Storm surge induced flux through multiple tidal passes of Lake Pontchartrain estuary during Hurricanes Gustav and Ike

In September 2008, Hurricanes Gustav and Ike generated major storm surges which impacted the Lake Pontchartrain estuary in Louisiana. This paper presents analyses of in situ measurements acquired during these storm events. The main data used in the analyses were from three bottom mounted moorings equipped with conductivity, temperature, and depth sensors, acoustic Doppler current profilers (ADCPs), and a semi-permanent laterally mounted horizontal acoustic Doppler profiler (ADP). These moorings were deployed in the three major tidal channels that connect Lake Pontchartrain with the coastal ocean. A process similar to tidal straining was observed: the vertical shear of the horizontal velocity was negligible during the inundation stage, but a shear of 0.8 m/s over a less than 5 m water column was recorded during the receding stage, 2–3 times the normal tidal oscillations. The surge reached its peak in the Industrial Canal 1.4–2.1 h before those in the other two channels. The inward flux of water lasted for a shorter time period than that of the outward flux. The inward flux was also observed to have much smaller magnitude than the outward flux (∼960–1200 vs. 2100–3100 million m³). The imbalance was believed to have been caused by the additional water into Lake Pontchartrain through some small rivers and inundation over the land plus rainfall from the hurricanes. The flux through the Industrial Canal was 8–12%, while the flux through the other two tidal passes ranged between 17% and 70% of the total, but mostly split roughly half-half of the remaining (∼88–92% of the total).     

车辆碾压作用下戈壁地表起尘浓度

通过野外观测车辆碾压作用下戈壁地表PM₁₀释放浓度,探讨其主要影响因素。针对戈壁区砾石、砂砾、砂质和砂土4种路面类型,应用TSI粉尘仪多次重复观测车辆碾压产生的PM₁₀浓度,进而阐明碾压次数、车速和地表水分等因素对起尘浓度的影响。结果表明：4种路面的平均起尘浓度依次为5.339、9.089、16.944、50.251 mg·m^-3,是自然状态下的5~50倍;起尘浓度随碾压次数增多而增大,其中砂土路情况下的增长最显著;随土层厚度的增大呈现出幂函数的增长趋势;降雨后路面起尘浓度显著减小,且降雨量会影响降雨后起尘浓度的变化趋势。最后提出了针对性的建议和措施以减弱车辆碾压导致的戈壁地表起尘。     

塔克拉玛干荒漠-绿洲过渡带尘卷风活动特征——以肖塘为例

利用1992—2011年塔克拉玛干沙漠北缘荒漠-绿洲过渡带肖塘气象站的观测资料,分析了该地区尘卷风的年、月变化规律及其与气象因子的关系。结果表明:(1) 1992—2011年尘卷风发生日数总体呈波动递减趋势;尘卷风主要发生在3—9月,占全年总日数的90.9%,其中4—7月占全年总日数的70%左右。(2)尘卷风月发生日数随月平均地表与1.5 m高处温差的增大而线性增加(r=0.875,P<0.01)。(3)尘卷风月发生日数随着月平均风速的增大而幂函数增加(r=0.89,P<0.01)。(4)尘卷风月发生日数随月平均相对湿度的增大而线性减少(r=-0.869,P<0.01)。     

2007-2017年中国沙尘气溶胶的三维分布特征及输送过程

利用最新发布的CALIPSO产品,构建了2007-2017年中国沙尘气溶胶的三维分布,并结合HYSPLIT-4模式和再分析数据,探讨了沙尘的三维输送过程。结果表明：中国的沙尘排放源区主要是塔克拉玛干沙漠和巴丹吉林沙漠,沙尘气溶胶出现频率分别为60%和35%。塔克拉玛干沙漠排放的沙尘主要（50%~70%）停留在源地0~6 000 m高度,少部分向东输送至甘肃和内蒙古;巴丹吉林沙漠排放的沙尘则主要向东输送。中国沙尘排放量在春季最大,向东输送最强;夏季,东亚夏季风限制了沙尘向东输送;秋季,沙尘排放减弱,输送强度和夏季相当;沙尘排放量在冬季最小,输送最弱。夏季,沙尘在输送过程中可被抬升至高度5 000 m以上,春季次之,秋、冬季的沙尘主要在低层大气输送。沙尘在向东输送的过程中被抬升并和当地人为污染物混合变为污染性沙尘,华北地区污染性沙尘出现频率高达30%;输送到海洋的沙尘也会与洋面上（0~3 000 m高度）的海盐气溶胶混合,出现频率约为10%。     

Sensitivity of hurricane surge to morphological parameters of coastal wetlands

Given the history and future risk of storm surge in the United States, functional storm protection techniques are needed to protect vital sectors of the economy and coastal communities. It is widely hypothesized that coastal wetlands offer protection from storm surge and wave action, though the extent of this protection is unknown due to the complexities of flow through vegetation. Here we present the sensitivity of storm-surge numerical modeling results to various coastal wetlands characteristics. An idealized grid domain and 400-km² marsh feature were used to evaluate the effects of marsh characteristics on hurricane surge, including the effects of bottom friction, elevation, and continuity (the ratio of healthy marsh to open water area within the total wetland area).Through coupled hydrodynamic and wave model simulations, it is confirmed that increased bottom friction reduces storm-surge levels for most storms. However, increases in depth associated with marsh elevation loss generally results in a reduction of surge. As marsh continuity is decreased, coastal surge increases as a result of enhanced surge conveyance into and out of the marsh. Storm surge is parameterized in terms of marsh morphology, namely marsh elevation, frictional characteristics, and degree of segmentation, which will assist in the justification for and optimization of marsh restoration in terms of storm protection.     

近岸海浪、风暴潮及海啸灾害远程实时监测系统的现场试验及应用

利用自主研发的近岸海浪、风暴潮及海啸灾害远程实时监测系统,在广东省阳江市闸坡附近海域进行了远程实时监测试验.文章介绍了监测系统的组成,对2007年9月1日-10月3日的观测记录进行了分析,计算出台风增水、波高和波周期,采用低通滤波方法获得重力外波.实验结果表明,研发的近岸海浪、风暴潮及海啸灾害远程实时监测系统可供实际推广应用.     

Mitigation of lunar dust adhesion by surface modification

Dust has been recognized as one of the greatest hazards in continued lunar exploration due to its tenacious adhesion to everything with which it comes into contact. Unfortunately, there is little known about the mechanisms of adhesion on widely varying surface types: van der Waals and electrostatic forces are the dominant forces under consideration here. Surface energy, roughness, mechanical properties and electronic properties are all known to contribute to the adhesion characteristics. An optimal solution to mitigate dust adhesion would be to identify the dominant components of the adhesive force and to reduce that force by surface modification. In this study, an ion beam process was used to modify (treat) the surfaces of three dramatically different materials spanning the range of conductor (black Kapton), semiconductor (silicon), and insulator (quartz). Adhesive forces between less than JSC-1 lunar simulants and these virgin/treated surfaces were measured in vacuum using a centrifugal force detachment method. We found that JSC-1 particles adhered less to treated silicon and quartz surfaces, correlated with a reduction in van der Waals force due to a reduced surface energy. The large reduction in adhesion for treated black Kapton is mainly due to the large decrease in the electrostatic (image) force that results from reduced contact charging. Materials in space and on the lunar surface will be directly exposed to high-energy ultraviolet radiation prior to being covered by dust, so the UV irradiation effects on surface adhesion were also examined. Both virgin and treated quartz surfaces are most affected by the UV-irradiation, showing dramatically increased adhesion.     

台风"碧利斯"的结构与江西暴雨诊断分析

利用T213资料、自动气象站加密资料和常规观测资料等,研究分析了0604号台风“碧利斯“的环流背景、移动路径、内部结构和外围暴雨的分布特征,并将其与0505号台风“海棠“、0513号台风“泰利“、0414号台风“云娜“,进行了对比分析.研究结果表明,台风暴雨与台风环流场、热力场的不对称有关,并不一定总是集中在环流中心附近.无论是对称结构,还是非对称结构,降水中心都与强对流云带位置相对应.“碧利斯“先西北行后向西折的路径,主要是受强大稳定的副热带高压引导,并表现为明显的不对称结构,东侧、南侧的积云对流较为旺盛,降水主要集中在移动路径的第三象限;850 hPa台风环流场表现为南部环流强盛,南海季风为西南急流的稳定维持提供了充沛的水汽条件;局地地形激发深厚的上升运动,进而产生庐山和赣南南部山区的大暴雨天气;垂直运动、散度、涡度、水汽通量、假相当位温等各物理量场,均与外围暴雨区有较好的对应关系.     

大地电场变化的频谱特征

处理了中国大陆地区嘉峪关、昌黎、崇明、蒙城、兴济、宝坻和阳原等7个台的地电场观测数据,应用最大熵谱方法研究了大地电场日变化、地电暴等谱成分的特征. 结果表明,大地电场日变化主要是12 h的半日波成分最强, 24~25 h的全日波和8 h周期成分次之; 地电暴是在大尺度空间同步发生的,其谱值高于日变化谱值约2～3个数量级,主要以较长周期成分为主. 这一结果初步解释了大地电场变化的主要谱成分的生成机制.      

Radiation pressure — a stabilizing agent of dust clouds in comets?

The internal dynamics of an illuminated dust cloud of finite optical thickness is investigated. The dependence of the radiation pressure on the optical depth makes the individual particles oscillate, in one dimension, around the accelerated centre of gravity of the cloud. The cloud moves as an entity, irrespectively of the velocity dispersion of the particles and their efficiency for radiation pressure. If the optical depth does not change, i.e. if the cloud does not expand laterally, its lifetime is unlimited. A contraction caused by energy dissipation in mechanical collissions between the dust particles is expected. The range of particle sizes which can be transported by such a “coherent cloud” is estimated, as well as the acceleration of the whole cloud. The structure of the cloud in real space and in velocity space is investigated. A comparison with the “striae” observed in the dust tails of great comets shows that the parent clouds of these striae may have been of the kind considered.