北冰洋Gakkel洋中脊的地幔熔融控制因素及非岩浆地壳增生   总被引：3，自引：0，他引：3  

张涛  高金耀  陈美  杨春国  沈中延  周志远  吴招才  孙运凡 《海洋学报(英文版)》2015,34(6):42-48

Spreading rate is a primary factor of mantle melting and tectonic behavior of the global mid-ocean ridges. The spreading rate of the Gakkel ridge decreases gradually from west to east. However, the Gakkel ridge can be divided into four thick-and-thin zones with varying crustal thicknesses along ridge axis. This phenomenon indicates that mantle melting of the Gakkel ridge is not a simple function of spreading rate. Mantle temperature, water content,mantle composition, and other factors are important in crustal accretion processes. Based on gravity-derived crustal thickness and wet melting model, we estimate that the mantle potential temperatures of the four zones are1 270, 1 220, 1 280, and 1 280°C(assuming that mantle water content equals to global average value), with corresponding mantle water contents of 210, 0, 340, and 280 mg/kg(assuming that mantle potential temperature is 1 260°C), respectivly. The western thinned crust zone is best modeled with low mantle temperature, whereas the other zones are mainly controlled by the enhanced conduction caused by the slower spreading rate. Along the Gakkel ridge, the crustal thickness is consistent with rock samples types. Predominated serpentinized peridotite and basalt are found in the area with crustal thickness 1.5 km and 2.5 km, respectively. The rock samples are including from basalt to peridotite in the area with crustal thickness between 1.5 and 2.5 km. Based on this consistency, the traditional magmatic accretion zone accounted for only 44% and amagmatic accretion accounted for 29% of the Gakkel ridge. The amagmatic accretion is a significant characteristic of the ultra-slow spreading ridge.  相似文献   

相似天气背景下深圳两次前汛期降水过程对比分析          下载免费PDF全文

李超  陈潜  赵春阳  张超 《山东气象》2021,41(2):24-33

在高空槽和低层切变线配合的相似环流背景下,2019 年 4 月 11 日深圳出现短时暴雨（ 简称“2019 年过程”）,2020 年 4 月 11 日以稳定性弱降水为主（ 简称“2020 年过程”）,利用 ERAS 再分析数据等对深圳这两次前汛期降水过程进行了对比分析。 结果表明,2019 年过程,温湿层结等对流条件和高空辐散条件较好,低空辐合动力条件相对较弱,在边界层辐合线触发下产生明显的中尺度对流系统（mesoscale convective system, MCS) 活动, 导致深圳出现短时强降水和雷暴大风。2020 年过程,低层辐合等动力条件较好,但对流条件相对较弱,降水以稳定性降水为主。 对比分析说明,温度和湿度层结条件较动力条件对华南前汛期 MCS 生成作用更为明显,强对流发生前 12 h深圳等珠三角地区 Q矢量辐合明显,对 MCS 活动以及强对流发生有较好的指示意义。  相似文献   

中国夏季干湿型热浪天气时空分布及环境舒适度评价          下载免费PDF全文

邓悦  屈文军 《山东气象》2021,41(2):34-45

基于中国气象局对热浪天气的定义并参考地理分区和热浪日湿度分级标准,定义连续3 d以上地面最高气温≥35 ℃的天气过程为热浪,选取 1960—2018 年 476 个地面气象站观测数据研究中国夏季干热型和湿热型热浪日数的时空分布特征及其变化趋势。结果表明,中国夏季热浪日数除新疆外呈现东南高、西北低的空间分布格局,江南地区夏季热浪发生日数最多（年均 15 d）。温湿指数和人体舒适度指数评价结果表明江淮地区热浪天气期间环境舒适度最差,热浪天气对人体的不利影响更显著。相对于内陆地区,沿海地区因海风影响午后气温显著降低,有利于缓解热浪天气的影响,因而沿海站点夏季热浪日数比邻近的内陆站点偏少。除黄淮地区外中国大多数站点热浪日数均呈现增加趋势,江苏、浙江沿海、广东、重庆、海南、新疆及广西东部热浪日数增加趋势显著（1 ～5 d·(10 a) -1,α=0.05）;中国东部和东南沿海湿热型热浪增加趋势显著,增幅达 1～5 d·(10 a) -1;浙江、江西北部、甘肃、新疆等地区干热型热浪日数显著增加（α=0.01）。1990 年以来全国夏季热浪天气发生更为频繁;其中 2000—2009 年间干热型热浪日数偏多,而 2010 年之后强湿热型热浪日所占比例增加。  相似文献   

干湿过程中花岗岩残积土抗拉强度变化研究     

汤连生  王昊  孙银磊  刘其鑫 《岩土力学》2022,43(7):1749-1760

利用自制的土体直拉强度测试仪,研究了重塑花岗岩残积土在不同含水率下、增湿过程和干燥过程中抗拉强度的变化规律,并从胶结力和湿吸力的角度讨论了抗拉强度变化规律的微观机制。结果表明：不同含水率条件下抗拉强度随含水率增加呈现先增后减,峰值两侧呈较好的指数规律;增湿过程中抗拉强度随含水率增加呈先增后减趋势,峰值两侧为一次函数规律;干燥过程中抗拉强度随含水率降低出现指数增加阶段、平稳阶段和小幅降低阶段3个阶段,其抗拉强度峰值为不同含水率条件下抗拉强度的4倍。花岗岩残积土在不同含水率和增湿过程中的抗拉强度的变化主要受湿吸力控制,而干燥过程中抗拉强度变化的同时受湿吸力和胶结力的控制,且胶结力对抗拉强度的贡献超过70%。土体的干燥开裂过程对应干燥过程中抗拉强度变化的几个阶段,干燥时湿吸力是土体内部拉应力的来源,这说明湿吸力既是抗拉强度的贡献者,同时也是抗拉强度的破坏者。该研究结果从另一种角度解释了土体抗拉强度的形成来源及其变化的主控因素。  相似文献   

Precipitation changes in wet and dry seasons over the 20th century simulated by two versions of the FGOALS model     

MA Shuangmei  ZHOU Tianjun 《大气科学进展》2015,32(6):839-854

Seasonal precipitation changes over the globe during the 20 th century simulated by two versions of the Flexible Global Ocean–Atmosphere–Land System(FGOALS) model are assessed. The two model versions differ in terms of their AGCM component, but the remaining parts of the system are almost identical. Both models reasonably reproduce the mean-state features of the timings of the wet and dry seasons and related precipitation amounts, with pattern correlation coefficients of 0.65–0.84 with observations. Globally averaged seasonal precipitation changes are analyzed. The results show that wet seasons get wetter and the annual range(precipitation difference between wet and dry seasons) increases during the 20 th century in the two models, with positive trends covering most parts of the globe, which is consistent with observations. However,both models show a moistening dry season, which is opposite to observations. Analysis of the globally averaged moisture budget in the historical climate simulations of the two models shows little change in the horizontal moisture advection in both the wet and dry seasons. The globally averaged seasonal precipitation changes are mainly dominated by the changes in evaporation and vertical moisture advection. Evaporation and vertical moisture advection combine to make wet seasons wetter and enhance the annual range. In the dry season, the opposite change of evaporation and vertical moisture advection leads to an insignificant change in precipitation. Vertical moisture advection is the most important term that determines the changes in precipitation, wherein the thermodynamic component is dominant and the dynamic component tends to offset the effect of the thermodynamic component.  相似文献   

大型桥梁桥塔监测的GNSS相对对流层延迟估计     

高兴旺  李付岗  张秋昭  吴来义  杨威  戴新军 《测绘科学》2021,46(2):42-47,70

针对大型桥梁桥塔与基站高程差异较大,残余对流层延迟成为影响全球卫星导航系统(GNSS)监测成功率与精度的主要因素之一。该文基于随机过程理论,对桥梁监测GNSS残余对流层湿延迟进行参数估计,有效地提高了桥梁塔顶监测GNSS模糊度固定率。通过采用对流层经验模型改正对流层干延迟,将基准站和塔顶观测站对流层湿延迟组成相对对流层湿延迟,并联合位置参数和模糊度参数建立双差卡尔曼模型,最后利用最小二乘模糊度降低相关平差法(LAMBDA)对双差模糊度进行固定,并估计位置参数与相对对流层延迟参数。实验结果表明,该方法可以有效估计相对对流层延迟,有效提高GNSS模糊度固定率。  相似文献   

温州“9．4”台风倒槽特大暴雨分析     

郑峰 《海洋通报(英文版)》2010,12(1):39-47

运用T106数值预报产品、MM5模式结合Q矢量计算NCEP资料、天气实况及卫星云图等非常规资料，对1999年9月4日凌晨在远离9909号热带风暴中心的浙江省温州市引发的特大暴雨进行了探讨。发现秋季在厦门以南至广东东部登陆的台风，在浙中南沿海形成台风倒槽，该倒槽内的暖湿切变线的中尺度对流复合体（Mesoscale Convective Complex，MCC）是引起特大暴雨的重要条件。从计算得出的Q矢量散度分布看，本次特大暴雨降水发生时间和量级与该时段内温州经历的强Q矢量散度梯度发展有密切联系。同时，温州呈东北-西南走向的海岸线及境内雁荡山脉有利地形的抬升作用，对本次热带风暴倒槽降水中局地特大暴雨的形成有重要贡献。  相似文献   

太湖流域公元960年以来的气候干湿变化研究   总被引：7，自引：11，他引：7  

王张华  陈中原  寇莹  陈宇 《地理科学》2002,22(5):546-551

利用史料和文献建立了太湖流域公元960-1992年的逐年干湿等级序列，对此序列进行了周期分析和突变分析。分析表明，本区近千年来的历史干湿气候变化是一种复合振动，其主周期是准100年，另外还有多个周期，这些周期与天体活动密切相关。统计还发现1247-1263年附近由干变湿和1618-1635年附近由湿变干的两次非局地性气候突变事件。其中，14、15世纪是太湖流域近千年来最湿润的时期，它可能是东亚地区大范围气候变湿波动的体现。  相似文献   

The 26.5 ka Oruanui eruption, New Zealand: an introduction and overview     

C. J. N. Wilson   《Journal of Volcanology and Geothermal Research》2001,112(1-4)

The 26.5 ka Oruanui eruption, from Taupo volcano in the central North Island of New Zealand, is the largest known ‘wet’ eruption, generating 430 km³ of fall deposits, 320 km³ of pyroclastic density–current (PDC) deposits (mostly ignimbrite) and 420 km³ of primary intracaldera material, equivalent to 530 km³ of magma. Erupted magma is >99% rhyolite and <1% relatively mafic compositions (52.3–63.3% SiO₂). The latter vary in abundance at different stratigraphic levels from 0.1 to 4 wt%, defining three ‘spikes’ that are used to correlate fall and coeval PDC activity. The eruption is divided into 10 phases on the basis of nine mappable fall units and a tenth, poorly preserved but volumetrically dominant fall unit. Fall units 1–9 individually range from 0.8 to 85 km³ and unit 10, by subtraction, is 265 km³; all fall deposits are of wide (plinian) to extremely wide dispersal. Fall deposits show a wide range of depositional states, from dry to water saturated, reflecting varied pyroclast:water ratios. Multiple bedding and normal grading in the fall deposits show the first third of the eruption was very spasmodic; short-lived but intense bursts of activity were separated by time breaks from zero up to several weeks to months. PDC activity occurred throughout the eruption. Both dilute and concentrated currents are inferred to have been present from deposit characteristics, with the latter being volumetrically dominant (>90%). PDC deposits range from mm- to cm-thick ultra-thin veneers enclosed within fall material to >200 m-thick ignimbrite in proximal areas. The farthest travelled (90 km), most energetic PDCs (velocities >100 m s⁻¹) occurred during phase 8, but the most voluminous PDC deposits were emplaced during phase 10. Grain size variations in the PDC deposits are complex, with changes seen vertically in thick, proximal accumulations being greater than those seen laterally from near-source to most-distal deposits. Modern Lake Taupo partly infills the caldera generated during this eruption; a 140 km² structural collapse area is concealed beneath the lake, while the lake outline reflects coeval peripheral and volcano–tectonic collapse. Early eruption phases saw shifting vent positions; development of the caldera to its maximum extent (indicated by lithic lag breccias) occurred during phase 10. The Oruanui eruption shows many unusual features; its episodic nature, wide range of depositional conditions in fall deposits of very wide dispersal, and complex interplay of fall and PDC activity.  相似文献   

用水热平衡模型估算青海湖古水文要素及水量平衡   总被引：7，自引：0，他引：7  

秦伯强 《海洋与湖沼》1997,28(6):611-616

根据水热平衡原理，推导了内陆湖泊水位高低（或面积大小）与流域降水及蒸发之间的定量关系，设计了青海湖古水量平衡计算模型。用现在的湖区气象要素及水量收支对模型进行了检验，然后将此模型用于估算全新世稳定暖湿期（7200－6000aB．P．）的青海湖古水文要素及水量平衡。结果显示，在全新世稳定暖湿期，青海湖流域的降水、蒸发及径流比现代高约32％，13％和67％。反映出该地区因气温高、降水增加造成的季风加强使得该地区的水量收支与现代相比有较大的不同。本方法用古湖水位来定量恢复古水文、气候参数，为此可以从古湖泊中提取古气候信息。  相似文献