Flux Variations Research Articles

The Behavior of BpSi Stars in the Far UV—Paper I: HD 22920

The analysis of five spectra of the Bp Si star HD 22920 recorded by the SWP camera on board the International Ultraviolet Explorer reveals variations of the far-ultraviolet flux of this star throughout its recently derived rotation period of 3.947 days. Spectra separated by half of the rotation period show variations of the FUV flux shortwards of 1700 Å. The Si ii autoionization lines in the region 1350 to 1460 Å clearly vary in phase with the Si ii doublet near 1530 Å. The FUV variations are caused by variations of the FUV Si ii continuous and line opacity as spots of overabundant silicon come into the line of sight while the star rotates.

Ignoring the Effects of Photovoltaic Array Deployment on Greenhouse Gas Emissions May Lead to Overestimation of the Contribution of Photovoltaic Power Generation to Greenhouse Gas Reduction.

Photovoltaic (PV) power generation is one of the world's most promising options for carbon emission reduction. However, whether the operation period of solar parks can increase greenhouse gas (GHG) emissions in hosting natural ecosystems has not been fully considered. Here, we conducted a field experiment to compensate for the lack of evaluation of the effects of PV array deployment on GHG emissions. Our results show that the PV arrays caused significant differences in air microclimate, soil properties, and vegetation characteristics. Simultaneously, PV arrays had more significant effects on CO2 and N2O emissions but a minor impact on CH4 uptake in the growing season. Of all the environmental variables included, soil temperature and moisture were the main drivers of GHG flux variation. The sustained flux global warming potential from the PV arrays significantly increased by 8.14% compared to the ambient grassland. Our evaluation models identified that the GHG footprint of PV arrays during the operation period on grasslands was 20.62 g CO2-eq kW h-1. Compared with our model estimates, GHG footprint estimates reported in previous studies were generally less by 25.46-50.76%. The contribution of PV power generation to GHG reduction may be overestimated without considering the impact of PV arrays on hosting ecosystems.

Global Radiative Flux Profile Data Set: Revised and Extended

AbstractThe third generation of the radiative flux profile data product, called ISCCP‐FH, is described. The revisions over the previous generation (called ISCCP‐FD) include improvements in the radiative model representation of gaseous and aerosol effects, as well as a refined statistical model of cloud vertical layer variations with cloud types, and increased spatial resolution. The new product benefits from the changes in the new H‐version of the ISCCP cloud products (called ISCCP‐H): higher spatial resolution, revised radiance calibration and treatment of ice clouds, treatment of aerosol effects, and revision of all the ancillary atmosphere and surface property products. The ISCCP‐FH product is evaluated against more direct measurements from the Clouds and the Earth’s Radiant Energy System and the Baseline Surface Radiation Network products, showing some small, overall reductions in average flux uncertainties; but the main results are similar to ISCCP‐FD: the ISCCP‐FH uncertainties remain ≲10 Wm−2 at the top‐of‐atmosphere (TOA) and ≲15 Wm−2 at surface for monthly, regional averages. The long‐term variations of TOA, surface and in‐atmosphere net fluxes are documented and the possible transient cloud feedback implications of a long‐term change of clouds are investigated. The cloud and flux variations from 1998 to 2012 suggest a positive cloud‐radiative feedback on the oceanic circulation and a negative feedback on the atmospheric circulation. This example demonstrates that the ISCCP‐FH product can provide useful diagnostic information about weather‐to‐interannual scale variations of radiation induced by changes in cloudiness as well as atmospheric and surface properties.

Near-real-time estimation of fossil fuel CO2 emissions from China based on atmospheric observations on Hateruma and Yonaguni Islands, Japan

We developed a near-real-time estimation method for temporal changes in fossil fuel CO2 (FFCO2) emissions from China for 3 months [January, February, March (JFM)] based on atmospheric CO2 and CH4 observations on Hateruma Island (HAT, 24.06° N, 123.81° E) and Yonaguni Island (YON, 24.47° N, 123.01° E), Japan. These two remote islands are in the downwind region of continental East Asia during winter because of the East Asian monsoon. Previous studies have revealed that monthly averages of synoptic-scale variability ratios of atmospheric CO2 and CH4 (ΔCO2/ΔCH4) observed at HAT and YON in JFM are sensitive to changes in continental emissions. From the analysis based on an atmospheric transport model with all components of CO2 and CH4 fluxes, we found that the ΔCO2/ΔCH4 ratio was linearly related to the FFCO2/CH4 emission ratio in China because calculating the variability ratio canceled out the transport influences. Using the simulated linear relationship, we converted the observed ΔCO2/ΔCH4 ratios into FFCO2/CH4 emission ratios in China. The change rates of the emission ratios for 2020–2022 were calculated relative to those for the preceding 9-year period (2011–2019), during which relatively stable ΔCO2/ΔCH4 ratios were observed. These changes in the emission ratios can be read as FFCO2 emission changes under the assumption of no interannual variations in CH4 emissions and biospheric CO2 fluxes for JFM. The resulting average changes in the FFCO2 emissions in January, February, and March 2020 were 17 ± 8%, − 36 ± 7%, and − 12 ± 8%, respectively, (− 10 ± 9% for JFM overall) relative to 2011–2019. These results were generally consistent with previous estimates. The emission changes for January, February, and March were 18 ± 8%, − 2 ± 10%, and 29 ± 12%, respectively, in 2021 (15 ± 10% for JFM overall) and 20 ± 9%, − 3 ± 10%, and − 10 ± 9%, respectively, in 2022 (2 ± 9% for JFM overall). These results suggest that the FFCO2 emissions from China rebounded to the normal level or set a new high record in early 2021 after a reduction during the COVID-19 lockdown. In addition, the estimated reduction in March 2022 might be attributed to the influence of a new wave of COVID-19 infections in Shanghai.

Determining the IBEX Ribbon Transverse Profile from ENA Temporal Variations: A Proof of Concept for IMAP Observations

Since its discovery in 2009, the IBEX energetic neutral atom (ENA) Ribbon has been a subject of numerous studies. It appears at energies ∼0.5–6 keV and is most pronounced at ∼1–3 keV. It is almost circular, ∼20°–40° wide, and its center lies near the pristine local interstellar magnetic field direction, whose field lines are draped around the heliosphere. The Ribbon intensity is enhanced above the more diffuse, globally distributed flux (GDF) and varies on timescales that are delayed compared to the underlying and slowly varying GDF. We present a novel method to infer the Ribbon boundaries and transverse profile of the Ribbon using sequential time variations of ENA fluxes, with minimal modeling assumptions involved. The method utilizes the difference in temporal evolution between the total Ribbon content and GDF fluxes. We then use the inferred Ribbon transverse profile to statistically quantify the GDF contribution to the observed peak Ribbon intensity to be ∼32.23% ± 3.15% in 2009–2011. This Ribbon separation method works best during times of gradual changes in solar wind output, and with high angular resolution and ENA counting statistics; results thus provide a proof of concept for the upcoming Interstellar Mapping and Acceleration Probe ENA measurements.

Tethys’s Heat Fluxes Varied with Time in the Ithaca Chasma and Telemus Basin Region

We investigated how lithospheric heat fluxes varied temporally and spatially on the Saturnian moon Tethys, focusing on the region of Ithaca Chasma that overprints Telemus Impact Basin. Our results, derived from flexure associated with Ithaca, indicate elastic thicknesses of 4.1 ± 0.3 km to 6.4 ± 0.4 km and heat fluxes ranging from 12 to 39 mW m−2 assuming a nonporous pure H2O ice lithosphere. Our results for Ithaca’s south limb are similar to previous estimates within the north limb, indicating consistent heat fluxes across a large spatial extent in this area. However, our estimates are lower than those for the older Telemus Basin (>60 mW m−2), revealing evidence that Tethys experienced a substantial temporal variation in heat fluxes in this region. Heat fluxes reflected by Ithaca are similar to previous estimates for Tethys’s two youngest impact basins, Melanthius and Odysseus, suggesting that Ithaca may also be relatively young. If Tethys’s lithosphere is porous, then our heat flux estimates for Ithaca Chasma drop to 12–38 mW m−2, 11–35 mW m−2, and 10–33 mW m−2 for 5%, 15%, and 25% porosities, respectively. If Tethys’s lithosphere includes ∼10% NH3-hydrates, then the estimates are 5–16 mW m−2, 5–15 mW m−2, 4–14 mW m−2, and 4–13 mW m−2 for 0%, 5%, 15%, and 25% porosities, respectively. Although we find that some ground-based reflectance spectra hint at 2.2 μm bands that may result from NH3-bearing species, the detected features are weak and may not result from surface constituents. Consequently, our heat flux estimates that assume a pure H2O ice lithosphere are likely more accurate.

Probing the Variation of Reverberation Lags along with X-Ray Flux in the AGN Mrk 704

Understanding the variation of lags with respect to the X-ray flux is important to explore the geometry of the inner region of the accretion disk in AGNs. We performed frequency-lag, energy–lag and spectral studies for two sets of observations, in order to investigate the variations in lags with respect to X-ray flux in the AGN source Mrk 704 using the XMM-Newton observatory. We divided one of the light curves into two sections which were noticed to exhibit a flux variation. The frequency-lag spectra in different energy domains revealed that reverberation (soft) lags varied along with the flux. For the first time, we show that the blurred reflection model can consistently explain the soft excess observed in the X-ray spectra for this source. The fluxes of soft (i.e., reflection) and hard components were noted to vary by ∼18% and ∼9% respectively, across the sections. The soft lag amplitude was found to be larger at the high flux state than the amplitude at the low flux state. Most importantly, we found that both frequency-lag and energy–lag spectra do not display significant variation between two observational data sets despite a flux variation of 43%. This phenomenon cannot be explained by the reflection model because the soft lag amplitudes must be larger in the high flux state. The probable scenario is that, in the low flux state, the obscuring cloud delays the reflected soft photons which increases the soft lag amplitude.

Characteristics of X-class flares of solar cycles 23 and 24 in X-ray and EUV bands

The characteristics of X-class flares of solar cycles 23 and 24 are examined based on the soft X-ray (0.1–0.8 nm) and EUV (26–34 nm) light curves. First, the commonly used correction factors for the center-to-limb variation of EUV flux are compared. Subsequently, enhancements in X-ray and EUV levels are used to calculate the relative apportionment of flare energy released in these two bands. The X-ray to EUV proportion of energy is found to be larger in the high X-class flares (X9.0 and stronger) as compared to the flares weaker than X9.0. The X-ray and EUV light curves revealed that the time of impulsive and thermal EUV peaks differed from X-ray peak by ∼0–25 min. The time differences had a broad range for weaker flares but reduced to within ∼7 min for high X-class flare events. Therefore, the present study brings out the general energetics and temporal evolution of phases of the X-class flares. Implications of the findings on solar flare studies and flare impact on terrestrial atmosphere are discussed.

Water seepage characteristics in porous media with various conduits: Insights from a multi-scale Darcy-Brinkman-Stokes approach

Conduits are widely distributed in porous media, such as natural rocks and soils, which could be the dominant water discharge channels. Investigations regarding the seepage process in such porous media with conduits are rather significant and have attracted many researchers’ attention. However, the conventional method to describe this type of seepage could not consider that in both the porous zone and fracture zone simultaneously. In this study, the multi-phase Darcy-Brinkman-Stokes (DBS) method is selected to simulate the seepage in porous rock with various conduits. The DBS method includes the Darcy method in the porous region and the Navier-Stokes method in the solid-free region. Accordingly, non-conduit porous rock, solid free pure conduit region, and porous rock with conduits are simulated respectively, using the approach accompanied by an open-source solver in OpenFoam. Comparing the experimental results and the results using Navier-Stokes (NS) simulation, the applicability of the DBS method to describe the seepage in a rock mass with conduits is verified. Using the DBS approach, three aspects of the investigations are then conducted, namely, flux variations with the aperture of the conduit, influence factors of the transition layer, and various situations of rectangular conduit. The simulation results show that the flow rate of rock mass with circular conduit and the maximum velocity of conduit are positively correlated with the circular aperture. And the width of the transition layer is positively correlated with aperture and permeability but independent of the pressure gradient. In addition, the law for the square conduit is similar to that of circular conduit, while the results of rectangular conduit show some different features.

Data-Driven-Model-Based Full-Region Optimal Mapping Method of Permanent Magnet Synchronous Motors in Wide Temperature Range

To improve the motor efficiency and expand the actual external characteristic region of electric vehicle permanent magnet synchronous motor (PMSM) drive systems, the optimal operation of mapping torque to d-q axis current is usually applied. Nevertheless, it is difficult to deal with the complex mechanism factors such as parameter saturation and temperature change for the traditional optimization method based on the basic voltage equation of PMSM. In this paper, a black-box-model-based torque–current optimization method is proposed, which does not rely on any information of the inner mechanism model, and the derivative-free, optimal, improved Nelder–Mead Simplex(NMS) method is used to minimize the copper loss and maximize the electromagnetic torque in the flux-weakening region. Moreover, a synchronous online compensation of the electromagnetic torque and optimal current angle is implemented, in view of the time variation of permanent magnet flux with temperature. Finally, through a comparison experiment with the nominal-parameters-based formula maximum torque per ampere (MTPA) method, the proposed method achieves higher torque accuracy and better efficiency performance in a wide temperature range with regard to a reasonable response speed.

Interannual variation of soil heat flux in a grass-dominated alpine tunda. Preliminary study from the Jeseníky Mts. (Short Communication)

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Interannual, sub-seasonal and spatial variations in growing season surface heat fluxes for the U.S. Corn Belt

Spatiotemporal variations in surface latent (LE) and sensible (H) heat fluxes from croplands and patches of remnant deciduous forest in the Midwest U.S. Corn Belt have been proposed to trigger “nonclassical mesoscale circulations” (NCMCs) in the atmosphere's boundary layer and moist convection, under suitable synoptic conditions. However, prior to evaluating the link between land use and land cover (LULC), NCMCs, and precipitation for the Corn Belt, it is necessary to better understand the interannual, sub-seasonal, and spatial variations in surface heat fluxes. Here, a nine-year warm season “climatology” (1999–2007) of daily afternoon and early evening averages of LE and H from two flux towers, representative of cropland (Bondville, IL) and deciduous forest (Morgan Monroe State Forest, IN), is analyzed for sub-seasonal and interannual variations in the convective fluxes. Wilcoxon signed rank tests show significant growing season and sub-seasonal anomalies in LE and H at both flux tower sites. Structural equation modeling relates these inter-growing season anomalies in LE and H to variations in net radiation, vapor pressure deficit, and temperature, while MODIS Normalized Difference Vegetation Index data link some of the sub-seasonal variations in the surface energy balance to phenology at the start of the growing season. Additional composite analysis of LE and H from the North American Regional Reanalysis shows characteristic spatial heterogeneities and significant differences in LE and H for different synoptic circulation patterns related to the variations in net radiation and LULC. These results highlight the importance of considering the sub-seasonal and spatial variations in surface heat fluxes of the Corn Belt for the range of synoptic conditions, within the context of this region's recent interannual climate variations and will help inform the search for LULC-influenced moist convection.

The Behavior of He-weak in the Far-UV—Paper I: HD 5737

The analysis of 28 spectra of the bright B6 He-weak star HD 5737 recorded by the SWP camera on board the International Ultraviolet Explorer reveals one instance of marginal variation of the far-ultraviolet flux of this star from 1300 up to 1700 Å. All the other large aperture spectra show a remarkably constant spectral energy distribution. Over the 6 yr of the IUE mission, HD 5737 has experienced at least two episodes of very strong absorption in the C iv resonance lines at 1548.19 and 1550.77 Å,

Water level of inland saline wetlands with implications for CO2 and CH4 fluxes during the autumn freeze-thaw period in Northeast China.

Zhalong wetland is the largest inland saline wetland in Asia and susceptible to imbalance and frequent flooding during the freeze-thaw period. Changes in water level and temperature can alter the rate of greenhouse gas release from wetlands and have the potential to alter Earth's carbon budget. However, there are few reports on how water level, temperature, and their interactions affect greenhouse gas flux in inland saline wetland during the freeze-thaw period. This study revealed the characteristics of CO2 and CH4 fluxes in Zhalong saline wetlands at different water levels during the autumn freeze-thaw period and clarifies the response of CO2 and CH4 fluxes to water levels. The significance analysis of cumulative CO2 fluxes at different water levels showed that water levels did not have a significant effect on cumulative CO2 release fluxes from wetlands. Water levels, temperature, soil moisture content, soil nitrate, and ammonium nitrogen content and organic carbon content could explain 24.5-98.9% of CO2 and CH4 flux variation. There were significant differences in the average and cumulative CH4 fluxes at different water levels. The higher the water levels, the higher the CH4 fluxes. In short, water level had a significant effect on wetland methane fluxes, but not on carbon dioxide fluxes.

Linking the interiors and surfaces of magnetic stars

ABSTRACTStrong magnetic fields are observed in a substantial fraction of upper main sequence stars and white dwarfs. Many such stars are observed to exhibit photometric modulations as the magnetic poles rotate in and out of view, which could be a consequence of magnetic perturbations to the star’s thermal structure. The magnetic pressure is typically larger than the gas pressure at the star’s photosphere, but much smaller than the gas pressure in the star’s interior, so the expected surface flux perturbations are not clear. We compute magnetically perturbed stellar structures of young $3 \, \mathrm{M}_\odot$ stars that are in both hydrostatic and thermal equilibrium, and which contain both poloidal and toroidal components of a dipolar magnetic field as expected for stable fossil fields. This provides semi-analytical models of such fields in baroclinic stably stratified regions. The star’s internal pressure, temperature, and flux perturbations can have a range of magnitudes, though we argue the most likely configurations exhibit flux perturbations much smaller than the ratio of surface magnetic pressure to surface gas pressure, but much larger than the ratio of surface magnetic pressure to central gas pressure. The magnetic pole is hotter than the equator in our models, but a cooler magnetic pole is possible depending on the magnetic field configuration. The expected flux variations for observed field strengths are δL/L ≲ 10−6, much smaller than those observed in magnetic stars, suggesting that observed perturbations stem from changes to the emergent spectrum rather than changes to the bolometric flux.

Multiepoch Detections of the Extended Atmosphere and Transmission Spectra of KELT-9b with a 1.5 m Telescope

Irradiated Jovian atmospheres are complex and dynamic and can undergo temporal variations due to the close proximity of their parent stars. Of the Jovian planets that have been cataloged to date, KELT-9b is the hottest gas giant known, with an equilibrium temperature of 4050 K. We probe the temporal variability of transmission spectroscopic signatures from KELT-9b via a set of archival multiyear ground-based transit observations, performed with the TRES facility on the 1.5 m reflector at the Fred Lawrence Whipple Observatory. Our observations confirm past detections of Fe i, Fe ii, and Mg i over multiple epochs, in addition to excess absorption at Hα, which is an indicator for ongoing mass loss. From our multiyear data set, the Hα light curve consistently deviates from a standard transit and follows a “W” shape that is deeper near ingress and egress and shallower midtransit. To search for and quantify any seasonal variations that may be present, we parameterize a “cometary tail” model to fit for the Hα transit. We find no detectable variations between the different observed epochs. Though a “cometary tail” describes the Hα flux variations well, we note that such a scenario requires a high density of neutral hydrogen in the n = 2 excited state far beyond the planetary atmosphere. Other scenarios, such as center-to-limb variations larger than that expected from 1D atmosphere models, may also contribute to the observed Hα transit shape. These multiepoch observations highlight the capabilities of small telescopes to provide temporal monitoring of the dynamics of exoplanet atmospheres.

Low-frequency quasi-periodic oscillation in MAXI J1820+070: Revealing distinct Compton and reflection contributions

ABSTRACT X-ray low-frequency quasi-periodic oscillations (LFQPOs) of black hole X-ray binaries, especially those type-C LFQPOs, are representative timing signal of black hole low/hard state and intermediate state, which has been suspected as to originate due to Lense-Thirring precession of the accretion flow. Here we report an analysis of one of the Insight-HXMT observations of the black hole transient MAXI J1820+070 taken near the flux peak of its hard spectral state during which strong type-C LFQPOs were detected in all three instruments up to photon energies above 150 keV. We obtained and analysed the short time-scale X-ray spectra corresponding to high- and low-intensity phases of the observed LFQPO waveform with a spectral model composed of Comptonization and disc reflection components. We found that the normalization of the spectral model is the primary parameter that varied between the low and high-intensity phases. The variation in the LFQPO flux at the hard X-ray band (≳100 keV) is from the Compton component alone, while the energy-dependent variation in the LFQPO flux at lower energies (≲30 keV) is mainly caused by the reflection component with a large reflection fraction in response to the incident Compton component. The observed X-ray LFQPOs thus should be understood as manifesting the original timing signals or beats in the hard Compton component, which gives rise to additional variability in softer energies due to disc reflection.

Optic Fiber Microsensor Reveals Specific Spatiotemporal Oxygen Uptake Profiles at the Mammalian Ocular Surface.

Oxygen (O2) uptake by cells and tissues is a critical indicator of metabolic demand, changes in microenvironment, and pathophysiology. O2 uptake from the atmosphere accounts for virtually all the O2 consumption in the avascular cornea; however, a detailed spatiotemporal profile of corneal O2 uptake (COU) remains undetermined. Here, we used a non-invasive self-referencing optical fiber O2 sensor-the scanning micro-optrode technique (SMOT)-to report the O2 partial pressure and flux variations at the ocular surface of rodents and non-human primates. In vivo spatial mapping in mice revealed a distinct COU, characterized by a centripetal gradient with a significantly higher O2 influx at the limbus and conjunctiva regions than at the center of the cornea. This regional COU profile was reproduced ex vivo in freshly enucleated eyes. The centripetal gradient was conserved across the following species analyzed: mice, rats, and rhesus monkeys. In vivo temporal mapping in mice showed a significant increase in the O2 flux in the limbus in the evening compared to other times. Altogether, the data unveiled a conserved centripetal COU profile, which may be associated with the limbal epithelial stem cells residing at the intersection of the limbus and conjunctiva. These physiological observations will serve as a useful baseline for comparative studies with contact lens wear, ocular disease, diabetes, etc. Moreover, the sensor may be applied to understand the responses of the cornea and other tissues to various insults, drugs, or changes in the environment.

On the Polar Bias in Ice Core 10Be Data

AbstractCosmogenic radionuclide records from polar ice cores provide unique insights into past cosmic ray flux variations. They allow reconstructions of past solar activity, space weather, and geomagnetic field changes, and provide insights into past carbon cycle changes. However, all these applications rely on the proportionality of the ice core radionuclide records to the global mean production rate changes. This premise has been long debated from a model and data‐perspective. Here, we address this issue through atmospheric mixing model experiments and comparison to independent data. We find that all mixing scenarios, which do not assume complete tropospheric mixing, result in a polar bias. This bias is more prominent for geomagnetic field changes than solar modulation changes. The most likely scenario, supported by independent geomagnetic field records and marine 10Be during the Laschamps geomagnetic field minimum, results in a dampening of geomagnetic field induced changes by 23%–37% and an enhancement of solar‐induced changes by 7%–8%. During the Holocene, we do not find conclusive evidence for a polar bias. We propose a correction function that allows deconvolving the glacial ice core record in order to restore proportionality to the global mean signal.

Fluxes of settling sediment particles and associated mercury in a coastal environment contaminated by past mining (Gulf of Trieste, northern Adriatic Sea)

PurposeAs the result of historical mining at Idrija (Slovenia), mercury (Hg) contamination in the Gulf of Trieste (northern Adriatic Sea) is still an issue of environmental concern. The element has been conveyed into the coastal area by the Isonzo/Soča River inputs of freshwater and suspended particles for centuries. This research aims to investigate the occurrence of Hg bound to the settling sediment particles (SSP) in the coastal water and to assess the sedimentary Hg fluxes.MethodsSettling sediment particles were collected at four sites located in the innermost sector of the Gulf, a shallow and sheltered embayment where the accumulation of fine sediments is promoted. Six sampling campaigns were performed under different environmental conditions in terms of discharge from the Isonzo River and 12 sediment traps were installed in the upper and bottom water column for SSP collection. Settling sediment particles (SSP) were collected approximately every 2 weeks and analysed for grain size and total Hg.ResultsSettling sediment particles (SSP) consisted predominantly of silt (77.7 ± 10.1%), showing a concentration of Hg ranging overall between 0.61 and 6.87 µg g−1. Regarding the daily SSP fluxes, the minimum (7.05 ± 3.26 g m−2 day−1) and the maximum (92.4 ± 69.0 g m−2 day−1) values were observed under conditions of low and high river discharge, respectively. The daily Hg fluxes displayed a notable variability, up to an order of magnitude, both in the surface water layer (3.07–94.6 µg m−2 day−1) and at the bottom (11.3–245 µg m−2 day−1), reaching the maximum values following periods of high river flow.ConclusionsThe Isonzo River inputs of suspended particulate matter continue to convey Hg into the Gulf of Trieste, especially following river flood events, which represent one of the most relevant natural factors affecting the variations of the Hg flux in the investigated area.