Plume Area Research Articles

Research of influence of the additional electrode on Hall thruster plume by particle-in-cell simulation**Project supported by the National Natural Science Foundation of China (Grant No. 51776047), the Key Project of the National Natural Science Foundation of China (Grant No. 51736003), the Civil Aerospace Pre-research Project (Grant No. D010509), and the Open Fund of Beijing Institute of Control Engineering (Grant No.

Hall thruster is an electric propulsion device for attitude control and position maintenance of satellites. The discharge process of Hall thruster will produce divergent plume. The plume will cause erosion, static electricity, and other interference to the main components, such as solar sailboard, satellite body, and thruster. Therefore, reducing the divergence of the plume is an important content in the research of thruster plume. The additional electrode to the plume area is a way to reduce the divergence angle of the plume, but there are few related studies. This paper uses the particle-in-cell (PIC) simulation method to simulate the effect of the additional electrode on the discharge of the Hall thruster, and further explains the effect mechanism of the additional electrode on parameters such as the electric field and plume divergence angle. The simulation results show that the existence of the additional electrode can enhance the potential near the additional position. The increase of the potential can effectively suppress the radial diffusion of ions, and effectively reduce the plume divergence angle. The simulation results show that when the additional electrode is 30 V, the half plume divergence angle can be reduced by 18.21%. However, the existence of additional electric electrode can also enhance the ion bombardment on the magnetic pole. The additional electrode is relatively outside, the plume divergence angle is relatively small, and it can avoid excessive ion bombardment on the magnetic pole. The research work of this paper can provide a reference for the beam design of Hall thruster.

Climatology of Maipo and Rapel river plumes off Central Chile from numerical simulations

River-influenced coastal areas are important ecosystems due to the critical influence of river runoff on nutrients and the structure of planktonic and benthic communities. Many studies have focused on the interaction among river runoff, wind, tides and river plume characteristics, and based on observations and modeling results. This study aims to improve our understanding about the circulation and seasonal pattern of river plumes off Central Chile, using climatological simulations in the Regional Ocean Modeling System (ROMS). Results were in reasonable agreement with satellite (MODIS) observations. The plumes exhibit a minimal area cover during summer-fall, with a northwest orientation as result of dominant southwesterly winds and low river discharges. A larger plume area is developed during June–September, as result of higher winter precipitations. The orientation of the plumes during winter is westward, driven by higher river discharges and winds blowing in the southeast direction. An interesting feature reproduced by the model was the trend to coalesce as observed in previous studies using satellite imagery.

Multi-objective optimization of permeable reactive barrier design for Cr(VI) removal from groundwater.

The present study aims to develop a practical approach for the optimal permeable reactive barrier (PRB) design towards Cr(VI) removal from groundwater. Batch and column experiments were performed to investigate the characteristics of the four proposed reactive materials; nanoscale zero-valent iron (Fe0), bimetallic nanoscale zero-valent iron (Fe0/Cu), activated carbon (AC) and sand/zeolite mixture (S/Z). Kinetic analysis and dynamic modeling of the experimental data were implemented to determine the controlling conditions of the reactive performance of the PRB's materials. The sensitivity index of the design parameters was examined as an indicator of their effect on the reactive responses. Moreover, the Response Surface Methodology (RSM) was considered for optimizing the design variables of the PRB based on the practical factorial analysis. Results revealed that Fe0 and Fe0/Cu showed high performance in Cr(VI) removal, with a slight superiority to Fe0, with final removal efficiency values of 89.7 and 84.1%, respectively. Kinetic analysis depicted that pseudo second order was the best fitting model for Cr(VI) removal in the four materials' cases. ANOVA statistical analysis revealed that quadratic polynomial model was the best model, corresponding to the highest correlation efficiency and adequate precision, to describe the relationships in the four PRB's cases between the selected dependent variables; resident time (tR), reactive material mass per sectional area of contaminant plume (M/A) and reactive material cost (CostPRB) towards the independent parameters; barrier thickness (b) and permeability (Kr). Additionally, sensitivity analysis has been conducted which depicted the high sensitivity, in the four PRB's cases, of average pore water velocity within the barrier (vr) vr and Kr with the highest and the second-highest sensitivity index (SI) values towards tR, respectively. The RSM-optimization revealed that Fe0 is the most feasible reactive material, comparing to the other considered materials, with respect to the optimal conditions regarding the long residency (tR=22 days) and low cost (b=0.521m), with around 95.2% desirability of its optimal solution. Overall, the current study represents a significant contribution and a vital step towards an accurate PRB's design based on previously determined optimal conditions.

Influence of Mississippi and Atchafalaya River plume in the winter coastal cooling of the Northwestern Gulf of Mexico

Sea surface temperature (SST) variability was analyzed in the Northwestern Gulf of Mexico over the period 1982–2018. This analysis was carried out by the combination of reanalysis databases (OISST1/4 and CFSR) and a hydrodynamic model (ROMS). SST warming is detected throughout the year with the exception of the Louisiana-Texas shelf where a cooling is observed during winter months (November–February). The existence of a different SST trend near coast with respect to open ocean is related to Mississippi and Atchafalaya River plumes. The bigger differences, between plume area cooling and ocean warming, are detected under the plume reinforcement driven by an increment in the freshwater discharge. The plume reinforcement increases the stratification and reduces the vertical mixing, favoring the atmospheric cooling of coastal SST during winter.

River plume monitoring in a deep valley reservoir using HJ-1 A/B images

River discharge carries suspended matter into lakes, reservoirs, estuaries, and coasts, resulting in obvious plumes in river mouths. River plumes are more likely to form in valley reservoirs due to the steep slopes in the basin, which may accelerate fluvial transport from upstream to the river mouth, causing a considerable particles load and increasing the appearance times and scale of river plumes during rainfall events. Information on the intensity and evolution of river plumes in valley reservoirs has important implications for understanding nearshore geomorphological processes and dynamics in the water quality surrounding river mouths. Taking the Xin’anjing Reservoir, a typical deep valley reservoir, as a case study, a plume index based on the relative reflectance height in the red band of HJ-1 A/B images was first proposed. Subsequently, we used seventeen HJ-1 A/B images during 10 heavy rainfall events from 2009 to 2014 to characterize the spatial–temporal variability in river plumes and illustrate the relation of the river plumes and total suspended matter (TSM) concentration to the amount of rainfall. The results indicated that 10 heavy rainfall events caused different plume areas varying from 41.26 to 148.12 km2, with an average area of 76.45 ± 35.03 km2. Significant positive correlations were observed between plume areas, TSM concentrations and rainfall amount (P < 0.005). The plumes would simultaneously emerge when the rapid surface flow reached the river mouth but increase to the maximum size after 2–3 days of these heavy rainfalls. These results confirmed that the HJ-1 A/B images combined with our proposed plume index could detect and monitor the formation and diffusion of river plumes in valley reservoirs during heavy rainfall events.

Effects of pylon geometry on mixing enhancement in a scramjet pylon-cavity flameholder

ABSTRACTNumerical investigation of the effect of pylon geometry within a pylon-cavity aided Supersonic Combustion Ramjet (SCRAMJET) combustor on mixing enhancement, flame-holding capability, fuel jet penetration and total pressure loss are conducted in the current study. RANS equations for compressed real gas are solved by coupled, implicit, second-order upwind solver. A two-equation SST model is used for turbulence modelling. Validation of the computational model is performed with the help of experimental data collected using surface pressure taps, Schlieren flow visualisation and particle image velocimetry (PIV). The study uses four distinct pylon geometry cases, which include the baseline geometry. Sonic injection of hydrogen fuel through a 1mm diameter hole at 2mm downstream of the pylon rear face along the axis of the test section floor is performed for every case. A crossflow of Mach number 2.2 at four bar absolute pressure and standard atmospheric temperature is maintained. A comparative study of mixing efficiency, total pressure loss, fuel jet penetration and fuel plume area fraction for the different cases evaluate the mixing performance. The simulations show that the Pylon 2 case gives a significant improvement in the performance parameters compared to the other geometries. It is observed that mixing efficiency and fuel jet penetration capability of the system are highly dependent on the streamwise vortex within the flameholder.

Revealing Plasma-Surface Interaction at Atmospheric Pressure: Imaging of Electric Field and Temperature inside the Targeted Material

The plasma-surface interaction is studied for a low temperature helium plasma jet generated at atmospheric pressure using Mueller polarimetry on an electro-optic target. The influence of the AC kHz operating frequency is examined by simultaneously obtaining images of the induced electric field and temperature of the target. The technique offers high sensitivity in the determination of the temperature variation on the level of single degrees. Simultaneously, the evolution of the electric field in the target caused by plasma-driven charge accumulation can be measured with the threshold of the order of 105 V/m. Even though a specific electro-optic crystal is used to obtain the results, they are generally applicable to dielectric targets under exposure of a plasma jet when they are of 0.5 mm thickness, have a dielectric constant greater than 4 and are at floating potential. Other techniques to examine the induced electric field in a target do not exist to the best of our knowledge, making this technique unique and necessary. The influence of the AC kHz operating frequency is important because many plasma jet designs used throughout the world operate at different frequency which changes the time between the ionization waves and hence the leftover species densities and stability of the plasma. Results for our jet show a linear operating regime between 20 and 50 kHz where the ionization waves are stable and the temperature increases linearly by 25 K. The charge deposition and induced electric fields do not increase significantly but the surface area does increase due to an extended surface propagation. Additionally, temperature mapping using a 100 μm GaAs probe of the plasma plume area has revealed a mild heat exchange causing a heating of several degrees of the helium core while the surrounding air slightly cools. This peculiarity is also observed without plasma in the gas plume.

PyTrx: A Python-Based Monoscopic Terrestrial Photogrammetry Toolset for Glaciology

Terrestrial time-lapse photogrammetry is a rapidly growing method for deriving measurements from glacial environments because it provides high spatio-temporal resolution records of change. Currently, however, the potential usefulness of time-lapse data is limited by the unavailability of user-friendly photogrammetry toolsets. Without prior knowledge in photogrammetry and computer coding, such data are used primarily to calculate ice flow velocities or to serve as qualitative records. PyTrx (available at https://github.com/PennyHow/PyTrx) is presented here as a Python-alternative toolset to widen the range of monoscopic photogrammetry (i.e. from a single viewpoint) toolsets on offer to the glaciology community. The toolset holds core photogrammetric functions for template generation, feature-tracking, image registration, and georectification (using a planar projective transformation model). In addition, PyTrx facilitates areal and line measurements, which can be detected from imagery using either an automated or manual approach. Examples of PyTrx's applications are demonstrated using time-lapse imagery from Kronebreen and Tunabreen, two tidewater glaciers in Svalbard. Products from these applications include ice flow velocities, surface areas of supraglacial lakes and meltwater plumes, and glacier terminus profiles.

Determination of Thermal Pollution Effect on End Part of Stream

The present study was conducted to evaluate the environmental impact of thermal effluent sources on the main water quality parameters at the low flow conditions. The low flow causes the flow velocity to be low which causes accumulation of any pollutant source. The study was performed by creating a 2-d model of the last reach of Rosetta branch at winter closure. Delft 3d software is used to create a hydro-dynamic model to simulate the flow pattern within a 5 km of the branch upstream Edfina regulator. Water quality model is coupled afterwards to simulate the water quality parameters. A base case scenario of the current state at the low flow condition is set up and calibrated. Another scenario is performed after adding a thermal pollutant source. Thermal power plant is used as an application of thermal pollutant source. Cooling water is with drawled from an intake and discharged back to the water source with a relatively higher temperature downstream the intake. A case study of Dairut thermal power plant which is planned to be constructed at this area is used. Hydrographic survey is performed to collect essential hydraulic data for the model. Field measurements are performed to collect water quality along the area. A numerical model was set up and the area was simulated. Results showed accumulation of thermal plume. The higher temperatures lowered the dissolved oxygen in the thermal plume area. On the other hand, BOD and NO3 values increased with different rates. Ammonium was positively affected and was lowered.

Effects of Mg content on keyhole behaviour during deep penetration laser welding of Al-Mg alloys

This paper concerns the effects of Mg content on keyhole behaviours during the laser welding process of 5754, 5083 and 5A06 Al-Mg alloys. The features of the vapour plume and keyhole area are extracted from high-speed images with image processing methods. The increase of Mg content leads to the increase of hydrodynamic pressure caused by metal evaporation and decrease of surface tension acting on the keyhole wall. The strong metal evaporation and decrease of surface tension help the formation of keyhole, which both result in a large size of keyhole with deep penetration and low frequency of keyhole collapse. However, the impact of metal vapour could be enhanced by the increase of evaporation and the decrease of both surface tension and viscosity, which leads to the frequent generation of swelling at the rear weldpool and poor formation of the weld bead.

DISTRIBUTION OF ARTIFICIAL RADIONUCLIDES IN AGGREGATE FRACTIONS OF SOILS IN THE VICINITY OF UNDERGROUND NUCLEAR TESTS CONDCUTED IN BOREHOLES AT “BALAPAN” SITE

The paper provides findings on distribution of artificial radionuclides in aggregate fractions of soils in radioactive fallout plumes near two Boreholes – 1301 and 1077 (the former ‘Balapan’ testing area), in which underground nuclear tests were conducted that differed in the nature of the real radiological situation. In the vicinity of Borehole 1301 in which an underground nuclear explosion was accompanied by the unforeseen release of debris into the atmosphere, the highest accumulation of 137Cs and 90Sr occurs in 250 to 1,000 µm fractions. Distribution of 241Am and 239+240Pu is characterized by two different tendencies – the predominant enrichment of 250 to 1,000 µm fractions in the near zone of the plume (up to 250 m) and predominantly enriched fractions of 5–8 µm and &lt;1 µm in the distant plume area (700 to 2,500 m). Near Borehole 1077, near which the underground explosion is assumed to have been accompanied by escaping radioactive inert gases, 137Cs and 90Sr are mainly concentrated in less than 5 µm fractions, 241Am and 239+240Pu – in fractions of 8–40 µm and &lt;1 µm.

Impact of excess and deficit river runoff on Bay of Bengal upper ocean characteristics using an ocean general circulation model

The present study investigates the impact of excess river runoff (eRR) and deficit river runoff (dRR) on the Bay of Bengal (BoB) upper ocean physics and circulation patterns using high resolution Modular Ocean Model version 5 (MOM5) simulations. The ocean model MOM5 was forced by 3-hourly surface fluxes and interannual river runoff from the Japanese 55-year Reanalysis (JRA-55). Sensitivity experiments are carried out with interannual and climatological river discharges from 1965 to 2016. Four positive river runoff anomaly years (1980, 1988, 1990, 2007) and four negative river runoff anomaly years (1979, 1986, 1992, 2009) during the satellite era, which are not influenced by the equatorial wind anomalies, are considered for the detailed analysis of eRR and dRR years. The study reveals that the distribution of salinity and the freshwater plume in eRR years differ significantly in the northern and western BoB from that of dRR years. The sea surface salinity difference is ~2 psu in the northern BoB and the advection of freshwater by the southward East India Coastal Current (EICC) reaches the southern part of the BoB and enters the Arabian Sea in the eRR years. A strong cooling is observed in eRR years over the plume distributed area during post-monsoon and the excess freshwater amplifies the EICC as well. The large inflow of freshwater during eRR years is closely associated with a shallow mixed layer depth (MLD), formation of a thick barrier layer (BL), and strong circulation and temperature inversions, while the dRR years accumulate more heat compared to the eRR years in the upper 100 m of the plume area. This study, therefore, provides evidence for the impact of freshwater discharge on the BoB upper ocean processes. These may have a large impact on the local air-sea coupled processes and so representing accurate river discharge in climate models is crucial. It is also found that the EICC and the basin-wide cyclonic gyre advect the barrier layer along the Indian east coast into the southeastern Arabian Sea. This is one of the first studies to incorporate interannual runoff of all the major rivers flowing into the BoB in an ocean general circulation model for investigations of BoB processes.

Fluvial and oceanographic influences on suspended sediment dispersal in the Magdalena River Estuary

The Magdalena River is the main contributor of fresh water and sediment to the Caribbean Sea. Hydrological inputs from the Magdalena River are 10,287 and 4068 m3 s−1 at high and low flows, respectively. Sediment delivery from the Magdalena River is among the largest in the world, with 142 × 106 t yr−1 of transported suspended matter. We used MODIS images to develop a regional model and assess the spatial and temporal variability of suspended sediment concentration at the mouth of the Magdalena River, map the extent of the turbidity plume using its morphometric properties, and identify the main fluvial and oceanographic factors associated with plume variability. We analyzed monthly average suspended sediment concentration data for the period 2003–2017. MODIS images were calibrated with in situ measurements of suspended sediment concentrations in surface waters of the study area. A finite mixing model was used to identify turbidity thresholds and define areas within the plume. Calculated suspended sediment concentrations indicate high turbidity in the Magdalena River mouth (178.6 ± 78.7 mg L−1), values that are of the same order of magnitude as those measured in the Yangtze, Huang He and Amazon River mouths. Calculated plume areas (diffuse, solid and mixing) and their shapes suggest that the Magdalena River plume has a limited area, related to conditions such as wind speed and direction, streamflow, and sediment transport. Calculated areas and shapes demonstrate the ability to generate a near-field area, which indicates the presence of a clear convergence front. The data also emphasize the importance of sediment transport from the Magdalena River to the Caribbean Sea. Such fluvial transport is important in the biogeochemistry of estuarine systems, especially in turbid estuaries, where there is marked variability in the distribution of sediment in surface waters.

On a relationship between the river runoff and the river plume area in the northeastern Black Sea

ABSTRACT The coastal zone of the northeastern part of the Black Sea is characterized by 80 small rivers with a runoff which may reach 800 m3 s−1. Maximum values of the runoff are related to heavy rain that occasionally occurs over the coastal zone. River runoff forms a river plume in the coastal zone of the sea, which, depending on the local wind speed and direction and current velocity and direction, amount of the runoff and density difference with sea water, may propagate in different directions from the river mouth, and may be involved in the mesoscale and sub-mesoscale circulation. The aim of this study is to investigate the relationship between the runoff of the main rivers along the Russian coast of the Black Sea and the area of the appropriate river plumes. In this paper, we compared the daily runoff from the Mzymta and Sochi rivers and the area of river plumes detected by high concentration of suspended matter acquired daily from Medium Resolution Imaging Spectrometer (MERIS) of satellite Envisat (Environmental Satellite) on different dates in 2006–2011. We took 1 g m−3 as a formal threshold to calculate an outer limit and area of the river plume because it better corresponds with the form of the plume on true colour satellite images. As a result, we obtained a linear regression between the river runoff and the river plume area with a correlation coefficient 0.99 for the Mzymta River and a parabolic regression for the Sochi River. A linear regression with a correlation coefficient 0.98 can be applied to the Sochi River as well. The slope of the linear regressions differs three times between these two rivers, which may be explained by a significantly different distance of hydrological gauge stations from the river mouths, as well as by physical and geochemical characteristics of the river mouths. Anyway, such relationships even though they can be specific for each river, will considerably help estimate areas of river plumes and identify coastal regions subject to environmental risks after heavy rain.

Role of plankton in the vertical flux in the East Siberian sea shelf

Role of plankton in the vertical flux in the East Siberian Sea was studied in the 69 cruise of the RV Akademik Mstislav Keldysh in September 2017. Vertical fluxes were measured in sediment traps samples collected in the area of Indigirka river plume and in the marine shelf area. Mass vertical flux and particulate organic carbon flux varied from 80 to 530 mg/м2/d and from 16 to 49 mgС/м2/d, accordingly. Phytoplankton in sediment traps was dominated by cysts and spores of diatoms and dinoflagellates. Phytoplankton flux increased with depths from 0.220.33 to 1.21.3 мgС/м2/d. Fecal pellet fluxes (712 mgС/м2/d) was almost similar at two studied stations and did not change with depth. Zooplankton in the traps was dominated by houses of larvacean and carcasses of copepods Jashnovia tolli and Calanus glacialis Flux of zooplankton varied from 3 to 17 mgС/m2/d. The influence of the continental runoff reflected in a decrease of the proportion of planktonogenic components in the vertical flux of organic carbon. In the river plume area their total contribution to organic carbon flux did not exceed 30%; on the marine shelf it reached 80%.

An empirical algorithm to seamlessly retrieve the concentration of suspended particulate matter from water color across ocean to turbid river mouths

We propose a globally applicable algorithm (GAASPM) to seamlessly retrieve the concentration of suspended particulate matter (SPM) (CSPM) from remote sensing reflectance (Rrs(λ)) across ocean to turbid river mouths without any hard-switching in its application. GAASPM is based on a calibrated relationship between CSPM and a generalized index for SPM (GISPM) from water color. The GISPM is mainly composed of three Rrs(λ) ratios (671, 745, and 862 nm over 551 nm, respectively), along with weighting factors assigned to each ratio. The weighting factors are introduced to ensure the progressive application of Rrs(λ) in the longer wavelengths for increasing CSPM. Calibration of GAASPM employed data collected from multiple estuarine and coastal regions of Europe, China, Argentina, and the USA with the measured CSPM spanning from 0.2 to 2068.8 mg/L. Inter-comparison with several recalibrated well-known CSPM retrieval algorithms demonstrates that GAASPM has the best retrieval accuracy over the entire CSPM range with a relative mean absolute difference (rMAD) of 41.3% (N = 437). This averaged uncertainty in GAASPM-derived CSPM is mostly attributed to the retrievals from less turbid waters where CSPM < 50 mg/L (rMAD = 50%, N = 214). GAASPM was further applied to the Visible Infrared Imaging Radiometer Suite (VIIRS) measurements over prominent coastal areas and produced reliable CSPM maps along with realistic spatial patterns. In contrast, applications of other CSPM algorithms resulted in less reliable CSPM maps with either unjustified numerical discontinuities in the CSPM spatial distribution or unsatisfactory retrieval accuracy. Therefore, we propose GAASPM as a preferred algorithm to retrieve CSPM over regions with a wide range of CSPM, such as river plume areas.

Ar-CO-liquid steel flow with decarburization chemical reaction in single snorkel refining furnace

As a new style refining equipment developed from the traditional RH furnace, Single Snorkel Refining Furnace (SSRF), which is also called as single snorkel RH, is widely used for producing ultra-low carbon steel. However, the effect of CO gas on fluid flow and decarburization is not reported in the existing literatures. Based on the Eulerian-Eulerian approach, a two-way coupling mathematical model considering CO gas is proposed to investigate the coupling phenomenon of Ar-CO-liquid steel flow and decarburization in SSRF. And the industrial experimental data is employed to validate the numerical result. In comparison with the one-way coupling model, the numerical result predicted by the two-way coupling model is closer to the industrial experimental data. The CO mole number, which is generated by the overall decarburization process, is about 3 times the argon mole number blown into the ladle, and the CO generation rate is greater than argon blowing rate at the first 12 min. Because of the stirring effect of CO gas, there are the more complex fluid flow, the stronger mass transfer, the greater decarburization rate and the lower carbon mass concentration in the liquid steel during decarburization. Besides, the Ar plume area predicted by the two-way coupling model is larger and it is closer to the center line of the snorkel. Therefore, the effect of CO gas on the fluid flow cannot be ignored and the two-way coupling model can describe the metallurgical phenomena in SSRF more precisely.

The role of river runoff in the Kara Sea surface layer acidification and carbonate system changes

This study aims to perform the results of the investigation of the Kara Sea carbonate system (CS) changes and the factors that determine it. The important feature of the Kara Sea water structure is strong stratification caused mainly by the Ob’ and Yenisey rivers discharge which is estimated as 81% of the total continental runoff to sea. Occurring climate changes, as an increase in the total volume of the Arctic Ocean water (due to melting of glaciers, sea ice decline and river runoff increase), air temperature and CO2 concentration growth should affect greatly the Kara Sea CS. However, riverine water influence seems to be the main driver of future acidification of the Kara Sea water due to permafrost thawing as it stores a great amount of buried carbon. An increase of carbon (mainly inorganic) flow to the sea will lead to carbonate equilibrium shift, oxidation of organic matter and release of CO2 that ultimately leads to a decrease in pH and therefore acidification. The area of the riverine plume depends on the amount of freshwater flowing into the sea and the conditions of the wind forcing. According to the data from Shirshov Institute cruises within the plume area aragonite saturation is below 1 that shows its state as acidified. Prevalence of pCO2 values in the freshened surface layer over the atmospheric shows that atmospheric carbon dioxide, apparently, cannot serve as the main driver for the acidification of the surface waters of the Kara Sea. At the shallow shelf to the north of the Ob′ Inlet mouth we observe acidification of the whole water column from surface to the bottom layer due to elevated riverine discharge and increase of flowing terrestrial carbon.

Estimation of CO2 Emissions from Wildfires Using OCO-2 Data

The biomass burning model (BBM) has been the most widely used method for estimation of trace gas emissions. Due to the difficulty and variability in obtaining various necessary parameters of BBM, a new method is needed to quickly and accurately calculate the trace gas emissions from wildfires. Here, we used satellite data from the Orbiting Carbon Observatory-2 (OCO-2) to calculate CO2 emissions from wildfires (the OCO-2 model). Four active wildfires in Siberia were selected in which OCO-2 points intersecting with smoke plumes identified by Aqua MODIS (MODerate-resolution Imaging Spectroradiometer) images. MODIS band 8, band 21 and MISR (Multi-angle Imaging SpectroRadiometer) data were used to identify the smoke plume area, burned area and smoke plume height, respectively. By contrast with BBM, which calculates CO2 emissions based on the bottom–top mode, the OCO-2 model estimates CO2 emissions based on the top–bottom mode. We used a linear regression model to compute CO2 concentration (XCO2) for each smoke plume pixel and then calculated CO2 emissions for each wildfire point. The CO2 mass of each smoke plume pixel was added to obtain the CO2 emissions from wildfires. After verifying our results with the BBM, we found that the biases were between 25.76% and 157.11% for the four active fires. The OCO-2 model displays the advantages of remote-sensing technology and is a useful tool for fire-emission monitoring, although we note some of its disadvantages. This study proposed a new perspective to estimate CO2 emissions from wildfire and effectively expands the applied range of OCO-2 satellite data.

Evaluation of enhancing CO2 sequestration by post-brine injection under different scenarios using the E300 compositional simulator

To accelerate the CO2 trapping in geological storage sites, several injection strategies have been proposed by researchers so far. However, the question remains unanswered as to which one of these injection strategies is the most efficient in terms of immobilising CO2 and more importantly, how these strategies might be improved. In this paper, we attempt to simulate a typical geological CO2 storage scheme in an aquifer using the E300 compositional reservoir simulator and subsequently investigate and compare the impact of various injection strategies on CO2 immobilising efficiency. Secondly, the impact of adding a short period of post-brine injection on various strategies is newly investigated.Our results reveal that using a relatively short period of post-brine injection can significantly improve total CO2 trapping efficiency in all the strategies. In general, by using post injection of brine, more CO2 is spread out through the aquifer and, as a consequence, by increasing the interfacial area of the CO2 plume, the amount of dissolution as a result of mass transfer increases significantly. Moreover, the effect of convection can become stronger in the case of post-brine injection creating a stronger density instability and thus a more rapid initiation of convection. Furthermore, when brine is injected into the system, CO2 is displaced away from the well resulting in a forced imbibition process and thereby enhancing the capillary trapping efficiency. The post-injection of brine has also one more particular effect in strategies of horizontal injection and simultaneous CO2/brine injection in different intervals. In this regard, post-brine injection creates a stronger downward pressure gradient that counters the tendency of the CO2 plume to rise and therefore retards the CO2 in reaching the top of the aquifer. This increases the time that the CO2 can be in contact with the fresh formation brine and so enhances the trapping efficiency.We envisage that the post-brine injection could enhance the total trapping efficiency of CO2 from 26%, 30.8%, 39.8% and 59.1% to 47.7%, 44.2%, 62% and 63.9%, when it was added into different strategies of CO2 continuous injection, simultaneous injection of CO2/brine in the same and different intervals and a horizontal system, respectively. However, our findings show that the effectiveness of post-brine injection may be reduced in high vertical permeability values and in this respect, capillary trapping can be more affected by vertical permeability variation. Furthermore, the results show that selection of the rate and duration of post-brine injection can have considerable effects on total CO2 trapping efficiency.