Inter - Monthly Variation Of Salinity In The Kuroshio Area Of ​​the East China Sea

Using the annually and monthly average salinity date World Ocean Atlas2009issued by NOAA in2010, combined with the global topography data from NGDC toanalyzing monthly salinity distribution throughout the flow path of the Kuroshio andthe feature which current on both sides of Ryukyu Islands how to exchange and thefeature which external fresh water how to intrude the west side of the Kuroshio underMatlab visualization techniques. The main draw conclusions as following:(l)It has three different layers above500m, which is including the upperlow-salinity, the middle higher-salinity and the deep high-salinity water. Obviously,upper low-salinity layer has significant and violet monthly change rfom the entranceto the outlet which mainly located in above100meters, salinity with each sectionthere has three clear stages: the growth stage, the prospeirty stage and the weakenstage. Higher-salinity layer has monthly changes obviously between each slices, butthe change is not very obvious in single slice in12months. Deep high-salinity layerhas not significantly monthly change in every slices.(2) There has differences salinity above500m in Kuroshio. Using the mean ofeach layers to describe the distribution of salinity in each layers, it will find that: thesalinity of every layers are all not less than33.8psu，and the layer of the highestsalinity are all at about150m in every months which the value is close34.8psu;Furthermore, under150m the monthly average of salinity were gradually decreasedwith the depth. However it has the same characteristic in each month, and there isalmost no difference.(3)There has horizontal space change in the value of salinity above500m inKuroshio. Above100m,higher-salinity area is mainly in the west of the RyukyuIslands，and even extends to most areas of the southwestern of Kyushu island，whichfrom the surface to deep gradually southward retreat to the nearby island ofKyushu，till in the depth of100m has no distribution; From the depth of150m todeeper area higher-salinity area occur southward retreating and eastward shrinking which to the narrow area in the west of the Ryukyu Islands east side and the sea ofeastern Taiwan side. In the depth of400m, higher-salinity area which in the east ofTaiwan has disappeared, and it is mainly in the eastern side of Kuroshio which also inwest of the Ryukyu Islands. Since June to December，in addition to the narrow area inthe west of Ryukyu islands, it is also distributed in the southwestern island of Kyushuin depth of500m.(4)Because of Ryukyu Trough, currents at the both sides of the Ryukyu Islandsoccur exchange, at up500m, high-salinity water in east of the Ryukyu Islands invadethe west water~the Kuroshio in the East China Sea.In regard to the intrusionstrength, that rfom40m to280m, it occurs high-salinity water,150m layer is thecore layer of high-salinity water intrusion. The east current of the Ryukyu Islands withhigh-salinity water invading the Kuroshio is stronger in March, May, June, September,October and November, is weaker in April and December(5)Therehas five different waterways which higher-salinity water in the east ofRyukyu Islands intrude Kuroshio，which are located in the south of Miyako Strait,between Yonaguni and Ishigaki，Miyako islands, Miyako strait，between Okinawa andAmami O Shima,s，east of Amami O Shima. The strength of invasion is weakengradually from the south to the notrh. It is relatively little difference in third andfourth waterway, and the invasion of each waterways has its own characteristics ineach month.(6)The impact of external freshwater to Kuroshio mainly relfected in something.For example: range of fresh water are gradually reduced from the surface to100m ineach month, even which are close to zero in100m； with the depth changing，rangehas similar curve in January，February, March, which the range of surface freshwaterareas were below500mesh and to100m are close to zero; with the depth changing，range also has similar curve in July,August,September，October,which the range ofsurface fresh water reached the maximum in each month and above40m freshwaterareas changed little,40m to90m showed a larger decreasing trend; April，May，Juneand November, December have all shown a significant transition, wbich decreasingrate is high above70m range from April to June, below70m the rate decreases. However, November and December is just the opposite, above40m it has smallerdecline rate and below40m the rate is high.(7)According to the difference of the source of freshwater, the entire low-salinitywhich in the west of Kuroshio is divided into three regions:F1, F2, F3. These threeregions have similar characteristics as the whole low salt area. However, there are alsodifferences among these regions, like that: not only July to October but also in June itreached a maximum salinity in surface of Fl，F3region; From January to Marchabove100m low salinity water was no invasion, and the gap of the strongest andweakest month which are low salt water intruding in F2region; In F3region only inMay and December are transitional months，what’s more, April have similar featuresin March to June,June and November have similar features in July to October whichcompared with the total area of freshwater.