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1.
This study examines species composition and abundance of appendicularians in the northwestern coastal waters of South China Sea based on in situ data obtained by 169 μm planktonic nets during summer and winter, and discusses the influence of environmental factors on their distribution and assemblages. A total of 19 appendicularian species (including one unidentified species) was collected. Species richness is higher in summer than in winter, and it increases from inshore to offshore waters. Average abundance of appendicularians is 103.1 (±198.1) and 54.6 (±111.1) ind. m−3 in summer and winter, respectively. The abundance distribution of appendicularians is generally high around inshore waters during summer and winter, and with a higher abundance assemblage along the eastern coast from Leizhou Peninsula to Hainan Island, especially at the eastern mouth of Qiongzhou Strait in summer. Oikopleurids accounted for 97.5% and 99.6% of total appendicularians abundance in summer and winter, and the region of high values was the same to that of total appendicularians abundance. Oikopleura longicauda, Oikopleura rufescens, and Oikopleura fusiformis are dominant species during summer and winter. Results showed that spatial distribution of species richness of appendicularians is considered to be the result of physical factors such as temperature and salinity in summer and winter, while variations in abundance of appendicularians are affected by the combination of physical and biological factors. In particular, variations of appendicularians abundance are affected by food availability in summer.  相似文献   

2.
The data of meteorological and oceanographic observations on the northwest shelf of the Black Sea for 1973–2000 are used to compute the characteristics of the entire area in the presence of hypoxia of waters under the pycnocline in the summer–autumn period and the area of surface waters with a level of salinity lower than 17.5‰ in May. The time of onset of the spring warming of air (stable transition through a temperature of 5°) is determined. A statistically significant positive trend of the air temperature (0.8° per 100 yr) is revealed in Odessa. The process of warming was observed mainly for the winter (1.5° per 100 yr) and spring (0.8° per 100 yr) periods and became especially intense since the beginning of the 1990s. On the basis of the data of correlation analyses, we establish a statistically significant relationship between the large-scale atmospheric processes [the index of North Atlantic Oscillation (NAO) and the wind conditions], the area of surface waters whose salinity is lower than 17.5‰, and the total area with hypoxia in the summer–autumn periods. For positive mean values of the NAO index (in January–March), we most often observe early spring with elevated repetition of the south and west winds with subsequent development of hypoxia in large areas of the northwest shelf. We propose an empirical regression model for the prediction of the total area of summer–autumn hypoxia of waters with predictors: the onset of the spring warming of air and the area of propagation of waters whose salinity is lower than 17.5‰ in May. The maximum error of prediction of the area with hypoxia does not exceed 5.5 ⋅ 103 km2, i.e., less than 2% of the total area of the northwest shelf in the Black Sea (to the north of 45°N).  相似文献   

3.
The first empirical orthogonal functions (EOF1s) of surface-air temperature fluctuations for Russia and its neighboring states within the period 1950–2005 are analyzed. The spatial distribution of the EOF1, the first principal components (PC1s) of the observed air temperature (averaged over the summer, July, December–March, and individual winter months), and their time variations (including trend parameters, some spectral characteristics, and the quantitative indices of relation to circulation indices (on the basis of multiple step-by-step regression)) are considered. Significant seasonal differences have been revealed: the winter air-temperature fluctuations are characterized by a higher (when compared to summer) spatial coherence, especially in the latitudinal direction. The EOF1 of the winter air temperature (averaged over December–March) describes its fluctuations for almost all of Russia; in this case, no less than 70% of the PC1 variability is due to variations in several circulation indices; the main contribution (60%) is made by both the North Atlantic Oscillation (NAO) and Scandinavian (SCAND) indices. On the whole, over the periods 1951–2005 and 1971–2005, the NAO contribution exceeds the SCAND contribution to the winter temperature variability; the NAO is associated with a more rapid increase in air temperature in 1968–1997 and with the 1971–2005 trend. In 1951–1970 the main contribution to air temperature fluctuations was made by SCAND; the SCAND contribution exceeds the NAO contribution in the periods 1951–2005 and 1971–2005. The 1971–2005 and 1968–1997 temperature trends are completely described by variations in the NAO (70%) and SCAND (30%) indices for January and February.  相似文献   

4.
Recent decadal salinity changes in the Greenland-Scotland overflow-derived deep waters are quantified using CTD data from repeated hydrographic sections in the Irminger Sea. The Denmark Strait Overflow Water salinity record shows the absence of any net change over the 1980s–2000s; changes in the Iceland–Scotland Overflow Water (ISOW) and in the deep water column (σ0 > 27.82), enclosing both overflows, show a distinct freshening reversal in the early 2000s. The observed freshening reversal is a lagged consequence of the persistent ISOW salinification that occurred upstream, in the Iceland Basin, after 1996 in response to salinification of the northeast Atlantic waters entrained into the overflow. The entrainment salinity increase is explained by the earlier documented North Atlantic Oscillation (NAO)-induced contraction of the subpolar gyre and corresponding northwestward advance of subtropical waters that followed the NAO decline in the mid-1990s and continued through the mid-2000s. Remarkably, the ISOW freshening reversal is not associated with changes in the overflow water salinity. This suggests that changes in the NAO-dependent relative contributions of subpolar and subtropical waters to the entrainment south of the Iceland–Scotland Ridge may dominate over changes in the Nordic Seas freshwater balance with respect to their effect on the ISOW salinity.  相似文献   

5.
Hydrographic observations on the Svinøy section, which runs NW from about 62°N on the Norwegian coast to 64°40′N on the prime meridian, have been used to investigate variations in the Atlantic inflow to the Nordic Seas. The data are from the winter 1955 to 1973 and from the spring and the summer 1978 to 1996. The observations show that in the summer there exist two cores of water with salinity above 35.25 at about 100 m depth, but in the spring and the winter the core furthest offshore is less distinct. Geostrophic calculations show that, for all data sets, there are two kernels with northward currents in the Svinøy section: one over the inner part of the continental slope (over 600–800 m depths) and one further offshore (over 1400–2500 m depth). The mean volume transports of Atlantic water in the section are 4.5, 5.0 and 5.6 Sv in spring, summer and winter, respectively. Results from an Empirical Orthogonal Function analysis of the summer data indicate that there is a dual structure in the section when interannual variations are considered. In the western part of the section the temperature and salinity are negatively correlated with the winter North Atlantic Oscillation index, but in the eastern part of the section they are weakly positively correlated. This is not found in the winter data from 1955 to 1973. The geostrophic volume transport in the summer through the Svinøy section is positively correlated with the NAO indices for winter and spring, where the March NAO index gave the best correlation. Also, the summer volume transports west and east in the section seem to be in opposite phase. From the summer data 1978 to 1996 there is a positive linear trend for the eastern transport (+2.4 Sv), but there is a negative linear trend for the western transport (−2.0 Sv). The transport through the whole section has increased by 1.1 Sv during the same similar period. The atmospheric conditions were different in years with relatively low temperatures and salinities in the western part of the section compared to those years with relatively high temperatures and salinities. It is proposed that interannual variations of temperature, salinity and volume transport in the Svinøy section are controlled mostly by a large-scale variable pressure system (i.e. the North Atlantic Oscillation index).  相似文献   

6.
黄海中南部头足类的群落结构与生物多样性   总被引：6，自引：1，他引：5  
为掌握黄海中南部头足类的群落结构及数量分布,作者根据2010~2011年间春、秋、冬3个季节的底拖网调查资料,对黄海中南部头足类的种类组成、生物量分布及生物多样性进行了研究。结果显示:3个季节共捕获头足类13种,隶属3目6科6属。各季节的优势种及其生物量比重分别为:春季——双喙耳乌贼(Sepiola birostrata)50.07%、秋季——针乌贼(Sepia esculenta)40.88%、冬季——枪乌贼(Loligo spp.)68.20%。各季节头足类平均资源密度分别为春季4.85 kg/km2、秋季2.52 kg/km2、冬季12.72 kg/km2,春秋两季间差异性不显著(P0.05),冬季与其他两季差异性显著(P0.05)。黄海中南部不同季节头足类的生物量分布变化较大,春季以西南及东北部密度最高,秋季以西南部密度最高,冬季以中部及东北部密度最高。头足类在各水深的垂直分布随季节变化。无论根据生物量还是丰度,种类丰富度指数、均匀度指数及Shannon-Wiener指数等多样性指数均以冬季最高,其次是春季,秋季最低。春季与冬季群落结构相似性较高,秋季与其他两个季节的群落结构相似性均较低。与1998~2000年同期相比,头足类种类数增加5种,相对资源密度增长了12%,枪乌贼类的生物量比重仍最高,耳乌贼类的比重提高,太平洋褶柔鱼的比重则大幅下降。  相似文献   

7.
东海浮游介形类(Ostracods)分布特征   总被引：7，自引：1，他引：7  
徐兆礼 《海洋学报》2006,28(2):101-108
根据1997~2000年东海(23°30'~33°00'N,118°30'~128°00'E)海域四季海洋调查资料,探讨了东海浮游介形类分布特征及与环境的关系.结果表明:东海浮游介形类丰度占浮游动物总丰度的3.47%;春、夏、秋和冬四季平均丰度分别为0.70,1.72,2.57和0.90个/m3;冬春季的短棒真浮萤(Euconchoecia chierchiae),夏季的后圆真浮萤(Euconchoecia maimai)和秋季的齿形海萤(Cypridi-na dentata)分别是各季的主要优势种;夏、秋季介形类总丰度与水文环境因子的线性相关性不显著,春季与表层盐度相关,冬季与表层温度相关.东海北部外海四季均有介形类高丰度区出现,但在东海北部近海长江口及其邻近舟山水域,介形类数量相对较低.在东海南部,冬春季高丰度区位于外海,夏秋季在近海.东海浮游介形类基本上是一大类较为典型的暖水性且具有集群行为的海洋浮游动物.介形类秋季高丰度区和较高丰度区的分布与太平洋褶柔鱼(Todarodes pacificus)、绿鳍马面鲀(Navodon Septentrionalis)、鲐鯵鱼类等渔场的位置基本一致,在渔业上有重要的意义.  相似文献   

8.
根据2014年4月至2015年1月于象山港海洋牧场示范区和对照区四季的浮游植物及同步的环境调查数据,对浮游植物的群落特征进行研究,并应用冗余分析(RDA)研究了该海域环境因子对浮游植物群落结构的影响。共鉴定出浮游植物95种,隶属于7门59属,主要由硅藻(64种)、绿藻(10种)和甲藻(9种)组成。优势种主要有琼氏圆筛藻(Coscinodiscus jonesianus)、太阳漂流藻(Planktoniella sol)和星脐圆筛藻(C.asteromphalus),且存在明显的季节演替现象。双因素分析结果表明:季节间,浮游植物丰度、多样性指数(Shannon-Wiener多样性、Pielou均匀度和Margalef丰富度)和环境因子(水温、盐度、p H、DO、NO_3-N、NO_2-N、NH_4-N、PO_4-P和Si O_3-Si)均存在极显著差异(P0.01),秋、春季全区丰度(121.59和79.39×10~4个/m~3)显著高于冬、夏季(13.05和7.05×10~4个/m~3),多样性指数均表现为冬夏秋春季;区域间,丰度、多样性指数和环境因子均无显著性差异(P0.05),示范区浮游植物丰度和多样性指数的四季均值都高于对照区。相似性聚类分析、多维尺度分析(n MDS)结果表明,浮游植物群落组成季节性差异显著,区域差异不显著。表明示范区的建设对浮游植物的生长有一定的积极作用,但效果不显著。RDA分析结果表明,盐度、温度、营养盐(NO_3-N、PO_4-P和Si O_3-Si)和DO是影响浮游植物群落结构的主要因子,各种浮游植物对环境因子的响应机制有所不同。  相似文献   

9.
《Oceanologica Acta》1999,22(3):353-364
The Bay of Guaratuba, whose area is approximately 45 km2, is a basin, situated to the south of Brazil (25° 52′ S; 48° 39′ W) and connected to the Atlantic ocean. In its northern part, a region of mangrove is found, under the influence of seasonal fluvial contributions, dominated by Laguncularia racemosa. The depth exceeds 6 m in some places. According to the period of the year, salinity varies between 3 and 37, and temperature between 15 and 28 °C. Several of the present fish species are exploited by commercial and recreational fisheries. This work describes characteristics of the fish populations occupying this mangrove, and temporal and spatial evolution of populations of the main species from available data on their biology. Between September 1993 and August 1996, fish samplings have been undertaken monthly by trawl, according to the same fishing effort (20 min), in channels of this ecosystem. Size, numerical abundance and weight of each individual of species were measured, as well as surface and bottom temperatures and bottom salinity. Species richness, Shannon-Weaver's diversity index were calculated and abundances were processed by the multivaried analysis. The global species richness is 61 species, distributed in 28 families; the better represented species are Sciaenidae (10), Gerreidae (5), Carangidae (5), Ariidae (4), Haemulidae (3), Serranidae (3), Bothidae (3). Each year, the number of species varies between 41 and 44, and a group of eight species represents between 80 to 90 % of the density and 75 % of the biomass. The constancy of this dominance is the main characteristic of this fish assemblage. The most represented species in abundance is Pomadasys corvinaeformis is the first two years, then Stellifer rastrifer. The group of eight main species is shared by 15 species in total, of which 13 for the density and 14 for the biomass. The most important monthly catches take place in winter season, during which one observes a decrease of water temperature and an increase of salinity. These species, however, being likely to be replaced by others according to the year or the season; one never finds the same composition in the assemblage which preserves always the same structures. Seasonal differences between seasons under marine (winter) and continental (summer) influences play a major role on the dynamics of fish in the Guaratuba mangrove. This ecosystem plays a functional role in the achievement of the life cycle of many permanent or temporary species. Those having succeeded to reach high levels of abundance are not represented in a uniform way in the course of the year, even when they reside permanently in the ecosystem. Periodic displacement strategies for self regulation of stocks abundance, are necessary mechanisms for these populations, which thus success to coexist in occupying the mangrove.  相似文献   

10.
2009年8,10,12月及2010年3月分别对烟台四十里湾的12个站位开展了四个航次的季节调查.研究发现浮游植物3门45属73种,其中硅藻46种,甲藻24种,褐胞藻3种.硅藻是构成调查区域浮游植物群落的主要类群.浮游植物种类与数量呈现出明显的季节变化特征.夏季(8月)物种数最多(57种),秋季(10月)次之(40种)...  相似文献   

11.
The distribution of toxic cyanobacterium Microcystis cf. aeruginosa in the severely polluted Golden Horn Estuary was studied from 1998 to 2000. Microcystis persisted at the upper estuary where the water circulation was poor and values ranged between 2.9 × 104 and 2.7 × 106 cells ml−1 throughout the study. Simultaneously measured physical (salinity, temperature, rainfall and secchi disc) and chemical parameters (nutrients and dissolved oxygen) were evaluated together with Microcystis data. Although the Microcystis blooms generally occur in summer due to the increase in temperature, the blooms were recorded in winter in the present study. The abundance of Microcystis depended on the variations in salinity and both blooms were recorded below S = 2. A moderate partial correlation between Microcystis abundance and salinity was detected in the presence of temperature, dissolved oxygen and precipitation data (r = −0.561, p = 0.002). The M. cf. aeruginosa abundance was low in the summer when the salinity was higher than winter. A remarkable increase in the eukaryotic phytoplankton abundance following the improvements in the water quality of the estuary occurred, whilst the Microcystis abundance remained below bloom level.  相似文献   

12.
At interannual to multidecadal time scales, much of the oceanographic and climatic variability in the North Atlantic Ocean can be associated with the North Atlantic Oscillation (NAO). While evidence suggests that there is a relationship between the NAO and zooplankton dynamics in the North Atlantic Ocean, the phytoplankton response to NAO-induced changes in the environment is less clear. Time series of monthly mean phytoplankton colour values, as compiled by the Continuous Plankton Recorder (CPR) survey, are analysed to infer relationships between the NAO and phytoplankton dynamics throughout the North Atlantic Ocean. While a few areas display highly significant (p < 0.05) trends in the CPR colour time series during the period 1948–2000, nominally significant (p < 0.20) positive trends are widespread across the basin, particularly on the continental shelves and in a transition zone stretching across the Central North Atlantic. When long-term trends are removed from both the NAO index and CPR colour time series, the correlation between them ceases to be significant. Several hypotheses are proposed to explain the observed variability in the CPR colour and its relationship with climate in the North Atlantic.  相似文献   

13.
We compared fish community structure in Guaratiba Mangrove, SE Brazil, among three seasons of the hydrological cycle [(i) spring, increasing temperature and rainfall, decreasing salinity; (ii) summer/early fall, high temperature and rainfall, intermediate salinity; (iii) late fall/winter, low temperature and rainfall, high salinity] and between the years 2002–2003 and 2008–2009. The aim was to test the hypothesis that the fish community structure changes seasonally, associated with seasonal changes in environmental conditions, and that changes occurred between the two yearly periods because of increased anthropogenic activities. The sampling protocol for the two surveys was identical. A total of 63 species was recorded, with 38 species occurring in 2002–2003, and 53 species in 2008–2009. The main changes in the mangrove's fish assemblage between 2002–2003 and 2008–2009 were (i) an increase in species richness, fish density and total biomass; and (ii) an increase in the zoobenthivorous species of gerreids Eucinostomus argenteus, Diapterus rhombeus and Ulaema lefroyi, and a decrease in the planktivorous clupeid Harengula clupeola. Other abundant species, such as the opportunistic atherinopsid. Atherinella brasiliensis, the detritivorous mullet Mugil liza and the zoobenthivorous pufferfish Sphoeroides testudineus did not differ in abundance between the two yearly periods. Ten species occurred only in 2002–2003, and 23 species only in 2008–2009, indicating significant changes in community structure over the 6‐year period. Seasonal changes in community structure were more conspicuous in 2008–2009, when species abundance and richness were greatest. The highest fish abundance was recorded in spring and in summer/early fall, and the lowest in late fall/winter. The increased abundance and richness over time may be at least partially attributable to protection policies because of the effective implementation of a biological reserve in the area.  相似文献   

14.
Spatial and temporal variation in fish assemblage structure of Koycegiz Lagoon–Estuarine System (KLES), located on the northwestern Turkish coast of Mediterranean, was investigated along an estuarine gradient where salinity ranged from 5 in upper reaches to 40 in lower reaches during October 1993–September 1994. Throughout the study, 42 species, consisting of marine (25), marine–estuarine-dependent (12), freshwater (3), catadromous (1), and estuarine resident (1) forms, were collected in trammel nets. Although species richness of marine species was greater than that of other groups, numerical contribution by marine species to the total catch was only 16%. Tilapia spp., the most abundant species mostly during summer and early spring at upper reaches, contributed 17% of the total samples. Among the seven species of Mugilidae, which contributed 42% of the total catch, Mugil cephalus, Liza aurata, and Liza salines contributed 10, 13, and 10% of the total catch, respectively. Consistent with findings from other studies, species richness and abundance were highest during late spring and summer and the lowest during winter and early spring. Samples from sites at or near the sea had more marine species. Samples from upper reaches had more freshwater and marine–estuarine-dependent species. Canonical correspondence analysis (CCA) indicated that salinity and turbidity were the most important environmental parameters affecting fishes. Sites near the sea were associated with high salinity and low turbidity, and sites in upper reaches had low salinity and high turbidity. Thus, the pattern observed in fish assemblage structure appears to be strongly influenced by species' responses to dominant salinity and turbidity gradients.  相似文献   

15.
长江口及其邻近陆架区夏季网采浮游植物及其影响因素   总被引：3，自引：1，他引：2  
2009年6、8月长江口及其邻近陆架区的网采样品中检出浮游植物9门395种(含223种硅藻与125种甲藻)。浮游植物丰度8月(3 077.15×104 cells/m3)显著高于6月(107.80×104 cells/m3)。随长江冲淡水势力增强,位于长江口的丰度高值区8月较6月更偏外侧。种类丰富度8月高于6月,但多样性和均匀度指数略低于6月。6月尖刺伪菱形藻和三角角藻占绝对优势,8月优势种主要有尖刺伪菱形藻、笔尖形根管藻和铁氏束毛藻。骨条藻虽非优势种,但在长江冲淡水区丰度较高。相似性分析和多维尺度分析表明,浮游植物群落组成时空差异显著。典范对应分析表明,温度和盐度是分别影响6、8月群落分布的首要因子。根据水动力和化学参数,该区浮游植物群落分布与环流变化和水团消长密切相关。  相似文献   

16.
We examined the interannual variability of Pacific Winter Water (PWW), both upstream in the northeastern Chukchi Sea and Barrow Canyon using mooring observations from 2000 to 2006, and downstream in the Canada Basin using hydrographic data acquired in 2002–2006. The interannual variation of PWW salinity is governed by two factors: (1) variability in the salinity of Pacific Water that flows northward through Bering Strait in winter; and (2) the input of salt associated with sea ice formation during winter in an intermittent coastal polynya located along the Alaskan coast between Cape Lisburne and Point Barrow. During the winters of 2000/2001 and 2001/2002 an increased transport of cold and saline PWW (S?>?33.5) to the basin via Barrow Canyon was observed. In 2000/2001 enhanced ice formation in the polynya contributed to the increased salinity of PWW, whereas in 2001/2002 the salinity of water entering through the Bering Strait was higher, and this resulted in more saline PWW being delivered to the basin. In the following four winters (2002/2003, 2003/2004, 2004/2005 and 2005/2006) the transport of cold and saline PWW in winter to the basin was less than that in the two preceding winters. In three of these four winters (2003/2004 being the exception) the coastal polynya was less active, thus reducing the input of salt due to brine enrichment. In the winter of 2003/2004, however, warmer water within the polynya region constrained ice formation and thus less cold and saline PWW was produced, despite the fact that the coastal polynya was active and frequently open.  相似文献   

17.
A modelling approach is proposed to evaluate the environmental dynamics of coastal lagoons. The water, heat and salt balances are addressed simultaneously, providing a better estimation of evaporation and water exchanges. Compared to traditional approaches, the model presented accounts for the effects of water salinity, heat storage and net energy advected in the water body. The model was applied daily to the Mar Menor coastal lagoon (SE Spain) from 2003 through 2006. Water exchanges with the Mediterranean Sea were estimated based on the monthly trend of the lagoon salinity and were correlated with monthly averages of wind speed. The mean daily water exchange with the sea was 1.77 hm3 d−1. This exchange accounted for only 1% of the heat losses in the lagoon heat balance, and it is the most important flow in the water balance. The mean annual evaporation flux amounted to 101.3 W m−2 (3.55 mm d−1), while the sensible heat flux amounted to 19.7 W m−2, leading to an annual Bowen ratio on the order of 0.19. To validate the model, daily water temperatures were predicted based on the daily heat balance of the water body and were compared with remote sensing data from water surface standard products.  相似文献   

18.
基于RDA与GAMs模型的东海近岸海域浮游动物与温盐关系   总被引：2，自引：1，他引：1  
为进一步探讨东海近岸海域浮游动物季节演替与温盐的变化关系，根据2013年5月(春季)、8月(夏季)和12月(冬季)东海近岸海域3个航次的浮游动物调查资料，利用冗余分析模型分析了优势种与温盐的变化关系，广义加性模型分析了生物多样性参数与温盐之间的关系。结果表明:(1)优势种季节演替较为明显，由春季2种演替成夏季10种，再更替为冬季5种，春季和冬季优势种的种类和生态类群相对单一，夏季较为丰富。(2)优势种时空分布是综合多层环境因子的结果，如春季中华哲水蚤(Calanus sinicus)与表层盐度和底层盐度正相关，夏季与表层温度和底层温度负相关，冬季与表层盐度正相关；春季五角水母(Muggiaea atlantica)与底层温度、底层盐度呈现较好的正相关；夏季盐度是决定暖水性和高温高盐性优势种分布的关键因子，且呈现较强的正相关；冬季真刺唇角水蚤(Labidocera euchaeta)、强壮滨箭虫(Aidanosagitta crassa)与表层温度关系密切，并呈现较强的负相关。(3)春季和冬季香农–威纳指数多样性指数与纬度呈负相关。(4)温度和盐度对生物多样性参数影响显著，但季节上又呈现出差异。  相似文献   

19.
虽然全球平均表面气温不断升高,但在冬季欧亚大陆经常出现年际-年代际尺度上的变冷趋势。利用美国国家环境预报中心(National Centers for Environmental Prediction,NCEP)再分析资料,指出冬季影响欧亚大陆变冷的大气环流主要是北大西洋涛动(North Atlantic Oscillation,NAO)和乌拉尔山阻塞(Ural blocking,UB)的环流组合。其中,NAO环流可以在年际尺度上作为背景环流影响UB过程对欧亚低温天气的作用。统计分析发现,在NAO正(负)位相(NAO+/NAO-)环流背景下UB的发生频率可以解释冬季平均UB发生频率的52%(13%),表明NAO+环流有利于下游阻塞形势出现。尽管如此,研究发现在NAO-环流背景下的UB事件平均给欧亚地区带来的降温幅度更强,约是NAO+环流背景下的2倍,而且亚洲降温区的位置偏北约5°、偏东约13.5°。中等强度的NAO+环流背景下UB事件对欧亚降温的贡献更显著,强的NAO+环流背景下,UB过程在欧亚大陆中纬度地区产生的冷异常较弱,这与NAO+环流在欧亚大陆北部产生的明显增温有关。而在NAO-环流背景下,欧亚大陆北部有明显的降温,UB环流的出现会进一步将冷空气向南输送影响我国,这种情况主要反映的是NAO-环流异常对欧亚地区降温的作用,因此NAO-环流越强降温越强烈。  相似文献   

20.
In this study we test Talley's hypothesis that Oyashio winter mixed-layer water (26.5–26.6σ θ) increases its density to produce the North Pacific Intermediate Water (NPIW) salinity minimum (26.7– 26.8σθ) in the Mixed Water Region, assuming a combination of cabbeling and double diffusion. The possible density change of Oyashio winter mixed-layer water is discussed using an instantaneous ratio of the change of temperature and salinity along any particular intrusion (R l ). We estimate the range of R l DD required to convert Oyashio winter mixed-layer water to the NPIW salinity minimum due to double diffusion, and then assume double-diffusive intrusions as this conversion mechanism. A double-diffusive intrusion model is used to estimate R l DD in a situation where salt fingering dominates vertical mixing, as well as to determine whether Oyashio winter mixed-layer water can become the NPIW salinity minimum. Possible density changes are estimated from the model R l DD by assuming the amount of density change due to cabbeling. From these results, we conclude that Oyashio winter mixed-layer water contributes to a freshening of the lighter layer of the NPIW salinity minimum (around 26.70σθ) in the MWR.  相似文献   

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