Mapping Diurnal Variability of the Wintertime Pearl River Plume Front from Himawari-8 Geostationary Satellite Observations

the spatial pattern of the wintertime Pearl River plume front (PRPF), and its variability on diurnal and spring-neap time scales are characterized from the geostationary meteorological Himawari-8 satellite, taking advantage of the satellite’s unique 10-minutely sea surface temperature sequential images. Our findings suggest that the PRPF in winter consists of three subfronts: the northern one north of 22°N 20′, the southern one south of 21°N 40′, and the middle one between 22°N 20′ and 21°N 40′. The time-varying trend of the frontal intensity generally exhibits a strong-weak-strong pattern, with the weakest plume front occurring at about 06:00 UTC, which is closely associated with net surface heat flux over the region. The comparison in frontal variability between the spring and neap tides shows that the plume front during the spring tide generally tends to be more diffuse for the frontal probability, move further offshore for the frontal position, and be weaker for the frontal intensity than those found during the neap tide. These great differences largely depend on the tidally induced stronger turbulent mixing during the spring tide while the wind stress only plays a secondary role in the process. To best of our knowledge, the distinct diurnal variations in PRPF with wide coverage are observed for the first time. This study demonstrates that the Himawari-8 geostationary satellite has great potential in characterizing high-frequency surface thermal fronts in considerable detail.

Safeguarding CO2 Storage in a Depleted Offshore Gas Field with Adaptive Approach of Monitoring, Measurement and Verification MMV

CO2 sequestration is a process for eternity with a possibility of zero-degree failure. One of the key components of the CO2 Sequestration Project is to have a site-specific, risk-based and adaptive Monitoring, Measurement and Verification (MMV) plan. The storage site has been studied thoroughly and is understood to be inherently safe for CO2 sequestration. However, it is incumbent on operator to manage and minimize storage risks. MMV planning is critical along with geological site selection, transportation and storage process. Geological evaluation study of the storage site suggests the containment capacity of identified large depleted gas reservoirs as well as long term conformance due to thick interval. The fault-seal analysis and reservoir integrity study contemplate long-term security of the CO2 storage. An integrated 3D reservoir dynamic simulation model coupled with geomechanical and geochemical models were performed. This helps in understanding storage capacity, trapping mechanisms, reservoir integrity, plume migration path, and injectivity. To demonstrate that CO2 plume migration can be mapped from the seismic, a 4D Seismic feasibility study was carried out using well and fluid data. Gassmann fluid substitution was performed in carbonate reservoir at well, and seismic response of several combination of fluid saturation scenarios on synthetic gathers were analyzed. The CO2 dispersion study, which incorporate integration of subsurface, geomatic and metocean & environment data along with leakage character information, was carried out to understand the potential leakage pathway along existing wells and faults which enable to design a monitoring plan accordingly. The monitoring of wells & reservoir integrity, overburden integrity will be carried out by Fiber Optic System to be installed in injection wells. Significant difference in seismic amplitude observed at the reservoir top during 4D seismic feasibility study for varying CO2 saturation suggests that monitoring of CO2 plume migration from seismic is possible. CO2 plume front with as low as 25% saturation can be discriminated provided seismic data has high signal noise ratio (SNR). 3D DAS-VSP acquisition modeling results show that a subsurface coverage of approximately 3 km2 per well is achievable. Laboratory injectivity studies and three-way coupled modelling simulations established that three injection wells will be required to achieve the target injection rate. As planned injection wells are field centric and storage site area is large, DAS-VSP find limited coverage to monitor the CO2 plume front. Hence, surface seismic acquisition will be an integral component of full field monitoring and time-lapsed evaluations for integrated MMV planning to monitor CO2 plume migration. The integrated MMV planning is designed to ensure that injected CO2 in the reservoir is intact and safely stored for hundreds of years after injection. Field specific MMV technologies for CO2 plume migration with proactive approach were identified after exercising pre-defined screening criteria.

Analysis of Pressure Response at an Observation Well against Pressure Build-Up by Early Stage of CO2 Geological Storage Project

To ensure a safe and stable CO2 storage, pressure responses at an observation well is expected to be an important and useful field monitoring items to estimate the CO2 storage behaviors and the aquifer parameters during and after injecting CO2, because it can detect whether the injected CO2 leaks to the ground surface or the bottom of the sea. In this study, pressure responses were simulated to present design factors such as well location and pressure transmitter of the observation well. Numerical simulations on the pressure response and the time-delay from pressure build-up after CO2 injection were conducted by considering aquifer parameters and distance from the CO2 injection well to an observation well. The measurement resolution of a pressure transmitter installed in the observation well was presented based on numerical simulation results of the pressure response against pressure build-up at the injection well and CO2 plume front propagations. Furthermore, the pressure response at an observation well was estimated by comparing the numerical simulation results with the curve of CO2 saturation and relative permeability. It was also suggested that the analytical solution can be used for the analysis of the pressure response tendency using pressure build-up and dimensionless parameters of hydraulic diffusivity. Thus, a criterion was established for selecting a pressure transducer installed at an observation well to monitor the pressure responses with sufficient accuracy and resolution, considering the distance from the injection well and the pressure build-up at the injection well, for future CCS projects.

The shelf sources of estuarine inflow

The inflow to an estuary originates on the shelf. It flushes the estuary and can bring in nutrients, heat, salt, and hypoxic water, having consequences for estuarine ecosystems and fjordic glacial melt. However, the source of estuarine inflow has only been explored in simple models that do not resolve interactions between inflow and outflow outside of the estuarine channel. This study addressed the estuary inflow problem using variations on a three-dimensional primitive equation model of an idealized estuarine channel next to a sloping, unstratified shelf with mixing provided by a single frequency, 12-hour tide. Inflow was identified using particle tracking, momentum budgets, and Total Exchange Flow. Inflow sources were found in shelf water downstream of the estuary, river plume water, and shelf water upstream of the estuary. Downstream is defined here with respect to the direction of coastal trapped wave propagation, which is to the right for an observer looking seaward from the estuary mouth in the northern hemisphere. Downstream of the estuary and offshore of the plume, the dynamics were quasi-geostrophic, consistent with previous simple models. The effect of this inflowing current on the geometry of the river plume front was found to be small. Novel sources of inflow were identified which originated from within the plume and upstream of the estuary.

Time-dependent Plume Front Positioning and Its Dynamics Coupled With Seasonal River Efflux

The time-dependent plume front fluctuation concerning different tidal phases and its dynamics coupled with seasonal river efflux in the shelf off Kochi, south west coast of India, were investigated using Finite Volume Community Ocean Model (FVCOM). The region is linked with a monsoonal estuary, featured by mixed semi-diurnal tide (1 m) and exhibited a highly complicated plume pattern. The rivalry between river efflux with tidal phases create plume fronts in the shelf, whose gradients fortified or weakened by mixing dynamics. Eventhough the incessant river efflux in the summer monsoon impart significant momentum in the shelf, the range of frontal fluctuation was curtailed to 2 km by strong monsoon currents. During transient phase of the season (fall inter-monsoon), the tidal forcings on plume positioning overwhelm the shelf currents, such that the plume front fluctuate between 6-17 km (range increased to ~11 km) from the inlet. In low tides, the region near to the inlets was almost homogenized (Rd<1). While, it gets more stratified in high tides due to the transport of high saline ambient water towards the inlet and also by the decreasing kinetic energy (Rd>1). The location of frontal zones suitable for the propagation of nonlinear waves (F≤1)will change in respect to the competition between river efflux and tide-topography interaction. The strong stratified plume front regions with increased Brunt Vaisala Frequency (BVF) in summer monsoon behave as active zones of non linear wave propagation only when the plume front decelerates from supercritical to subcritical. During dry season, the F≤1 was satisfied at limited locations, but the absence of BVFmax zone (frequency >0.3 s-1) revealed that the amplitude of such nonlinear waves would be considerably small. The study divulge that tidally pulsating plume front fluctuates between 3-18 km from inlet and also highlights that the propagation of nonlinear waves with considerable amplitude will depend on both the plume front velocity and the Brunt Vaisala Frequency of the water column.

Experimental characterization of speech aerosol dispersion dynamics

Contact and inhalation of virions-carrying human aerosols represent the primary transmission pathway for airborne diseases including the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Relative to sneezing and coughing, non-symptomatic aerosol-producing activities such as speaking are highly understudied. The dispersions of aerosols from vocalization by a human subject are hereby quantified using high-speed particle image velocimetry. Syllables of different aerosol production rates were tested and compared to coughing. Results indicate aerosol productions and penetrations are not correlated. E.g. ‘ti’ and ‘ma’ have similar production rates but only ‘ti’ penetrated as far as coughs. All cases exhibited a rapidly penetrating “jet phase” followed by a slow “puff phase.” Immediate dilution of aerosols was prevented by vortex ring flow structures that concentrated particles toward the plume-front. A high-fidelity assessment of risks to exposure must account for aerosol production rate, penetration, plume direction and the prevailing air current.

A Study on the Plasma Plume Expansion Dynamics of Nanosecond Laser Ablating Al/PTFE

To study the plasma plume expansion dynamics of nanosecond laser ablating Al/PTFE, the Al/PTFE propellant was prepared by a molding sintering method and the rapid expansion process of the plasma plume was photographed using fast photography technology. The effects of the proportion of Al, laser energy and ambient pressure on plasma plume expansion dynamics are analyzed. The results show that the plume expansion process of laser ablating Al/PTFE plasma can be divided into three stages and this phenomenon has not been reported in the literature. The Al powder doped in PTFE will block part of the laser transmission into the propellant, thus reducing the laser absorption depth of the propellant. In the case of short pulse laser ablation, the reaction rate between Al and PTFE is optimal when the reductant is slightly higher than the oxidant. As the laser energy increases, the light intensity of the plasma becomes stronger, the plasma size becomes larger and the existence time of plasma becomes longer. In the first stage plume, the plume expands freely at the ambient pressure of 0.005 Pa and the plume expansion distance is linearly related to time, while the shock wave formed at the interface between the plume front and the ambient gas at the ambient pressure of 5 Pa and the expansion can be described by S-T theory.

Observations of Shoaling Density Current Regime Changes in Internal Wave Interactions

We present in situ and remote observations of a Mississippi plume front in the Louisiana Bight. The plume propagated freely across the bight, rather than as a coastal current. The observed cross-front circulation pattern is typical of density currents, as are the small width (≈100 m) of the plume front and the presence of surface frontal convergence. A comparison of observations with stratified density current theory is conducted. Additionally, subcritical to supercritical transitions of frontal propagation speed relative to internal gravity wave (IGW) speed are demonstrated to occur. That is in part due to IGW speed reduction with decrease in seabed depth during the frontal propagation toward the shore. Theoretical steady-state density current propagation speed is in good agreement with the observations in the critical and supercritical regimes but not in the inherently unsteady subcritical regime. The latter may be due to interaction of IGW with the front, an effect previously demonstrated only in laboratory and numerical experiments. In the critical regime, finite-amplitude IGWs form and remain locked to the front. A critical to supercritical transition eventually occurs as the ambient conditions change during frontal propagation, after which IGWs are not supported at the front. The subcritical (critical) to critical (supercritical) transition is related to Froude number ahead (under) the front, consistently with theory. Finally, we find that the front-locked IGW (critical) regime is itself dependent on significant nonlinear speed enhancement of the IGW by their growth to finite amplitude at the front.

Numerical Study on Vertically Rising Time of Plumes in Stairwells of High-rise Buildings

The vulnerabilities of high-rise buildings to fires and the safe evacuation of the occupants therein have been consistently highlighted in the media. Unexpected natural disasters that occur frequently such as earthquakes increase the potential risk in large cities. If an earthquake with a magnitude that exceeds the load for safety design occurs and causes a fire in a high-rise building, it would lead to serious casualties among the occupants evacuating the building. This study represented the stairs in high-rise buildings using several full-scale models and examined the characteristics of a high temperature plume rising vertically from the ignition source using numerical analysis with Fire Dynamics Simulator (FDS). We analyzed the effects of calorific value and ventilation in the middle floors and examined the time taken by a plume rising vertically from the stairs to reach each floor. Furthermore, the empirical line suggested by McCaffrey (1979) was used to compare the characteristics of a plume rising vertically inside stairs and in a limited space with those of a plume rising vertically in an open space. Based on the time taken by a plume front to rise, which is calculated based on numerical analyses, this study identified and suggested an experiment equation to make it possible to predict the time taken by a plume to rise from the stairs in a typical high-rise building.