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1.
Base flows are important for tropical regions with pronounced dry seasons, which are facing increasing water demands. Base flow generation, however, is one of the most challenging hydrological processes to characterize in the tropics. In many years during the May–December wet season in the Panama Canal Watershed (PCW), base flows in rivers abruptly increase. This increase persists until the start of the December–April dry season. Understanding this unusual base flow jump (BFJ) behaviour is critical to improve water provisioning in the seasonal tropics, especially during droughts and extended dry seasons. This study developed an integrated approach combining piecewise regression on cumulative average base flow and sensitivity analysis to calculate the timing and magnitude of BFJ. Rainfall, forest cover, mean land surface slope, catchment area, and estimated subsurface storage were tested as predictors for the occurrence and magnitude of the BFJs in seven subcatchments of the PCW. Sensitivity analysis on correlated predictors allowed ranking of predictor contributions due to isolated and cross-correlation effects. Correlations between observed BFJs and BFJs predicted by watershed and rainfall-related predictors were 0.92 and 0.65 for BFJ timing and magnitude, respectively. Forest cover was the second most significant predictor after cumulative rainfall for jump magnitude, owing to larger subsurface storage and groundwater recharge in forests than pastures. Catchments in the mountainous eastern PCW always generated larger jumps due to their higher rainfall and greater forest cover than the western PCW catchments. The cross-correlations between predictors contributed to more than 50% of the jump variances. The results demonstrate the importance of rainfall gradient and catchment characteristics in affecting the sudden and sustained BFJs, which can help inform land management decisions intended to enhance water supplies in the tropics. This study underscores the need for more research to further understand the hydrological processes involved in the BFJ phenomenon, including better BFJ models and field characterizations, to help improve tropical ecosystem services under a changing environment.  相似文献   
2.
利用1979~2015年JTWC(Joint Typhoon Warning Center)最佳路径资料(2001~2015年资料用于台风风圈结构分析)及ERA-interim(0.5°×0.5°)再分析数据,统计分析我国海南岛附近区域(15.5°N~23.5°N,106°E~116°E)热带气旋(Tropical Cyclone,简称TC)低层风场的变化特征。结果表明:(1)年均5.5个TC于4~12月主要以西偏北路径进入该区域,其中海南岛东南侧海域TC出现频率最高且强TC比例最多,而岛西北区域出现频率最低,强TC比例最少。(2)TC中心位于海南岛不同方位时,其外围低层风场分布具有不同的非对称特征,且大风出现比率也各有差异;TC中心位于海南岛上时出现大风比率最高,位于岛南侧时次之,位于岛北侧时最小。(3)该区域TC平均最大风速半径(RMW)为58.3 km;TC位于岛上时RMW最大,而位于岛西南侧最小。(4)TC近中心最大风速由海上向陆地急剧减小,其高值中心主要位于雷州半岛东侧及西侧海域。(5)研究区域内TC的34节风圈半径在TC环流的东侧大而西侧小,强TC大而弱TC小。(6)不同区域TC变形程度有所差异。平均而言,位于岛西南侧TC变形最大而位于岛东南侧时变形最小。  相似文献   
3.
熊秋芬  张玉婷  姜晓飞  张雅乐 《气象》2018,44(10):1267-1274
利用常规高空、地面观测资料、FY-2E卫星云图和NCEP再分析场,分析了2013年11月25日发生在中国东北东部的暴雪天气过程,并用HYSPLIT模式模拟了暴雪区上空气块的轨迹。结果表明:卫星云图显示暴雪发生在锢囚气旋的钩状云区中,且具有中尺度特征。钩状云区不同代表点、不同层次25日08时120 h气块的后向轨迹计算结果表明,在每个代表点的6条轨迹中,只有1条轨迹来自新疆以西地区的对流层上层,其他5条轨迹均来自蒙古国或我国北方地区的对流层中低层。几乎每条轨迹对应的气块在东移或南移时先以水平运动为主,伴有弱的下沉;中低层气块在72~24 h经过渤海湾和日本海;而中上层气块则主要经过黄海或东海,到达降雪区前几小时气块移速快并有明显的上升运动。对钩状云区不同代表点1500和3000 m上空120 h后向轨迹中气块湿度分析表明,来自东亚大陆的气块水汽含量并不大、相对湿度也小于60%,但在经过渤海湾和日本海时,海气交换使得气块的含水量和相对湿度均呈增加的趋势;特别是气块途径日本海的时间和距离越长,水汽含量越多。因此暴雪区的水汽主要来自日本海,其次是渤海湾。在降雪发生前几小时,气块随偏南风或东南风快速北移,相对湿度接近饱和并伴有上升运动,从而引起降雪。  相似文献   
4.
2017年冬季(2017年12月—2018年2月)大气环流特征为:北半球极涡呈偶极型分布,中高纬度呈4波型。12月,亚洲中东部中高纬度环流经向度较大,有利于冷空气南下。2018年1月,西伯利亚冷高压较12月更强,冷空气自北向南影响我国近海。2月,冷空气活动减弱,有温带气旋入海并发展。我国近海出现了19次8级以上大风过程,其中冷空气大风过程14次,冷空气和温带气旋共同影响的大风过程2次,冷空气与热带气旋共同影响的大风过程1次,热带气旋大风过程2次。2 m以上的海浪过程有19次,未出现2 m以上大浪的天数仅有10 d。我国近海出现6次比较明显的海雾过程,出雾区域在北部湾附近海域,出雾时间在夜间—早晨时段。西北太平洋和南海共生成4个台风。海面温度整体呈下降趋势。  相似文献   
5.
“7·20” 华北和北京大暴雨过程的分析   总被引:3,自引:1,他引:2  
赵思雄  孙建华  鲁蓉  傅慎明 《气象》2018,44(3):351-360
本文对2016年7月19—21日华北及北京的特大暴雨作了研究和讨论。研究表明,该次暴雨为诸多有利因素所致:前期副热带高压呈带状稳定维持,中旬末东退,后呈"东高西低"分布,华北处于槽前辐合上升区,有利对流发生。高空西来槽停滞加深(并切断)与低层江淮暖性倒槽叠加,快速发生发展成为一深厚的气旋,出现了高低空系统的耦合。有一支暖(湿)输送带自南向北推进至关重要,源地可追踪至南中国海等低纬度地区,水汽通量辐合大值区先后经长江、黄淮至华北,有明显的中低纬度系统的相互作用。2016年的"7·20"暴雨和2012年"7·21"暴雨均存在明显的多尺度特征,但其具体特征有所不同。前者强烈对流活动稍弱于后者,降水趋势平稳,然而由于其大尺度强迫持续时间长,累积降水量仍然较大。本文主要集中于一些事实的分析,对于该次暴雨的机理尚需作进一步研究。  相似文献   
6.
In this paper, 1416 conventional ground-based meteorological observation stations on the mainland of China were subdivided into groups of differing spatial density. Data from each subgroup were then used to analyze variations in the tropical cyclone (TC) precipitation statistics derived from each subgroup across the mainland of China (excluding Taiwan, Hong Kong, and Macao), as well as in two regions (east China and south China) and three provinces (Guangdong, Hainan, and Jiangxi) between 1981 and 2010. The results showed that for the mainland of China, total precipitation, mean annual precipitation, mean daily precipitation, and its spatial distribution were the same regardless of the spatial density of the stations. However, some minor differences were evident with respect to precipitation extremes and their spatial distribution. Overall, there were no significant variations in the TC precipitation statistics calculated from different station density schemes for the mainland of China. The regional and provincial results showed no significant differences in mean daily precipitation, but this was not the case for the maximum daily precipitation and torrential rain frequency. The maximum daily precipitation calculated from the lower-density station data was slightly less than that based on the higher-density station schemes, and this effect should be taken into consideration when interpreting regional climate statistics. The impact of station density on TC precipitation characteristics was more obvious for Hainan than for Guangdong or Jiangxi provinces. In addition, the effects were greater for south China (including Guangxi Zhuang Autonomous region, Guangdong, and Hainan provinces) than east China (including Shandong, Jiangsu, Zhejiang, Shanghai, Fujian, Anhui, and Jiangxi provinces). Furthermore, the analysis proved that the statistical climatic characteristics began to change significantly when the station spacing was between 40 and 50 km, which are close to the mean spacing for all stations across the mainland of China. Moreover, TC areal precipitation parameters, including mean total areal precipitation and mean daily areal precipitation, also began to change significantly when the spacing was between 40 and 50 km, and were completely different when it was between 100 and 200 km.  相似文献   
7.
Tropical cyclones and their devastating impacts are of great concern to coastal communities globally. An appropriate approach integrating climate change scenarios at local scales is essential for producing detailed risk models to support cyclone mitigation measures. This study developed a simple cyclone risk-modelling approach under present and future climate change scenarios using geospatial techniques at local scales, and tested using a case study in Sarankhola Upazila from coastal Bangladesh. Linear storm-surge models were developed up to 100-year return periods. A local sea level rise scenario of 0.34?m for the year 2050 was integrated with surge models to assess the climate change impact. The resultant storm-surge models were used in the risk-modelling procedures. The developed risk models successfully identified the spatial extent and levels of risk that match with actual extent and levels within an acceptable limit of deviation. The result showed that cyclone risk areas increased with the increase of return period. The study also revealed that climate change scenario intensified the cyclone risk area by 5–10% in every return period. The findings indicate this approach has the potential to model cyclone risk in other similar coastal environments for developing mitigation plans and strategies.  相似文献   
8.
In this study, the micro- and macro-physical properties, thermal structure and precipitation characteristics of cyclone eye walls and their surrounding spiral clouds were analysed with CloudSat and TRMM data for five tropical cyclones (TCs) in 2013. The results show that the ice-phase clouds of a mature TC are mainly above 5 km. With increasing altitude, the cloud droplet effective radius decreases, and the particle number concentration increases. Ice water content first increases and then decreases with increasing height. In the eye area, in addition to the well-known warm-core area, another warm core is also apparent around the eye at a height of 8 to 15 km. The horizontal distribution of precipitation is characterized by large-scale stratiform precipitation mixed with independent convective precipitation. The height of precipitation is mostly below 7.5 km, and the heavy rain is mainly below 5 km. When the peripheral convective clouds are strong enough, ice particles would be generated, thus providing conditions that are favourable for the formation of precipitation below.  相似文献   
9.
刘甫  明杰  张翰  田娣 《热带气象学报》2020,36(4):552-561
利用日本多功能运输卫星(Multi-functional Transport Satellite,简称为MTSAT-2)逐小时云顶亮温资料、Climate Prediction Center Morphing Technique(CMORPH)逐3小时降水资料及南海北部的现场观测资料,对2014年第16号热带气旋"凤凰"的结构演变和远距离洋面上的海洋响应特征进行了研究。结果表明:高空环流形势场的变化主导了"凤凰"的移动方向,调整其云系结构;"凤凰"过境期间测站处气压和气温明显下降,风速和相对湿度有所增加,并伴随有多次阵性降雨过程,最大降雨量可达174 mm/h;"凤凰"引起的强混合的热泵作用导致测站处海洋混合层冷却加深,三个站位观测到的最大海表面降温分别为0.53 ℃(站位2)、0.50 ℃(站位4)、1.18 ℃(站位5);"凤凰"期间海表面盐度下降,且强降盐过程与降水时段具有较好的时间一致性,降水时段内,三个站位观测到的表层最大降盐量分别为0.557 psu(站位2)、0.407 psu(站位4)、0.773 psu(站位5)。   相似文献   
10.
Coastal boulder fields provide clues to long-term frequency-magnitude patterns of coastal flooding events and have the potential to play an important role in coastal hazard assessment. Mapping boulders in the field is time and labour-intensive, and work on intertidal reef platforms, as in the present study, is physically challenging. By addressing coastal scientists who are not specialists in remote sensing, this contribution reports on the possibilities and limitations of digital applications in boulder mapping in Eastern Samar, Philippines, where recent supertyphoons Haiyan and Hagupit induced high waves, coastal flooding and boulder transport. It is demonstrated how satellite imagery of sub-metre resolution (from Pléiades and WorldView-3 imagery) enables efficient analysis of transport vectors and distances of larger boulders, reflecting variation in latitudes of both typhoon tracks and approaching angles of typhoon-generated waves. During the investigated events, boulders with a-axes of up to 8 m were clearly identified to have been shifted for up to 32 m, mostly along the seaward margin of the boulder field. It is, however, hard to keep track of smaller boulders, and the length of a-axes and b-axes including their orientation is often impossible to map with sufficient accuracy. Orthophotographs and digital surface models created through the application of an unmanned aerial vehicle and the ‘Structure from Motion’ technique provide ultra-high-resolution data, and have the potential to not only improve the results of satellite image analysis, but also those from field mapping and may significantly reduce overall time in the field. Orthophotographs permit unequivocal mapping of a-axes and b-axes including their orientation, while precise values for c-axes can be derived from the respective digital surface models. Volume of boulders is best inferred from boulder-specific Structure from Motion-based three-dimensional models. Battery power, flight speed and altitude determine the limits of the area covered, while patches shielded by the boulders are difficult to resolve. For some tasks, field mapping remains mandatory and cannot be replaced by currently available remote sensing tools: for example, sampling for rock type, density and age dating, recording of lithological separation of boulders from the underlying geological unit and of geomorphic features on a millimetre to decimetre-scale, or documentation of fine-grained sediment transport in between the boulders in supratidal settings. In terms of future events, the digital products presented here will provide a valuable reference to track boulder transport on a centimetre to decimetre-scale and to better understand the hydrodynamics of extreme-wave events on a fringing reef coastline.  相似文献   
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