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Numerical experiments using a regional ocean–atmosphere coupled general circulation model show the influence of Indian Ocean Dipole (IOD) events on the Pacific Ocean through the oceanic channel known as the Indonesian Throughflow (ITF) by isolating the role of the atmospheric bridge. The 2019 Positive IOD and 2016 Negative IOD events can force enhanced and decreased ITF transport through subsurface processes. Currents and sea level anomalies allowed a thorough comparison between 2016 and 2019 IOD events. The upwelling and downwelling Kelvin waves can propagate through the Indonesian seas along the Sumatra–Java island chain, forcing SSHA in the southeastern basin to grow quickly and reach the western Pacific Ocean. The numerical results suggest that the 2016 negative IOD could cause an El Nino-like state and that the 2019 positive IOD could cause a La Nina-like state in the Pacific Ocean.

Initial errors in the tropical Indian Ocean (IO-related initial errors) that are most likely to yield the Spring Prediction Barrier (SPB) for La Nina forecasts are explored by using the CESM model. These initial errors can be classified into two types. Type-1 initial error consists of positive sea temperature errors in the western Indian Ocean and negative sea temperature errors in the eastern Indian Ocean, while the spatial structure of Type-2 initial error is nearly opposite. Both kinds of IO-related initial errors induce positive prediction errors of sea temperature in the Pacific Ocean, leading to under-prediction of La Nina events. Type-1 initial error in the tropical Indian Ocean mainly influences the SSTA in the tropical Pacific Ocean via atmospheric bridge, leading to the development of localized sea temperature errors in the eastern Pacific Ocean. However, for Type-2 initial error, its positive sea temperature errors in the eastern Indian Ocean can induce downwelling error and influence La Nina predictions through an oceanic channel called Indonesian Throughflow. Based on the location of largest SPB-related initial errors, the sensitive area in the tropical Indian Ocean for La Nina predictions is identified. Furthermore, sensitivity experiments show that applying targeted observations in this sensitive area is very useful in decreasing prediction errors of La Nina. Therefore, adopting a targeted observation strategy in the tropical Indian Ocean is a promising approach toward increasing ENSO prediction skill.

Thickness and stratigraphic settings of soils covering slopes potentially control susceptibility to initiation of rainfall-induced shallow landslides due to their local effect on slope hydrological response. Notwithstanding the relevance of the assessment of hazard to shallow landsliding at a distributed scale by approaches based on a coupled modelling of slope hydrological response and slope stability, the spatial variability of soil thickness and stratigraphic settings are factors poorly considered in the literature. Under these premises, this paper advances the well-known case study of rainfall-induced shallow landslides involving ash-fall pyroclastic soils covering the peri-Vesuvian mountains (Campania, southern Italy). In such a unique geomorphological setting, the soil covering is formed by alternating loose ash-fall pyroclastic deposits and paleosols, with high contrasts in hydraulic conductivity and total thickness decreasing as the slope angle increases, thus leading to the establishment of lateral flow and an increase of pore water pressure in localised sectors of the slope where soil horizon thickness is less. In particular, we investigate the effects, on hillslope hydrological regime and slope stability, of irregular bedrock topography, spatial variability of soil thickness and vertical hydraulic heterogeneity of soil horizons, by using a coupled three-dimensional hydrological and a probabilistic infinite slope stability model. The modelling is applied on a sample mountain catchment, located on Sarno Mountains (Campania, southern Italy), and calibrated using physics-based rainfall thresholds derived from the literature. The results obtained under five simulated constant rainfall intensities (2.5, 5, 10, 20 and 40 mm h−1) show an increase of soil pressure head and major failure probability corresponding to stratigraphic and morphological discontinuities, where a soil thickness reduction occurs. The outcomes obtained from modelling match the hypothesis of the formation of lateral throughflow due to the effect of intense rainfall, which leads to the increase of soil water pressure head and water content, up to values of near-saturation, in narrow zones of the slope, such as those of downslope reduction of total soil thickness and pinching out of soil horizons. The approach proposed can be conceived as a further advance in the comprehension of slope hydrological processes at a detailed scale and their effects on slope stability under given rainfall and antecedent soil hydrological conditions, therefore in predicting the most susceptible areas to initiation of rainfall-induced shallow landslides and the related I-D rainfall thresholds. Results obtained demonstrate the occurrence of a slope hydrological response depending on the spatial variability of soil thickness and leading to focus slope instability in specific slope sectors. The approach proposed is conceived to be potentially exportable to other slope environments for which a spatial modelling of soil thickness would be possible.

The South China Sea (SCS) experienced a significant reduction in warming rate (− 0.01 °C decade−1, $$p>0.10$$ p > 0.10 ) during 1999–2010 following an accelerated and unprecedented warming (+ 0.15 °C decade−1, $$p p < 0.01 ) in the last three decades (1970–1998). However, most global climate models of the CMIP5 RCP4.5 scenario failed to capture this SCS warming slowdown. In this study, we identify two drivers through numerical simulations by using a regional high-resolution, ocean–atmosphere coupled climate model: the major variance (75%) in the sea surface warming slowdown could be explained by the strengthened winter monsoon over the SCS, and the minor variance (12%) could be explained by the changes in the upper ocean circulations. The winter monsoon over the SCS is likely linked to the La Niña-like SST pattern in the eastern tropical Pacific, which strengthens the Walker circulation and results in anticyclonic circulation over the northwestern Pacific. This enhanced winter monsoon is the atmospheric driver that slows down the SCS basin-scale warming, while the largest reduction of the warming rate occurs in the northern SCS that can be attributed to the oceanic throughflow via the Luzon Strait. These findings could have important implications for future climate projections over the SCS and adjacent oceans.

In the current article, the impact of varying gravitational field and flow on the beginning of nanofluid convective instability in a permeable medium layer is studied numerically utilizing Galerkin technique. The permeable layer is directed to a regular vertical throughflow and irregular descendent gravitational force which changes with the length from the layer. The influences of three types of gravitational force inconsistency: (a) linear, (b) parabolic, and (c) exponential are examined on the formation of nanofluid convective instability with vanish nanoparticle flux condition at the plates. Results proved that the throughflow factor $$Q$$ and gravity inconsistency factor $$\delta$$ suspend the start of convective instability, while the nanoparticle Rayleigh-Darcy number $$R_{{{\text{np}}}}$$ and the altered diffusivity ratio $${\text{NA}}_{{{\text{nf}}}}$$ quick the start of nanofluid convection. The measurement of the convective cells diminishes with $$R_{{{\text{np}}}}$$ and $${\text{NA}}_{{{\text{nf}}}}$$ , while $$Q$$ , $$\delta$$ and the altered nanofluid Lewis number $${\text{Le}}_{{{\text{nf}}}}$$ have duel effects on the measurement of convective cells.

Sea straits are known for important sites to modify water-mass properties and transport nutrients through vigorous vertical mixing. The first microstructure measurements ever taken in the Tsugaru Strait, between the Sea of Japan and the Northwest Pacific Ocean, showed elevated turbulent mixing. The turbulent energy dissipation rate was especially enhanced to O(10−6 W kg−1) via an internal hydraulic jump when the throughflow passed over an abrupt sill. Beyond the sill, the associated vertical eddy diffusivity reached O(10−2 m2 s−1) and the vertical turbulent nitrate flux below the subsurface chlorophyll-a maximum layer was estimated to reach 1 mmolN m−2 day−1, which could elevate the new production of phytoplankton within the layer. Large vertical velocities exceeding 0.1 m s−1 were also observed near the seafloor of the sill where the flow was hydraulically controlled. A simple advection–diffusion model suggested that the energy dissipation rate of O(10−5 W kg−1) was necessary to reproduce the observed modification of subsurface salinity maximum across the strait. Upwelling and/or vertical straining associated with the internal hydraulic jump is also believed to play an important role in the water-mass modification in the strait and could enhance new primary production for a wide area downstream.

A long-term increasing trend in the transport of the Japan Sea Throughflow is observed from sea-level differences across the Tsushima Strait. Tidal gauge observations show sea level at Hakata, Japan, increasing at a higher rate than that at Busan, Korea. Numerical modeling results suggest that this increasing trend is forced by a northward shift in the Kuroshio axis. As the Kuroshio axis moves northward, sea level along the southern coast of Japan increases. The signal then propagates anticyclonically along the coast as topographic Rossby waves and Kelvin waves, raising sea level and, thus, increasing transport through the Tsushima Strait.

Helium isotopes in the ocean are very useful tracers of hydrothermal input and deep-sea circulation. Unlike labile trace elements, noble gases are inert and do not react with other substances in the water column. Previous studies in the Indian Ocean showed that helium isotopes in the region were discharged mainly from the central Indian midocean ridge, convergent boundaries, and the Pacific Ocean via currents that flow through the Indonesian archipelago. These Indonesian waters then exit out as the Indonesian Throughflow (ITF) into the Indian Ocean through shallow sills. The ITF plays a significant role in global climate, because it serves as the main pathway of thermocline waters between the Pacific Ocean and Indian Ocean. We present new helium isotope data from International Indian Ocean Expedition (IIOE-2) at the east Indian Ocean in December 2018. Helium isotopes were measured using a Noble Gas Mass Spectrometer at the Atmosphere and Ocean Research Institute, The University of Tokyo. We compare our data with those from previous expeditions and discuss the source and distribution of helium isotopes near Java. Waters with high excess 3He from the ITF were observed at 1000 m. Application of two-components mixing model enabled us to estimate ITF fraction in the observed area and to clarify the ITF flow in the deep layer. Moreover, flow rate of the deep ITF from Savu sill to Indian Ocean was estimated to be ~ 0.8–1.6 Sv. Based on stations near the Java coast, there could be a deep current or hydrothermal source at 3000 m that advects water enriched in 3He southwards along the Java Island.

The onset of double-diffusive convection in an electrically conducting fluid-saturated porous layer is studied. The convective flow in the porous medium is induced by horizontal temperature and concentration gradients with net horizontal mass throughflow. The effect of magnetic field on the instability of convection is taken into consideration. The stability of the steady-state solution is investigated in two different approaches, namely the linear instability analysis and nonlinear stability analysis. The nonlinear stability analysis is performed by constructing the energy functional. The eigenvalue problems which are derived from the stability analyses are numerically integrated using the shooting and Runge–Kutta methods. The variation in the critical thermal Rayleigh number against each flow governing parameter is shown graphically. It is observed that Hartman number $$Ha^{2}$$ delays the onset of convection to commence and helps to reduce the region of subcritical instabilities. When the solute is concentrated at lower boundary of the porous layer, the onset of convection is in the form of stationary modes, but it switches to oscillatory mode of convection when the solute is concentrated at upper boundary. Interestingly, Hartman number $$Ha^{2}$$ plays an important role in delaying this transition from stationary mode to oscillatory mode of convection.

A linear stability analysis for the onset of mixed convection in a saturated porous medium through an absolute instability of both two- and three-dimensional disturbances is performed. Relevant control parameters associated with the inclined temperature gradient and the vertical throughflow are the vertical and horizontal Rayleigh numbers, $$R_{\mathrm{v}}$$ and $$R_{\mathrm{h}}$$, and the vertical Peclet number, $$Q_{\mathrm{v}}$$, respectively. This work extends previous studies on the very same problem in two fronts. For two-dimensional disturbances, the present results do not agree with the literature for a few of the parametric conditions reported. This is caused by the collision of the convectively unstable downstream propagating branch with multiple upstream propagating branches, which generates several saddle points and, hence, makes the identification of the correct pinching point more difficult. In other words, literature results are all saddle points but not always pinching points. For three-dimensional disturbances, this issue is not present and the current results agree with the literature. On the other hand, due to the inherent difficulties associated with a three-dimensional absolute instability analysis, literature results have only been able to report the group velocities at the onset of convective instability. When their real parts are zero, transition occurs directly from stable to absolutely unstable. Otherwise, transition occurs from stable to convectively unstable first and nothing can be said about the onset of absolute instability. In this work, a novel technique recently developed by the authors allowed the identification of the onset of absolute instability under all parametric conditions investigated in the literature, extending earlier results. Doing so confirmed the dichotomy already observed in these earlier studies, i.e., the onset of absolute instability for two- and three-dimensional longitudinal modes indeed differs.

The onset of convection in a porous layer saturated by a power-law fluid is here investigated. The walls are considered to be isothermal, isobaric and permeable in such a way that a vertical throughflow is described. The threshold for a buoyancy-driven cellular flow is investigated by means of a linear stability analysis. This study consists in introducing disturbances with small amplitude. The disturbances are plane waves, i.e. a normal modes stability analysis of the basic stationary solution is performed. The resulting problem is an ordinary differential equation eigenvalue problem which is solved numerically by coupling the Runge–Kutta method with the shooting method. Results are presented in the form of marginal stability curves and their critical points representing the values of the control parameters such that the growth rate of the disturbances is zero. It is found that, among roll disturbances, the most unstable modes are stationary and uniform with infinite wavelength. For this reason, an asymptotic analysis for vanishing wave numbers is carried out. The results of this asymptotic analysis are obtained analytically displaying a very good agreement with the numerical solution. It is found that vertical throughflow plays a destabilising role for pseudoplastic fluids and a stabilising role for dilatant fluids.

Double-diffusive convective instability of horizontal throughflow in a power-law fluid saturated porous layer is investigated. The boundaries of this horizontal porous layer are impermeable, isothermal and isosolutal. The generalized Darcy’s equation for power-law fluid is employed in the momentum balance, along with Oberbeck–Boussinesq approximation for buoyancy effect in the system. It is considered that the viscous dissipation is non-negligible. The basic temperature and concentration profiles for the considered horizontal throughflow are determined analytically, and the linear stability analysis is performed on this basic solution. The eigenvalue problem is solved numerically using bvp4c in MATLAB. The conditions for the onset of instability of base flow in terms of critical Rayleigh number and the corresponding wave number are obtained. It is found that critical values are affected by the flow governing parameters such as the Peclet number (Pe), power-law index (n), viscous dissipation (Ge), angle of inclination $$(\alpha )$$ , buoyancy ratio (N) and Lewis number (Le). For the considered range of these parameter values, the instability of the basic flow is discussed for the convective rolls. It is observed that instability of any general convective roll lies between that of the longitudinal and transverse rolls. Also, the effect of viscous dissipation on the onset of instability for both the longitudinal and transverse rolls is discussed in detail. This source of heating inside the porous layer increases the thermal instability of base flow. Further, the asymptotic analysis for vanishingly small Peclet number is presented as $$Pe = 0$$ is a singular point. The boundary between the stationary and the oscillatory instabilities is given using the buoyancy ratio parameter and the Lewis number in this limiting case of $$Pe\rightarrow 0$$ .

The south Indian Ocean has shown an unprecedented sea-level rise during the early 21st Century. Sea-level rise in the south Indian Ocean is found to be 37% quicker than the global mean sea-level during 2000–2015. Observational datasets and long-term proxy records identify Pacific origin of the south Indian Ocean sea-level rise. Our results indicate that co-evolution of the cold phase of Pacific decadal oscillation (PDO) and prolonged La Nina-like condition enhances the equatorial Pacific easterlies. Stronger in-phase association of these major Pacific climate modes and equatorial Pacific easterlies enhances the Indonesian throughflow (ITF), transporting fresh and warm water anomalies from western tropical Pacific into the south Indian Ocean. As a result, south Indian Ocean sea-level rise has accelerated more than the global, with 40% contribution from the halosteric sea level primarily through the ITF transport and a secondary from the local processes during 2000–2015. The co-evolution of PDO and the south Indian Ocean sea level is also evident from the long-term proxy records indicating that the association is part of an internal mode of variability modulated on decadal time-scales. The finding from the study cautions that accelerated heat and freshwater intrusion from the western Pacific with the co-evolution of PDO and La Nina-like condition may lead to the accelerated sea-level rise and marine heat waves in the south Indian Ocean imposing threats to the life of coral reefs and marine ecosystems.

A high-resolution Arctic Ocean-Finite Volume Community Ocean Model (AO-FVCOM) and observational current data from 14 mooring stations in Bering Strait and surrounding regions between 1990 and 2015 were used to study the seasonal and in-terannual variability of Bering Strait throughflow (BST). AO-FVCOM represented the BST with a climatological northward flux of 1.06Sv, which was close to the observational mean of 0.94 + 0.26Sv. From the model results, the strongest volume flux was in summer, approximately 45% larger than that in winter. Interannual variability of BST was also indicated in the model results, and the maximum and minimum annual mean transports are in 2007 and 2012, respectively. AO-FVCOM showed larger differences from the observations in 2000, 2002, and 2015 than in other years, which may be related to the limitation of atmospheric forcing for the model. According to the driving mechanisms of BST, sea level difference (SLD) across the strait dominates the northward volume transport, and local wind is also important in forcing the seasonal variability of the BST and SLD patterns to change the BST indirectly.

Using GFDL CM2p1 (Geophysical Fluid Dynamics Laboratory Climate Model, version 2p1), the effects of initial sea temperature errors on the predictability of the Indian Ocean Dipole (IOD) are explored. When initial temperature errors are superimposed on the tropical Indian Ocean, a winter predictability barrier (WPB) and a summer predictability barrier (SPB) exist in IOD predictions. The existence of the WPB has a close relation with El Ni?o-Southern Oscillation (ENSO) in the winter of the growing phase of positive IOD events. That is, when ENSO exists in winter, no WPB appears in IOD predictions, and vice versa. In contrast, there is no inherent connection between the existence of the SPB and ENSO. Only the dominant spatial pattern of SPB-related initial errors is studied in this paper, which presents a significant west-east dipole pattern in the tropical Indian Ocean and is similar to that of WPB-related initial errors in previous studies. The SPB-related initial errors superimposed on the tropical Indian Ocean induce the sea surface temperature (SST) and wind anomalies in the tropical Pacific Ocean. Then, under the interaction between the Indian and Pacific oceans through the atmospheric bridge and Indonesian Throughflow, a west-east dipole pattern of SST errors appears in summer, which is further strengthened under the Bjerknes feedback and yields a significant SPB.

Besides the Indonesian throughflow (ITF), the South China Sea throughflow (SCSTF) also contributes to the water transport from the Pacific to the Indian Ocean. However, this South China Sea (SCS) branch at the Karimata Strait is poorly observed until 2007, even though its importance has been suggested by numerical studies for decades. In this paper, we review the nearly 10-year field measurement in the Karimata Strait by the execution of the projects of “SCS-Indonesian Seas Transport/Exchange (SITE) and Impacts on Seasonal Fish Migration” and “The Transport, Internal Waves and Mixing in the Indonesian Throughflow regions (TIMIT) and Impacts on Marine Ecosystem”, which extend the observations from the western Indonesian seas to the east to include the main channels of the ITF, is introduced. Some major achievements from these projects are summarized.

Based on the high-resolution Eulerian fields of an ocean general circulation model simulation, the heat contribution of the Indonesian throughflow (ITF) to the Indian Ocean is estimated by Lagrangian tracing method. The heat transport of each particle of ITF waters is calculated by tracing temperature change along the trajectory until the particle exits the Indian Ocean. The simulation reveals that the ITF waters flow westward and branch near Madagascar, further showing the ITF waters are redistributed in both northern and southern Indian Ocean. Heat budget analysis indicates that the ITF waters gain 0.41 PW (Petawatts, 1015 W) in the northern Indian Ocean and lose 0.56 PW in the southern Indian Ocean, respectively. As a result, the ITF waters warm the whole Indian Ocean basin with only 0.15 PW, which shows an “insignificant” role of ITF on the Indian Ocean because of the heat exchange compensation between northern and southern Indian Ocean. Furthermore, the tracing pathways show that the ITF waters mainly flow out the Indian Ocean at both sides of the basin via Agulhas Current and Leeuwin Current. About 89% of the ITF waters leave along western boundary and the rest 11% along eastern boundary. Compared to seeding section, 0.10 PW and 0.05 PW are released to the Indian Ocean, respectively.

So far, large uncertainties of the Indonesian throughflow (ITF) reside in the eastern Indonesian seas, such as the Maluku Sea and the Halmahera Sea. In this study, the water sources of the Maluku Sea and the Halmahera Sea are diagnosed at seasonal and interannual timescales and at different vertical layers, using the state-of-the-art simulations of the Ocean General Circulation Model (OGCM) for Earth Simulator (OFES). Asian monsoon leaves clear seasonal footprints on the eastern Indonesian seas. Consequently, the subsurface waters (around 24.5σθ and at ~150 m) in both the Maluku Sea and the Halmahera Sea stem from the South Pacific (SP) during winter monsoon, but during summer monsoon the Maluku Sea is from the North Pacific (NP), and the Halmahera Sea is a mixture of waters originating from the NP and the SP. The monsoon impact decreases with depth, so that in the Maluku Sea, the intermediate water (around 26.8σθ and at ~480 m) is always from the northern Banda Sea and the Halmahera Sea water is mainly from the SP in winter and the Banda Sea in summer. The deep waters (around 27.2σθ and at ~1 040 m) in both seas are from the SP, with weak seasonal variability. At the interannual timescale, the subsurface water in the Maluku Sea originates from the NP/SP during El Nino/La Nina, while the subsurface water in the Halmahera Sea always originates from the SP. Similar to the seasonal variability, the intermediate water in Maluku Sea mainly comes from the Banda Sea and the Halmahera Sea always originates from the SP. The deep waters in both seas are from the SP. Our findings are helpful for drawing a comprehensive picture of the water properties in the Indonesian seas and will contribute to a better understanding of the ocean-atmosphere interaction over the maritime continent.

The Island Rule, derived from the Sverdrup theory, is widely used to estimate and analyze water transport through a strait. Previous studies presented single- or multi-island rules with either lateral or bottom friction. In this paper, an analytical model of wind-driven circulation is assumed based on linear dynamics. Considering both lateral and bottom friction, the analytic solutions of the transport streamfunction around the islands are derived and the volume transport through the channel is presented. The results are similar to those of Wajsowicz, but the frictional constants represent different values. The analytic solution shows that the relationship between the lateral frictional and bottom frictional dissipation is complex in terms of the frictional constants. To understand the interaction between the two friction types, lateral and bottom friction values were randomly chosen on a barotropic beta plane. The result shows an approximately linear relationship between the lateral and bottom friction in consisting of the combined frictional constants. We studied the effect of the channel width on the transport through the channel. The results show that the friction enhances the flow under some widths, which is similar to the flow behavior when only the lateral friction is considered. We also compared the transport through the channel at different depths and founded that the deeper the water, the smaller the transport reduction ratio when the horizontal eddy viscosity coefficient and the bottom drag coefficient remained constants. To further present the combined role of lateral frictional and bottom frictional dissipation, we compared our model with the model of Wajsowicz for two islands, where only the lateral or bottom friction were considered, with different channel widths. The results showed that the effect of the lateral friction is greater than the bottom friction when the channel is narrow, especially in the Munk boundary layer thickness. When the channel is much wider than the Munk boundary layer thickness, the role of the bottom friction is greater than that of the lateral friction. The model was applied to the Indonesian throughflow and yielded a reduction of approximately 20% in the transport.

A 1.5-layer quasi-geostrophic reduced gravity model is used to study the hysteresis of a periodic or leaking western boundary current (WBC) flowing by a gap. When the periods of the WBC variations are much longer than the Rossby adjustment time scales of the circulation in the vicinity of the gap, the Hopf bifurcations during the Reincrease and Re-decrease loops are delayed to produce a new domain of hysteresis of the Reynolds numbers, and the critical Reynolds numbers of the WBC regime transitions change significantly, with the domain of the hysteresis Reynolds number larger for shorter periodic forcing. When the periods of the WBC variations are comparable to those of the Rossby adjustment time scales of the circulation in the vicinity of the gap, the WBC path inside the gap becomes periodic without hysteresis. The intrusion of the WBC into the western basin generally gets smaller as the period decreases. In addition, the partial leakage of the WBC transport through the gap into the western basin is found to have significant impact on the hysteresis loop of the WBC path when the leaked transport is larger than 1/2 of the WBC. Both the intrusion extent and the critical Reynolds numbers of the WBC regime transition are changed, and the larger the throughflow transport, the larger the change.

Deep aquifers typically serve as a key source of drinking water due to their good groundwater quality. Then the identification of deep aquifers recharge areas provides the local administration with a management tool to protect groundwater, through the implementation of legislative measures for the control of pollution sources. However, the location and size of recharge areas of deep aquifers are often difficult to define and generally require a large amount of data. The aim of this paper is to propose a method to identify potential recharge, throughflow and discharge areas of deep aquifers on a regional scale, due to their hydrodynamic features. As the proposed method identifies where deep-aquifer recharge can occur, but not the recharge rate, delimited areas are defined as “potential”. Particularly, the method analyses piezometric level differences between shallow and deep aquifers to understand groundwater flow direction. The areas where groundwater flow is downward are delimited as potential recharge areas of deep aquifers (PRADAs). The method represents a qualitative approach to the identification of PRADAs, because it permits to narrow down large plain areas extension, highlighting where potentially recharge areas are located. Then PRADAs location and shape can be defined effectively, expanding data sets and furthering analyses (hydrogeological reconstruction, hydraulic connectivity, hydro-chemical and isotopic methods…) in the identified areas. The hydrogeological setting investigated by this method is representative of many anthropized and groundwater-demanding plains around the world that require to be protected. Thus, the method represents a suitable approach for PRADAs’ identification in such settings, especially in low-income countries, where resource availability for studies and analyses is scarce. This method was then applied to a plain area of Northwest Italy, and the locations and sizes of potential recharge, throughflow and discharge areas of deep aquifers were identified on a regional scale.

The implication of a uniform horizontal throughflow on the linear stability of buoyancy-driven convection in a vertical fluid layer is studied. The vertical boundaries of the fluid layer are rigid-permeable and holding at uniform but different temperatures. The instability to small-amplitude perturbations is tested by parameterizing the basic stationary flow through the Peclet number and the Prandtl number (representative of liquid mercury, air, water and oil). A modal analysis is performed, and the stability eigenvalue problem is solved numerically using the Chebyshev collocation method. The neutral stability curves are presented, and the critical values of the wave number, wave speed as well as the Grashof number are computed for different prescribed values of the governing parameters. The effect of horizontal throughflow on the stability of fluid flow is found to be dependent on the values of Prandtl number, and their intricacies have been discussed in detail. The results for the case of no throughflow are also highlighted as a particular case from the present study.

The Liulin Spring catchment in Shanxi Province has abundant karst groundwater resources that play a supporting role in the economic and social development of the Lvliang region. Research on the factors controlling the chemical evolution of karst groundwater can be of great significance for the sustainable utilization and effective protection of groundwater resources in the basin. In this study, the major ions of karst groundwater have been studied to identify the hydrogeochemical processes and regional evolution using 29 samples that were collected in 2014 from the recharge area, throughflow area, discharge area and stagnant area of the catchment. The results showed that the temperature and the concentrations of Na+, Ca2+, Mg2+, Cl−, HCO3− and SO42− increased with the increasing distance from the recharge area to the throughflow area, to the discharge area and then to the stagnant area. The chemical composition of karst groundwater in both recharge area and throughflow area was mainly derived from carbonate dissolution, while it was largely controlled by the weathering of silicate minerals in the discharge area, and dominated by the dissolution of both silicates and gypsum in the stagnant areas. The K+, Na+ and Cl− were mainly sourced from the dissolution of salt rock, while the Ca2+, Mg2+, HCO3−, and SO42− were mainly derived from the dissolution of calcite, dolomite, and gypsum. The hydrochemical types of karst groundwater changed from HCO3-Ca • Mg type in the recharge area to HCO3 • SO4-Ca • Mg type in the throughflow area and to HCO3 • SO4-Ca • Na • Mg type in the discharge area, and finally evolved into Cl • HCO3-Na • Ca, Cl • HCO3-Na type and Cl-Na • Ca type in the stagnant area. The results of this study will be useful to effectively guide the sustainable utilization and the integrated planning of water resources in the Liulin Spring catchment.

The Indonesian sea is the only low-latitude pathway connecting two tropical oceans, which plays an important role in the coupled ocean-atmosphere mode in the Indo-Pacific sector. A small change in the sea surface temperature (SST) in the Indonesian sea has a significant influence on the precipitation and air-sea heat flux. During the past 33 years, the SST in the Indonesian sea has indicated a warming trend on the average of 0.19 ± 0.04 decade−1, which is larger than global SST warming trend. Moreover, the warming trend indicates seasonal variations, in which maximum trend occurred during boreal summer season. Investigation on the potential driver for this warming trend, namely, the net surface heat flux, resulted in an opposite trend (cooling trend), while the Ekman pumping and the wind mixing only play a minor role on the SST warming. Here, we proposed the upper layer process associated with an increasing trend in precipitation and decreasing trend in mixed layer depth (MLD) for the SST warming within the Indonesian seas. Shoaling of MLD gives a favorable condition for the surface heat flux to warm the surface ocean. However, shoaling of MLD could not solely explain the total SST warming within the Indonesian seas. The seasonal dependence in the warming trend, highest during boreal summer, was significantly related to the Indo-Pacific climate modes, namely the negative Indian Ocean Dipole (IOD) and La Niña events. Higher warming trend observed in the south of Makassar Strait and in the eastern Indonesian seas, in the vicinity of the Maluku Sea and the northeastern part of the Banda Sea, was significantly associated with the La Niña event. Meanwhile, strong warming trend observed in the Karimata Strait and Java Sea, and in the Flores Sea south of Sulawesi Island seems to be enhanced by the negative IOD event. Our rough quantitative estimate of the possible mechanism leading to the SST warming suggests that other mechanism might be at work in warming the SST within the Indonesian seas. Horizontal heat advection associated with an increasing trend of the heat transport from the Pacific into the Indian Ocean by the Indonesian Throughflow (ITF) might play a role in causing the warming trend within the Indonesian seas. However, to what extend this heat advection could modulate the SST warming is still unresolved in the present study. Further study based on realistic model output as well as long-term observational records is necessary to describe the dynamics underlying the warming trend within the Indonesian seas.

Paleo reconstructions and model simulations have suggested the Bering Strait plays a pivotal role in climate change. However, the contribution of the Bering Strait throughflow to oceanic meridional heat transport (OMHT) is about 100 times smaller than the OMHT at low latitudes in the modern climate and it is generally ignored. Based on model simulations under modern and Last Glacial Maximum (LGM, ~21 ka; ka=thousand years ago) climate conditions, this study highlights the importance of the Bering Strait throughflow to OMHT. The interbasin OMHT induced by the Bering Strait throughflow is estimated by interbasin-intrabasin decomposition. Similar to barotropic-baroclinic-horizontal decomposition, we assume the nonzero net mass transport induced by interbasin throughflows is uniform across the entire section, and the interbasin term is separated to force zero net mass transport for the intrabasin term. Based on interbasinintrabasin decomposition, the contribution of the Bering Strait throughflow is determined as ~0.02 PW (1 PW=10 15 W) under the modern climate, and zero under the LGM climate because the closed Bering Strait blocked interbasin throughflows. The contribution of the Bering Strait throughflow to OMHT is rather small, consistent with previous studies. However, comparisons of OMHT under modern and LGM climate conditions indicate the mean absolute changes are typically 0.05 and 0.20 PW in the North Atlantic and North Pacific, respectively. Thus, the contribution of the Bering Strait throughflow should not be ignored when comparing OMHT under different climate conditions.

Since the end of the twentieth century, the global mean surface temperature (GMST) exhibited a shift from a rapid warming to an unexpected deceleration. An anomalous heat was transported from the Pacific Ocean into the Indian Ocean through a strengthened Indonesian Throughflow during the same period. Within this background, it is essential to continue tracking the fate of the anomalous heat arriving in the Indian Ocean to form a comprehensive picture of the global ocean energy redistribution. The anomalous heat may continue flowing westward into the Atlantic Ocean along the main pathway of the regional ocean currents via the South Equatorial Current (SEC) and Agulhas Current. However, here we examine an alternate pathway: a southward heat transport in conjunction with a weakened SEC, diverting the canonical westward transport. This additional transport pathway causes an increase in heat content in the South Indian Ocean mid-latitudes (15–30°S, 95–110°E), may contribute to the Southern Ocean warming, and intensifies hemispheric asymmetry of oceanic heat content. The heat increase has important climate impacts such as changes to rainfall and increased coral bleaching over the western coast of Australia. The new path discovered here may be an essential route of heat transport linking the tropical Indo-Pacific Ocean and the Southern Ocean in 2003–2012.

The onset of double-diffusive convective instability of a horizontal throughflow induced by viscous dissipation in a fluid-saturated porous layer of high permeability is investigated. The porous layer is infinitely long along the horizontal direction and is bounded by two rigid surfaces maintained at constant, but different solute concentrations. The lower surface is thermally insulated, whereas the upper surface is considered to be isothermal. The Darcy–Brinkman model is adopted for deriving the equations governing flow in the medium, and the Soret effect is considered to persist in the flow. The instability in the base flow is considered to be induced by the non-negligible viscous heating. Disturbances in the base flow are assumed in the form of oblique rolls, where the longitudinal and the transverse rolls are at two extreme inclinations. The disturbance functions are assumed to be of O(1). It is considered that $$Ge\ll 1$$ and $$|Pe|\gg 1$$ , where Ge is the Gebhart number and Pe is the Peclet number. The eigenvalue problem with coupled ordinary differential equations governing the disturbances in the flow is solved numerically using bvp4c in MATLAB. Results obtained depict that the flow is most stable in the Brinkman regime and the longitudinal rolls are the preferred mode of instability. The solute concentration gradient and the Soret parameter have both stabilizing and destabilizing effect on the flow in the medium, when the values of both are either positive or negative. However, they have either monotonically stabilizing or monotonically destabilizing effect on the flow, when the values of both have opposite signs.

An important supplement for ocean observing systems, the Northwestern Tropical Pacific Ocean (NWTPO) mooring array including 15 moorings equipped with Acoustic Doppler Current Profilers (ADCP) devices was developed by the Chinese Academy of Sciences and deployed in 2013. This study assessed the performance of this mooring array in monitoring the intra-seasonal and low-frequency (above 91 days) variability of oceanic currents by conducting targeted observation analyses using an ensemble-based method. Key regions for monitoring intra-seasonal variability of the NWTPO circulation are the equator, Indonesian throughflow (ITF), headstream of the North Equatorial Countercurrent (NECC), and Subtropical Countercurrent (STCC). For monitoring intra-seasonal variability, the range of each mooring is confined to a local scale. Therefore, NWTPO moorings cannot adequately resolve intra-seasonal variability in areas of the ITF, the headstream of the NECC, and STCC due to location constraints of the moorings. For monitoring low-frequency variability of NWTPO circulation, the key regions are the Western Boundary Current (WBC), NECC, and the Equatorial Undercurrent (EUC). NWTPO moorings performed relatively well in monitoring the low-frequency variability, as indicated by the strong background correlations between each of the currents. The NWTPO mooring array plays an important role in monitoring the location and intensity of background currents. Because moorings are costly and require a high-density distribution for optimal performance, understanding the multi-timescale dynamical nature of the NWTPO current system is critical for the deploying future moorings in this region.

Using velocity profiles observed by bottom-mounted ADCPs, we identified strong intraseasonal variability in the Sunda Strait throughflow. This intraseasonal variability, with typical periods of 20–40 days and the strongest energy occurring in the boreal spring, can reverse the Sunda Strait throughflow. Further analysis showed this intraseasonal variability to be closely related to local zonal wind and the sea level gradient along the strait. These observations confirm for the first time the existence of Kelvin-wave-like signals in the Sunda Strait, propagating from the equatorial Indian Ocean. This study also provides new insights into the effects of Kelvin waves on the Sunda Strait throughflow.

The linear stability analysis of vertical throughflow of power law fluid for double-diffusive convection with Soret effect in a porous channel is investigated in this study. The upper and lower boundaries are assumed to be permeable, isothermal and isosolutal. The linear stability of vertical through flow is influenced by the interactions among the non-Newtonian Rayleigh number (Ra), Buoyancy ratio (N), Lewis number (Le), Peclet number (Pe), Soret parameter (Sr) and power law index (n). The results indicate that the Soret parameter has a significant influence on convective instability of power law fluid. It has also been noticed that buoyancy ratio has a dual effect on the instability of fluid flow. Further, it is noticed that the basic temperature and concentration profiles have singularities at $$Pe = 0$$ and $$Le = 1$$ , the convective instability is looked into for the limiting case of $$Pe\rightarrow 0$$ and $$Le \rightarrow 1$$ . For the case of pure thermal convection with no vertical throughflow, the present numerical results coincide with the solution of standard Horton–Rogers–Lapwood problem. The present results for critical Rayleigh number obtained using bvp4c and two-term Galerkin approximation are compared with those available in the literature and are tabulated.

The correlation between transport via the Bering Strait throughflow (BTF) and sea surface salinity (SSS) in the Bering Sea has been examined mainly using an atmosphere–ocean–ice coupled climate model that has an eddy-permitting ocean component. The SSS anomaly in the northwestern Bering Sea is high from winter to spring when the BTF transport anomaly is large in the cold season. Similar features can be seen in an observation dataset and two kinds of ocean data assimilation product. BTF transport is strongly correlated with sea surface height (SSH) in the northeastern Bering Sea, the southwestern Chukchi Sea and the East Siberian Sea. The SSH along the Russian coast in the Arctic Ocean is uncorrelated with the SSH in the Bering Sea, the meaning being that the Arctic SSH affects the BTF and the SSS independently of the SSH in the Bering Sea. The low SSH along the Siberian coast is correlated with easterly wind anomalies over the Laptev Sea and north of the New Siberian Islands. The relationship between the low Siberian-coast SSH and the high SSS in the Bering Sea, however, is not confirmed in 10 years of satellite-derived SSH. Mixed-layer salt budget analysis has revealed that the high SSS anomalies are mainly caused by the increases of horizontal advective salt convergence north of 62.5°N, and by the decreases of sea-ice melting south of 62.5°N, through the strengthening of the near-surface northeastward currents. In the warm season, these two factors fade and the salinization disappears.

With the aid of numerical method, both flow field and its accompanied loss mechanism within the rotating cavity are investigated in detail in the 1st part of the two parts paper. For ease of comparison, rotating cavity is further classified as the rotor-stator cavity case and the rotor-rotor cavity case. Results indicate that flow within both kinds of the cavity act as the inviscid flow except that the flow near walls, neighboring the lower G region and in the vicinity of the rotating orifices. In the regions except such inviscid-flow-dominate domains, the theoretical core rotation factor can be safely used to predict the swirl ratio within the cavity. When detailed flow pattern is considered, Ekman-type flow exists near periphery of the surface’s boundary layer where viscous effect is non-negligible. However, due to the complex profile of the simulated cavity case, vortices structure is varied within the cavity. By comparison, swirl ratio can be used to predict the magnitude of loss. Due to the relatively evident rotating effects of the rotor-rotor cavity, swirl ratio even increases to 1.4 in the current model, which means that flow is moving faster than the surrounding disc. Further investigation finds that this kind of highly rotating flow is accompanied with serious undesirable pressure loss. Parenthetically, unlike its counterpart, swirl ratio above 1.0 doesn’t happen when fluid passes through the rotor-stator cavity. So it is suggested that rotor-rotor flow cavity with the superimposed inward throughflow should be avoided in the engine design or certain measurements should be provided when such structure design is unavoidable. Simulation done in the current paper is meaningful since these dimensional parameters are typical in the design of state-of-art. Relatively lower range of Re φ and C w is not considered in the current two parts paper.

Using satellite and in-situ observations, ocean reanalysis products and model simulations, we show a distinct reversal of the North Indian Ocean (NIO, north of 5°S) sea level decadal trend between 1993–2003 and 2004–3013, after the global mean sea level rise is removed. Sea level falls from 1993 to 2003 (Period I) but rises sharply from 2004 to 2013 (Period II). Steric height, which is dominated by thermosteric sea level of the upper 700 m, explains most of the observed reversal, including the spatial patterns of sea level change. The decadal change of surface turbulent heat flux acts in concert with the change of meridional heat transport at 5°S, with both being driven by decadal change of surface winds over the Indian Ocean, to cause sea level fall during Period I and rise during Period II. While the effect of surface net heat flux is consistent among various data sets, the uncertainty is larger for meridional heat transport, which shows both qualitative and quantitative differences amongst different reanalyses. The effect of the Indonesian Throughflow on heat content and thus thermosteric sea level is limited to the South Indian Ocean, and has little influence on the NIO. Our new results point to the importance of surface winds in causing decadal sea level change of the NIO.

The circumferential fluctuation (CF) source terms induced by the inviscid blade force can affect the inlet distribution of flow parameters and radial equilibrium of swept and bowed blades. However, these phenomena cannot be adequately described by throughflow methods based on the axisymmetric assumption. A transport model for the CF stresses is proposed and correlated to the distribution of circulation to reflect the effect of the inviscid blade force. To investigate the effect of the inlet CFs on swept and bowed blades, the model is integrated into a throughflow model and applied to a series of cascades with different sweep and bow angles. For swept cascades, the CF source terms change the distributions of incidence angles, as well as the radial equilibrium at the inlet of the blade passage. And the influence is enhanced as the absolute value of the sweep angle increases. For bowed cascades, the distributions of incidence angles are also altered. For both cases, the model can offer a good prediction of the inlet CF source terms, and prove to exert a better prediction of blade design key parameters such as flow angles.

Horizontal and vertical distributions of δ18O and δ13C were investigated in shells of four planktonic foraminiferal species, Globigerinoides ruber, Globigerinoides sacculifer, Pulleniatina obliquiloculata and Neogloboquedrina dutertrei, from a total of 62 core-top sediment samples from the Indonesian throughflow region. Results were compared to modern hydrologic conditions in order to explore potential of proxies in reconstructing fluvial discharge and upper ocean water column characteristics in this region. Our results show that, in the Makassar Strait, both of depleted δ18O and δ13C of these four species were linked to freshwater input. In the Bali Sea, however, depleted δ18O and δ13C for these species may be due to different reasons. Depleted δ18O was a result of freshwater input and as well influenced by along-shore currents while depleted δ13C was more likely due to the Java-Sumatra upwelling. Comparison of shell δ18O records and hydrographic data of World Ocean Atlas 2005 suggests that G. ruber and G. sacculifer calcify within the mixed-layer, respectively at 0–50 m and 20–75 m water depth, and P. obliquiloculata and N. dutertrei within the upper thermocline, both at 75–125 m water depth. N. dutertrei calcifies at slightly deeper water depth than P. obliquiloculata does. In general, δ13C values of both G. ruber and G. sacculifer are larger than those of P. obliquiloculata and N. dutertrei at all sites, possibly related to depth habitats of these species and vertical distribution of nutrients in the Indonesian throughflow region.

In this paper, thermal instability in a horizontal nanofluid-saturated porous layer with vertical through flow and quadratic drag is investigated. The important effects of Brownian motion and thermophoresis are included in the model of nanofluid, while for porous medium the modified Forchheimer-extended Darcy model is employed. The criterion for both stationary and oscillatory convection is derived analytically with and without through flow and quadratic drag effects. It is found that oscillatory convection is possible only for the case of a bottom-heavy nanoparticle distribution.

In this study, nonlinear stability analysis of double-diffusive convection in a horizontal fluid saturated porous layer has been investigated. Concentration based internal heat source and vertical throughflow effects are considered during investigation. Energy method has been implemented to develop the nonlinear stability analysis. Runge–Kutta and shooting methods have been used to solve the eigenvalue problem. Critical thermal Rayleigh number is obtained for assigned values of governing parameters. Results of linear and nonlinear theories have been compared. It is observed that for downward throughflow, when Peclet number Pe is high, the effect of concentration based internal heat source $$\gamma $$ is insignificant.

In this paper, we present an analytical study on the onset of convection in a horizontal layer of a saturated porous medium, uniformly heated from below but with a non-uniform basic temperature gradient resulting from a pulsating vertical throughflow. We applied two methods to analyze this problem: the frozen profile and the averaged equations. We found that the two approaches lead to essentially the same results and discussed physical implications of this finding, in particular, with respect to fundamental differences between the throughflow modulation and the temperature modulation problems.

In this paper, a novel engineering platform for throughflow analysis based on streamline curvature approach is developed for the research of a 5-stage compressor. The method includes several types of improved loss and deviation angle models, which are combined with the authors’ adjustments for the purpose of reflecting the influences of three-dimensional internal flow in high-loaded multistage compressors with higher accuracy. In order to validate the reliability and robustness of the method, a series of test cases, including a subsonic compressor P&W 3S1, a transonic rotor NASA Rotor 1B and especially an advanced high pressure core compressor GE E3 HPC, are conducted. Then the computation procedure is applied to the research of a 5-stage compressor which is designed for developing an industrial gas turbine. The overall performance and aerodynamic configuration predicted by the procedure, both at design- and part-speed conditions, are analyzed and compared with experimental results, which show a good agreement. Further discussion regarding the universality of the method compared with CFD is made afterwards. The throughflow method is verified as a reliable and convenient tool for aerodynamic design and performance prediction of modern high-loaded compressors. This method is also qualified for use in the further optimization of the 5-stage compressor.

Based on monthly mean Simple Ocean Data Assimilation (SODA) products from 1958 to 2007, this study analyzes the seasonal and interannual variability of the North Equatorial Current (NEC) bifurcation latitude and the Indonesian Throughflow (ITF) volume transport. Further, Empirical Mode Decomposition (EMD) method and lag-correlation analysis are employed to reveal the relationships between the NEC bifurcation location, NEC and ITF volume transport and ENSO events. The analysis results of the seasonal variability show that the annual mean location of NEC bifurcation in upper layer occurs at 14.33°N and ITF volume transport has a maximum value in summer, a minimum value in winter and an annual mean transport of 7.75×106 m3/s. The interannual variability analysis indicates that the variability of NEC bifurcation location can be treated as a precursor of El Nino. The correlation coefficient between the two reaches the maximum of 0.53 with a time lag of 2 months. The ITF volume transport is positively related with El Nino events with a maximum coefficient of 0.60 by 3 months. The NEC bifurcation location is positively correlated with the ITF volume transport with a correlation coefficient of 0.43.

A non-autonomous complex Ginzburg-Landau equation (CGLE) for the finite amplitude of convection is derived, and a method is presented here to determine the amplitude of this convection with a weakly nonlinear thermal instability for an oscillatory mode under throughflow and gravity modulation. Only infinitesimal disturbances are considered. The disturbances in velocity, temperature, and solutal fields are treated by a perturbation expansion in powers of the amplitude of the applied gravity field. Throughflow can stabilize or destabilize the system for stress free and isothermal boundary conditions. The Nusselt and Sherwood numbers are obtained numerically to present the results of heat and mass transfer. It is found that throughflow and gravity modulation can be used alternately to heat and mass transfer. Further, oscillatory flow, rather than stationary flow, enhances heat and mass transfer.

The stability of convection in a horizontal porous layer which is saturated with fluid and induced by horizontal temperature gradients subjected to horizontal mass flow is investigated by means of linear and nonlinear stability analysis. The effects of variable gravity field and vertical throughflow are also considered in this analysis. The nonlinear stability analysis part has been developed via energy functional. Shooting and Runge–Kutta methods have been used to solve eigenvalue problem in both cases. Critical vertical thermal Rayleigh numbers for both linear and nonlinear analyses $$R_\mathrm{L}$$ and $$R_\mathrm{E}$$ are evaluated for different values of horizontal Rayleigh number $$R_x$$ , horizontal Peclet number Pe, vertical Peclet number $$Q_\mathrm{v}$$ and variable gravity parameter $$\eta $$ . Comparison is made between linear and nonlinear stability results. It has been observed that linear stability results are overpredicting the onset of convection compared with nonlinear theory, and hence subcritical instabilities would arise before one gets the onset of linear stability threshold.

A model for double-diffusive convection in an anisotropic porous layer with a constant throughflow is explored, with penetrative convection being simulated via an internal heat source and subjected to a vertical magnetic field and variable gravity effect. The validity of both the linear instability and global nonlinear stability thresholds are tested using three dimensional simulation. Our results show that the linear theory produce a good prediction on the onset of instability in the steady state throughflow. It is known that as Rc increases the onset of convection is more likely to be via oscillatory convection as opposed to steady convection, and the three dimensional simulation results show that as Rc increases, the actual threshold moving toward the nonlinear stability threshold and the behaviour of the perturbation of the solutions becomes more oscillated.

Porous horizontal layers are considered. A class of non-constant porous throughflows, 2D in vertical planes, is obtained. The global stability conditions and the "cold convection instability'' conditions are investigated.

The South China Sea (SCS) throughflow (SCSTF) enters the SCS from the Luzon Strait and exits it through the straits to the south. Using a coupled general circulation model (CGCM), this study reveals impacts of the SCSTF on the mean state and El Nino/Southern Oscillation (ENSO). It is found that the model’s sea surface temperature becomes cooler in the eastern and far western equatorial Pacific and south of Japan, but significantly warmer in the SCS, when the SCSTF is blocked. The warming in the SCS is likely a result of accumulated surface heat flux which otherwise would be transported out of the SCS by the SCSTF. Furthermore, the dominant period of ENSO is 4 years when the SCSTF is allowed, but it becomes 5 years when the SCSTF is blocked. This is because the meridional extent of zonal wind anomalies becomes broader and the Walker Circulation in the Indian Ocean becomes stronger in the no-SCSTF case. On the other hand, changes in the zonal location of zonal wind anomalies, the phase speed of baroclinic Kelvin waves, the occurrence of westerly wind bursts, and strength of atmospheric feedbacks do not contribute to the difference between the two experiments even though they are known to influence the ENSO period. The climatic importance of the SCSTF has been so far overlooked because of its small volume transport compared with other major currents in the global ocean, but the present work shows for the first time its possible impacts on ENSO.

Lag correlations between sea surface temperature anomalies (SSTA) in the southeastern tropical Indian Ocean (STIO) in fall and Nino 3.4 SSTA in the eastern equatorial Pacific in the following fall are subjected to decadal variation, with positive correlations during some decades and negative correlations during others. Negative correlations are smaller and of shorter duration than positive correlations. Variations in lag correlations suggest that the use of the Indian Ocean Dipole (IOD) as a predictor of the El Nino-Southern Oscillation (ENSO) at a lead time of one year is not effective during some decades. In this study, lag correlations between IOD and ENSO anomalies were analyzed to investigate why the IOD-ENSO teleconnection disappears during decades with negative correlations. Anomalies induced by the IOD in the equatorial Pacific Ocean during decades with negative correlations are still present, but at a greater depth than in decades with positive correlations, resulting in a lack of response to oceanic channel dynamics in the cold tongue SSTA. Lag correlations between oceanic anomalies in the west Pacific warm pool in fall and the equatorial Pacific cold tongue with a one-year time lag are significantly positive during decades with negative correlations. These results suggest that oceanic channel dynamics are overwhelmed by ocean-atmosphere coupling over the equatorial Pacific Ocean during decades with negative correlations. Therefore, the Indonesian throughflow is not effective as a link between IOD signals and the equatorial Pacific ENSO.

The problem of thermal convection in a horizontal layer of ferrofluid-saturated porous medium is investigated theoretically in the presence of a uniform vertical magnetic field and throughflow. The flow in the porous medium is described by the modified Brinkman equation with fluid viscosity different from effective viscosity. The rigid, however permeable ferromagnetic boundaries are considered to be insulated to temperature perturbations. The resulting eigenvalue problem is solved both numerically using the Galerkin technique and analytically using regular perturbation technique with wave number a as a perturbation parameter and observed that the results complement with each other. The direction of throughflow has no influence on the stability characteristics of the system, and the effect of throughflow-dependent Peclet number Q is to delay the onset of ferroconvection. The Prandtl number Pr(>1) has insignificant while the nonlinearity of fluid magnetization parameter M 3 has no influence on the onset of ferroconvection. Besides, an increase in the value of the Darcy number Da and the magnetic number M 1 is to hasten, while an increase in the ratio of viscosity parameter λ is to delay the onset of ferroconvection.

Observed hiatus or accelerated warming phenomena are compared with numerical simulations from the Coupled Model Intercomparison Project Phase 5 (CMIP5) archives, and the associated physical mechanisms are explored based on the CMIP5 models. Decadal trends in total ocean heat content (OHC) are strongly constrained by net top-of-atmosphere (TOA) radiation. During hiatus decades, most CMIP5 models exhibit a significant decrease in the SST and upper OHC and a significant increase of heat penetrating into the subsurface or deep ocean, opposite to the accelerated warming decades. The shallow meridional overturning of the Pacific subtropical cell experiences a significant strengthening (slowdown) for the hiatus (accelerated warming) decades associated with the strengthened (weakened) trade winds over the tropical Pacific. Both surface heating and ocean dynamics contribute to the decadal changes in SST over the Indian Ocean, and the Indonesian Throughflow has a close relationship with the changes of subsurface temperature in the Indian Ocean. The Atlantic Meridional Overturing Circulation (Antarctic Bottom Water) tends to weaken (strengthen) during hiatus decades, opposite to the accelerated warming decades. In short, the results highlight the important roles of air-sea interactions and ocean circulations for modulation of surface and subsurface temperature.

A wave–tide–circulation coupled model is used to simulate upwelling off the south coast of Java, Indonesia. The results show that the vertical velocity off East Java is stronger than other parts in this area. The strongest vertical velocity is located approximately at 80 m depth. The annual averaged values of upwelling are 2.3 × 10−6 and 1.06 × 10−5 m/s for south of West Java and south of East Java, respectively. The vertical velocity from the model shows that upwelling off West Java has seasonal variability, while it is quite steady and strong off East Java. Additional numerical experiments show that the wind is not the dominant factor for the steady upwelling off the southern part of East Java. It is then hypothesized that the Indonesian Throughflow (ITF) may be responsible for the upwelling. To test this hypothesis, two scenarios are implemented, both of which block the outflow of the ITF. Sensitive study shows that the ITF plays a key role in the formation of East Java upwelling. The effect of the ITF can account for about 55 %–65 % of the upwelling.