匹配、野外布设标志控制点、优选平差模型、精化测图操作等改进方式,以提高大比例尺航测精度;组建无人飞艇低空航测系统,对提出的技术方法予以实现;最后给出了山西境内近30个县市建成区1∶500测绘生产实践的部分验证成果。 相似文献
106.
CHENG Xiaogan LIN Xiubin WU Lei CHEN Hanlin XIAO Ancheng GONG Junfeng ZHANG Fengqi YANG Shufeng 《《地质学报》英文版》2016,90(3):870-883
Determining the spatio-temporal distribution of the deformation tied to the India-Eurasian convergence and the impact of pre-existing weaknesses on the Cenozoic crustal deformation is significant for understanding how the convergence between India and Eurasia contributed to the development of the Tibetan Plateau. The exhumation history of the northeastern Tibetan Plateau was addressed in this research using a new apatite fission track (AFT) study in the North Qaidam thrust belt (NQTB). Three granite samples collected from the Qaidam Shan pluton in the north tied to the Qaidam Shan thrust, with AFT ages clustering in the Eocene to Miocene. The other thirteen samples obtained from the Luliang Shan and Yuka plutons in the south related to the Luliang Shan thrust and they have showed predominantly the Cretaceous AFT ages. Related thermal history modeling based on grain ages and track lengths indicates rapid cooling events during the Eocene-early Oligocene and since late Miocene within the Qaidam Shan, in contrast to those in the Cretaceous and since the Oligocene-Miocene in the Luliang Shan and Yuka region. The results, combined with published the Cretaceous thermochronological ages in the Qaidam Shan region, suggest that the NQTB had undergo rapid exhumation during the accretions along the southern Asian Andean-type margin prior to the India-Eurasian collision. The Cenozoic deformation initially took place in the North Qaidam thrust belt by the Eocene, which is consistent with the recent claim that the deformation of the northeastern Tibetan Plateau initiated in the Eocene as a response to continental collision between India and Eurasia. The immediate deformation responding to the collision is tentatively attributed to the pre-existing weaknesses of the lithosphere, and therefore the deformation of the northeastern Tibetan Plateau should be regarded as a boundary-condition-dependent process. 相似文献
107.
JIAO Yangquan WU Liqun RONG Hui PENG Yunbiao MIAO Aisheng WANG Xiaoming 《《地质学报》英文版》2016,90(6):2117-2132
Outcrop and drill hole data show that the Jurassic coal measures in the northeastern Ordos Basin are composed mainly of the Yan'an Formation and the lowstand system tract of the Zhiluo Formation,and there is a regional unconformity between them. The Dongsheng uranium deposit is associated with the Jurassic coal measures. Research data indicate that the Jurassic coal measures in the study area have a certain hydrocarbon-generating capacity,although the metamorphic grade is low(Ro=0.40%–0.58%). In the Dongsheng region alone,the accumulative amount of generated coalbed methane(CBM) is about 2028.29 × 108 –2218.72 × 108 m~3; the residual amount is about 50.92 × 108 m~3,and the lost amount is about 1977 × 108 m~3. Analysis of the burial history of the host rocks and the evolutionary history of the Dongsheng uranium deposit suggests that the Jurassic coal measures generated hydrocarbon mainly from Middle Jurassic to Early Crataceous,which is the main mineralization phase of the Dongsheng uranium deposit. By the Late Cretaceous,a mass of CBM dissipated due to the strong tectonic uplift,and the Dongsheng uranium deposit stepped into the preservation phase. Therefore,the low-mature hydrocarbon-containing fluid in the Jurassic coal measures not only served as a reducing agent for the formation of sandstone-type uranium deposits,but also rendered the second reduction of paleo-interlayer oxidation zone and become the primary reducing agent for ore conservation. Regional strata correlation reveals that the sandstone-type uranium reservoir at the bottom of the Zhiluo Formation is in contact with the underlying industrial coal seams in the Yan'an Formation through incision or in the form of an unconformity surface. In the Dongsheng region with poorly developed fault systems,the unconformity surface and scour surface served as the main migration pathways for low-mature hydrocarbon-containing fluid migrating to the uranium reservoir. 相似文献
108.
109.
云南腾冲火山盆地深部存在岩浆囊是人们关注的问题,多方面进行了大量的研究且存在不同意见。作者此前依据低电阻异常推断出位于小空山、大空山、黑空山等火山口的下部,深13~30 km范围内东西向25 km,南北向30km的低电阻率的岩浆囊,其东侧为大盈江断裂。文章利用反射地震、重力、航空磁测资料进一步探讨了岩浆囊的其他地球物理特征。由于火山喷发,不仅在火山口附近形成了局部物质亏损,而且,岩浆囊本身也亏损了岩浆物质,在重力上延图中滤去了表层的火山局部负重力异常后,呈现出大空山北侧的与低阻体相对应的负重力异常,这与岩浆囊高温熔融状态含水低密度物质有密切关系。整体的重力负异常印证了低阻岩浆囊的存在。腾冲马站岩浆囊的温度为397~651°C,平均温度为524°C,其主体中心部位不可能存在磁性体。对航磁资料的处理,消除表层火山岩影响后,仍然发现有较强磁异常,其平面投影范围与低阻体相近,推断磁异常是岩浆囊顶层,在15 km深度以上范围内,随着岩浆囊体温度逐步下降,当低于480°C以后会形成新的铁磁性矿物,因此,在囊体上层出现了范围与囊体相近的较强的磁性体。反射地震仅仅在浅部较清楚地观测到较连续的反射波界面,是浅部火山岩、含水层、以及花岗岩顶界面的反映。向深部反射界面很不连续推测是由于多次岩浆上涌,其喷发时间有先后,成分有差异,故岩浆囊物质的不均匀性,虽然由于含水、矿化、熔融体构成了低电阻的共性,可温度的不均匀,却又显示了不同期次岩浆成分有变化,由岩浆囊向地表的通道上,东部花岗岩下为高速,相对于较低温度的物质,在小空山、大空山和黑空山深部沿大盈江断裂带有东西两个大的隐伏花岗岩体之间是最新的火山喷发通道,具有相对低速的通道。 相似文献
110.