Impact of synoptic processes and river discharge on the thermohaline structure in the east Siberian Sea shelf

The thermohaline structure of waters in the East Siberian Sea coastal zone in September 2000, 2003, and 2004 is investigated. It is found that the spatial variability of thermohaline characteristics was determined by various synoptic conditions observed over the East Siberian Sea during the summer-autumn season and by fluctuations in the river discharge. In surface layers, plume fronts are identified. Under conditions of cyclonic atmospheric circulation of 2003, fresh waters spread as a narrow jet along the coast. During anticyclonic circulation of 2004, some meridional fronts existed. Horizontal gradients of thermohaline characteristics were 0.01–0.02°C/km and 0.03–0.07 psu/km off the Indigirka River and 0.02–0.03°C/km and 0.06–0.09 psu/km near the Kolyma River mouth being an order of magnitude less than the vertical ones. The stratification of coastal waters was amplified as the river and ice-melted runoff increased. In the thermohalocline, the average Brunt-Väisälä frequency was 0.042 s^?1 (in 2000), 0.068 s^?1 (in 2003), and 0.074 s^?1 (in 2004).     

The monsoonal regimes of upper‐hydrospheric structure in the tropical Indian Ocean

Abstract

In response to the alternations between the boreal summer Southwest and the winter Northeast monsoons, the upper‐hydrospheric structure of the tropical Indian Ocean experiences drastic seasonal changes. All year‐round the zone 10–20°S is characterized by a thick and deep thermocline and a ridge in ocean surface topography, while at 0–10°S a tongue protruding from the African coast eastward features a thin and shallow thermocline and a trough in the ocean surface. The trough and ridge mark the equatorial and polar boundaries of the South Equatorial Current. The eastward depression of isotherms and the rise of the ocean surface along the equator are most pronounced around May‐June and November‐December, or lagging somewhat behind the jet‐like surface currents, which are forced by the strong westerly winds sweeping the equatorial zone during limited intervals of the monsoon transitions. Monsoonal changes are particularly dramatic in the northwestern Indian Ocean. From June to August, the thermocline rises and surface waters cool off the coasts of Somalia and Arabia, while in the south‐central Arabian Sea isothermal surfaces bulge downward and the thermocline deepens, with two different centres that appear related to the well known pair of whirls in the surface circulation. During the boreal summer Southwest monsoon, relatively fresh waters appear off the coasts of Somalia and Arabia, further reflecting coastal upwelling; by contrast, downwelling in the central Arabian Sea is accompanied by a core of relatively saline waters. Salinity is overall smallest in the rainfall‐abundant Southeast Asian waters and the Bay of Bengal and large in the desertic regions of the Red Sea and the Persian Gulf. Particularly prominent is a tongue of relatively fresh waters centred somewhat to the south of 10°S extending from the Timor Sea towards the western Indian Ocean and reflecting intrusion from the Southeast Asian seas and the Western Pacific.     

Simulation of the interannual variability of the wind-driven Arctic sea-ice cover during 1958–1998

A thermodynamic-dynamic sea-ice model based on a granular material rheology developed by Tremblay and Mysak is used to study the interannual variability of the Arctic sea-ice cover during the 41-year period 1958–98. Monthly wind stress forcing derived from the National Centers for Environmental Prediction (NCEP) Reanalysis data is used to produce the year-to-year variations in the sea-ice circulation and thickness. We focus on analyzing the variability of the sea-ice volume in the Arctic Basin and the subsequent changes in sea-ice export into the Greenland Sea via Fram Strait. The relative contributions of the Fram Strait sea-ice thickness and velocity anomalies to the sea-ice export anomalies are first investigated, and the former is shown to be particularly important during several large export events. The sea-ice export anomalies for these events are next linked to prior sea-ice volume anomalies in the Arctic Basin. The origin and evolution of the sea-ice volume anomalies are then related to the sea-ice circulation and atmospheric forcing patterns in the Arctic. Large sea-ice export anomalies are generally preceded by large volume anomalies formed along the East Siberian coast due to anomalous winds which occur when the Arctic High is centered closer than usual to this coastal area. When the center of this High relocates over the Beaufort Sea and the Icelandic Low extends far into the Arctic Basin, the ice volume anomalies are transported to the Fram Strait region via the Transpolar Drift Stream. Finally, the link between the sea-ice export and the North Atlantic Oscillation (NAO) index is briefly discussed. The overall results from this study show that the Arctic Basin and its ice volume anomalies must be considered in order to fully understand the export through Fram Strait. Received: 27 January 1999 / Accepted: 8 July 1999     

Generation and termination of Indian Ocean dipole events in 2003, 2006 and 2007

Evolution of Indian Ocean Dipole (IOD) events in 2003, 2006 and 2007 is investigated using observational and re-analysis data products. Efforts are made to understand various processes involved in three phases of IOD events; activation, maturation and termination. Three different triggers are found to activate the IOD events. In preceding months leading to the IOD evolution, the thermocline in southeastern Indian Ocean shoals by reflection of near equatorial upwelling Rossby waves at the East African coast into anomalous upwelling equatorial Kelvin waves. Strengthening (weakening) of northern (southern) portion of ITCZ in March/April and May/June of IOD years, leads to strengthening of alongshore winds along Sumatra/Java coasts. With the combined shallow thermocline and increased latent heat flux due to enhanced wind speeds, the SST in the southeastern Indian Ocean cools in following months. On intraseasonal time scales convection-suppressing phase of Madden-Julian oscillation (MJO) propagates from west to east in May/June of IOD year, and easterlies associated with this phase of MJO causes further shoaling of thermocline in southeastern Indian Ocean, through anomalous upwelling Kelvin wave. All these three mechanisms appear to be involved in initiating IOD event in 2006. On the other hand, except the strengthening/weakening of ITCZ, all other mechanisms are involved in activation of 2003 IOD event. Activation of 2007 IOD event was due to propagation of convection-suppressing MJO in May/June and strengthening of mean winds along Sumatra/Java coast from March to June through changes in convection. The IOD events matured into full-fledged events in the following months after activation, by surface heat fluxes, vertical and horizontal advection of cool waters supported by local along-shore upwelling favorable winds and remote equatorial easterly wind anomalies through excitation of upwelling Kelvin waves. Propagating MJO signals in the tropical Indian Ocean brings significant changes in evolution of IOD events on MJO time scales. Termination of 2003 and 2007 IOD events is achieved by strong convection-enhancing MJOs propagating from west to east in the tropical Indian Ocean which deepen the thermocline in the southeastern equatorial Indian Ocean. IOD event in 2006 was terminated by seasonal reversal of monsoon winds along Sumatra/Java coasts which stops the local coastal upwelling.     

Transient climate change scenario simulation of the Mediterranean Sea for the twenty-first century using a high-resolution ocean circulation model

A scenario of the Mediterranean Sea is performed for the twenty-first century based on an ocean modelling approach. A climate change IPCC-A2 scenario run with an atmosphere regional climate model is used to force a Mediterranean Sea high-resolution ocean model over the 1960–2099 period. For comparison, a control simulation as long as the scenario has also been carried out under present climate fluxes. This control run shows air–sea fluxes in agreement with observations, stable temperature and salinity characteristics and a realistic thermohaline circulation simulating the different intermediate and deep water masses described in the literature. During the scenario, warming and saltening are simulated for the surface (+3.1°C and + 0.48 psu for the Mediterranean Sea at the end of the twenty-first century) and for the deeper layers (+1.5°C and + 0.23 psu on average). These simulated trends are in agreement with observed trends for the Mediterranean Sea over the last decades. In addition, the Mediterranean thermohaline circulation (MTHC) is strongly weakened at the end of the twenty-first century. This behaviour is mainly due to the decrease in surface density and so the decrease in winter deep-water formation. At the end of the twenty-first century, the MTHC weakening can be evaluated as −40% for the intermediate waters and −80% for the deep circulation with respect to present-climate conditions. The characteristics of the Mediterranean Outflow Waters flowing into the Atlantic Ocean are also strongly influenced during the scenario.     

Satellite monitoring of pollution in the Russian sector of the Azov and Black Seas in 2003–2007

The results of satellite monitoring of pollution in the Russian sector of the Azov-Black Sea basin in 2003–2007 are considered. Within the framework of this work, a technology of monitoring the state and pollution of the water environment from satellite information received during this period from Russian and foreign satellites has been developed. With this technology, the coastal pollution parameters and hydrometeorological characteristics of the water environment in the area of observation were mapped operationally; 14 types of different satellite information products were issued daily; and the results were generalized over 3 days, ten days, a month, and a period of observation. Long-term satellite monitoring makes it possible to determine and analyze typical situations of pollution distribution in the coastal waters and to detect new circulation elements that transport pollutants, thus purifying the water environment. For example, for the first time, it was found from satellite data that the contribution of a small-scale circulation of waters of the Russian sector of the Black Sea to the transport and distribution of pollutants is commensurable with the contribution of the Main Black Sea Current and coastal anticyclonic eddies. The regularities in the dynamics of pollution distribution promote the increased reliability of charting of the environmental situation, including the prediction of dynamics of pollution spreading.     

两次不同ENSO背景下云南冬季极端冷事件的成因分析

2008年初和2016年初分别经历了一次中等强度以上的La Ni?a和El Ni?o事件,在不同的厄尔尼诺-南方涛动（El Ni?o/Southern Oscillation,ENSO）背景下,云南均发生了低温雨雪冰冻天气。本文利用大气环流、海表温度、云南124个观测站逐月温度等资料,通过多种统计方法探讨了不同ENSO背景下极端冷事件发生的原因。结果表明：1)2008年初和2016年初云南冬季极端冷事件在2月表现更明显。2）不同ENSO背景下,2月大气环流和云南气温变化差异较大。La Ni?a(El Ni?o)年西伯利亚高压加强（减弱）,位势高度场北（西）高南（东）低,西太平洋副高偏弱（强）,菲律宾异常（反）气旋西北侧异常北（南）风加强,东亚冬季风偏强（弱）,云南东部气温偏低（高）。3)2008年和2016年的东北太平洋大气环流异常对赤道中东太平洋海温异常均有响应,同时2008年赤道中东太平洋冷海温作用激发的菲律宾气旋西部偏北气流对东亚冬季风的加强和向南活动有重要影响,而2016年赤道中东太平洋暖海温对菲律宾地区环流变化的影响并不显著。4）北极涛动（Arctic Oscillation...     

A Model Simulation of Future Oceanic Conditions along the British Columbia Continental Shelf. Part II: Results and Analyses

An ocean circulation model for the British Columbia continental shelf is run with future initial conditions and forcing fields downscaled from the North American Regional Climate Change Assessment Program archive. Average seasonal sea surface temperatures for the period 2065 to 2078 are projected to increase by between 0.5° and 2.0°C with respect to analogous averages from 1995 to 2008. Seasonal sea surface salinities are projected to decrease by as much as 2.0 over the same period, though there are some regions where and periods when small increases are projected. Though stronger winter winds result in larger Haida Eddies, slightly stronger summer winds along the western Vancouver Island shelf do not result in appreciable changes to either the cross-shelf upwelling or to the magnitude of Juan de Fuca Eddies or the timing of their formation. However, increased flows are projected in some seasons for the Rose Spit, Middle Bank, and Goose Island Bank eddies. More precipitation over the watersheds emptying into coastal waters produces larger freshwater discharges and, in particular, a stronger estuarine flow in Juan de Fuca Strait and a stronger Vancouver Island Coastal Current. Generally increasing winds and decreasing density mean that the winter minus summer range of sea surface heights is projected to increase all along the coast.     

CO<Subscript>2</Subscript> dynamics on the shelf of the East Siberian Sea

Expedition data obtained in the coastal-shelf zone of the East Siberian Sea in September 2003, 2004, and 2008 are generalized. Studies of carbonate system in water and CO₂ fluxes between ocean and atmosphere in this region confirmed that it was reasonable to divide the water area studied into two biogeochemical provinces and that the ecosystem of its coastal part is mainly of a heterotrophic nature. In different years, the extent of water supersaturation in carbon dioxide in the East Siberian Sea and the area of the CO₂ release significantly changed. Geographic localization of the atmosphere action centers over the Arctic and their intensity were main determining factors; that told both on the formation of a basic character of the atmospheric and hydrological processes and on the dynamics of the CO₂ exchange between water and air.     

The Siberian High and climate change over middle to high latitude Asia

Summary The Siberian High is the most important atmospheric centre of action in Eurasia during the winter months. Here its variability and relationship with temperature and precipitation is investigated for the period 1922 to 2000. The pronounced weakening of the Siberian High during the last ∼ 20 years is its most remarkable feature. Mean temperature, averaged over middle to high latitude Asia (30° E–140° E, 30° N–70° N), is correlated with the Siberian High central intensity (SHCI) with correlation coefficient of − 0.58 (1922–1999), and for precipitation, the correlation coefficient is − 0.44 (1922–1998). Taking the Arctic Oscillation (AO), the SHCI, the Eurasian teleconnection pattern (EU), and the Southern Oscillation (SO) index into account, 72 percent of the variance in temperature can be explained for the period 1949–1997 (for precipitation the variance is 26 percent), with the AO alone explaining 30 percent of the variance, and the Siberian High contributing 24 percent. The precipitation variance explained by the Siberian High is only 9.8 percent of the total. Received January 2, 2001 Revised November 24, 2001     

Possible contribution of Arctic sea ice decline to intense warming over Siberia in June

西伯利亚地区异常的升温可能会给生态系统带来灾难性的影响.本文从气候角度分析西伯利亚地区初夏升温的特征以及北极海冰减小的可能贡献.观测和再分析资料表明,1979-2020年间西伯利亚地区6月地表气温有很强的升温趋势(0.9℃/10年),明显高于同纬度地区平均的升温趋势(0.46℃/10年).升温从地表延伸至300hPa左...     

从2011/2012和2015/2016年冬季大气环流异常看北极海冰以及前期夏季北极大气环流异常的作用

利用美国NCEP/NCAR、欧洲中心ERA-Interim再分析资料,以及英国哈得来中心海冰密集度资料,通过诊断分析和数值模拟试验,研究了2011/2012和2015/2016年两个冬季大气环流异常的主要特征和可能原因。结果表明,尽管热带太平洋海温背景截然不同（分别为弱的拉尼娜事件和强厄尔尼诺事件）,但这两个冬季西伯利亚高压均异常偏强,自1979年以来其强度分别排第1和第5位。前期秋季北极海冰异常偏少是导致这两个冬季西伯利亚高压偏强的主要原因。更为重要的是,前期夏季北冰洋表面反气旋风场,以及其上空对流层中、低层平均气温偏高,加强了北极海冰偏少对冬季大气变率的负反馈,进一步促进了西伯利亚高压的加强,从而有利于东亚地区冬季阶段性强严寒的出现。因此,夏季北极大气环流的动力和热力状态不仅影响夏、秋季北极海冰,而且对海冰偏少影响亚洲冬季气候变率有重要调节作用。2015/2016年冬季强厄尔尼诺事件并不能掩盖来自北极海冰和大气环流的影响。      

An unusual anomaly of ice conditions in the eastern seas of the Russian Arctic and in the arctic basin in summer 2007

It is demonstrated that during the whole annual cycle of ice cover evolution in 2006–2007 in the eastern seas of the Russian Arctic and in the Arctic basin, the factors whose effect led to the formation of an extremely large anomaly of ice conditions in summer 2007 were revealed. By the end of summer, the ice melted on the huge water area of 3500000 km². In September, the ice edge between the meridians of 150° E-170° W reached the parallel of 85° N. The estimates of the open water area being formed due to the ice melting and its drifting edge shift are given.     

Wind effects on the upwelling variability in the coastal zone of Primorye (the northwest of the Sea of Japan)

The variability of upwelling events in the coastal zone of Primorye in the northwestern part of the Sea of Japan is studied using the SeaWinds/QuikSCAT scatterometer wind data for the period of 1999-2009. The intensity of upwelling is defined by the wind-induced offshore Ekman transport (the upwelling index). It was found that along the southern coast of Primorye upwelling events occur from September to March (April). The winter monsoon period is the most favorable for the upwelling development. In the eastern part of the coastal zone of Primorye upwelling is observed in transitional seasons between winter and summer monsoon (February-April and September-October). On the northeastern coast of Primorye, the upwelling season is from August to October (November). The common feature of the coastal zone of Primorye is a wind-driven upwelling in autumn (September-October). The interannual variability of winter upwelling along the southern coast of Primorye is related to the East Asia high pressure center (the Siberian High). The upwelling intensifies in the years with positive air pressure anomalies in the Siberian High and weakens in the years with negative anomalies.     

Simulation of the Atlantic meridional overturning circulation in an atmosphere–ocean global coupled model. Part I: a mechanism governing the variability of ocean convection in a preindustrial experiment

A preindustrial climate experiment was conducted with the third version of the CNRM global atmosphere–ocean–sea ice coupled model (CNRM-CM3) for the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4). This experiment is used to investigate the main physical processes involved in the variability of the North Atlantic ocean convection and the induced variability of the Atlantic meridional overturning circulation (MOC). Three ocean convection sites are simulated, in the Labrador, Irminger and Greenland–Iceland–Norwegian (GIN) Seas in agreement with observations. A mechanism linking the variability of the Arctic sea ice cover and convection in the GIN Seas is highlighted. Contrary to previous suggested mechanisms, in CNRM-CM3 the latter is not modulated by the variability of freshwater export through Fram Strait. Instead, the variability of convection is mainly driven by the variability of the sea ice edge position in the Greenland Sea. In this area, the surface freshwater balance is dominated by the freshwater input due to the melting of sea ice. The ice edge position is modulated either by northwestward geostrophic current anomalies or by an intensification of northerly winds. In the model, stronger than average northerly winds force simultaneous intense convective events in the Irminger and GIN Seas. Convection interacts with the thermohaline circulation on timescales of 5–10 years, which translates into MOC anomalies propagating southward from the convection sites.     

Anatomy of the synoptic conditions occurring over southern Greece during the second half of the 20th century. Part I. Winter and summer

Summary ?In this study a methodology for grouping seasonal circulation types occurring over an area is introduced. This procedure combines the surface air mass characteristics affecting the area with the synoptic conditions prevailing over it. Factor Analysis and Cluster Analysis are used to derive the circulation types, based on surface meteorological data and surface pressure grid data. The methods are applied to Athens, Greece, using data over the period 1954–1999 for winter (December, January, February) and summer (June, July, August) seasons. The daily circulation types are analyzed at surface level and their temporal evolution is examined via transition matrices. 315 grid points are used covering the area between 25° N to 60° N and 10° W to 40° E. This analysis derives 8 circulation types for the winter and 4 for the summer. A reduction in cyclonic activity and an increase in anticyclonic activity in the Central Mediterranean are detected in the late 1980s and early 1990s during the winter period. During summer the etesian winds and the local flows are dominant over Athens. Received February 20, 2002; accepted January 9, 2003 Published online May 26, 2003     

Variability of Fram Strait sea ice export: causes, impacts and feedbacks in a coupled climate model

Analyses of a 500-year control integration of the global coupled atmosphere–sea ice–ocean model ECHAM5.0/MPI-OM show a high variability in the ice export through Fram Strait on interannual to decadal timescales. This variability is mainly determined by variations in the sea level pressure gradient across Fram Strait and thus geostrophic wind stress. Ice thickness anomalies, formed at the Siberian coast and in the Chukchi Sea, propagate across the Arctic to Fram Strait and contribute to the variability of the ice export on a timescale of about 9 years. Large anomalies of the ice export through Fram Strait cause fresh water signals, which reach the Labrador Sea after 1–2 years and lead to significant changes in the deep convection. The associated anomalies in ice cover and ocean heat release have a significant impact on air temperature in the Labrador Sea and on the large-scale atmospheric circulation. This affects the sea ice transport and distribution in the Arctic again. Sensitivity studies, simulating the effect of large ice exports through Fram Strait, show that the isolated effect of a prescribed ice/fresh water anomaly is very important for the climate variability in the Labrador Sea. Thus, the ice export through Fram Strait can be used for predictability of Labrador Sea climate up to 2 years in advance.     

秋季北极海冰对EP型ENSO的非线性响应

利用1961—2015年Hadley中心逐月海表温度资料、海冰密集度资料以及NCEP/NCAR再分析资料,探讨了秋季北极海冰对于EP型ENSO事件的异常响应,并进一步研究了这种异常响应的可能原因。结果表明,秋季北极海冰对EP型ENSO的响应具有非线性,特别是喀拉海海域(60°～90°E,70°～80°N)海冰无论在EP型El Ni?o或是La Ni?a位相,均表现为显著的负异常。进一步研究发现,不同ENSO位相造成该区域海冰异常偏少的机制有明显不同。EP型El Ni?o年秋季菲律宾附近海域对流活动被抑制,所激发的经向波列在高纬地区形成异常反气旋环流,其南风分量向喀拉海输送暖平流,造成海冰异常偏少。而EP型La Ni?a年喀拉海海域则主要受到来自大西洋开放性海域西风异常的影响,合成结果和个例年均显示EP型La Ni?a年秋季北大西洋上空存在一个显著的西风急流中心,有利于北大西洋开放性海域较暖海水向下游输送,进而影响喀拉海海冰。这些结果表明,热带外地区大气环流场对EP型ENSO的非线性响应导致了喀拉海海冰对EP型ENSO事件的响应也表现出明显的非线性。     

An instability theory of air-sea interaction for coastal upwelling

A surface wind (seabreeze), thermally generated by differential sea surface temperature, is introduced to Gill-Clarke’s model (1974) through wind stress for investigating the effects of Seabreeze on coastal upwelling. A coupled air-sea system is treated as an eigenvalue problem. The solutions show that the thermally forced local winds break down the coastal Kelvin wave into three parts: small-scale (L<100 km) growing and stationary modes, mesoscale (100 km200 km) coastal Kelvin modes. The consistency of the length scale between the most growing mode predicted by this model and the observed cold/warm alternation pattern of surface water near the Peruvian Coast (around 15oS) implies that Seabreeze may play some role in coastal upwelling.     

Variability of the Somali Current and eddies during the southwest monsoon regimes

The meso-scale eddies and currents in the Arabian Sea are analyzed using different satellite observations, Simple Oceanic Data Assimilation (SODA) reanalysis, and Ocean Reanalysis System 4 (ORAS4) from 1993 to 2016 to investigate the impacts of Southwest (SW) Monsoon strength on Somali Current (SC) mesoscale circulations such as the Great Whirl (GW), the Socotra Eddy (SE), the Southern Gyre (SG), and smaller eddies. Increased Ekman pumping during stronger SW monsoons strengthens coastal upwelling along the Somali coast. The Arabian Sea basin-wide anticyclonic circulation and presence of the GW form mesoscale circulation patterns favourable to advection of upwelled waters eastward into the central Arabian Sea. In September, after the SW monsoon winds reach peak strength in July and August, a higher number of discrete anticyclonic eddies with higher ( > 20 cm) sea surface height anomalies develop in strong and normal intensity SW monsoon seasons than weaker SW monsoon seasons.