多波束测深表层声速误差的动态影响及改正方法

表层声速不准确会对多波束测深波束的归位产生影响,对于平面换能器阵,使波束角产生偏差,从而影响波束最终位置,但Snell常数保持不变;对于曲面换能器阵,虽然波束未束控不产生波束角偏差,但Snell常数发生改变,会使波束在传播过程中出现折射误差,对深水环境测量不利。对于表层声速误差带来的水深误差,外部波束比内部波束受到的影响更严重。当表层声速无法实时准确获取时,根据内外部波束对水深的影响大小识别表层声速误差的存在,通过逐步调整表层声速值,计算波束指向角差值,再重新进行声线跟踪,计算改正后的波束位置,消除其带来的水深的影响,完成表层声速误差的改正。文中用实测数据进行了验证,对多波束测深数据质量的改善有一定的参考意义。     

近30年我国高空风速变化趋势分析

1980-2006年间采用全国119个探空站14个等压面的月平均风速资料,分析了我国高空对流层和平流层下层风速变化的时间和空间特征,并和同期地面风速变化进行了对比.结果表明,我国近27年对流层中下层和对流层上层风速呈下降趋势,年平均风速线性变化速率分别为-0.10 m·s-1·(10a)-1和-0.17 m·s-1·(10a)-1,均未通过0.05显著性水平检验;平流层下层全国年平均风速呈上升趋势,上升速率为0.24 m·s-1·(10a)-1,亦未通过O.05显著性水平检验.同期全国地面风速则呈现更显著的降低趋势,年平均风速线性变化速率为-0.16 m·s-1·(10a)-1,通过了0.05显著性水平检验.我国地面气象站记录的平均风速减弱可能受到大尺度大气环流变化的影响,更可能与台站附近观测环境变化和城市化等人为因素影响有密切关系.     

登陆我国热带气旋中心最低气压和最大风速关系研究

热带气旋(TC)登陆时中心最大风速会发生明显衰减,研究此时的风压关系对风暴潮模拟和预测具有重要意义。采用中国气象局上海台风研究所数据资料,对1949—2016年风压关系序列的一致性进行检验,登陆风压关系公式拟合及误差分析。结果表明:1970s后风压关系发生变异;新公式在计算登陆风速时要优于原公式,尤其是大风速情况下;相同气压下台风在近岸时风速明显小于大洋中,且登陆时风速越大衰减越剧烈。     

An analysis of soil crust strength in relation to potential abrasion by saltating particles

Wind erosion depends on the ease with which particles can be detached from the soil surface, but suitable tests to characterize this property are not available. Two possible methods to determine surface soil strength in the field were therefore compared on a range of artificially ‘crusted’ surfaces. These were made by spraying or tension wetting aggregates (10–2, 2–0.5 and <0.5 mm) from a structurally unstable sandy loam, followed by drying. Each test involved measuring the force exerted on a probe driven at a steady rate into the surface, using either a flat-tipped 0.6 mm diameter penetrometer or a flat-ended cylindrical punch with inner and outer diameters of 5 and 6 mm, respectively. Both probes showed that crusts could be produced reproducibly. Depending on the probe and aggregate size, penetration mainly occurred either as a result of aggregates being deflected out of the pathway of the probe or by genuine rupture of aggregates or of the crusted surface. The penetrometer, because it was comparable to the size of sand grains, gave results that can be used to characterize surface erodibility to saltating particles. The punch gave results that would be unsuitable for this purpose, as would other strength tests that are on too large a scale. Penetrometer results were analyzed to calculate the energy required for penetration. It was thus possible to demonstrate that only the spray-wetted fine aggregates had a surface that could undergo large-scale rupture by saltating sand grains. For all other surfaces, saltating particles would be unable to supply sufficient energy to rupture aggregates or the crusted surface. Erosion could only occur by a slower process of abrasion in which smaller particles or aggregates are chipped away from the surface. However, it is shown that saltating particles could rupture the interaggregate bonding in the 2–0.5 mm aggregate surfaces, thus permitting creep. An alternative and potentially simpler way of characterizing surface erodibility by using a surface modulus of elasticity is also discussed. Our results demonstrate that the small diameter penetrometer is a promising technique for characterizing erodibility of aggregated and crusted surfaces. © 1997 by John Wiley & Sons, Ltd.     

基于PIES观测东沙群岛附近声传播变化

本研究旨在将PIES观测数据应用于海洋水声环境的监测。利用一次南海PIES观测数据,反演得到温盐剖面,进而计算声场信息。结合观测期间的暖涡及台风事件对反演及计算结果进行了分析验证。结果表明,PIES能够在长期连续观测中较为敏感地捕获上层水体及表面声道的变化特征,为水声通信、探测及潜航路径规划等提供参考,在水声研究及海洋军事环境保障中都具有良好的应用前景。     

1951—2017年热带气旋移动速度特征统计分析

热带气旋移动速度是目前热带气旋研究热点之一。本文利用1951—2017年中国国家气象局最佳路径集资料,系统分析了西北太平洋海域热带气旋不同强度等级移动速度的年代际特征,初步探讨其原因,并对不同强度等级移动速度的分布特征进行系统诊断。结果表明,1951—2017年间平均移动速度(所有强度等级平均及对于大部分强度等级)呈现出减慢趋势,且主要体现在强热带气旋等级移动速度减慢;热带气旋向高纬度迁移趋势理论上将使移动速度增大而移动速度仍然减慢,说明气候因素是引起移动速度减慢的一个重要因素;不同强度等级平均移动速度、增强阶段基本相当,减弱阶段随强度减弱在初、中期明显增加,之后又逐渐减小,变性气旋移动速度显著增加;不同强度等级速度概率分布,增强阶段基本相同且相对集中,减弱阶段差异较大且相对分散,变性气旋最为分散。     

从二维地转风到三维涡旋运动

给出了大气三维涡旋运动基本态所满足的简洁的偏微分方程. 大气涡旋运动存在低压辐合上升和高压辐散下沉的基本状况，基本态的三维速度场可以用流函数和对流速度势分解，且具有螺旋结构. 当Reynolds数Re→∞时，涡旋运动就化为地转风，涡旋运动近似就化为地转风近似.     

冷空气引起的飞船主着陆场区偏北大风的特征分析及预报

分析了飞船主着陆场区1981—1999年1—4月和9—12月因冷空气而产生的偏北大风的过程中气候概况及其天气特征。通过分析发现:主着陆场区因冷空气引起的偏北大风以春季最频繁,秋、冬季最稀少;一天当中偏北大风以午后出现频率最大,午夜出现频率最少;对于不同季节的气压和温度,春、秋两季变化剧烈,冬季相对较小;在大风出现前24小时,主着陆场区的欧亚中高纬度大气环流以两槽一脊型、一槽一脊型、贝湖低压型为主;冷空气入侵前24小时,欧亚天气图上主着陆场区上游低层850hPa中高纬度有明显的冷中心,地面图场区上游冷高压中心的分布主要有3个区域:贝加尔湖西南至新疆、贝加尔湖到内蒙中北部、贝加尔湖西北部。大风前24小时在35～45°N、100～115°E等压线密集,等压线一般都在4根以上。     

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

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.     

The control of wind strength on the barchan to parabolic dune transition

The evolution of barchan-to-parabolic dunes can be driven by vegetation establishment, which may be linked to climate change and/or human activity. However, little is known of the impact of changes in wind strength on vegetation development and the resulting impacts on the evolution of dune morphology and sedimentological characteristics. To address this issue, we studied the morphology and grain-size characteristics of barchan, barchan-to-parabolic and parabolic dunes in the Mu Us Desert in north China, which was combined with an analysis of changes in normalized difference vegetation index (NDVI) and climatic variables during 1982–2018. The results reveal a trend of increasing growing-season NDVI which was related to a significant decrease in drift potential (DP). Therefore, we suggest that the initiation of dune transformation was caused by the reduced wind strength which favored the establishment and development of vegetation. To reveal the response of sedimentological reorganization during the processes of dune transformation, grain-size characteristics along the longitudinal profile of the three different types of dunes were examined. The decreasing wind strength led to the transport of fine sands on the upper part of the windward face of the dunes, resulting in a progressive coarsening of the grain-size distribution (GSD) and a reduction in dune height at the crest area. No distinct trend in sorting and mean grain-size was observed on the windward slope of the barchan-to-parabolic dune, indicating that the sand in transit had little influence on the GSD. Conversely, progressive sorting and coarsening of the sand occurred towards the crest of the parabolic dune. This indicates that vegetation development limited the transport of sand from upwind of the dune, and affected a shift in the dune source material to the underlying source deposits, or to reworked pre-existing aeolian deposits, and resulted in the trapping of sand in the crest area. © 2020 John Wiley & Sons, Ltd.