Variability of the North Pacific Current and its bifurcation

The North Pacific Current (NPC) bifurcates approaching the west coast of North America into a subpolar branch that forms the Alaska Current, and a subtropical branch that includes the California Current. The variability of this current system is discussed using numerical results from a wind-driven, reduced-gravity model. Indices of the strength of the subpolar and subtropical components of the NPC are examined based on output from multi-decadal simulations with the numerical model. This shows periods of both correlated and anti-correlated variability of the subpolar and subtropical gyres. A decomposition of the gyre transport time series indicates that the dominant mode of variability is a “breathing” mode in which the subpolar and subtropical gyres co-vary in response to fluctuations in the strength of the NPC. This finding is consistent with an analysis of dynamic height data of limited duration from the array of Argo drifting floats.The variability of the NPC is also examined using sea surface height (SSH) data from satellite altimetry over the period 1993-2005. The leading mode of SSH over the northeast Pacific dominates the variability of the NPC and is shown to be associated with in-phase variations in the transport of the subtropical and subpolar gyres. A strong correlation is found between time-dependent fluctuations in SSH across the NPC and variations in the strength of the transport of the NPC in the model. This agreement provides evidence for variability of the NPC occuring in direct response to large-scale atmospheric forcing.     

1993和1994年东海黑潮的变异

基于“长风丸”1993～1994年共8个航次的水文调查资料,采用改进逆方法计算了东海黑潮的流速、流量和热通量.计算结果表明:(1)PN断面黑潮流速在秋季时均呈双核结构;而在其他季节,有时为单核,有时为双核;黑潮主核心皆位于坡折处.黑潮以东及黑潮以下都存在南向逆流.(2)TK断面较复杂,可出现单、双或三核结构.在吐噶喇海峡中部、北部出现流核的机率较高.海峡南端及海峡深处都存在西向逆流,而且海峡南端的逆流在秋季较强.(3)在A断面,对马暖流核心位于陆坡上,但有时偏西或偏东.Vmax值的变动范围为26～46cm/s.黄海暖流位于其西侧,流速则相对减小.(4)东海黑潮流量在这两年中,在春季均出现最小值,在夏季出现最大或较大值.黑潮流量,以PN断面为例,每年四季平均流量值1994年与1993年几乎相同,但略小于1992年的平均流量值.8个航次中通过PN、TK断面的平均净流量分别为27.1×106和25.0×106m3/s.(5)8个航次中,通过PN、TK断面的热通量的平均值分别为1.99×1015和1.78×1015W.(6)在计算海域秋季和冬季均是由海洋向大气放热;夏季则均从大气吸热;春季则不确定.海面上热交换率在冬季最大,而春、夏季较小.     

Variability of the Kuroshio in the East China Sea in 1993 and 1994

INTRODUCTIONTherearemanyworksabouttheKuroshioVTintheEastChinaSeaanditsseasonalvariabil*ThisprojectwassupportedbytheNationalNaturalScienceFoundationofChinaundercontractNo.49776287.1.SecondinstituteofOceanography,StateOceanicAdministration,Hangzhou310012,Chinaity(Guan,1988;Nishizawaetal.,1982;SunandKaneko,1993;Yuanetal.,1990,1993,1994,1995).Thecomputationmethodusedtobethedynamicmethod(Guan,1988;Nishizawaetal.,1982;SunandKaneko,1993),butrecentlytheinverseandthemodifiedinversemetho…     

Variability of shore and shoreline evolution

Shore and shoreline evolution both due to natural and human-induced causes or factors can be variable over a wide range of different temporal and/or spatial scales. Our capability to understand and especially predict this variability is still limited. This can lead to misinterpretation of coastal change information, which hampers informed decision making and the subsequent design and implementation of (soft) engineering interventions. Collecting and describing example observations of shore and shoreline variability is one way to support and improve such human intervention. This paper describes causes and factors for the variability and the resulting possible evolutions of wave-dominated shores and shorelines, which are illustrated by a number of case studies. The new element of this work is that the variability is described in terms of a range of different time and space scales, which helps to structure such analysis. However, it is difficult to generalise the results for arbitrary situations, especially on decadal time scales. Scientific and engineering improvements require more quantitative insight into the physical mechanisms behind the free and forced shore behaviour responsible for the variability.     

Variability in the Hydrographic and Biological Features of the Gulf of Naples

Abstract. Recent observations of physico-chemical and biological parameters in the Gulf of Naples are summarized. The water masses present within the Gulf during the various periods of the year are described. The temporal and spatial distribution of surface nutrients (N-NO₃, P-PO₄, Si-SiO₄) and chlorophyll a are reported and the areas exposed to local eutrophication are identified. Biweekly sampling at a reference station has permitted us also to identify both phytoplankton and zooplankton seasonal cycles. The morphology of the basin and the uneven land runoff distribution are interpreted as causal to the variability of chemico-physical parameters and of the associated biological communities, giving rise to two subsystems (coastal and "open water") within the Gulf.     

南大西洋副热带偶极子的年际变化

南大西洋副热带偶极子(South Atlantic Subtropical Dipole;SASD)为南大西洋海洋与大气相互作用的主要模态。它的空间型为海表面温度异常呈现东北-西南偶极子分布。当SASD指数大于1,为SASD正事件,小于-1,为负事件。根据1960-2016年HadISST(Hadley Center Global Sea Ice and Sea Surface Temperature)数据,本文鉴别出57年中共发生6次正事件和9次负事件。SASD存在显著的5~8年周期的年际变化特征。本文进一步利用1992-2016年ECCO2(Estimating the Circulation and Climate of the Ocean,PhaseⅡ)模式数据,根据温度倾向方程分别诊断了SASD西南极和东北极的混合层温度变化。诊断结果表明,SASD的年际变化主要来自于表面热力强迫项的年际变化。考虑到表面热力强迫项主要由短波辐射项控制,SASD的年际变化最终来源于短波辐射项的年际变化。     

Variability and predictability of Antarctic krill swarm structure

Swarming is a fundamental part of the life of Euphausia superba, yet we still know very little about what drives the considerable variability in swarm shape, size and biomass. We examined swarms across the Scotia Sea in January and February 2003 using a Simrad EK60 (38 and 120 kHz) echosounder, concurrent with net sampling. The acoustic data were analysed through applying a swarm-identification algorithm and then filtering out all non-krill targets. The area, length, height, depth, packing-concentration and inter-swarm distance of 4525 swarms was derived by this method. Hierarchical clustering revealed 2 principal swarm types, which differed in both their dimensions and packing-concentrations. Type 1 swarms were generally small (<50 m long) and were not very tightly packed (<10 ind. m⁻³), whereas type 2 swarms were an order of magnitude larger and had packing concentrations up to 10 times greater. Further sub-divisions of these types identified small and standard swarms within the type 1 group and large and superswarms within the type 2 group. A minor group (swarm type 3) was also found, containing swarms that were isolated (>100 km away from the next swarm). The distribution of swarm types over the survey grid was examined with respect to a number of potential explanatory variables describing both the environment and the internal-state of krill (namely maturity, body length, body condition). Most variables were spatially averaged over scales of 100 km and so mainly had a mesoscale perspective. The exception was the level of light (photosynthetically active radiation (PAR)) for which measurements were specific to each swarm. A binary logistic model was constructed from four variables found to have significant explanatory power (P<0.05): surface fluorescence, PAR, krill maturity and krill body length. Larger (type 2) swarms were more commonly found during nighttime or when it was overcast during the day, when surface fluorescence was low, and when the krill were small and immature. A strong pattern of diel vertical migration was not observed although the larger and denser swarms tended to occur more often at night than during the day. The vast majority of krill were contained within a minor fraction of the total number of swarms. These krill-rich swarms were more common in areas dominated by small and immature krill. We propose that, at the mesoscale level, the structure of swarms switches from being predominantly large and tightly packed to smaller and more diffuse as krill grow and mature. This pattern is further modulated according to feeding conditions and then level of light.     

Variability of the Kuroshio in the East China Sea in 1992

INTRODUCTIONMostofpreviousstudiesshowthatthedynamicmethodswereoftenusedtocomputethevelocityandVToftheKuroshiointheEastChinaSea(Guan,1988;Nishizawaetal.,1982;SunandKaneko,1993).Duringrecentyearsdifferentkindsofinversemethodshavebeentriedby*ThisprojectwassupportedbytheNationalNaturalScienceFoundationofChinaundercontractNo.49776287.1.Secondinstituteofoceanography,StateOceanicAdministration,Hangzhou310012,ChinaYuanetul(1988,1991,1992a,1992b,1993,1994,1995).Theircalculatedresultsshowt…     

Decadal Variability of Subsurface Temperature in the Central North Pacific

Decadal variability of subsurface temperature in the North Pacific has been investigated. Two dominant regions were found; the central subarctic region (CSa) and the north-eastern subtropical region (NESt). In CSa, cooling (warming) of wintertime subsurface temperature corresponds to the large (small) temperature gradient and southward (northward) shift of subsurface temperature front, associated with the increase (decrease) of positive wind stress curl and the southward (northward) shift of curl τ zero line with 2 years delay. It is suggested that the relocation of subtropical-subarctic boundary plays an important role. In NESt, importance of heat flux through the sea surface and heat divergence in the Ekman layer is also discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Spatio-Temporal Variability of the Phase of Total Ozone Quasi-Decennial Oscillations

The SBUV/SBUV2 (65° S–65° N) and Bodeker Scientific (90° S–90° N) satellite databases have been used for composite and cross-wavelet analyses of the spatio-temporal variability of phase relations between a 11-year cycle of solar activity (SA) and quasi-decennial oscillations (QDOs) of total ozone content (TOC). For globally average TOC values, the QDO maxima coincide in phase with the solar-activity maxima, and amplitude variations of TOC correlate with those of the 11-year solar cycle. According to the analysis of amplitude and phase of QDOs for the zonal average TOC fields, a QDO amplitude is about 6–7 Dobson Units (DU) in the high northern and southern latitudes, and it does not exceed 2–3 DU in the tropic regions. The latitudinal TOC variations are distinguished by a delay of the quasi-decennial oscillation phase in the southern latitudes in comparison with the northern latitudes. The TOC maxima phase coincides with the SA maxima phase in the tropic regions; the TOC variations go ahead of the SA variations, on average, in moderate and high latitudes of the Northern Hemisphere; the TOC variations are behind the SA variations in the Southern Hemisphere. The phase delay between TOC QDO maxima in the northern and southern latitudes appears to increase in the course of time, and the TOC quasi-decennial variations in the Arctic and Antarctic subpolar regions occur approximately in an antiphase over the last two decades.     

Salinity Biases and the Variability of the Atlantic Meridional Overturning Circulation in GFDL-CM3

Ocean Science Journal - The variability of the Atlantic Meridional Overturning Circulation (AMOC) and the Meridional Freshwater Transport (Mov) at 24°N, 11°S, and 30°S, simulated...     

Interannual Variability of Primary Production in the East Siberian Sea

Oceanology - Interannual variability (2002–2018) of primary production, surface seawater temperature (T0), photosynthetically active radiation (PAR) and ice cover area in the East Siberian...     

Variability of Evaporation and Precipitation over the Ocean from Satellite Data

HOAPS-3 and PMWC satellite archives for 1988–2008 are used to estimate moisture-exchange components between the ocean and atmosphere (evaporation, precipitation, and the difference between them or effective evaporation). Moisture-exchange components for the entire World Ocean and for the North Atlantic Ocean within 30°–60° N are calculated. A strong overestimation of the global values of effective evaporation by HOAPS data (mainly caused by a decrease in precipitation) is shown. In the interannual variability of effective evaporation, there is clearly an overestimated positive trend, which contradicts the real increase in the Global Sea Level. Large systematic errors in moisture-exchange components are revealed for the North Atlantic water area. According to HOAPS data, there is a significant underestimation of evaporation and effective evaporation. According to PMWC data, the amount of precipitation is significantly overestimated and evaporation is underestimated. As a consequence, effective evaporation becomes negative, which is impossible. Low accuracy in the estimation of moisture-exchange components and the need to improve old estimates and develop new evaporation and precipitation databases based on satellite data are noted.     

2000年东海黑潮和琉球群岛以东海流的变异 Ⅱ.冲绳岛东南海域海流及其附近中尺度涡的变异

基于日本“长风丸”调查船在2000年5个航次水文资料及同时期QuikSCAT风场资料,采用改进逆方法计算了冲绳岛东南海域海流的流速与流量等,获得了以下主要结果.(1)在琉球群岛以东海区1~2,4,7,10与11月分别为东北风,东北风,东南风,偏东风,东北风.风速在4与7月较小,1~2,10与11月较大.表层风海流只有7月时偏北向,其余月偏西方向.(2)琉球海流是琉球群岛以东一支东北向的西边界流.琉球海流结构:最大流速在5个航次中1~2,4,7,10与11月分别为40 cm/s以上,15,20,20与55 cm/s.琉球海流的核心一般位于次表层.琉球海流在5个航次中垂向方向可达1 200 m以深,在琉球海流以深存在弱的、西南向海流.(3)琉球海流的流量在1~2与11月时最大,分别为20×106与14.5×10 m3/s,而在4月时流量最小,只有3.1×106m3/s.这表明琉球海流的流量在2000年季节变化很大.(4)在5个调查航次中,琉球海流以东调查海域都存在尺度不同的、各种冷的气旋式和暖的反气旋式涡.1~2月时,计算区域中部与东部,分别存在反气旋暖涡W1,W2和气旋式冷涡C1,C2;在4月时存在一对较强的、水平尺度都较大的、暖的反气旋涡和冷的气旋式涡,在它们中间出现南向流,它们可能组成一个偶极子等.这些表明,在5个航次中,琉球群岛以东调查海域存在各种强度不等的中尺度涡,其变化都很大.(5)琉球海流的流量受其附近各种涡的影响很大,特别是涡的强度增大时,可能减少琉球海流的流量.(6)在5个调查航次中,琉球群岛以东调查海域都存在南向流,其中11月时最大,其流量大于15×106m3/s,其次在1~2月,其流量大于10×106m3/s,在4月最小,流量约为3×106m3/s.上述南向流的季节变化趋向与琉球海流的季节变化趋向基本一致.     

1992年东海黑潮的变异

基于1992年4个航次的水文调查资料,运用改进逆方法计算了东海黑潮的流速、流量和热通量．计算结果表明：（1）PN断面黑潮在春季和秋季都有两个流核,冬季和夏季则只有一个流核．主核心皆位于坡折处．Vmax值春季最大,冬季和夏季次之,而秋季最小．黑潮以东及以下都存在逆流．（2）TK断面黑潮在冬季为两核,春、夏季为3核．海峡南端及海峡深处存在西向逆流．（3）通过A断面的对马暖流Vmax值在秋季最大,冬季最小．黄海暖流位于其西侧,相对较弱．（4）通过PN断面净北向流量夏季最大,秋季最小,而冬、春季介于上述二者之间,1992年四季平均值为28．0×106m3/s;TK断面的净东向流量也是在夏季最大;A断面净北向流量则在秋季最大．（5）PN断面4个航次的平均热通量为2．03×1015W．TK断面3个航次的平均热通量为2．00×1015W．（6）在计算海区,冬、春和秋季都是由海洋向大气放热;夏季则从大气吸热．冬季海面上热交换率最大,而夏季热交换率最小．关键词##4东海;;黑潮;;季节变化     

Variability and propagation of Labrador Sea Water in the southern subpolar North Atlantic

The variability of two modes of Labrador Sea Water (LSW) (upper and deep Labrador Sea Water) and their respective spreading in the interior North Atlantic Ocean are investigated by means of repeated ship surveys carried out along the zonal WOCE line A2/AR19 located at 43–48°N (1993–2007) and along the GOOS line at about 48–51°N (1997–2002). Hydrographic section data are complemented by temperature, salinity, and velocity time series recorded by two moorings. They have been deployed at the western flank of the Mid-Atlantic Ridge (MAR) in the Newfoundland Basin during 1996–2004. The analysis of hydrographic anomalies at various longitudes points to a gradual eastward propagation of LSW-related signals, which happens on time scales of 3–6 years from the formation region towards the MAR. Interactions of the North Atlantic Current (NAC) with the Deep Western Boundary Current (DWBC) close to Flemish Cap point to the NAC being the main distributor of the different types of LSW into the interior of the Newfoundland Basin. Comparisons between the ship data and the mooring records revealed that the mooring sites are located in a region affected by highly variable flow. The mooring time series demonstrate an elevated level of variability with eddy activity and variability associated with the NAC considerably influencing the LSW signals in this region. Hydrographic data taken from Argo profiles from the vicinity of the mooring sites turned out to mimic quite well the temporal evolution captured by the moorings. There is some indication of occasional southward flow in the LSW layer near the MAR. If this can be considered as a hint to an interior LSW-route, it is at least of minor importance in comparison to the DWBC. It acts as an important supplier for the interior North Atlantic, distributing older and recently formed LSW modes southward along the MAR.     

Variability of the Kuroshio in the East China Sea in 1995

INTRODUCTIONTherearemanyresearchworksabbottheKUrOShioVTanditSSeaSOnalvacationintheEastChinaho(GUan,1988;Nishizawaetal.,1982;TangandTaShiro,1993;SunandKaneko,1993;Yuanetal.,1990;Yuanetal.,1993;Yuanetal.,1994;Yuanetal.,1995;LiuandYuan,1997a,b).~previou...     

Variability in the speciation of iron in the northern North Sea

Variations in the speciation of iron in the northern North Sea were investigated in an area covering at least two different water masses and an algal bloom, using a combination of techniques. Catalytic cathodic stripping voltammetry was used to measure the concentrations of reactive iron (Fe_R) and total iron (Fe_T) in unfiltered samples, while dissolved iron (Fe_D) was measured by GFAAS after extraction of filtered sea water. Fe_R was defined by the amount of iron that complexed with 20 μM 1-nitroso-2-napthol (NN) at pH 6.9. Fe_T was determined after UV-digestion at pH 2.4. Concentrations of natural organic iron complexing ligands and values for conditional stability constants, were determined in unfiltered samples by titration. Mean concentrations of 1.3 nM for Fe_R, 10.0 nM for Fe_T and 1.7 nM for Fe_D were obtained for the area sampled. Fe_R concentrations increased towards the south of the area investigated, as a result of the increased influence of continental run off. Fe_R concentrations were found to be enhanced below the nutricline (below 40 m) as a result of the remineralisation of organic material. Enhanced levels of Fe_T were observed in some surface samples and in samples collected below 30 m at stations in the south of the area studied, thought to be a result of high concentrations of biogenic particulate material and the resuspended sediments respectively. Fe_D concentrations varied between values similar to those of Fe_T in samples from the north of the area to values similar to those of Fe_R in the south. The bloom was thought to have influenced the distribution of both Fe_R and Fe_T, but less evidence was observed for any influence on Fe_R and Fe_D. The concentration of organic complexing ligands, which could possibly include a contribution from adsorption sites on particulate material, increased slightly in the bloom area and in North Sea waters. Iron was found to be fully (99.9%) complexed by the organic complexing ligands at a pH of 6.9 and largely complexed (82–96%) at pH 8. The ligands were almost saturated with iron suggesting that the ligand concentration could limit the concentration of iron occurring as dissolved species.     

Seasonal Variability of Thermohaline Front in the Central South China Sea

An upper layer thermohaline front across the South China Sea (SCS) basin from the South Vietnamese coast (around 15°N) to Luzon Island (around 19°N) has been identified using the Navy's open domain Generalized Digital Environmental Model (GDEM) monthly mean temperature and salinity data on a 0.5° × 0.5° grid. This front does not occur at the surface in summer. The strength of this front is around 1°C/100 km at the surface and 1.4°C/100 km at the subsurface (50 m deep). A cross-basin current, inverted using the P-vector method, is associating with the front. Meandering and eddies have been identified along this current. Seasonal and vertical variabilities of the thermohaline structure across this front are reported in this paper. This revised version was published online in July 2006 with corrections to the Cover Date.     

Temporal Variability of High Vertical Wavenumber Shear over the Izu-Ogasawara Ridge

Recent numerical studies (Hibiya et al., 1996, 1998, 2002) showed that the energy cascade across the internal wave spectrum down to small dissipation scales was under strong control of parametric subharmonic instabilities (PSI) which transfer energy from low vertical mode double-inertial frequency internal waves to high vertical mode near-inertial internal waves. To see whether or not the numerically-predicted energy cascade process is actually dominant in the real deep ocean, we examine the temporal variability of vertical profiles of horizontal velocity observed by deploying a number of expendable current profilers (XCPs) at one location near the Izu-Ogasawara Ridge. By calculating EOFs, we find the observed velocity profiles are dominated by low mode semidiurnal (∼double-inertial frequency) internal tides and high mode near-inertial internal waves. Furthermore, we find that the WKB-stretched vertical scales of the near-inertial current shear are about 250 sm and 100 sm. The observed features are reasonably explained if the energy cascade down to small dissipation scales is dominated by PSI.