NUMERICAL STUDY ON THE ROLE OF VORTICAL AND DIVERGENT COMPONENTS OF WIND STRESS IN ENSO CYCLE

The 1960-1991 monthly mean FSU (Florida State University)wind stress data aredecomposed into a vortical and a divergent component with each of which to force the model oceanin the context of a two-layer tropical Pacific model.Evidence suggests that for the seasonalvariation the ocean forcing does not produce a realistic cold tongue using either of the componentsand the tongue will not be effectively improved in its intensity and pattern even if the componentsare doubled or halved:the utilization of climatic mean wind stress(no decomposition is done of thewind stress)that contains its seasonal variation will lead to a realistic SST distribution on which isimposed,separately,the interannual anomalies of each of the components so as to get the SSTApattern:under the action of the interannual anomaly of the vortical(divergent)component therearises qnite intense SSTA oscillation marked by noticeable ENSO periods(feeble SSTA withhigher oscillation frequency for obscure ENSO periods),thereby illustrating that the roles of thetwo components differ from each other in the genesis of SST variation on a seasonal and aninterannual basis such that a realistic cold tongue pattern follows under the joint effects on themodel ocean of the two components of wind stress while rational E1 Nino/La Nina phenomenaresult under the forcing of an anomalous wind stress vortical component.Moreover,the divergentcomponent is innegligible in generating a mean climatic condition of the ocean sector but of lessimportance compared to the vortical component in ENSO development.     

Tides in the Tongan Region of the Pacific Ocean

Tidal levels and currents in the Tongan region of the Pacific were simulated using a two-dimensional frequency-domain finite element model. The eight major diurnal and semidiurnal tidal constituents were modeled successfully, using open boundary conditions taken from a global tidal model based on the Topex/Poseidon satellite altimeter. Comparison of model results with observations from the single tide gauge site in the area were later used to adjust the boundary conditions. The validity of omitting horizontal eddy viscosity from the finite element model was checked by running an equivalent finite difference model. The results show that although the submarine Tongan ridge does not appear to trap tidal energy, there are residual tidal currents and possible recirculations which are capable of influencing biological productivity around Tonga. The model results are reduced to a simple method for predicting tidal heights in outlying areas, based only on the tidal calendar for the capital, Nuku'alofa.     

凤城市赛马镇风洞洞穴特征及发育基本条件

赛马镇风洞是我国东北规模较大的岩溶洞穴,洞长在2000m以上,已探测长度1265m.风洞具有纵坡降较小、支洞繁多、形态奇异及国内罕见的溶蚀景观“天锅”等特征.岩性、构造、水文地质特征等是控制洞穴发育的基本条件.风洞的发育约始于中更新世40万年前.     

风浪作用下水生植物对水流结构的影响——以太湖中两种典型沉水植物为例

为研究风浪作用下水生植物对水流结构的影响,选取太湖中两种典型沉水植物(苦草与马来眼子菜)为研究对象,分别对苦草植物斑块与马来眼子菜植物斑块内外水体的瞬时流速进行野外现场测量,利用瞬时流速的能量谱分布将波浪流速与紊动流速分离,分别分析水生植物对时均流速、波浪流速以及紊动能的影响。风浪影响下,水体中存在流向与测量时近水面处盛行风向一致的水流;波浪流速以垂向流速为主,且波浪流速自水面向床底逐渐减小;紊动能在水面处达到最大值,并向床底方向逐渐减小。与无植被条件相比,苦草与马来眼子菜的存在减小了时均流速、波浪流速以及紊动能。两种植物形态上的差异,导致其对水流结构的影响不同:苦草叶片阻流面积在冠层中部达到最大,使得时均流速与波浪流速在苦草中部位置的减小程度最大;马来眼子菜叶片主要集中于冠层顶部(水面附近),其对时均流速以及波浪流速的减小作用在水面处达到最大。     

基于偏最小二乘回归的区域换式风速预报订正技术研究

利用偏最小二乘回归技术,将预报产品作为自变量,相应的自动气象站观测资料作为因变量,对2013-2016年冬季浙江省中尺度区域模式预报近地面风速进行订正和评估。所选956站中多数站点风速订正后有所改善,通过定量分析可知浙江西部地区整体改善效果最好,其中效果明显站点占91.7%;中部地区改善效果明显站点占86.5%;东部沿海地区改善效果略差,明显改善的站点占67%。各地级市整体表现均不错,除舟山地区为49.9%外,其他地区风速改善比例均超过50%。选取2017年1月20日浙江东北地区沿海大风过程分析发现订正后的风速与观测风速更为接近,在定海大岛站点(靠里)中表现尤为明显,订正后的结果具有显著参考价值。     

Impact of Cloud Microphysical Processes on the Simulation of Typhoon Rananim near Shore. Part II: Typhoon Intensity and Track

The impact of cloud microphysical processes on the simulated intensity and track of Typhoon Rananim is discussed and analyzed in the second part of this study. The results indicate that when the cooling effect due to evaporation of rain water is excluded, the simulated 36-h maximum surface wind speed of Typhoon Rananim is about 7 m s⁻¹ greater than that from all other experiments; however, the typhoon landfall location has the biggest bias of about 150 km against the control experiment. The simulated strong outer rainbands and the vertical shear of the environmental flow are unfavorable for the deepening and maintenance of the typhoon and result in its intensity loss near the landfall. It is the cloud microphysical processes that strengthen and create the outer spiral rainbands, which then increase the local convergence away from the typhoon center and prevent more moisture and energy transport to the inner core of the typhoon. The developed outer rainbands are supposed to bring dry and cold air mass from the middle troposphere to the planetary boundary layer (PBL). The other branch of the cold airflow comes from the evaporation of rain water itself in the PBL while the droplets are falling. Thus, the cut-off of the warm and moist air to the inner core and the invasion of cold and dry air to the eyewall region are expected to bring about the intensity reduction of the modeled typhoon. Therefore, the deepening and maintenance of Typhoon Rananim during its landing are better simulated through the reduction of these two kinds of model errors.     

Granule ripples in the Kumtagh Desert,China: Morphology,grain size and influencing factors

Granule ripples are found mainly in four regions of the Kumtagh Desert in China; they are characterized by an asymmetrical shape, with gentle lower slopes on both sides and abrupt crests. The ripples tend to be oriented perpendicular to the prevailing winds, except when they form near obstacles such as yardangs. The wavelengths (λ) range between 0·31 m and 26 m and heights (h) range from 0·015 m to 1 m. The relationship between wavelength and height can be described by a simple linear function, and the mean ripple index (λ/h) is about 20·4 for the study sites. The sediments are poorly sorted, with negative to very negative skewness at lee and stoss slopes and between‐ripple troughs, which confirms the ‘poured in’ and ‘shadow’ appearance described by previous researchers. The bimodal or trimodal distributions of grains (with modes of ?1·16φ, ?0·5φ and 3·16φ) and the enrichment of coarse particles at the ripple surface (with coarse granule contents ranging between 5·2% and 62·1%) indicate that the underlying layer is the original sediment source and that the granule ripples resist erosional processes. Although the impact of saltating particles and, consequently, the creep and reptation of coarse grains are responsible for granule ripple initiation at a micro‐scale, however, the characteristics of local sediments, wind regimes and topographical obstacles, as well as the feedbacks among bedform and airflow, more strongly affect the development and alignment of granule ripples at a macro‐scale.     

风电场风资源测量与计算的精度控制

根据多个复杂地形风电场观测操作实践和大量观测数据的计算分析,提出了对观测数据和计算质量精度控制的主要措施,包括:复杂地形测风站布设的5个原则,仪器的合理选型和设置;对由于测风仪固有的系统误差和缺测数据的插补订正可能引起的计算误差进行了定量估算,通过对大量实测数据的对比计算显示:①目前普遍采用的进口风速计的相对偏差在1.6%～5.25%之间,由此可导致轮毂高度附近的年平均风功率密度误差在5%以上,最大达13.8%;②在季风气候区、复杂地形和风的年变率较大的地区,进行缺测数据插补订正时,应选取同季或同一主导风向的数据作为插补订正的基础数据,否则可能导致其平均风功率密度相对误差达20%～50%.     

Gamma-ray bursts: optical afterglows in the deep Newtonian phase

Gamma-ray burst remnants become trans-relativistic typically in days to tens of days, and they enter the deep Newtonian phase in tens of days to months, during which the majority of shock-accelerated electrons will no longer be highly relativistic. However, a small portion of electrons are still accelerated to ultra-relativistic speeds and are capable of emitting synchrotron radiation. The distribution function for electrons is re-derived here so that synchrotron emission from these relativistic electrons can be calculated. Based on the revised model, optical afterglows from both isotropic fireballs and highly collimated jets are studied numerically, and compared to analytical results. In the beamed cases, it is found that, in addition to the steepening due to the edge effect and the lateral expansion effect, the light curves are universally characterized by a flattening during the deep Newtonian phase.