Role of ocean upper layer warm water in the rapid intensification of tropical cyclones: A case study of typhoon Rammasun(1409)

Rammasun intensified rapidly from tropical storm to super typhoon in the northern South China Sea（NSCS）before its landfall on Hainan Island. Analysis of observed data shows that the anomalous ocean upper layer warm water（WW） is important to the rapid intensification of Rammasun. During the period of Rammasun, sea surface temperature（SST） in the NSCS was much warmer than the climatological SST. The anomalous WW supplied more energy to Rammasun, resulting in its rapid intensification. Numerical simulations further confirm that the NSCS WW plays an important role in the rapid intensification of Rammasun. As the WW is removed, the intensification of Rammasun is only 25 h Pa, which is 58.1% of that in the original SST-forced run.

Primary productivity in the western tropical Pacific and equatorial warm waters

Primary productivity in the western tropical Pacific and equatorial warm waters was studied in the WOCE cruise in November of 1991 and the TOGA-COARE cruise from November of 1992 to February of 1993.It is shown that the total amount of integrated chlorophyll a(chloro a)was 19 79 mg/m 2 in depthof0～150 m and the average daily primary productivity was 171 mg/(m 2·d)(C)appeared in the western tropical Pacific while a higher chloro a(21 68 mg/m 2)and primary productivity [228 mg/(m 2·d)(C)]were observed in the equatorial warm waters.The highest chloro a was found at the coastal stations of Philippines and Irian while the lowest chloro a was at the offshore areas bounded by 2°～4°N.The distribution pattern of chloro a biomass was related to different physical processes.Upwelling,which may have led to a high biomass, was a critical factor changing the distributions of temperature,salinity and nutrient in these areas.

Protozoan colonization on artificial substrates in relation to water quality in a tropical Indian harbour

A field study was conducted to evaluate the protozoan colonization patterns on artificial substrates in relation to organic pollution within a tropical harbour. The composition of protozoans and their succession rates on artificial substrates(polyurethane foam units) were compared between two field stations(A and B), and their presence were considered with regards to the prevailing water quality conditions at the study sites. Altogether 44 genera of flagellates and ciliates were documented. The common genera of flagellates encountered included Monas, Polytoma, and Chromalina. Among the ciliates, the predominant genera were Tetrahymena, Vorticella, Lagynophyra, and Heloiphyra. These groups exhibited characteristic successional patterns in relation to ambient water quality. At Station A, located close to the sewage outfall, the water quality parameters included poor Secchi disc transparency(0.48m), dissolved oxygen of 1.93 mg/ml, salinity of 18 psu, and temperature 31.3 ℃. Here, the nanoflagellates( spumella ) colonized first, followed by microcilliate( Tetrahymena ) and sessile form( Vorticella ). Station B, located on the seaward side, was characterized by relatively less stressed environmental conditions with transparency 1.85m and dissolved oxygen value of 6 04 mg/ml. Salinity of 27.27 psu, and mean temperature of 30 ℃ were recorded at “B'. At this station, the nanoflagellate Polytoma was first documented to colonize on the substrates, followed by microcilliate( Lagynophrya ) and suctorid( Heliophyra ). These findings support the use of protozoans as indicator species for evaluating the hazards posed by organic pollution to natural estuarine communities.

Water masses in the far western equatorial Pacific during the winters of 2010 and 2012

Conductivity-temperature-depth（CTD）data obtained during the 2010 La Nina winter and the 2012 normal winter,combined with concurrent Argo profiling float data,provide a quasi-synoptic description of the water mass distributions and their variations in the far western equatorial Pacific Ocean.The water mass connection between the western Pacific and the east Indonesian seas is emphasized.Analysis indicates that the North Pacific Tropical Water（NPTW,S〉34.9）carried by the Mindanao Current southward and the South Pacific Tropical Water（SPTW,S〉35.1）from the southern hemisphere meet in the area.Observations suggest that the southward transport of the NPTW is stronger in 2010 than in 2012 due to enhanced advection of the Mindanao Current.The distribution of SPTW,which crosses the equator in the northwest direction and retroflects back to the interior Pacific Ocean,is found to retreat from 4°–5°N in2012 to 2°–3°N in 2010 La Ni？a peak in the 130°E section.A relatively fresh tropical subsurface water is identified in between the NPTW and the SPTW,moving eastward with the North Equatorial Countercurrent into the equatorial Pacific Ocean.However,the salinity maximum of this subsurface fresh water is found to decrease eastward,suggesting that the salinity maximum is generated either by strong diapycnal mixing or by isopycnal mixing of temporally entrained Indonesian sea water into the area.

The westward intrusion of south Pacific water at the western tip of the New Guinea Island

From the eastern Indonesian cruise from November 14 to 23, 2007, CTD （conductivity, temperature, depth profiler）/ADCP （acoustic Doppler current profiler）casting and seawater sampling were done at 25 stations around Waigeo Island near New Guinea Island. It was found overall westward intrusion of the south Pacific waters into the Seram Sea and southward spreading of the north and south Pacific waters into the Seram Sea. There is westward residual flow along the channel between Waigeo and New Guinea within upper 200 m with the maximum speed up to 50 cm/s, and much weaker eastward flow in the lower layer （〈 10 cm/s） due to blocking by the shallow sill at the west of the Dampier Strait. The abrupt change of bottom topography induces active horizontal and vertical mixing which results in a three-layered current system with a major through-flow of-0.99 Sv （Sv = 106 ma/s） into the Seram Sea; the transports in the upper and the lower layers are -1.14 Sv and -0.24 Sv （westward）, respectively, and in the middle there is a return flow with the transoort of ＋0.39 Sv （eastward）.

A quasi-synoptic interpretation of water mass distribution and circulation in the western North Pacific:I.Water mass distribution

With high-resolution conductivity-temperature-depth （CTD） observations conducted in Oct.-Nov. 2005, this study provides a detailed quasi-synoptic description of the North Pacific Tropic Water （NPTW）, North Pacific Intermediate Water （NPIW） and Antarctic Intermediate Water （AAIW） in the western North Pacific. Some novel features are found. NPTW enters the western ocean with highest-salinity core off shore at 15°-18°N, and then splits to flow northward and southward along the western boundary. Its salinity decreases and density increases outside the core region. NPIW spreads westward north of 15°N with lowest salinity off shore at 21°N, but mainly hugs the Mindanao coast south of 12°N. It shoals and thins toward the south, with salinity increasing and density decreasing. AAIW extends to higher latitude off shore than that in shore, and it is traced as a salinity minimum to only 10°N at 130°E. Most of the South Pacific waters turn northeastward rather than directly flow northward upon reaching to the Mindanao coast, indicating the eastward shift of the Mindanao Undercurrent （MUC）.

ANALYSIS OF RAINSTORMS ASSOCIATED WITH SIMILAR TRACK TROPICAL CYCLONES HAITANG (0505) AND BILIS (0604)

It is generally thought that the influence of comparable track typhoons is approximately similar, but in fact their wind and especially their rainstorm distribution are often very different. Therefore, a contrastive analysis of rainstorms by tropical cyclones (TCs) Haitang (0505) and Bilis (0604), which are of a similar track, is designed to help understand the mechanism of the TC rainstorm and to improve forecasting skills. The daily rainfall of TC Haitang (0505) and Bilis (0604) is diagnosed and compared. The result indicates that these two TCs have similar precipitation distribution before landfall but different precipitation characteristics after landfall. Using NCEP/GFS analysis data, the synoptic situation is analyzed; water vapor transportation is discussed regarding the calculated water vapor flux and divergence. The results show that the heavy rainfall in the Zhejiang and Fujian Provinces associated with Haitang (0505) and Bilis (0604) before landfall results from a peripheral easterly wind, a combination of the tropical cyclone and the terrain. After landfall and moving far inland of the storm, the precipitation of Haitang is caused by water vapor convergence carried by its own circulation; it is much weaker than that in the coastal area. One of the important contributing factors to heavy rainstorms in southeast Zhejiang is a southeast jet stream, which is maintained over the southeast coast. In contrast, the South China Sea monsoon circulation transports large amounts of water vapor into Bilis – when a water-vapor transport belt south of the tropical cyclone significantly strengthens – which strengthens the transport. Then, it causes water vapor flux to converge on the south side of Bilis and diverge on the north side. Precipitation is much stronger on the south side than that on the north side. After Bilis travels far inland, the cold air guided by a north trough travels into the TC and remarkably enhances precipitation. In summary, combining vertical wind shear with water vapor transportation is a good way to predict rainstorms associated with landing tropical cyclones.

Climatology and seasonal variability of the Mindanao Undercurrent based on OFES data

The simulation of an ocean general circulation model for the earth simulator （OFES） is transformed to an isopycnal coordinate to investigate the spatial structure and seasonal variability of the Mindanao Under- current （MUC）. The results show that （1） potential density surfaces, δ0=26.5 and δ0=27.5, can be chosen to encompass the M UC layer. Southern Pacilic tropical water （SPTW）, Antarctic Intermediate Water （AAIW） and high potential density water （HPDW） constitute the MUC. （2） Climatologically, the MOC exists in the form of dual-core. In some months, the dual-core structure changes to a single-core structure. （3） Choosing section at 8°N for calculating the transport of the MUC transport is reliable. Potential density constraint provides a good method for calculating the transport of the MOC. （4） The annual mean transport of the MUC is 8.34 × 106 m3/s and varies considerably with seasons： stronger in late spring and weaker in winter.

Deviation of the Lagrangian particle tracing method in the evaluation of the Southern Hemisphere annual subduction rate

The classical Lagrangian particle tracing method is widely used in the evaluation of the ocean annual subduction rate.However,our analysis indicates that in addition to neglecting the effect of mixing,there are two possible deviations in the method:one is an overestimation due to not considering that the amount of subducted water at the source location may be inadequate during the late winter of the first year when the mixed layer becomes shallow;the other one is an underestimation due to the neglect of the effective subduction caused by strong vertical pumping.Quantitative analysis shows that these two deviations mainly exist in the low-latitude subduction areas of the South Pacific and South Atlantic.The two deviations have very similar distribution areas and can partially off set each other.However,the overall deviation is still large,and the maximum relative deviation ratio can reach 50%;therefore,it cannot be ignored.