On some interrelations in the dynamics of tropical cyclonic activity

A chronological series of tropical cyclones is a flow of cyclonic activity where the bursts and calms of cyclonic activity alternate. Some interrelations between the stages of cyclonic activity have been studied. We derive the dependence that the length of the time interval between two consecutive of bursts of cyclonic activity have on a number of parameters of the first burst and the calm between the bursts. We find that one can estimate the intensity of the subsequent burst on the basis of the intensity of the previous burst. We derive a regression between the value of burst energy at a given time and the value of energy in the same burst for 1–3 days.     

Some interrelations between the stages of development of tropical cyclones

Energy interdependence between groups of tropical cyclones separated by time intervals of cyclonic “calm” is investigated. A linear negative interrelation between the total powers of such groups is revealed. The groups consist of real tropical cyclones that occurred within the active cyclonic zone in the northwestern Pacific. The corresponding regression relationships are obtained. Interrelation between the stages of development of seasonal cyclonic activity is revealed. Semidiurnal total powers (power elements) are chosen as “operational” objects with the use of which the sought-for interrelation is established. Regressions were obtained separately for each season: the number of elements and their powers are related by a negative power relation. The result obtained is supposed to serve as a certain basis for the probabilistic prediction of cyclonic activity during the season.     

Effects of deep-sea eddies on the northern KwaZulu-Natal shelf,South Africa

This paper describes the westward movement of a cyclonic eddy across the Mozambique Channel and the subsequent south-westward propagation of the eddy along the east coast of South Africa and its interaction with the shelf. A hydrographic survey on 13 September 2006 off Nine-mile Reef (NMR), Sodwana Bay, showed a well-developed Agulhas Current along the continental shelf inshore of a cyclonic eddy flanked by two anti-cyclonic eddies, further offshore. A satellite-tracked drifter and complementary altimetry data confirmed the dimensions of the eddy and tracked its movement towards the coast. Shelf-edge upwelling was measured at NMR by an underwater temperature recorder (UTR) when the cyclonic eddy first came into contact with the shelf and again when the cyclonic eddy interacted with the leading edge of the anti-cyclonic eddy moving onto the shelf. Further shelf–eddy interactions off Aliwal Shoal, south of Durban, and consequent upwelling were similarly caused by the same cyclonic eddy as it progressed south-westward along the east coast. Analysis of UTR data between 2004 and 2006 indicated that between two and five cyclonic eddies impact the shelf off NMR per year.     

Modern sediment supply to the lower delta plain of the Ganges-Brahmaputra River in Bangladesh

Vibracores and auger samples collected from the lower (tidal) delta plain of the Ganges-Brahmaputra River in Bangladesh were examined to determine whether the area is a significant sink for riverine sediments. Measurements of ¹³⁷Cs activity and radiocarbon in the sediments indicate sediment accumulation is taking place on decadal and millennial time scales at rates reaching 1.1 cm/year. The sediment of the lower delta plain is primarily derived from an offshore source after having originally been supplied by the Ganges-Brahmaputra river system, carried westward by prevailing currents and advected inland by monsoonal coastal setup and cyclonic events.     

Patterns of upper layer circulation variability in the South China Sea from satellite altimetry using the self-organizing map

Patterns of the South China Sea (SCS) circulation variability are extracted from merged satellite altimetry data from October 1992 through August 2004 by using the self-organizing map (SOM). The annual cycle, seasonal and inter-annual variations of the SCS surface circulation are identified through the evolution of the characteristic circulation patterns. The annual cycle of the SCS gener- al circulation patterns is described as a change between two opposite basin-scale SW-NE oriented gyres embedded with eddies: low sea surface height anomaly (SSHA) (cyclonic) in winter and high SSHA (anticyclonic) in summer half year. The transition starts from July--August (January--February) with a high (low) SSHA tongue east of Vietnam around 12°～14° N, which de- velopa into a big anticyclonic (cyclonic) gyre while moving eastward to the deep basin. During the transitions, a dipole structure, cyclonic (anticyclonic) in the north and anticyclonic (cyclonic) in the south, may be formed southeast off Vietnam with a strong zonal jet around 10°～12° N. The seasonal variation is modulated by the interannual variations. Besides the strong 1997/1998 e- vent in response to the peak Pacific El Nino in 1997, the overall SCS sea level is found to have a significant rise during 1999～ 2001, however, in summer 2004 the overall SCS sea level is lower and the basin-wide anticyclonic gyre becomes weaker than the other years.     

南海大尺度动力场年循环和年际变化

应用COADS风应力、Levitus温度资料，描述南海上层海洋动力场的年循环及其与热力场之间的关系和南海大尺度动力场的年际变化。针对冬、夏2个季节，分析Sverdrup环流场与上层海温之间的关系。研究发现，上层海温变化与上层海洋环流基本结构非常相似，即上层海温变化在一定程度上反映了南海Sverdrup平衡，而且随着浓度的增加，平均海温场与流函数场之间的对应关系更好。本文还着重分析了El Nino期间和La Nina期间的南海异常流函数场。研究发现，异常流函数场在El Nino期间的夏季主要是强化南海自身的环流结构，即强化南部反气旋式涡流（gvre)和强化北部气旋式涡流；冬季则削弱整个南海的气旋式流场。LaNina期间对夏季环流态的影响主要集中在南海北部，即削弱北部气旋式涡流，而对于南海南部的影响甚微；冬季则强化整个南海的气旋式流场。     

Mutual Dynamics of Tropical Cyclones

Izvestiya, Atmospheric and Oceanic Physics - Interrelations of an energy nature in the dynamics of cyclonic activity of tropical cyclones (TCs) are considered. The relationships, represented by...     

Numerical Study of the Upper-Layer Circulation in the South China Sea

Upper-layer circulation in the South China Sea has been investigated using a three-dimensional primitive equation eddy-resolving model. The model domain covers the region from 99° to 122°E and from 3° to 23°N. The model is forced by the monthly averaged European Centre for Medium-Range Weather Forecasts (ECMWF) model winds and the climatological monthly sea surface temperature data from National Oceanographic Data Center (NODC). Inflow and outflow through the Taiwan Strait and the Sunda shelf are prescribed monthly from the Wyrtki estimates. Inflow of the Kuroshio branch current in the Luzon Strait is assumed to have a constant volume transport of 12 Sv (1 Sv = 10⁶ m³/s), and the outflow from the open boundary to the east of Taiwan is adjusted to ensure the net volume transport through all open boundaries is zero at any instant. The model reveals that a cyclonic circulation exists all year round in the northern South China Sea. During the winter time this cyclonic eddy is located off the northwest of Luzon, coinciding with the region of positive wind stress curl in this season. This cyclonic eddy moves northward in spring due to the weakening of the northeast winds. The cyclonic circulation becomes weak and stays in the continental slope region in the northern South China Sea in the summer period. The southwest wind can raise the water level along the west coast of Luzon, but there is no anticyclonic circulation in the northern South China Sea. After the onset of the northeast monsoon winds in fall, the cyclonic eddy moves back to the region off the west coast of Luzon. In the southern South China Sea and off the Vietnam coast, the model predicts a similar flow structure as in the previous related studies. This revised version was published online in July 2006 with corrections to the Cover Date.     

On Some Similar Regularities of Cyclonic and Seismic Activity

Izvestiya, Atmospheric and Oceanic Physics - Similar regularities of cyclonic and seismic activity have been revealed. This research is based on information on tropical cyclones and earthquakes in...     

Variant for estimating the activity of tropical cyclone groups in the world ocean

Izvestiya, Atmospheric and Oceanic Physics - It is especially important to know the character and the intensity level of tropical cyclone (TC) activity when the system for estimating the cyclonic...     

南海上层环流季节变化的诊断计算

通过一个全球的二维诊断模型,采用Levitus温盐资料和COADS风应力资料,并结合动力计算来研究南海上层环流的季节变化。计算结果与其它模式结果和观测结果非常相似。南海北部(南部)全年存在一气旋式(反气旋式)环流。在冬季气旋式环流几乎占据了整个南海,夏季则以反气旋式环流为主。泰国湾的环流在冬季(夏季)是气旋式的(反气旋的)。南海的西边界流有明显的季节变化,其在冬季从卡里马塔海峡流出南海,夏季部分西边界流从台湾海峡流出南海。越南离岸流在春季就开始出现,其位置比夏季的越南离岸流的位置偏北。     

Numerical modeling of hydrophysical fields of the Black Sea under the conditions of alternation of atmospheric circulation processes

The hydrological regime of the Black Sea in the conditions of permanent alternation of atmospheric circulation processes was investigated on the basis of a baroclinic prognostic model of the sea dynamics. In the model, variations in the wind action were expressed as permanent alternation of 24 wind types characteristic of the Black Sea basin throughout the year. Thermohaline impact of the atmosphere was taken into account by specifying the annual trends of temperature and salinity at the sea surface, which was established from multiyear means of these parameters. The problem was solved numerically on the basis of the method of two-cycle splitting with the use of the grid with a horizontal spacing of 5 km. Results of the numerical experiment showed that, under the influence of a strong nonstationarity of atmospheric processes, the water circulation in the upper layer of the Black Sea changes qualitatively and quantitatively. The upper 20–30-m layer of the sea is particularly sensitive to atmospheric circulation variations. For any character of atmospheric circulation, the Black Sea circulation below this layer is nearly always cyclonic with internal cyclonic rotations.     

On one possibility of studying the cyclonic regime

The dynamics of some characteristics of a cyclonic situation (cyclonic regime) of the northwestern Pacific cyclonic zone is studied. The characteristics that are considered are the density of cyclonic energy at a point (intensity) and the power over a given area. In the model, the intensity at a point is defined as the sum of all intensities of preceding cyclones, with consideration for their spatial and temporal separation from the given point. Power for a given moment and a given area is defined as the sum of intensities over this area. Cyclonically active seasons are considered. The dynamics of the power was estimated for areas of different size. It is shown that the point values of cyclonic intensity, at the times of their maximum, are statistically related to one another by a negative power-law dependence. Periodicity is observed in the time evolution of the power in different areas.     

南海环流动力机制研究综述

南海的环流复杂,但通过近20 a来的研究工作,国内外学者对此已取得了不少的成果.本文就南海环流框架性的问题,综述了有关的文献,认为对南海上层海洋三方面的环流分量的驱动机制已有了初步的认识.这三方面分别是:(1)准季节性风场;(2)黑潮向南海的净输运;(3)黑潮向南海的涡度平流输送.但是对这些驱动的时空变化仍相当不清楚.三者皆增强了南海北部的海盆尺度气旋式环流,其强化的西南向西边界流靠近东沙群岛,建议称为“东沙海流”.没有水文证据显示黑潮水是以分支形式进入南海,其向南海的输运也不可能主要通过中尺度涡过程,具体机制有待研究.每年在南海生成的中尺度涡平均约有10个,风场与沿岸地形所生成的强风应力旋度可能是其主要的驱动机制.作为框架性的认识,也有三方面的工作进行得较少,即:(1)吕宋海峡的上层水交换;(2)南海的中尺度涡生成机制,虽然强风应力旋度及前述的第三种环流驱动机制也有中尺度涡伴生;(3)自吕宋海峡进入的深层水对南海上层海洋环流的影响.     

Topographic effect of a marine ridge on the spin-down of a cyclonic eddy with mean flow

The topographic effect of a meridional marine ridge on the spin-down of a cyclonic eddy, which is embedded in a zonal mean flow, is examined by use of a two layer numerical model. It is shown that the cyclonic eddy initially given on the eastern flank of the marine ridge decays in a short time. This result is common to all cases with the different volume transports of the mean flow (3070 Sv) and of the cyclonic eddy (1535 Sv). During the decay process, the cyclonic eddy shifts mainly northward into the shallower region, which is different from the dominant westward shift of the isolated cyclonic eddy. If the mean flow across over the marine ridge at the more northern latitude, the cyclonic eddy spins down more rapidly. A mean flow shifts zonal or south-eastward over a western side of the ridge, while it deflects north-eastward over an eastern side. The deflection angle of mean flow over the ridge depends on the intensity of lower layer velocity and density stratification. It is suggested that the topographic effect of the meridional marine ridge on the cyclonic eddy with mean flow is influenced both by the global phenomena that controls the inclination of the mean flow from zonal direction and by the local phenomena that controls the intensity of the topographic effect of the marine ridge.     

Hydrography and circulation south of Cyprus in late summer 1995 and in spring 1996

The hydrodynamical characteristics of the area south of Cyprus in the Levantine Sea were examined in late summer 1995 and in spring 1996. Analysis of the CTD data collected, provided a new dynamic picture of the Cyprus Basin and revealed the existence of the Cyprus Basin cyclonic eddy. The latter circulated to the south of Cyprus and exhibited marked seasonality. Production of Levantine Intermediate Water in the area of the latter eddy occurred. Occasionally, between the Cyprus Basin cyclonic eddy and the southern coast of Cyprus a warm current, the Cyprus coastal current appears to intrude from the east. In late summer 1995, the spatial fluctuations of the mid-Mediterranean jet, the main current of the Eastern Mediterranean Sea, caused the splitting of the Cyprus Basin cyclonic eddy, into two smaller cyclonic ones. During spring 1996, however, the Cyprus Basin cyclonic eddy appears as a single large vortex, occupying the greater part of the area south of Cyprus, and flanked to the south by the Cyprus anticyclonic eddy.     

广西主要港湾余流特征及其对物质输运的影响

广西5个主要海湾各有自己的环流特征：铁山湾存在一个反气旋涡，廉州湾存在一个海湾尺度的气旋环流，钦州湾青菜头南端存在一个气旋式环流，防城湾口有一个气旋环流。珍珠湾余流，在深水航道内自湾内指向湾外。冬季，受北风影响，各湾从湾内流向湾外的余流分量加强。由于反气旋或气旋环流存在，形成和环流相应的泥沙输运。     

On the cyclonic circulation mechanism in the Black Sea

This paper discusses the results of numerical experiments on the generation of a large-scale circulation in the sea carried out in the framework of a multilayer quasi-isopycnic model. The role played by wind vorticity, non-uniformity of the heat flux through the sea surface, and the fluxes of mass, salt, and heat across the liquid lateral boundaries is studied separately. It is shown that wind with cyclonic vorticity induces cyclonic vorticity in the upper layers of the sea and anticyclonic vorticity in the lower layer. A uniform wind having even a non-uniform heat flux does not give rise to a cyclonic circulation in the sea. Within the period calculated (410 years), the heat, mass, and salt fluxes through the lateral boundaries also do not result in a cyclonic circulation; this is apparently connected with the fact that the solution has not reached steady-state conditions in this period.Translated by Mikhail M. Trufanov.     

南海冬、夏季环流的三维数值模拟

本文利用一个斜压三维陆架海模式——HAMSOM模式对12月份和8月份的南海环流进行数值模拟,结果为:对上层流场,在12月份,在西沙群岛－中沙群岛海区间呈现一个气旋式环流,在越南中部东岸存在一支南向西边界流,在金兰湾的远海为一局地反气旋涡,在南海南部,主要表现为万安滩的气旋式大弯曲(气旋涡)及在北康暗沙北侧的反气旋涡;在8月份,在东沙群岛－中沙群岛－吕宋岛西侧海域间存在一大尺度的气旋涡,在南海西部主要表现为以西沙群岛南部的气旋涡与金兰湾－礼乐滩间的反气旋式大环流相对峙的局面,同时在万安滩东侧有－气旋涡.由于斜压效应、底形效应的作用,使冬、夏季的南海南部中层流场几乎与上层流场相反.     

P矢量方法在南海夏季环流诊断计算中的应用

基于1998年6～7月南海调查航次的CTD资料,对南海环流采用最近发展的P矢量方法进行诊断计算.计算结果:黑潮向西入侵南海,然后做反气旋弯曲向东北方向流动,最终有通过巴士海峡流出南海的趋势.在南海北部存在一个气旋性环流,这个环流的强度和范围随深度增加而减小.该环流的冷中心位置随深度增加稍向南移.南海中部、越南以东海域存在一个明显的气旋涡和反气旋涡,尤其在200m及其以上水层均相当稳定,反气旋涡位于越南以东,其中心位置在11°53'N,111°50'E,气旋涡的中心位置在13°17'N,112°55'E,两者的尺度皆约为250km.吕宋岛西侧存在一个反气旋涡.在计算海区南部、巴拉望岛西南海域,100m以上层存在一个反气旋式涡.从各层流场分布均可以显示海流在西部强化的现象.