气候变暖对湖泊热力及溶解氧分层影响研究进展

气候变暖对湖泊物理、化学、生物和生态系统有着复杂而深刻的直接和间接影响,而具体影响随研究区域和水体表现不尽相同。气候变暖通过改变湖泊热力和溶解氧分层进而影响湖泊生物过程和生态系统结构与功能。从全球湖泊变暖趋势、长期缓慢气温上升、极端高温事件以及气候情景模拟等方面详细综述了气候变暖对湖泊热力及溶解氧分层影响的研究进展。研究表明,全球不同区域湖泊均存在不同程度的变暖趋势;长期缓慢气温上升和短期极端高温均会造成湖泊热力分层提前,分层结束推迟,分层时间延长,混合层和温跃层深度下降,以及热稳定性增加;相伴随的是溶解氧扩散深度和氧跃层深度明显下降,加剧了湖泊底部好氧和厌氧环境。除了这种直接影响外,气候变暖引起的流域降水、入湖物质的变化以及风速的变化也会对湖泊热力和溶解氧分层产生许多间接的影响,因此未来仍然需要更多的实验证据、经验和数值模型来验证和预测气候变暖对湖泊热力及溶解氧分层的影响。     

东南极普里兹湾陆隆区脊状沉积体的结构和形成过程

东南极普里兹湾陆隆区发育数个近垂直陆缘的脊状沉积体,这些沉积体记录了区域冰川活动和底流变化的历史。本文主要利用多道地震资料和水深资料对这些脊状沉积体的平面展布、走向上的结构差异进行了研究,在此基础上讨论了不同脊状沉积体的形成过程。结果表明研究区内脊状沉积体有两种不同结构类型:西部Wild峡谷两侧不对称发育的浊流堤岸沉积形成两个平行峡谷的脊状沉积体;东部数个脊状沉积体的形成与其下长期存在的浊流活动引起的穿时沉积间断面有关。不同峡谷的浊流活动起始时代不一,西部的Wild峡谷起始时代和陆隆区冰海沉积起始时代(P1)一致;东部Wilkins峡谷以及Murray峡谷从后期的P3(约26.1 Ma)开始,代表普里兹湾地区的一次冰川极盛事件。研究区所有峡谷及其浊流活动均随时间向海扩展,造成相应的脊状沉积体向海扩展。在脊状沉积体外缘区域,浊流输送而来的细粒沉积物在向西的底流作用下形成大型深海沉积物波。     

2011日本东北大地震前震余震重力效应分析

针对2011年日本东北大地震(Tohoku-Oki地震)发生前后较短时间内的多次较大前震和余震和主震混在一起,不利于提取出主震同震信号的问题,该文利用弹性位错理论模拟计算了Tohoku-Oki地震一次较大前震和两次较大余震的同震重力变化,讨论了这3次地震单独和综合的重力效应,并与主震重力变化对比分析,认为这3次前震和余震引起的重力变化数值较大,影响范围广,会直接影响到Tohoku-Oki地震主震的同震重力信号提取,所以需要作为重要误差考虑。     

Determination of allowable subgrade frost heave with the pavement roughness index in numerical analysis

Frost heave is an upward swelling of soil during cryogenic conditions in cold regions. It is caused by the accumulation of ice crystals in subgrade soil, which grow upwards when freezing temperatures penetrate into the subgrade. This study establishes the allowable soil subgrade frost heave based on the roughness standard of asphalt pavement in China, and aims to balance the pavement design and frost heave resistance of subgrades in cold regions. We formulated a mechanical model of pavement supported by the boundary conditions of differential frost heave, based on the elastic layered system theory. The differential soil subgrade frost heave was modeled as a sinusoidal function, and the allowable frost heave and the roughness index were modeled as the displacement boundaries for the top and bottom of the pavement structure. Then the allowable frost heave was back-calculated according to the roughness standard. Numerical results show that the allowable frost heave depends on the pavement structure, material properties, the highway grade, and other factors. In order to ensure that the actual soil subgrade frost heave is lower than the allowable frost heave, pavement structures and materials need to be selected and designed carefully. The numerical method proposed here can be applied to establish the frost heave resistance of subgrade when the pavement structure and materials are determined.     

基于反射地震资料探讨泥河湾盆地的新生代和中生代地层

查明泥河湾盆地新生界及中生界地层序列及基底的分布与赋存形态是研究泥河湾盆地形成机制的基础性工作。本研究在泥河湾盆地桑干河与壶流河交接处附近采集了四条测线的反射地震数据,通过对精细处理后的地震剖面进行详细分析,在剖面上厘定了三个具有明显强反射标志的地层,即古近系的玄武岩、侏罗系上统的含煤地层和侏罗系下统的含煤地层;其中,新近系沉积层与古近系玄武岩界面在地震剖面上出现的双程旅行时为0.3~0.6s,深度范围为300~500m,而第四系泥河湾组底界由南西到北东逐渐加深,其界面深度为200~300m;侏罗系上统含煤地层在地震剖面上出现的双程旅行时在0.8s上下波动,其深度约为1200m,探测出侏罗系上统顶界面的深度范围为800~1100m;侏罗系下统含煤地层在地震剖面上出现的双程旅行时为1.0~1.4s,深度范围为1800~2000m,由此推测出中生界侏罗系与古生界寒武系地层分界线的深度为2000m左右;根据地震反射波阻抗差别推测出新元古界和太古界地层的分界面在地震剖面上出现的时间约为2.5s,其深度为4000m左右。本研究通过四条反射地震测线的数据基本上查明了泥河湾盆地位于探测区处第四系泥河湾组底界面的深度分布范围及起伏形态、侏罗系上统顶界面和下统底界面的大致埋深,为查明泥河湾盆地新生界及中生界地层序列提供了基础性的参考信息。     

2020年夏季海洋天气评述

2020年夏季（6—8月）,北半球极涡呈现明显的单极型分布,极涡主体位于北极圈内,中心偏向东半球,中高纬环流呈现4波型分布。6—7月,西太平洋副热带高压较常年平均偏强,且位置偏西偏南,不利于热带气旋活动。2020年夏季共有8个热带气旋在西北太平洋和南海生成,其中7月没有热带气旋生成。除西北太平洋和南海之外,其他热带洋面另有20个热带气旋生成,其中北大西洋11个,东太平洋8个,北印度洋1个。受偏南暖湿气流的影响,我国北方海域多海雾天气。同时受入海气旋活动影响,多海上大风过程。夏季近海海域共出现了7次比较明显的海雾过程,其中6月3次,7月1次,8月3次。大风过程出现了10次, 2次由热带气旋影响,7次与入海气旋活动有关。发生2 m以上的大浪过程12次,6—8月分别出现了4次、5次和3次。     

The Relationship Between Abnormal Meiyu and Medium-Term Scale Wave Perturbation Energy Propagation Along the East Asian Subtropical Westerly Jet

The East Asian subtropical westerly jet(EASWJ) is one of the most important factors modulating the Meiyu rainfall in the Yangtze-Huaihe River Basin, China. This article analyzed periods of the medium-term EASWJ variation,wave packet distribution and energy propagation of Rossby waves along the EASWJ during Meiyu season, and investigated their possible influence on abnormal Meiyu rain. The results showed that during the medium-term scale atmospheric dynamic process, the evolution of the EASWJ in Meiyu season was mainly characterized by the changes of3-8 d synoptic-scale and 10-15 d low-frequency Rossby waves. The strong perturbation wave packet and energy propagation of the 3-8 d synoptic-scale and 10-15 d low-frequency Rossby waves are mostly concentrated in the East Asian region of 90°-150°E, where the two wave trains of perturbation wave packets and wave-activity flux divergence coexist in zonal and meridional directions, and converge on the EASWJ. Besides, the wave trains of perturbation wave packet and wave-activity flux divergence in wet Meiyu years are more systematically westward than those in dry Meiyu years, and they are shown in the inverse phases between each other. In wet(dry) Meiyu year, the perturbation wave packet high-value area of the 10-15 d low-frequency variability is located between the Aral Sea and the Lake Balkhash(in the northeastern part of China), while over eastern China the wave-activity flux is convergent and strong(divergent and weak), and the high-level jets are strong and southward(weak and northward). Because of the coupling of high and low level atmosphere and high-level strong(weak) divergence on the south side of the jet over the Yangtze-Huaihe River Basin, the low-level southwest wind and vertically ascending motion are strengthened(weakened), which is(is not)conducive to precipitation increase in the Yangtze-Huaihe River Basin. These findings would help to better understand the impact mechanisms of the EASWJ activities on abnormal Meiyu from the perspective of medium-term scale Rossby wave energy propagation.     

Month-Long Simulations of Gravity Waves over North America and North Atlantic in Comparison with Satellite Observations

Mesoscale simulations of gravity waves in the upper troposphere and lower stratosphere over North America and North Atlantic Ocean in January 2003 are compared with satellite radiance measurements from the Advanced Microwave Sounding Unit-A (AMSU-A). Four regions of strong gravity wave (GW) activities are found in the model simulations and the AMSU-A observations: the northwestern Atlantic, the U.S. Rockies, the Appalachians, and Greenland. GWs over the northwestern Atlantic Ocean are associated with the midlatitude baroclinic jet-front system, while the other three regions are apparently related to high topography. Model simulations are further used to analyze momentum fluxes in the zonal and meridional directions. It is found that strong westward momentum fluxes are prevalent over these regions over the whole period. Despite qualitative agreement between model simulations and satellite measurements, sensitivity experiments demonstrate that the simulated GWs are sensitive to the model spin-up time.     

青藏高原大地形对华南持续性暴雨影响的数值试验

利用新一代中尺度数值预报模式WRF3.2及NCEP/NCAR 逐日4次1°×1°的FNL再分析资料,通过有、无青藏高原以及将高原高度降低到临界高度的数值试验,研究了青藏高原大地形对我国华南地区2010 年5 月一次持续性暴雨过程的影响。试验结果表明:高原大地形对降水的影响显著,随着高原高度的升高,降水增多,高原以东地区的雨带也由北向南移动;高原地形的机械阻挡作用使迎风坡一侧的近地面层附近为强上升运动,背风坡为下沉运动,并分别对应降水的峰值和谷值区;高原对西风气流的爬流、绕流作用明显,高原升高后爬坡作用减弱,以绕流作用为主;高原的加热作用使气流过高原时南支减弱,北支加强,并加强了高原及其东部地区低层的正涡度和高层的负涡度,使高原上空为强烈的上升运动;高原的热力作用使西太平洋副热带高压位置偏南、偏西并稳定维持;高原大地形对形成稳定的高原季风环流圈有重要作用;高原地形高度的作用有利于定常波的形成,波动中心对应强上升运动,形成降水的大值区,稳定维持的定常波使得降水持续集中在同一地区,造成持续性暴雨。