Residual Circulation Research Articles

A 3D Numerical Study on the Tidal Asymmetry, Residual Circulation and Saline Intrusion in the Gironde Estuary (France)

A full 3D numerical model is used for studying tidal asymmetry, estuarine circulation, and saline intrusion in the Gironde estuary. The model is calibrated and verified using the data measured during two field surveys in the Gironde estuary. Harmonic analysis of numerical results is proposed to understand how the superposition of M2, M4 and M6 components generate a complex estuarine circulation and salinity intrusion in the Gironde estuary. The numerical results show that the M6 component plays a significant role as important as the M4 one in modifying the nature of tidal asymmetry, especially in the Gironde upper estuary. In this case, the use of the phase lag between M2 and M4, neglecting M6, to predict the tidal asymmetry nature could produce errors. The effect of asymmetrical tides on saline intrusion and residual circulation is specifically discussed here.

Stratosphere-troposphere coupling during stratospheric extremes in the 2022/23 winter

Using the ERA5 reanalysis, sea surface temperature, sea ice observations, and the real-time multivariate Madden-Julian Oscillation (MJO) index, the evolution of the stratospheric extreme circulation in the winter of 2022/2023 is explored. The stratospheric polar vortex was disturbed three times in the 2022/23 winter, contrasted with only one disturbance during the other three recent winters with an SSW. Possible favorable conditions for the strong stratospheric disturbances and their effects on stratospheric ozone, water vapor distribution, and near-surface temperature were examined. Around 7 December 2022 when a short but strong pulse of planetary wavenumber 2 appeared from the troposphere to stratosphere, a weakened and elongated stratospheric polar vortex formed at 10 hPa. This pulse is related to the intensifying Ural ridge and the deepening East Asian trough. After the first stratospheric disturbance, a large fraction of cold anomalies occurred in the Eurasian continent. A lagged impact after these stratospheric disturbances was observed as strong cold anomalies formed in North America from 13 to 23 December. On 28 January 2023, a minor SSW event occurred due to a displacement of the stratospheric polar vortex. A strong pulse of eddy heat flux contributed alternately by planetary wavenumber 1 and 2 showed a large accumulative effect on the stratospheric disturbance. However, the downward impact of this second disturbance was weak, and cold surges were not noticeable after this minor SSW. The third stratospheric disturbance this winter is a major displace-type SSW that occurred on 16 February 2023, and the total eddy heat flux primarily contributed by planetary wavenumber 1 increased rapidly. Following the major SSW, the North American continent was covered by large patches of strong cold anomalies until the end of March. During the three disturbances, the residual circulation correspondingly strengthened. The water vapor and ozone in the middle and lower layers of the polar stratosphere showed positive anomaly disturbances, especially after the major SSW onset. The unprecedented frequent stratospheric disturbances in winter 2022/23 were accompanied by severe loss of Barents-Laptev Sea ice and anomalously cold tropical Pacific sea surface temperatures (La Niña), which have been reported to be conducive to the enhancement of planetary waves 1 and 2 respectively. Further, two weeks before the major SSW, existing MJO developed into phases 4–6, also contributing to the occurrence of major SSW.

Injection strategy – a driver of atmospheric circulation and ozone response to stratospheric aerosol geoengineering

Abstract. Despite offsetting global mean surface temperature, various studies demonstrated that stratospheric aerosol injection (SAI) could influence the recovery of stratospheric ozone and have important impacts on stratospheric and tropospheric circulation, thereby potentially playing an important role in modulating regional and seasonal climate variability. However, so far, most of the assessments of such an approach have come from climate model simulations in which SO2 is injected only in a single location or a set of locations. Here we use CESM2-WACCM6 SAI simulations under a comprehensive set of SAI strategies achieving the same global mean surface temperature with different locations and/or timing of injections, namely an equatorial injection, an annual injection of equal amounts of SO2 at 15∘ N and 15∘ S, an annual injection of equal amounts of SO2 at 30∘ N and 30∘ S, and a polar strategy injecting SO2 at 60∘ N and 60∘ S only in spring in each hemisphere. We demonstrate that despite achieving the same global mean surface temperature, the different strategies result in contrastingly different magnitudes of the aerosol-induced lower stratospheric warming, stratospheric moistening, strengthening of stratospheric polar jets in both hemispheres, and changes in the speed of the residual circulation. These impacts tend to maximise under the equatorial injection strategy and become smaller as the aerosols are injected away from the Equator into the subtropics and higher latitudes. In conjunction with the differences in direct radiative impacts at the surface, these different stratospheric changes drive different impacts on the extratropical modes of variability (Northern and Southern Annular modes), including important consequences on the northern winter surface climate, and on the intensity of tropical tropospheric Walker and Hadley circulations, which drive tropical precipitation patterns. Finally, we demonstrate that the choice of injection strategy also plays a first-order role in the future evolution of stratospheric ozone under SAI throughout the globe. Overall, our results contribute to an increased understanding of the fine interplay of various radiative, dynamical, and chemical processes driving the atmospheric circulation and ozone response to SAI and lay the foundation for designing an optimal SAI strategy that could form a basis of future multi-model intercomparisons.

Unexpected DE3 Tide in the Southern Summer Mesosphere

AbstractSimulation of the January 2017 period using a gravity‐wave resolving global circulation model (HIAMCM) reveals a predominant eastward propagating diurnal tide with zonal wavenumber three (DE3) in the southern summer mesosphere from about 60 to 90 km height at middle to high latitudes. We provide observational evidence based on MERRA‐2 reanalysis and Sounding the Atmosphere using Broadband Emission Radiometry satellite observations for the validity of this result. The attenuation of the DE3 below the mesopause generates a significant eastward Eliassen‐Palm flux divergence that contributes to the residual circulation. We also show that the diurnal tide in the northern summer mesosphere likely consists of mainly eastward propagating components. These findings contradict the common perception of a weak diurnal tide in the summer mesosphere.

Ozone and water vapor variability in the polar middle atmosphere observed with ground-based microwave radiometers

Abstract. Leveraging continuous ozone and water vapor measurements with the two ground-based radiometers GROMOS-C and MIAWARA-C at Ny-Ålesund, Svalbard (79∘ N, 12∘ E) that started in September 2015 and combining MERRA-2 and Aura-MLS datasets, we analyze the interannual behavior and differences in ozone and water vapor and compile climatologies of both trace gases describing the annual variation of ozone and water vapor at polar latitudes. A climatological comparison of the measurements from our ground-based radiometers with reanalysis and satellite data was performed. Overall differences between GROMOS-C and Aura-MLS ozone volume mixing ratio (VMR) climatology are mainly within ±7 % throughout the middle and upper stratosphere and exceed 10 % in the lower mesosphere (1–0.1 hPa) in March and October. For the water vapor climatology, the average 5 % agreement is between MIAWARA-C and Aura-MLS water vapor VMR values throughout the stratosphere and mesosphere (100–0.01 hPa). The comparison to MERRA-2 yields an agreement that reveals discrepancies larger than 50 % above 0.2 hPa depending on the implemented radiative transfer schemes and other model physics. Furthermore, we perform a conjugate latitude comparison by defining a virtual station in the Southern Hemisphere at the geographic coordinate (79∘ S, 12∘ E) to investigate interhemispheric differences in the atmospheric compositions. Both trace gases show much more pronounced interannual and seasonal variability in the Northern Hemisphere than in the Southern Hemisphere. We estimate the effective water vapor transport vertical velocities corresponding to upwelling and downwelling periods driven by the residual circulation. In the Northern Hemisphere, the water vapor ascent rate (5 May to 20 June in 2015, 2016, 2017, 2018, and 2021 and 15 April to 31 May in 2019 and 2020) is 3.4 ± 1.9 mm s−1 from MIAWARA-C and 4.6 ± 1.8 mm s−1 from Aura-MLS, and the descent rate (15 September to 31 October in 2015–2021) is 5.0 ± 1.1 mm s−1 from MIAWARA-C and 5.4 ± 1.5 mm s−1 from Aura-MLS at the altitude range of about 50–70 km. The water vapor ascent (15 October to 30 November in 2015–2021) and descent rates (15 March to 30 April in 2015–2021) in the Southern Hemisphere are 5.2 ± 0.8 and 2.6 ± 1.4 mm s−1 from Aura-MLS, respectively. The water vapor transport vertical velocities analysis further reveals a higher variability in the Northern Hemisphere and is suitable to monitor and characterize the evolution of the northern and southern polar dynamics linked to the polar vortex as a function of time and altitude.

Residual circulation budget analysis in a Wells turbine with leading-edge micro-cylinders

To further interpret the control mechanisms of leading-edge micro-cylinders for flow separation in a Wells turbine, the residual circulation budget was performed through an improved triple decomposition method that the computational cost was reduced by 38.2%.The intensity of the leading-edge vortex (LEV), free of shear effects, was tracked under typical conditions. Meanwhile, disturbance physics was dissected by splitting the contributions of shear, swirling, and straining motions to the flow from dominant modes, captured by the proper orthogonal decomposition method under typical working conditions. The influence of micro-cylinders on the spatiotemporal evolution of the LEV has been discussed in detail. The results indicate that the accumulative shaft power of the turbine is improved by 54.2% through the micro-cylinders operating by suppressing the swirling intensity near the leading edge and weakening the instability of the boundary layer. Moreover, low-frequency disturbances could be significantly weakened and tended to transfer to higher-order modes with lower energy. Under the stall condition, the shear layer flux and diffusive flux dominated the LEV circulation rate. In contrast to the referential model, as the cylinders blocked the LEV trajectory after falling, the annihilation slowed down with an intensified accumulative circulation of the LEV.

Influence of Stratosphere Polar Vortex Variability on the Mesosphere, Thermosphere, and Ionosphere

AbstractThe Whole Atmosphere Community Climate Model with thermosphere‐ionosphere eXtension (WACCM‐X) is used to investigate the influence of stratosphere polar vortex variability on the mesosphere, thermosphere, and ionosphere during Northern Hemisphere winter. Based on 40 simulated Northern Hemisphere winters, the mesosphere and lower thermosphere (MLT) residual circulation is found to depend on whether the stratosphere polar vortex is strong or weak. In particular, during weak stratosphere polar vortex time periods, the MLT circulation anomalies are characterized by clockwise and anti‐clockwise flow in the Northern and Southern Hemispheres, respectively. Opposite, though weaker, anomalies are found to occur during time periods when the stratosphere polar vortex is strong. The MLT circulation anomalies influence the composition of the lower thermosphere, leading to ±5% changes in the thermosphere column integrated atomic oxygen to molecular nitrogen ratio (ΣO/N2). Large differences between strong and weak stratosphere polar vortex events are also found to occur in the semidiurnal migrating tide (SW2) in the MLT, which leads to ±15%–20% differences in the SW2 component of the ionosphere total electron content (TEC) at low latitudes. The WACCM‐X simulation results indicate that variability in the stratosphere polar vortex can explain ∼30% and ∼18% of the quiet time variability in thermosphere ΣO/N2 and the SW2 component of TEC during Northern Hemisphere winter, respectively.

Evaluating the long-term geomorphic process in-relation to hydrodynamics in the central coastal zone of Bangladesh

The central coast of Bangladesh is dynamic for its geographical location, hydrodynamic characteristics and residual flow. The research employed the Digital Shoreline Analysis System (DSAS), an ArcGIS extension tool, to conduct a historical trend analysis of shoreline. The study demonstrates that the central coast is eroding to the north and accreting to the south. The highest accretion value was found as 195.42 m/year, whereas the maximum value of erosion was estimated as −185.83 m/year, according to End Point Rate (EPR). The Linear Regression Rate (LRR) indicates that the average rate of erosion and accretion are −17.77 m/year and 17.88 m/year, respectively. Meanwhile, using Weighted Linear Regression (WLR), 0.48% of all transects demonstrated statistically significant erosion, while 0.43% showed statistically significant accretion. During the wet season, heavy river discharge leads to a low salt level in the ocean. Ocean currents hit central coast of Bangladesh from east to west, affecting the majority of the islands in the Meghna Estuary in the dry season. Changes in current directions can be seen during the wet seasons. Southern central coast areas are hit by south-east currents that split in two directions. The Sandwip Channel has a flow of 10,000 to 15,000 m³ s−1 northward. The Tetulia River, Shahbazpur Channel, and Hatia-Sandwip flow southward at rates ranging from 3000 to 17,000 m³ s−1, 14,000 to 60,000 m³ s−1, and 7000 to 39,000 m³ s−1, respectively. In the Meghna Estuary, the combined forces result in a counter-clockwise residual circulation, with the northward flow in the Sandwip channel and southbound flow in the Hatia and Shahbazpur channels. As a result of hydrodynamic, ocean currents, and residual flow, the Central Coast of Bangladesh is continually changing in appearance.

Residual circulations and wind conditions affect the transport and distribution of Pb

Hydrodynamic conditions affect the dispersion and transportation of pollutants. In this study, 102 surface water samples were collected and numerical simulations were conducted by coupling SWAT (Soil and Water Assessment Tool) and MIKE 21 models to investigate the effect of hydrodynamic conditions on the transport and distribution of Pb in Jiaozhou Bay, China. The tidal current velocity was lowest at flood tide and highest at ebb tide in summer, mainly due to the strong runoff caused by heavy rainfall in summer. The velocity of the residual current near the bay mouth was high, with an average value of 0.32 m/s. The residual currents had alternating clockwise and counter-clockwise circulations of different diameters in the bay mouth and the northern bay. The circulation diameter in the bay mouth area was large, and the circulation extended from the bay mouth to the Yellow Sea. Due to the small circulation diameters and opposite directions of the adjacent circulations in the northern bay, pollutants were easily trapped there. The dissolved Pb particles released from the northern bay mainly migrated to the shore, while the dissolved Pb particles released from the bay mouth tended to migrate to the Yellow Sea. The dominant wind directions and residual currents were the main driving forces affecting the trajectories of the particle tracking simulations. The dissolved Pb concentration in the water was high near shore and in the southwestern bay and under the combined effects of tidal residual current, wind force, and river and wastewater inputs. The low Pb concentration near the bay mouth was mainly influenced by the high residual current velocity. These results can provide improved insights into the mechanism of Pb transport and distribution in a semi-enclosed bay.

Wind-induced switch of estuarine residual circulations and sediment transport in microtidal bay

To reveal the mechanism for the transport of water and suspended sediments by wind-induced estuarine residual circulations, in situ moorings of acoustic Doppler current profilers were conducted in microtidal Onsan Bay. Water circulation within the bay was characterized by freshwater discharge from the river and free exchange with the open sea, showing current seaward outflow and landward inflow in the western (M1) and eastern (M2) flanks of the navigation channel, respectively. This circulation was influenced by the intrusion of alongshore currents strengthened (weakened) by the northerly (southerly) winds. In M1, seaward outflow was dominant, except for surface disturbances caused by winds. Meanwhile, the classical estuarine circulation (72% of the entire period) in M2, which prevailed under the southerly winds, was switched into the reversed estuarine circulation when the stress of the northerly wind persistently exceeded 0.005 Pa (> 5 h). The water transport (Trw) in M1 did not significantly vary depending on the wind direction, but the Trw in M2 could be reduced by 53% within 10 m above the bed as the southerly winds were transited into northerly winds. Over the entire period, Trw tended to be mutually compensated for and balanced by the circulation system between M1 and M2. On average, however, the sediment transport (Trsed) in M2 was 37% higher than M1, indicating that the suspended sediments were preferentially deposited within the bay. Most of the suspended sediments causing the deposition within the bay were mainly transported by estuarine residual circulation rather than tidal pumping. In M2, the frequent resuspension events of the fine-grained sediments (d50 = 6 μm) due to the high variability of the along-channel current velocity could maintain a sediment concentration of 18 mg l−1 in the bottom layer. These suspended sediments responded mainly to landward current in bottom layer (classical estuarine circulation) rather than seaward current (reversed estuarine circulation), contributing to increase in Trsed. Considering that the prevailing winds from 2013 to 2020 in Onsan Bay mainly create a favorable condition for the development of the classical estuarine circulation, the sedimentation is expected to persist.

Stratospheric Ozone Changes Damp the CO2-Induced Acceleration of the Brewer–Dobson Circulation

Abstract The increase of atmospheric CO2 concentrations changes the atmospheric temperature distribution, which in turn affects the circulation. A robust circulation response to CO2 forcing is the strengthening of the stratospheric Brewer–Dobson circulation (BDC), with associated consequences for transport of trace gases such as ozone. Ozone is further affected by the CO2-induced stratospheric cooling via the temperature dependency of ozone chemistry. These ozone changes in turn influence stratospheric temperatures and thereby modify the CO2-induced circulation changes. In this study, we perform dedicated model simulations to quantify the modification of the circulation response to CO2 forcing by stratospheric ozone. Specifically, we compare simulations of the atmosphere with preindustrial and with quadrupled CO2 climate conditions, in which stratospheric ozone is held fixed or is adapted to the new climate state. The results of the residual circulation and mean age of air show that ozone changes damp the CO2-induced BDC increase by up to 20%. This damping of the BDC strengthening is linked to an ozone-induced relative enhancement of the meridional temperature gradient in the lower stratosphere in summer, thereby leading to stronger stratospheric easterlies that suppress wave propagation. Additionally, we find a systematic weakening of the polar vortices in winter and spring. In the Southern Hemisphere, ozone reduces the CO2-induced delay of the final warming date by 50%. Significance Statement A robust circulation response to enhanced CO2 is the strengthening of the equator-to-pole circulation in the stratosphere, the so-called Brewer–Dobson circulation (BDC), which affects the ozone layer by tracer transport. This in turn alters stratospheric temperatures and thereby modifies the stratospheric circulation. In the present study, we perform model experiments to quantify the ozone-induced circulation changes caused by quadrupled CO2 concentrations. The results show that ozone changes damp the CO2-induced BDC strengthening due to radiative effects of the redistributed ozone layer by enhanced CO2. These ozone modifications lead to strengthened stratospheric easterlies in summer and decelerated westerlies in winter and spring. Moreover, the ozone changes reduce the CO2-induced delay of the polar vortex break down date in the Southern Hemisphere.

Effect of Freshwater Discharge From Estuary Dam on Residual Circulation in Bifurcated Channel

AbstractThe residual structure of the inner part of the Yeongsan River estuary has been reported to be a multi‐layer vertical structure, unlike the two‐layer vertical structure of a typical estuary, due to irregular freshwater discharge. The inner estuary has a main channel connected to the open sea, and a bifurcated channel system (sub‐channel) in its central part, which can affect the residual current. In this study, field observations of three‐dimensional velocity and salinity were conducted to understand the discharge effects on the residual current at bifurcated channels. The residual flows were estimated using least‐squares harmonic analysis. The relative contributions of advection acceleration and friction terms to nonlinear effects were evaluated using along‐channel momentum balance. In the absence of freshwater discharge, the flow patterns were dominated by tidal dynamics in the sub‐channel rather than the main channel, whereas most flow patterns during freshwater discharge were dominated by near‐surface strong velocity in the main channel. A multi‐layer vertical residual structure was observed during the non‐discharge period in the main channel, which was caused by the insertion of upstream residual flow from the sub‐channel. Nonlinear effects occurred at the bifurcation point of the two channels. During the non‐discharge period, the advection term was most dominant, whereas the vertical friction term was dominant during the discharge period. Moreover, the magnitude of the horizontal friction term was larger than that of the advection term. Therefore, freshwater discharge can lead to an increase in the friction term, which in turn can markedly affect the residual circulation.

Molecular epidemiology of pneumococcal carriage in children from Seville, following implementation of the PCV13 immunization program in Andalusia, Spain

IntroductionThe 13-valent pneumococcal conjugate vaccine (PCV13) universal vaccination programme was introduced in December 2016 in Andalusia. MethodsA cross-sectional study was conducted on the molecular epidemiology of pneumococcal nasopharyngeal colonization. A total of 397 healthy children were recruited from primary healthcare centres in Seville for the periods 1/4/2018 to 28/2/2020 and 1/11/2021 to 28/2/2022 (PCV13 period). Data from a previous carriage study conducted among healthy and sick children from 1/01/2006 to 30/06/2008 (PCV7 period), were used for comparison of serotype/genotype distributions and antibiotic resistance rates. ResultsOverall, 76 (19%) children were colonized with S. pneumoniae during the PCV13 period and there were information available from 154 isolates collected during the PCV7 period. Colonization with PCV13 serotypes declined significantly in the PCV13 period compared with historical controls (11% vs 38%, p = 0.0001), being serotypes 19F (8%), 3 (1%) and 6B (1%) the only circulating vaccine types. Serotypes 15B/C and 11A were the most frequently identified non-PCV13 serotypes during the PCV13 period (14% and 11%, respectively); the later one increased significantly between time periods (p = 0.04). Serotype 11A was exclusively associated in the PCV13 period with ampicillin-resistant variants of the Spain9V-ST156 clone (ST6521 and genetically related ST14698), not detected in the preceding period. ConclusionsThere was a residual circulation of vaccine types following PCV13 introduction, apart from serotype 19F. Serotype 11A increased between PCV13 and PCV7 periods due to emergence and clonal expansion of ampicillin-resistant genotype ST6521.

The Climatology of Elevated Stratopause Events in the UA‐ICON Model and the Contribution of Gravity Waves

AbstractThe climatologies of the stratopause height and temperature in the UA‐ICON model are examined by comparing them to 17‐years (2005–2021) of Microwave Limb Sounder (MLS) observations. In addition, the elevated stratopause (ES) event occurrence, their main characteristics, and driving mechanisms in the UA‐ICON model are examined using three 30‐year time‐slice experiments. While UA‐ICON reasonably simulates the large‐scale stratopause properties similar to MLS observations, at polar latitudes in the Southern Hemisphere the stratopause is ∼8 K warmer and ∼3 km higher than observed. A time lag of about two months also exists in the occurrence of the tropical semiannual oscillation of the stratopause compared to the observations. ES events occur in ∼20% of the boreal winters, after major sudden stratospheric warmings (SSWs). Compared to the SSWs not followed by ES events (SSW‐only), the ES events are associated with the persistent tropospheric forcing and prolonged anomalies of the stratospheric jet. Our modeling results suggest that the contributions of both gravity waves (GW)s and resolved waves are important in explaining the enhanced residual circulation following ES events compared to the SSW‐only events but their contributions vary through the lifetime of ES events. We emphasize the role of the resolved wave drag in the ES formation as in the sensitivity test when the non‐orographic GW drag is absent, the anomalously enhanced resolved wave forcing in the mesosphere gives rise to the formation of the elevated stratopause at about 85 km.

The Holton–Tan mechanism under stratospheric aerosol intervention

Abstract. The teleconnection between the quasi-biennial oscillation (QBO) and the Arctic stratospheric polar vortex, or the Holton–Tan (HT) relationship, may change in a warmer climate or one with stratospheric aerosol intervention (SAI) compared to the present-day climate (PDC). Our results from an Earth system model indicate that, under both global warming (based on RCP8.5 emission scenario) and SAI scenarios, the HT relationship weakens in early winter (November–December), although it is closer to PDC under SAI than under the RCP8.5 scenario. In contrast, the HT relationship in the middle to late winter period (January–February) does not change considerably in response to either RCP8.5 or SAI scenarios compared to PDC. While the weakening of the HT relationship under the RCP8.5 scenario is likely due to the weaker QBO wind amplitudes at the Equator, another physical mechanism must be responsible for the weaker HT relationship under SAI scenarios, since the amplitude of the QBO wind is comparable to the PDC. The strength of the polar vortex does not change under the RCP8.5 scenario compared to PDC, but it becomes stronger under SAI; we attribute the weakening of the HT relationship under SAI to a stronger polar vortex. In general, the changes in the HT relationship cannot be explained by changes to the critical line; the changes in the residual circulation (particularly due to the gravity wave contributions) are important in explaining the changes in the HT relationship under RCP8.5 and SAI scenarios.

Theoretical Foundation of the Linear Relationship between the Midlatitude Eddy Heat Flux and Fall-to-Spring Polar Ozone Buildup

Abstract It has been demonstrated that there is a globally unified linear relationship between the interannual variations of the fall-to-spring polar ozone accumulation and the winter-mean poleward eddy heat flux on the 100 hPa pressure surface. The foundation of this relationship is investigated using time-slice experiments on a chemistry–climate model with two levels of ozone-depleting substances (ODSs). The features of the transport field are interpreted by decomposing the horizontal ozone flux caused by the residual circulation into contributing processes including the eddy heat flux with the aid of the transformed Eulerian-mean momentum equation followed by rearrangement of terms. The linear relationship between the interannual variations of the fall-to-spring ozone buildup integrated poleward and above a reference point Pref on a meridional plane and the poleward eddy heat flux during the corresponding period at Pref is realized for each hemisphere implying that the interhemispheric unification should be treated with caution. This relationship is interpreted using the fact that the interannual variation of poleward ozone transport in the upper stratosphere is captured well by the vertical convergence of the constituent-based Eliassen–Palm (EP) flux (), which is defined as the product of the constituent (ozone) mixing ratio and EP flux. The eddy momentum flux contributes to the meridional ozone transport in combination with the eddy heat flux in the form of the divergence of , although it is not responsible for realizing the linear relationship. The dependence of the linearity on the location of Pref and ODS levels is discussed.

Downdrift Port Siltation Adjacent to a River Mouth: Effects of Mesotidal Conditions and Typhoon

The Zhuoshui River has one of the highest sediment yields in the world. The riverine sediment may have been transported away from the river mouth by strong tidal currents and deposited in a navigational channel and a harbor basin south of the Zhuoshui River. This study describes the dispersal of riverine sediments in mesotidal conditions, including transport processes of sediments via river plumes, initial deposition, resuspension, and long-term net accumulation. Our results revealed that the distribution of suspended sediment concentration (SSC) and the transport process of the river plume was markedly modulated by tidal currents in a north–south direction. Under high-discharge conditions, energetic winds and ocean currents interrupted the offshore propagation of the sediment-laden river plume with a high SSC to the ocean. The plume, induced by typhoon floods, was either propagated northward due to the Coriolis effect or was deposited near the river mouth. The sediments deposited within the inner shelf were resuspended by intensive tidal currents and transported through southward residual circulations to the navigation channel south of the river mouth.

Stratospheric Modulation of Tropical Upper-Tropospheric Warming-Induced Circulation Changes in an Idealized General Circulation Model

Abstract The stratospheric polar vortex is dynamically coupled to the tropospheric circulation. Therefore, a better mechanistic understanding of this coupled system is important to interpret past and future circulation changes correctly. Previously, idealized simulations with a dry dynamical-core general circulation model and imposed tropical upper-tropospheric warming (TUTW) have shown that a critical warming level exists at which the polar vortex transitions from a weak and variable to a strong and stable regime. Here, we investigate the dynamical mechanism responsible for this regime transition and its influence on the troposphere by performing similar idealized experiments with (REF) and without a polar vortex (NPV). According to the critical-layer control mechanism, the strengthened upper flank of the subtropical jet in response to TUTW leads to an accelerated wave-driven residual circulation in both experiments. For the REF experiment, the stronger residual circulation is associated with changes in the lower-stratospheric thermal structure that are consistent with an equatorward shift of the polar vortex. At a certain threshold of TUTW in the REF experiment, the tropospheric jet and the stratospheric polar vortex form a confined waveguide for planetary-scale waves that presumably favors downward wave coupling events. Consistently, the polar vortex strengthens in combination with an enhanced poleward shift of the tropospheric jet compared to the NPV experiment. Overall, these idealized experiments suggest that a polar vortex strengthening can be caused by greenhouse gas–induced warmings via modifications of the waveguide. This mechanism might also be relevant to understand the polar vortex changes in more complex models.

Surface Convergence Zones due to Lagrangian Residual Flow in Tidally Driven Estuaries

Abstract Buoyant material, such as floating debris, marine organisms, and spilled oil, is aggregated and trapped within estuaries. Traditionally, the aggregation of buoyant material is assumed to be a consequence of converging Eulerian surface currents, often associated with lateral (cross-estuary) density gradients that drive baroclinic lateral circulations. This study explores an alternative aggregation mechanism due to tidally driven Lagrangian residual circulations without Eulerian convergence zones and without lateral density variation. In a tidally driven estuary, the depth-dependent tidal phase of the lateral velocity varies across the estuary. This study demonstrates that the lateral movement of surface trapped material follows the tidal phase, resulting in a lateral Lagrangian residual circulation known as Stokes drift for small-amplitude motions. For steeper bathymetry, the lateral change in tidal phase is greater and the corresponding lateral Lagrangian residual flow faster. At local depth extrema, e.g., in the thalweg, depth does not vary laterally, so that the associated tidal phase is laterally constant. Therefore, the Stokes drift is weak near depth extrema resulting in Lagrangian convergence zones where buoyant material concentrates. These ideas are evaluated employing an idealized analytic model in which the along-estuary tidal flow is driven by an imposed barotropic pressure gradient, whereas cross-estuary flow is induced by the Coriolis force. Model results highlight that convergence zones due to Lagrangian residual velocities are efficient in forming persistent aggregation regions of buoyant material along the estuary. Significance Statement Our study focuses on the aggregation of buoyant material (e.g., debris, oil, organisms) in estuaries. Traditionally, the aggregation of buoyant material is assumed to be a consequence of converging Eulerian surface currents, often associated with lateral (cross-estuary) density gradients that drive baroclinic lateral circulations. Our study explores an alternative aggregation mechanism due to tidally driven Lagrangian residual circulations without Eulerian convergence zones and without lateral density variation. Our results highlight that convergence zones due to Lagrangian residual velocities are efficient in forming persistent aggregation regions of buoyant material along the estuary.

Epidemiología molecular de la colonización nasofaríngea neumocócica en niños de Sevilla, tras la implementación del programa de vacunación con VNC13 en Andalucía (España)

BackgroundThe 13-valent pneumococcal conjugate vaccine (PCV13) universal vaccination program was introduced in December 2016 in Andalusia. MethodsA cross-sectional study was conducted on the molecular epidemiology of pneumococcal nasopharyngeal colonization. A total of 397 healthy children were recruited from primary healthcare centres in Seville for the periods 1/4/2018 to 28/2/2020 and 1/11/2021 to 28/2/2022 (PCV13 period). Data from a previous carriage study conducted among healthy and sick children from 1/01/2006 to 30/06/2008 (PCV7 period) were used for comparison of serotype/genotype distributions and antibiotic resistance rates. ResultsOverall, 76 (19%) children were colonized with S. pneumoniae during the PCV13 period and there were information available from 154 isolates collected during the PCV7 period. Colonization with PCV13 serotypes declined significantly in the PCV13 period compared with historical controls (11 vs. 38%, P=0.0001), being serotypes 19F (8%), 3 (1%) and 6B (1%) the only circulating vaccine types. Serotypes 15B/C and 11A were the most frequently identified non-PCV13 serotypes during the PCV13 period (14% and 11%, respectively); the later one increased significantly between time periods (P=0.04). Serotype 11A was exclusively associated in the PCV13 period with ampicillin-resistant variants of the Spain9V-ST156 clone (ST6521 and genetically related ST14698), not detected in the preceding period. ConclusionsThere was a residual circulation of vaccine types following PCV13 introduction, apart from serotype 19F. Serotype 11A increased between PCV13 and PCV7 periods due to emergence and clonal expansion of ampicillin-resistant genotype ST6521.