Diagnostic Study of an Extreme Explosive Cyclone over the Kuroshio/Kuroshio Extension Region

Explosive cyclones(ECs)occur frequently over the Kuroshio/Kuroshio Extension region.The most rapidly intensified EC over the Kuroshio/Kuroshio Extension region during the 42 years(1979-2020)of cold seasons(October-April)was studied to reveal the variations of the key factors at different explosive-developing stages.This EC had weak low-level baroclinicity,mid-level cyclonic-vorticity advection,and strong low-level water vapor convergence at the initial explosive-developing stage.The low-level baroclinicity and mid-level cyclonic-vorticity advection increased substantially during the maximum-deepening-rate stage.The diagnostic analyses using the Zwack-Okossi equation showed that diabatic heating was the main contributor to the initial rapid intensification of this EC.The cyclonic-vorticity advection and warm-air advection enhanced rapidly in the middle and upper troposphere and contributed to the maximum rapid intensification,whereas the diabatic heating weakened slightly in the mid-low troposphere.The relative contribution of the diabatic heating decreased from the initial explosive-developing stage to the maximum-deepening-rate stage due to the enhancement of other factors(the cyclonic-vorticity advection and warm-air advection).Furthermore,the physical factors contributing to this EC varied with the explosive-developing stage.The non-key factors at the initial explosive-developing stage need attention to forecast the rapid intensification.

The study of the Kuroshio in the East China Sea and the currents east of the Ryukyu Islands

In this study, the inverse method is used to compute the Kuroshio in the East China Sea and southeast of Kyushu and the currents east of the Ryukyu Islands, on the basis of hydrographic data obtained during September-October, 1987 by R/V Chofu Maru. The results show that: (1)A part of the Taiwan Warm Current has a tendency to converge to the shelf break; (2) the Kuroshio flows across the section C3 (PN) with a reduced current width, and the velocity of the Kuroshio at the section C3 increases and its maximum current speed is about 158 cm/s, and its volume transport here is about 26×106m3/s; (3) the Kuroshio has two current cores at the sections C3 (PN) and B2 (at the Tokara Strait); (4) the currents east of the Ryukyu Islands are found to flow northward over the Ryukyu Trench during September-October, 1987. The velocities of the currents are not strong throughout the depths. At the section C2 east of the Ryukyu Islands, the maximum current speed is at the 699 m levei and its magnitude is 25 cm/s, and its volume transport is about 21×06 m3/s; (5) the volume transports of the Kuroshio through the sections B2 (at the Tokara Strait) and C6 (southeast of Kyushu) are 23. 33, 67. 31×106 m3/s, respectively; (6) there are two meso-scale anticyclonic warm eddies between 135° E and the area east of the Ryukyu Islands, and their characters and hydrographic structure are discussed.

The influence of the surface heat fluxes of the Kuroshio key-area on meiyu rainfall in the Changjiang River region

On the basis, of the surface heat fluxes of the Kuroshio key-area (26°-30°N, 125°-30°E)in March andApril, the climatologicai influence of the Kuroshio heat fluxes on meiyu rainfall in the Changjiang River (Yangtse River) region are studied. The results are concluded as follows;the surface heat fluxes of the Kuroshio key-area have certain influence on meiyu rainfall in the Changjiang River region during June and July. The correctness rates for the five stations in the Changjing River region (i. e. Wuhan, Jiujiang, Anqing,Nanjing and Shanghai)are in the range of 9/20-13/20. The surface heat fluxes influence mainly on the homogeneous rainfall pattern,the correctness rates come to 7/10-8/10 for the lower valley of the Changjiang River. The estimation expression of the meiyu rainfall for Shanghai consisting of the surface heat flux and the sea surface temperature anomaly of the Kuroshio key area agrees well with the actual meiyu rainfall condition.

The continental shelf wave of the East China Sea and its effect on the Kuroshio

The free shelf wave theory is applied to the practical case of the continental shelf in the East China Sea to analyse the effects of the shelf wave on the Kuroshio. The results indicate that the shelf wave in lower frequency travels from north to south and its phase velocity is proportional to the Kuroshio's current velocity) the maximum current velocity of the Kuroshio lies at the continental margin. The analytical solutions obtained indicate that the hydrodynamic characters of the sea region over the shelf present band structure. The horizontal motion ( x -component) caused by the shelf wave at the margin may be one of the causes for generating wavy pattern of the Kuroshio's axis .

Comparison of the seven large meanders of the Kuroshio

In this paper, a comparison among the seven large meanders of the Kuroshio is made in order to probe into their similarity and differences. The major results are described as follows.1. Although the three phases for the seven large meanders such as their formations, maturity, as well as decline are very similar to one another, each meander has its own trivial difference in detail.2.The paths of the first six large meanders in the mature phase may be classified into ten types: U1, V1, U2, V2, U1', V1', U2', V2',φ and W.3.The seven large meanders may be grouped into two patterns, i. e. , pattern Ⅰ and pattern Ⅱ. Pattern Ⅰ includes the first and the fourth large meanders, and pattern Ⅱ includes the rest of the above meanders.4. Four standards for identifying the large meanders of the Kuroshio are put forward.

The variation of the Kuroshio during 1986-1988

On the basis of the analysis of the data obtained from five cruises of the R/V Xiangyanghong 09 and the data from Japan, it is shown that a large meander of the Kuroshio appeared again during 1986-1988. The processes of formation , maturity and decline of this large meander are discussed in this study. The variation of the volume transport at Section Kb (PN) in the East China Sea is related to the large meander of the Kuroshio in the area south of Japan. By using maximum entropy spectrum analysis,the volume transport of the Kuroshio and the swing of its axis are analysed and their major periods are obained.

Transport patterns of micro nutrient elements from the continental shelf of the East China Sea to the Kuroshio area

On the basis of the in situ data of DO2, pH, SiO2. PO4-P, NO3-N and NO2-N collected in the north of the East China Sea during 1987-1988, the following points are mainly expounded.1.The inorgonic nutrients are obviously affected by continent runoff in the north of the East China Sea. Their distributions are characteristic of its distribution of terrigenous materials.2.There are three transport paths of nutrients from the shelf to the Kuroshio area. The first is mixing-diffusing-advec-tion and upwelling process, the process of biology and biochemistry belongs to the second, and the sinking process is the last one.3.The swing of the Kuroshio axis affectes both the range of the migration of substances through mixing-diffusing-advec-tion process and the upwelling degree of the subsurface Kuroshio water to the shelf.4.Most part of the substances sink as macroparticles to the deep layer before reaching the Kuroshio area.

The circulation in the southern Huanghai Sea and northern East China Sea in June 1999

On the basis of hydrographic data and current measurement (the mooring system, vessel-mounted ADCP and toward ADCP) data obtained in June 1999, the circulations in the southern Huanghai Sea (HS) and northern East China Sea (ECS) are computed by using the modified inverse method. The Kuroshio flows northeastward through eastern part of the investigated region and has the main core at Section PN, a northward flow at the easternmost part of Section PN, a weaker anti-cyclonic eddy between these two northward flows, and a weak cyclonic eddy at the western part of Section PN. The above current structure is one type of the current structures at Section PN in ECS. The net northward volume transport (VT) of the Kuroshio and the offshore branch of Taiwan Warm Current (TWCOB) through Section PN is about 26.2 x 10(6) m(3)/s in June 1999. The VT of the inshore branch of Taiwan Warm Current (TWCIB) through the investigated region is about 0.4 x 10(6) m(3)/s. The Taiwan Warm Current (TWC) has much effect on the currents over the continental shelf. The Huanghai Sea Coastal Current (HSCC) flows southeastward and enters into the northwestern part of investigated region, and flows to turn cyclonically, and then it flows northeastward, due to the influences of the Taiwan Warm Current and topography. There is a cyclonic eddy south of Cheju Island where the Huanghai Sea Coastal Current flows to turn cyclonically. It has the feature of high dense and cold water. The uniform and cold water is occurred in the layer from about 30 m level to the bottom between Stations C306 and C311 at the northernmost Section C3. It is a southern part of the Huanghai Sea Cold Water Mass (HSCWM).