Structure Of Circulation Research Articles

ИСПОЛЬЗОВАНИЕ РАЗРАБАТЫВАЕМОЙ АВТОНОМНОЙ РОБОТОТЕХНИЧЕСКОЙ СИСТЕМЫ «МОБИЛЬНЫЙ БИОЛОГ» ДЛЯ ИССЛЕДОВАНИЯ ЭКОСИСТЕМЫ АНТАРКТИКИ

The paper addresses the issues of using the developed autonomous robotic system to study the influence of water dynamics parameters on the density of Antarctic krill accumulations in traditional areas. With the help of this system, potentially vulnerable natural and ecological habitats of Antarctic krill can be identified, based on the data from which solutions for their conservation and stabilization can be proposed. An autonomous robotic system allows for such continuous monitoring to observe the basic trophic levels of ecosystems, the effects of changes in sea ice conditions, and other Antarctic environmental factors affecting the marine ecosystem. The application of the proposed method allows simultaneous measurements of environmental parameters in order to assess the relationship between the physical parameters of sea currents and biological processes. By integrating the system data with ship and satellite data in postprocessing, the response of Antarctic krill populations to multifactorial stresses can be assessed. The work was carried out according to the state assignment No. 0128-2021-0002 (“Mechanisms for the formation of the circulation structures of the World Ocean: key processes in the boundary layers and their role in ocean dynamics based on expeditionary studies, numerical and laboratory modeling”).

Dual circulation development model and credit growth

This paper empirically examines the impact of the economic dual circulation structure (DCS) on credit growth for the first time, thus expanding the existing literature on economic structure and credit growth. Using China's provincial data from 1995 to 2021, findings indicate that DCS significantly reduces credit growth, in areas with high ratio of value-added of service-to-manufacturing or with high technological innovation level, this negative effect become more significant. Additionally, fixed investment is one mechanism of this effect. our research is helpful for understanding China's sustainable economic growth and credit growth.

Characteristics of summer tropopause folds over southeastern Central Asia and their influences on precipitation

Tropopause folding activities in the summer play a significant role in atmospheric circulations and weather anomalies. Using rain gauge data and the Climate Prediction Center (CPC) precipitation observations as well as the ERA5 reanalysis dataset during July–August (JA) of 1979–2020, three-dimensional circulation structure during 592 frequent tropopause fold days that occurred over southeastern Central Asia and their impacts on precipitation over Central Asia and western China are investigated. During the frequent tropopause fold days, a significant dipole precipitation anomaly pattern is observed with negative precipitation anomalies over Central Asia and positive precipitation anomalies over western China. The contribution of precipitation (extreme precipitation) in the frequent tropopause fold days to the JA climatology over the northwestern slope of the Tibetan Plateau (TP) and the southern Tarim Basin can reach above 40% (50%). Compared with that in no fold days, daily mean precipitation in the frequent tropopause fold days can increase to three times over the northwestern TP and the Tarim Basin. Strong upward motions associated with low level convergence (high level divergence) and high specific humidity are found downstream of the fold region, which is favorable for the occurrence of precipitation, especially extreme precipitation over western China. In contrast, strong downward motions associated with low level divergence (high level convergence) and low specific humidity suppress the occurrence of precipitation over Central Asia. Further analysis reveals that precipitation over western China is closely related to the strength of tropopause fold, with significant positive correlation over the northwestern TP and the Tarim Basin. As the tropopause fold strengthens, the intensity of upward motion and specific humidity in the middle to lower troposphere downstream of the fold region increase, resulting in changes in the frequency and location of precipitation over western China. These findings highlight important impacts of the atmosphere around the tropopause on precipitation over western China.

Lateral Circulation in an Elongated Curved Tidal Channel

Abstract The dynamic theory of curvature-induced lateral circulation has been developed for open channel flows but not for oscillatory tides. A linear three-dimensional analytical model was developed to investigate the lateral circulation in an elongated tidal channel with mildly curved bends of which the radius of curvature is larger than the width. The curvature-induced lateral circulation has two components with the same amplitude, namely, a periodic component having an overtide frequency and a steady component. The combination of the two components allows the strength of the lateral circulation to vary periodically and the rotation direction to be unchanged during a tidal period. Friction modifies the strength and structure of the lateral circulation. The phase between the lateral flow and streamwise tidal flow decreases with increasing friction, indicating that the two flows are not necessarily in phase unless friction is strong. The lateral circulations driven by the Coriolis and curvature centrifugal forces augment each other during one phase and compete in the opposite phase, and the relative importance of the two circulations is determined by the Rossby number and friction. The adaptation time is the same for spinup and spindown of the curvature-induced lateral circulation and is determined by water depth and vertical eddy viscosity. The estimation of the adaptation time depends on the leading modes because the transition solution of the curvature-induced lateral circulation comprises a series of cosine modes. These results provide a theoretical basis for interpreting curvature-induced lateral circulation in tidal channels and coastal headlands. Significance Statement The dynamic theory of curvature-induced lateral circulation in a tidal flow remains unexplored. The purpose of this study is to understand the essentials of curvature-induced lateral circulation in an elongated tidal channel using a three-dimensional analytical model. The results showed that the curvature-induced lateral circulation has two components with the same amplitude: a periodic component having an overtide frequency and a steady component. This is significantly different from the curvature-induced lateral circulation associated with open channel flows, which is steady and in phase with the streamwise flow. Future work may show the role of curvature-induced lateral circulation in streamwise dynamics and mass transport.

Development of an Objective Methodology for Identifying the Sea-Breeze Circulation and Associated Low-Level Jet in the New York Bight

Abstract In a midlatitude coastal region such as the New York Bight (NYB), the general thermodynamic structure and dynamics of the sea-breeze circulation is poorly understood. The NYB sea-breeze circulation is often amplified by and coterminous with other regional characteristics and phenomena such as complex coastal topology, a low-level jet (LLJ), and coastal upwelling. While typically considered a summertime phenomenon, the NYB sea-breeze circulation occurs year-round. This study creates a methodology to objectively identify sea-breeze days and their associated LLJs from 2010 to 2020. Filtering parameters include surface-based observations of sea level pressure (SLP) gradient and diurnal tendencies, afternoon wind speed and direction tendencies, air temperature gradient, and the dewpoint depression. LLJs associated with the sea-breeze circulation typically occur within 150–300 m MSL and are identified using a coastal New York State Mesonet (NYSM) profiler site. Along coastal Long Island, there are on average 32 sea-breeze days annually, featuring winds consistently backing to the south and strengthening at or around 1800 UTC (1400 EDT). The NYB LLJ is most frequent in the summer months. Sea-breeze days are classified into two categories: classic and hybrid. A classic sea breeze is driven primarily by both cross-shore pressure and temperature gradients, with light background winds; while a hybrid sea breeze occurs in combination with other larger-scale features, such as frontal systems. Both types of sea breeze are similarly distributed with a maximum frequency during July.

Cold Collar Reproduced by a Venus GCM With the Akatsuki Horizontal Wind Assimilation

AbstractThe thermal structure of the upper atmosphere in the Venus polar region is reproduced by the assimilation of horizontal winds in low‐ and mid‐latitudes derived from the Akatsuki ultra‐violet images. The obtained structure is well consistent with infrared and radio occultation measurements. In particular, the unique thermal features in the Venus polar vortex such as the cold collar and the warm polar region in our model are realistic: the level where the cold collar is located and the temperature difference between the cold collar and the warm polar region are consistent with data. The reasons why the thermal structure of the upper atmosphere in the Venus polar region is realistic are that the zonal wind distribution around the cloud top level and the structure of the residual mean meridional circulation induced by the thermal tides are improved with respect to the model without data assimilation. Our results also suggest that the thermal structure in the Venus upper polar region is closely related to the atmospheric dynamics.

Determining the Impact of Boundary Layer Schemes on the Secondary Circulation of Typhoon Faxai Using Radar Observations in the Gray Zone

Abstract Using detailed radar observation data for Typhoon Faxai, which made landfall in the Tokyo metropolitan area in 2019, a sensitivity test of the boundary layer (BL) schemes for a numerical weather prediction (NWP) model was conducted for gray-zone numerical simulations with a grid spacing of 250 m. We compared the results of our simulations using an NWP model with radar observations that captured the BL and the secondary circulation structures of Faxai. We used three BL schemes based on a Reynolds-averaged model, the gray-zone model, and a large-eddy simulation (LES) model: the Mellor–Yamada–Nakanishi–Niino level 3 (MYNN3) scheme, the Anisotropic Deardorff Model (ADM) scheme, and the Deardorff (DDF) scheme, respectively. The turbulence kinetic energy was the smallest, and the inflow near Earth’s surface the strongest, in the gray-zone simulation with the DDF scheme. This simulation also produced values for BL thickness and secondary circulation that were the closest to observation and reproduced horizontal roll structures whose scale was larger than the observation. Neither experiment using the MYNN3 scheme or the ADM scheme produced rolls, but the parameterized turbulence seemed to estimate the effects of the rolls. However, their BL heights were higher than observed, suggesting that the MYNN3 and ADM schemes are not appropriate for a 250 m grid simulation of the present case. These results are also confirmed against LES with 50 m grid spacing in which the DDF scheme is used. In summary, this study provides insights into the interpretation of the properties of BL schemes in the gray zone.

Law of Monetary Circulation: System Analysis

System analysis is necessary to establish the boundaries of the law of money circulation and describe the mechanism of its functioning. The concept of the monetary system, which is an integral category reflecting the structure of monetary circulation, allows establishing systemic links between the institutions of money circulation. The elements of the monetary system accurately describe the composition, boundaries and nature of the internal relations of social relations related to the subject matter of the law of monetary circulation. The institutions of the law of money circulation underlie the relations that make up the content of credit money and mediate their emission, as well as relations for the organization and regulation of money circulation, the need for which is due to the fiat nature of money. The institutions of the law of monetary circulation have different industry affiliations, but there is a close functional relationship between them, due to the unity of purpose and the distribution of tasks within the mechanism of monetary circulation. The legal regulation of the circulation of modern money has a private law and public law basis. Interaction between institutions is implemented within the framework of complex legal relations.

Effective Mechanical Thrombectomy for Posterior Circulation Ischemia Using Magnetic Resonance Imaging-based Arterial Structures.

To improve the success of mechanical thrombectomy, three-dimensional turbo spin-echo (3D-TSE) sequences on T2WI can be employed to estimate the vascular structure of the posterior circulation. In addition to the short imaging time of 3D-TSE T2WI (33 sec), it can visualize the outer diameter of the main cerebral artery, including the occluded vessels. However, to date, the efficacy of mechanical thrombectomy in the posterior circulation remains unclear, and safer and more efficient mechanical thrombectomy procedures are required. Assessment of the anatomical variations in the posterior circulation using 3D-TSE T2WI is valuable for access decisions, device selection, and safe device guidance and retrieval techniques to the target vessel. Herein, we present representative cases of basilar artery and posterior cerebral artery occlusions in our institute and describe the utility of preoperative 3D-TSE T2WI in these patients.

Meridional‐Width Variability of Near‐Equatorial Zonal Currents Along 80.5°E on Seasonal to Interannual Timescales in the Indian Ocean

AbstractNear‐equatorial zonal currents along 80.5°E in the upper Indian Ocean are key to tropical inter‐basin hydrographic exchanges. However, their meridional‐width variability and underlying causes have remained elusive. In this study, we use satellite‐derived ocean current data to reexamine the latitudinal structure of Wyrtki jets (WJs), Monsoon Circulation (MC), and South Equatorial Countercurrent (SECC) along 80.5°E on seasonal to interannual timescales. The WJs are characterized by a transient semiannual feature within the latitudinal range of 2.5°S–3°N, whereas the MC and the SECC have a dominant annual period within the latitudinal range of 3°–5.5°N and 2.5°–6°S, respectively. Empirical orthogonal function (EOF) analysis separates the seasonal latitudinal boundaries of the WJs, the MC, and the SECC, and reveals their interannual variability in response to anomalous wind forcing. EOFs1–3 represent the WJ, MC, and SECC modes accounting for 54%, 19%, and 14% of the total variance, respectively. The near‐equatorial zonal currents are asymmetrically responsive to the Indian Ocean Dipole (IOD), with an abnormally strong westward current resulting from the latitudinal superposition of the WJ and SECC modes in the autumn of 1997, 2006, and 2015 during strong positive IOD events. However, the abnormally enhanced eastward WJs occurred only during weak IOD events in the autumn of 1995, 1999, and 2005, accompanied by latitudinal destructive interference of strong westward SECC. Model sensitivity experiments show that the asymmetric response of near‐equatorial zonal currents to climate modes is closely related to the spatial differences in large‐scale wind anomalies associated with wind‐driven and eastern‐boundary‐generated waves.

Formation of the Layered Circulation in South China Sea With the Mixing Stimulated Exchanging Current Through Luzon Strait

AbstractUsing the layered circulation in the South China Sea (SCS) as an example, a process‐oriented simulation was conducted to explore how the lateral exchanging current and basin circulation responded to the contrasting mixing in the marginal sea‐open ocean system and to the internal modulation over basin slope. Under conditions of intensified turbulent mixing () in the SCS, a crossing Luzon Strait density difference was generated and the net ageostrophic pressure gradient force drove the layered exchanging current with intensified westward deep intrusion into the SCS and an eastward middle outflow. The lateral exchanging current in turn developed a layered basin circulation in the semi‐enclosed middle and deep layers through directly providing external planetary vorticity flux, and releasing the internal potential energy indirectly. The vertical migration of the layered circulation structure over bottom slope owing to flow‐topography interaction is the major intrinsic response to the external exchanging current particularly in the semi‐enclosed deep basin. Although a small was adequate to maintain the basic layered circulation pattern, an intensified was required to extend the deep cyclonic circulation to the bottom. The intrusion of the western boundary current from open ocean not only maintained the strong upper cyclonic circulation but also intensified deep intrusion and modulated the deep layer circulation through vertical coupling. Both the deep density difference between the SCS and open ocean as well as associated vertical coupling should be considered to well understand the intensity of water exchange and the consequent layered circulation in the SCS.

Observation of near-inertial waves in the wake of four typhoons in the northern South China Sea

Based on the velocity and temperature data recorded by two acoustic Doppler current profilers (ADCPs) at a mooring system deployed in the northern South China Sea (SCS), this study investigates the characteristics of near-inertial waves (NIWs) induced by typhoons Bebinca, Barijat, Mangkhut and Yutu in 2018. For the dynamical response, besides the motion of near inertial frequency induced by typhoons, the motion of 2 f ([1.80–2.20] f, f is the local inertial frequency) and f D1 (a harmonic wave with a frequency equal to the sum of frequencies of NIWs and diurnal tides) frequency will also increase. For near-inertial motions, the maximum near-inertial kinetic energy (NIKE) is confined to depths above 150 m. For stronger (weaker) wind forcing, the longer (shorter) the response time of the ocean to the atmospheric forcing is, and the shorter (longer) the response time is required in relaxation stage. There are upward and downward propagating energies after the passage of typhoons, and the upward propagating energy mainly occur in the stage of the geostrophic balance adjustment. The current structure suggests that the NIWs in the vertical direction are two antisymmetric rotary vortices in a near-inertial period, which is similar to the structure of the Langmuir circulation. Besides, the horizontal near-inertial currents (NICs) are much stronger than the vertical NICs, and the stronger the NIWs are, the stronger the horizontal NICs relative to the vertical NICs are. For the temperature response, the temperature variation reflects a clear stratified vertical structure. In the forcing stage, the upper layer becomes colder, the lower layer becomes warmer, and the thickness and intensity of the thermocline decrease. In the relaxation stage, the upper layer warms and the lower layer cools, and the thickness and intensity of thermocline increase.

Causality‐Based Deep Learning Forecast of the Kuroshio Volume Transport in the East China Sea

AbstractThe Kuroshio volume transport (KVT) in the East China Sea has enormous impacts on navigation, circulation structure, ecological environment, and local climate. In this study, we aim to forecast the daily variability of the KVT at three different sections using the deep learning method. We train the deep learning model using data from 1982 to 2008 and validate the model with data of 2009–2010 and subsequently test it with data of 2011–2015. Four deep learning models, including Artificial Neural Network, Temporal Convolutional Network, Gated Recurrent Unit, and Long Short‐Term Memory (LSTM) models, are first tested to choose the best prediction model. As a result, the LSTM has the best performance for the KVT prediction at each section. We then employ a multivariate causal analysis method to identify the factors affecting the KVT at the current section, such as upstream and downstream KVT, regional mean wind stress, sea surface height and temperature and combine this method with the LSTM model to construct an information flow causality‐based LSTM (IFC‐LSTM) model for predicting daily KVT variability. The results indicate that IFC‐LSTM has the highest forecast skill compared to the standard LSTM (only input KVT at the current section into the LSTM), ALL‐LSTM (input all nine variables into the LSTM), multiple linear regression, and persistence model, which can forecast the KVT variability from 23 to 27 days in advance at the three sections with relative improvement rates of 12.5%–50%.

ВЛИЯНИЕ СПОСОБОВ УСВОЕНИЯ СПУТНИКОВЫХ ДАННЫХ O ТЕМПЕРАТУРЕ ПОВЕРХНОСТИ МОРЯ НА ВОСПРОИЗВЕДЕНИЕ ГИДРОФИЗИЧЕСКИХ ПОЛЕЙ ЧЕРНОГО, АЗОВСКОГО И МРАМОРНОГО МОРЕЙ В МОДЕЛИ INMOM

The results are analyzed of the simulation of hydrophysical fields of the Black, Azov, and Marmara seas with the Institute of Numerical Mathematics Ocean Model (INMOM) implemented with a spatial resolution of 4 km, with various assimilation technique for sea surface temperature (SST) data from the SEVIRI sensor installed on MSG satellites. The relaxation (so called nudging) and the ensemble optimal interpolation (EnOI) with various assimilation time frequencies (3-, 6-, 12-, and 24-hour assimilation windows) were used as assimilation methods. It was shown that the assimilation of SST data via the EnOI made it possible to reproduce hydrophysical fields more accurately than via nudging or without assimilation at all. Even with the assimilation of SST data irregularly distributed over space and time, a decrease in the calculation error was observed over the entire sea area, and the structures of the zones of temperature rise or drop were more correctly simulated. The best results were achieved with via the EnOI assimilation with an increasing assimilation frequency over time. When SST data were assimilated using the EnOI, the mean error decreased from 0.16°C (24-hour assimilation window) to 0.08°C (3-hour assimilation window); accordingly, the absolute mean error decreased from 1.03 to 0.33°C, and the standard deviation decreased from 1.33 to 0.42°C. In addition, assimilation using the EnOI 3-hour window improved the reproduction of SST during the period of convection cooling. The assimilation of SST data also led to changes in the structure of the surface sea circulation. In some areas, the direction of currents varied within 5°-10°, and the velocity modulus changed by 3-5%. The assimilation of SST data only slightly reduced errors in the structure of the model vertical temperature profile, which can reach 2°C at depths of 30-40 m. At depths greater than 100 m, deviations did not exceed 0.05°C.

Relationship between the hadley circulation and tropical SST meridional structures under different thermal conditions in the indo-pacific warm pool

The Hadley circulation (HC), as a thermally driven large-scale meridional circulation, acts a significant role in the changes of global climate. The modulation of Indo-Pacific warm pool (IPWP) thermal conditions on the relationship between the HC and different tropical sea surface temperature (SST) meridional structures was investigated. Based on the two components of HC and SST, one equatorially asymmetric component (HEA for HC, SEA for SST) and one equatorially symmetric component (HES for HC, SES for SST), the connections of HC to different SST variations in the warm and cold IPWP are explored. The result demonstrates that the relationship of the HC to tropical SST is suppressed in the cold IPWP conditions, whereas it is equivalent to the climatology in the warm IPWP conditions. The plausible mechanism is that the cold (warm) IPWP events are in concordance with the La Niña (El Niño) decay phase. The La Niña decay phase are associated with significant equatorially asymmetric SST anomalies within the IPWP, generating an anomalous meridional circulation and favoring a strengthened equatorially asymmetric anomalous meridional circulation. By contrast, the SST anomalies associated with El Niño decay phase are insignificant. The role of La Niña decay conditions in determining the suppressed connection between SST and HC is further verified by exploring the result after 1979. A similar suppressed response contrast has been detected. Therefore, the results demonstrate that warm and cold ENSO events have impacts on the interannual thermal conditions of IPWP, whereby it plays considerable role in impacting the relationship between the HC and tropical SST. Particularly, with the rapid warming, the interconnection between ENSO events and thermal conditions of IPWP under different timescales could be altered, the influence of which on the responses of the HC to tropical SST remains uncertain and is worthy further researching.

Flow Structure and Short-Term Riverbed Evolution in Curved Flumes

River bending is the major effect responsible for bed topography and bank changes. In this study, fluid velocity (measured by a three-dimensional Doppler advanced point current meter) and bed topographical data have been collected in 40 sections of an experimental model. The whole flume was composed of an organic glass bend, upstream and downstream water tanks, two transition straight sections, a circulation pump, and a connection pipeline. Each section has been found to be characterized by a primary circulation and a small reverse circulation, with some sections even presenting three more or more circulation structures. The minimum circulation intensity has been detected in proximity to the top of the curved channel, while a region with small longitudinal velocity has been observed near the concave bank of each bend, corresponding to the flat bed formed after a short period of scouring. The maximum sediment deposition and scour depth in the presence of a uniform distribution of living flexible vegetation within 10 cm of the flume wall have been found to be smaller than those observed in the tests conducted without vegetation.

On the Hamiltonian and geometric structure of Langmuir circulation

<abstract><p>The Craik-Leibovich equation (CL) serves as the theoretical model for Langmuir circulation. We show that the CL equation can be reduced to the dual space of a certain Lie algebra central extension. On this space, the CL equation can be rewritten as a Hamiltonian equation corresponding to the kinetic energy. Additionally, we provide an explanation of the appearance of this central extension structure through an averaging theory for Langmuir circulation. Lastly, we prove a stability theorem for two-dimensional steady flows of the CL equation. The paper also contains two examples of stable steady CL flows.</p></abstract>

Large‐eddy simulation of soil moisture heterogeneity‐induced secondary circulation with ambient winds

AbstractLand surface heterogeneity in conjunction with ambient winds influences the convective atmospheric boundary layer by affecting the distribution of incoming solar radiation and forming secondary circulations. This study performed coupled large‐eddy simulation (ICON‐LEM) with a land surface model (TERRA‐ML) over a flat river corridor mimicked by soil moisture heterogeneity to investigate the impact of ambient winds on secondary circulations. The coupled model employed double‐periodic boundary conditions with a spatial scale of 4.8 km. All simulations used the same idealized initial atmospheric conditions with constant incident radiation of 700 W⋅m−2 and various ambient winds with different speeds (0 to 16 m⋅s−1) and directions (e.g., cross‐river, parallel‐river, and mixed). The atmospheric states are decomposed into ensemble‐averaged, mesoscale, and turbulence. The results show that the secondary circulation structure persists under the parallel‐river wind conditions independently of the wind speed but is destroyed when the cross‐river wind is stronger than 2 m⋅s−1. The soil moisture and wind speed determine the influence on the surface energy distribution independent of the wind direction. However, secondary circulations increase advection and dispersive heat flux while decreasing turbulent energy flux. The vertical profiles of the wind variance reflect the secondary circulation, and the maximum value of the mesoscale vertical wind variance indicates the secondary circulation strength. The secondary circulation strength positively scales with the Bowen ratio, stability parameter (−Zi/L), and thermal heterogeneity parameter under cross‐river wind and mixed wind conditions. The proposed similarity analyses and scaling approach provide a new quantitative perspective on the impact of the ambient wind under heteronomous soil moisture conditions on secondary circulation.

Effects of Water Masses and Circulation on the Surface Water Partial Pressure of Carbon Dioxide in Summer in Eastern Beibu Gulf, China

A gulf is a typical ecological zone where carbon cycle is jointly affected by complex environmental factors and strong human activities, and the Beibu Gulf has complex water masses and circulation structures. In this study, we used underway, continuous observational data of the surface water partial pressure of carbon dioxide (pCO2), temperature (SST), salinity (SSS), dissolved oxygen (DO), and chlorophyll α along with vertical profile observations of temperature, salinity, carbonate system parameters and nutrients to determine the spatiotemporal variations and research effects of water masses and circulation on summer pCO2 in the eastern part of Beibu Gulf. In the summers of 2011 and 2014, the mean pCO2 in the eastern part of Beibu Gulf was 417 μatm and 405 μatm, respectively, and the mean sea–air CO2 flux was 3.3 mmol m−2 d−1 and 1.6 mmol m−2 d−1, respectively. In the summer of 2011, the northern part of the Beibu Gulf was controlled by a cyclonic circulation, and pCO2 at the center of the cyclonic circulation increased by more than 15 μatm to a mean value of more than 10 μatm above that of the surrounding waters. The southern part of the Beibu Gulf was affected by an anticyclonic circulation and western coastal water masses, with a high temperature, low salinity, low pCO2, and downwelling surface waters. In the summer of 2011, the mean pCO2 was approximately 17 μatm lower than that in the surrounding waters, and no clear downwelling was observed in summer 2014. The eastern part of Beibu Gulf was a source of atmospheric CO2 in the summer, only the region affected by the northern coastal water in the eastern part of Beibu Gulf was a sink of atmospheric CO2, and pCO2 had distinctly different spatiotemporal distributions under the influence of complex water masses and circulation structures.

Magnetic-free unidirectional polarization rotation and free-space optical isolators and circulators

Optical nonreciprocity is an essential concept in optical signal processing and communication. The traditional way to achieve nonreciprocity is using magneto-optical nonreciprocal polarization rotation, which is incompatible with existing on-chip integration due to the applied magnetic field. Here, we theoretically and experimentally realize unidirectional polarization rotation with a magnetic-free mechanism using atomic ensembles. Free-space isolators and circulators are further formed based on the nonreciprocity of polarization rotation. As only one direction of the signal changes its polarization, the forward transmission and backward isolation can be adjusted separately. Compared with the existing magnetic-free circulators that rely on high-Q factor cavities or Mach–Zehnder interferometers, we experimentally realized circulators in free space. This dramatically simplifies the magnetic-free circulator structure and provides better stability.