Tidal Vorticity around a Coastal Promontory

The vorticity generation around a coastal promontory is examined using a transport vorticity equation. The complete vorticity balance analysis is made for the transient and residual vorticity generations around an idealized, symmetric promontory. The topographic vorticity tendency is found to be the dominant forcing term in the production of transient tidal vorticities. This result is different from the previous works which emphasized the effects of lateral and bottom frictions. The residual vorticity balance is between advection and topographic vorticity tendency. The model results are consistent with the observations off Gay Head, Massachusetts. Also, the stability of a promontory as well as the offshore sand bank formation are studied by examining the sand transport pattern around the promontory. Strong deposition occurs off the tip of the promontory while erosion occurs along the upstream slope of the promontory suggesting that an originally symmetric promontory tends to incline cyclonically from the axis normal to the tidal stream. Such tendency is indeed found among coastal promontories.     

226Ra and 228Ra in the seawater of the western Yellow Sea

1Introduction Therearefourradiumisotopesinnature,ofwhich224Ra,226Raand228Rahavebeenwidelyinvestigated inmarineresearch,butthespecificactivityof223Rais toolowtobemeasured,therefore,itsapplicationsarelimited(Moore,1969;Broeckeretal.,1976;KuandLin,1976;Nozak…     

Modeling of the eddy viscosity by breaking waves

Breaking wave induced nearsurface turbulence has important consequences for many physical and biochemical processes including water column and nutrients mixing,heat and gases exchange across air-sea interface.The energy loss from wave breaking and the bubble plume penetration depth are estimated.As a consequence,the vertical distribution of the turbulent kinetic energy(TKE),the TKE dissipation rate and the eddy viscosity induced by wave breaking are also provided.It is indicated that model results are found to be consistent with the observational evidence that most TKE generated by wave breaking is lost within a depth of a few meters near the sea surface.High turbulence level with intensities of eddy viscosity induced by breaking is nearly four orders larger than υwl(=κuwz),the value predicted for the wall layer scaling close to the surface,where uw is the friction velocity in water,κ with 0.4 is the von Kármán constant,and z is the water depth,and the strength of the eddy viscosity depends both on wind speed and sea state,and decays rapidly through the depth.This leads to the conclusion that the breaking wave induced vertical mixing is mainly limited to the near surface layer,well above the classical values expected from the similarity theory.Deeper down,however,the effects of wave breaking on the vertical mixing become less important.     

中沙群岛海域春夏交季温盐分布特征

中沙群岛主要由中沙大环礁和黄岩岛组成,其温盐分布对于本区渔业生产、航海保障和水下通讯等具有重要意义。尤其是春夏之交的季节转换时期,该海域水温和盐度及其相应的跃层特性存在显著的季节变化,掌握其季节变化特征具有重要现实意义。本文基于2019年5月（南海春夏季风转换期）中沙大环礁、黄岩岛和2020年6月（夏季风爆发期）中沙大环礁海域大面站调查数据分析,发现中沙大环礁海域水温和盐度分布特征在夏季风爆发前后具有显著的差异性,2个航次的温跃层分布也呈现出较大不同,2019年5月黄岩岛海域温盐中上层分布与中沙大环礁相似,但底层有所差异,跃层深度也较大。2020年6月中沙大环礁内水体升温较快,各层水温均高于2019年5月,其中以底层水体升温最为显著;2019年5月中沙大环礁内水温水平梯度较大,且随着水深加大水平梯度也越大,2020年6日水平温度梯度逐渐减小。2个航次的盐度分布与水温分布较为相似。结合调查时段的海表热通量变化和卫星高度计资料分析认为,2019年5月中沙大环礁西南部海洋吸热高于东北部,故表层水温西南高东北低;2020年6月至7月环礁西南部海洋吸热低于东北部,故表层水温西南低东北高。由于中尺...     

用多普勒雷达资料对一次区域性暴雨的中尺度分析

利用多普勒雷达资料,对2006年6月2日夜间出现在陕西中部和北部地区的区域性暴雨过程进行分析。结果发现:低层暖湿急流和弱冷空气相互作用产生的两条中尺度辐合线是这一地区出现大暴雨的主要影响系统;低空东南急流为降水区提供的大量的水汽和不稳定能量堆积,在弱冷空气的触发下释放,是产生大暴雨的主要原因;低空急流的输送方向与中尺度辐合线的移动方向,决定了未来辐合线的发展状态;低空急流的日变化引起了暴雨夜发性。     

中尺度自动气象站故障维护与分析

针对中尺度自动气象站的构成以及出现的故障现象、故障原因等进行分析,提出故障维护的具体方法与措施,以提高中尺度自动气象设备运行能力。     

一次东风波及其诱生低涡发生发展的诊断和数值试验

利用NCEP 1x1再分析资料诊断2001年8月3~4日发生在浙南闽北的东风波及其诱生中尺度低涡的暴雨过程。根据螺旋度(Helicity)分析了过程中的暴雨演变以及雁荡山脉[1]诱生中尺度低涡发生发展的原因。同时,利用中尺度有限区域模式MM5V2对该东风波诱生中尺度低涡进行模拟。结果表明:螺旋度大值中心和锋区的强度和位置的演变较好反映了暴雨落区和中尺度低涡的诱生、移动。螺旋度的时空演变对暴雨发生有很好的预示意义,高、低层螺旋度的低层正值辐合与高层负值辐散的配置是引起降水的重要机制;螺旋度计算较中尺度模式诱生低涡的初生位置、路径预报准确率高,两者集成可以提高诱生低涡的预报准确率。     

广西中尺度数值模式格点产品检验系统

根据WMO规定的数值预报标准化检验方案开发的数值预报格点产品检验系统,可以实时检验广西中尺度数值预报产品及9210下发的多种数值产品,可为数值模式的改进及数值产品的业务化应用提供直接的参考依据。     

Buoyancy and The Sensible Heat Flux Budget Within Dense Canopies

In contrast to atmospheric surface-layer (ASL) turbulence, a linear relationship between turbulent heat fluxes (F_T) and vertical gradients of mean air temperature within canopies is frustrated by numerous factors, including local variation in heat sources and sinks and large-scale eddy motion whose signature is often linked with the ejection-sweep cycle. Furthermore, how atmospheric stability modifies such a relationship remains poorly understood, especially in stable canopy flows. To date, no explicit model exists for relating F_T to the mean air temperature gradient, buoyancy, and the statistical properties of the ejection-sweep cycle within the canopy volume. Using third-order cumulant expansion methods (CEM) and the heat flux budget equation, a “diagnostic” analytical relationship that links ejections and sweeps and the sensible heat flux for a wide range of atmospheric stability classes is derived. Closure model assumptions that relate scalar dissipation rates with sensible heat flux, and the validity of CEM in linking ejections and sweeps with the triple scalar-velocity correlations, were tested for a mixed hardwood forest in Lavarone, Italy. We showed that when the heat sources (S_T) and F_T have the same sign (i.e. the canopy is heating and sensible heat flux is positive), sweeps dominate the sensible heat flux. Conversely, if S_T and F_T are opposite in sign, standard gradient-diffusion closure model predict that ejections must dominate the sensible heat flux.