Coastal ridge constructive processes at a multi-decadal scale in Barreta Island (southern Portugal)     

Xabier Herrero  Susana Costas  Katerina Kombiadou 《地球表面变化过程与地形》2020,45(2):411-423

Multiple ridges across prograding coasts may display variable geometries, commonly expressed through varying elevations. Changes in ridge elevation have been traditionally related to the occurrence of fluctuating progradation rates, which might, in turn, be driven by shifting environmental conditions. Here, we explore the geometry and growth mechanisms of multiple ridges, generated at Barreta Island (Ria Formosa, southern Portugal), as a consequence of the rapid progradation of the island over the last 70 years, following the artificial fixation of the downdrift Faro-Olhão inlet with jetties in 1955. The variability in the morphology of these features was analysed in combination with available wind and wave data, in order to better distinguish growth mechanisms and understand the main parameters determining the final geometry of the observed ridges. The results suggest that (1) most of the identified ridges fall in the beach ridge classification, as they have been mostly built by marine processes, and (2) the parameters derived from, or closely related to wave climate variability (e.g. progradation rates, storm occurrence) can jointly explain most of the observed morphological changes, while aeolian processes played a secondary role. Indeed, ridge geometry appears mainly controlled by progradation rates, with higher ridges associated with lower progradation rates. Progradation rate, in turn, is mostly related to longshore wave power, storminess, and the occurrence storm groups. Yet, the final configuration of ridges can also be affected by runup levels and onshore winds. Therefore, establishing the relation between ridge geometry and wave climate is not a straightforward task, because of the complex processes and interactions that control coastal morphodynamics. © 2019 John Wiley & Sons, Ltd.  相似文献   

Thresholds for post-wildfire debris flows: Insights from the Pinal Fire,Arizona, USA     

Carissa A. Raymond  Luke A. McGuire  Ann M. Youberg  Dennis M. Staley  Jason W. Kean 《地球表面变化过程与地形》2020,45(6):1349-1360

Wildfire significantly alters the hydrologic properties of a burned area, leading to increases in overland flow, erosion, and the potential for runoff-generated debris flows. The initiation of debris flows in recently burned areas is well characterized by rainfall intensity-duration (ID) thresholds. However, there is currently a paucity of data quantifying the rainfall intensities required to trigger post-wildfire debris flows, which limits our understanding of how and why rainfall ID thresholds vary in different climatic and geologic settings. In this study, we monitored debris-flow activity following the Pinal Fire in central Arizona, which differs from both a climatic and hydrogeomorphic perspective from other regions in the western United States where ID thresholds for post-wildfire debris flows are well established, namely the Transverse Ranges of southern California. Since the peak rainfall intensity within a rainstorm may exceed the rainfall intensity required to trigger a debris flow, the development of robust rainfall ID thresholds requires knowledge of the timing of debris flows within rainstorms. Existing post-wildfire debris-flow studies in Arizona only constrain the peak rainfall intensity within debris-flow-producing storms, which may far exceed the intensity that actually triggered the observed debris flow. In this study, we used pressure transducers within five burned drainage basins to constrain the timing of debris flows within rainstorms. Rainfall ID thresholds derived here from triggering rainfall intensities are, on average, 22 mm h⁻¹ lower than ID thresholds derived under the assumption that the triggering intensity is equal to the maximum rainfall intensity recorded during a rainstorm. We then use a hydrologic model to demonstrate that the magnitude of the 15-min rainfall ID threshold at the Pinal Fire site is associated with the rainfall intensity required to exceed a recently proposed dimensionless discharge threshold for debris-flow initiation. Model results further suggest that previously observed differences in regional ID thresholds between Arizona and the San Gabriel Mountains of southern California may be attributed, in large part, to differences in the hydraulic properties of burned soils. © 2019 John Wiley & Sons, Ltd.  相似文献   

基于时相变化的晴空条件下Himawari-8 AHI火点检测     

鄢俊洁  瞿建华  冉茂农  张芳芳 《遥感学报》2020,24(5):571-577

Himawari-8静止气象卫星具有高空间分辨率、高观测频次和高时效特点,对于火点检测具有很强优势。对Himawari-8卫星的3.9μm和11.2μm两通道亮温进行了连续时相变化研究,得出两通道的亮温在时间上的变化差值稳定且规律明显。根据两通道的亮温时相特征,考虑白天可见光对3.9μm通道的影响,并结合火点产生时引起的亮温变化特征,提出了适用于晴空条件下改进的火点检测算法。在多处进行了此算法的实验,例如2018-11-27 T 16:40(UTC时)河北张家口市桥东区一化工厂附近发生的严重爆炸起火事件以及2019-02-28澳大利亚西南部发生的火灾事件,均快速有效的检测到了火点。实验表明,改进的火点检测算法能很好的进行火点检测,并能解决晨昏交界、冰雪下垫面、常规火源点、太阳耀光等火点检测的难题。  相似文献   

敦煌-格尔木铁路沿线风动力环境特征     

鱼燕萍  张克存  安志山  张余 《中国沙漠》2020,40(1):41-48

敦煌-格尔木铁路沿线地形复杂、起沙因素多变、沙源丰富，沙害问题日益严重。目前对其风沙活动规律还未有研究，不利于防沙工作的开展。为此，通过对自北向南的5个观测点（S1、S2、S3、S4、S5）风速和风向的观测、计算和分析，利用平均风速、起沙风况及输沙势对敦格铁路沿线的风动力环境特征进行研究。结果表明：S5、S4和S3的风况对铁路风沙灾害防治意义较大。S5年平均风速、起沙风频率和输沙势最大，春季风沙活动最为强烈，且风向单一、风力强劲，风沙运动方向基本与铁路垂直，沙粒易在铁路附近堆积。S4夏季风沙活动最为强烈；S3春季风沙活动最为强烈，且风向单一，S4和S3的风沙运动方向与铁路夹角小于90°，附近沙源广阔，铁路易受风沙侵蚀，阻碍交通运营。  相似文献   

地理大数据挖掘——目标、内涵与研究问题     

裴韬  宋辞  郭思慧  舒华  刘亚溪  杜云艳  马廷  周成虎 《地理学报(英文版)》2020,30(2):251-266

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Upper ocean high resolution regional modeling of the Arabian Sea and Bay of Bengal     

Suneet Dwivedi  Alok Kumar Mishr  Atul Srivastava 《海洋学报(英文版)》2019,38(5):32-50

In this paper, effort is made to demonstrate the quality of high-resolution regional ocean circulation model in realistically simulating the circulation and variability properties of the northern Indian Ocean(10°S–25°N,45°–100°E) covering the Arabian Sea(AS) and Bay of Bengal(BoB). The model run using the open boundary conditions is carried out at 10 km horizontal resolution and highest vertical resolution of 2 m in the upper ocean.The surface and sub-surface structure of hydrographic variables(temperature and salinity) and currents is compared against the observations during 1998–2014(17 years). In particular, the seasonal variability of the sea surface temperature, sea surface salinity, and surface currents over the model domain is studied. The highresolution model's ability in correct estimation of the spatio-temporal mixed layer depth(MLD) variability of the AS and BoB is also shown. The lowest MLD values are observed during spring(March-April-May) and highest during winter(December-January-February) seasons. The maximum MLD in the AS(BoB) during December to February reaches 150 m (67 m). On the other hand, the minimum MLD in these regions during March-April-May becomes as low as 11–12 m. The influence of wind stress, net heat flux and freshwater flux on the seasonal variability of the MLD is discussed. The physical processes controlling the seasonal cycle of sea surface temperature are investigated by carrying out mixed layer heat budget analysis. It is found that air-sea fluxes play a dominant role in the seasonal evolution of sea surface temperature of the northern Indian Ocean and the contribution of horizontal advection, vertical entrainment and diffusion processes is small. The upper ocean zonal and meridional volume transport across different sections in the AS and BoB is also computed. The seasonal variability of the transports is studied in the context of monsoonal currents.  相似文献   

刘公岛海洋牧场底层海水溶解氧浓度的变化特征     

李兆钦  李欣  孙利元  刘子洲  顾艳镇  翟方国  李培良 《海洋与湖沼》2019,50(1):86-99

由于缺乏长期观测资料,前人对山东半岛邻近海域海水溶解氧的时间变化和空间分布特征的研究较少。本文基于威海刘公岛海洋牧场于2016年7月20日至2017年3月14日期间,利用生态环境实时在线观测系统获得的底层海水的温度、盐度、水深、溶解氧数据,分析了该牧场海水溶解氧浓度的时间变化特征及其影响因素,并探讨了低氧灾害发生的可能性。结果表明在观测期间,该牧场海水溶解氧浓度以季节变化为主,冬季最大、夏季最小,其中2月份平均值最高,约为10.86mg/L,8月份平均值最低,约为5.91mg/L。同时海水溶解氧浓度也存在显著的小时变化和日变化,且变化幅度于8月份最大、3月份最小。影响海水溶解氧浓度变化的主要因素是海水温度,溶解氧浓度随着温度的季节性变化而变化。夏季,水体分层会使溶解氧浓度发生大幅度的降低,大风过程对于溶解氧浓度也有一定的影响,通过打破夏季的季节性温跃层使水体发生垂向混合从而为海底提供氧气,但大风过程之后的几天会出现溶解氧浓度降低的现象。本次研究发现刘公岛海洋牧场在观测期间不存在低氧现象。  相似文献   

顾及基准站坐标动态特性与稳定性的区域框架构建     

蒋光伟  王斌  王延伟  李康  孙洋洋 《地球物理学进展》2020,(1):8-15

基准站受构造运动与非线性因素的影响,如何构建高精度、现势性强的精细区域框架是位置服务与形变分析的的关键.笔者提出顾及基准站坐标动态特性与稳定性的区域框架构建方法.以我国西部与东部某城市的多年连续运行基准站数据为例进行试算比对,试验结果表明:该方法是可行的,较好地顾及了基准站的坐标特性与非线性影响,考虑了基准站的垂直运动规律,可构建高精度的区域基准,可发现区域基准的微动态变化.  相似文献   

辽宁省数字化形变观测自然干扰分析     

姚菲菲  宫长盛  梁永信 《地震地磁观测与研究》2020,41(4):148-156

对数字形变观测过程中辽宁丹东地震台、营口地震台、抚顺地震台、朝阳地震台DSQ水管仪、SS-Y伸缩仪存在的自然干扰现象进行研究，对其机理和数据形态作了对比分析，为快速、准确地判别自然干扰提供了科学依据。  相似文献   

云南广南县老寨湾金矿地质特征及找矿标志     

高李阳  顾雄  吴小梅 《云南地质》2020,(1):71-75

广南县老寨湾金矿位于滇、黔、桂“金三角”重要成矿区带上,金矿体矿体呈似层状赋存于断层构造破碎带或层间构造破碎带中,构造控矿明显。矿体围岩均为下泥盆统坡松冲组第一段(D1ps1)硅化石英砂岩;矿床成因属中-低温热液叠加改造型金矿床,断层构造、硅化等矿化蚀变及地球化学异常是重要的找矿标志。  相似文献