Lagrangian Trajectory Analysis Research Articles

Unraveling the Non‐Homogeneous Dispersion Processes in Ocean and Coastal Circulations Using a Clustering Approach

AbstractDispersion processes in environmental flows have been traditionally studied under the strong assumption of homogeneous, isotropic and stationary turbulence. To overcome this limitation, we propose a new approach that combines autocorrelation analysis of simulated Lagrangian trajectories together with unsupervised clustering. To test the approach, we consider several dynamic scenarios around a coastal gulf, subject to different forcing, in order to compare our method with other approaches. Lagrangian trajectories forced by the varying coastal circulation exhibited different behaviors, looping and non‐looping paths, and produced a variety of Lagrangian autocorrelation functions. Our approach proves to be able to reveal spatio‐temporal variations in ocean dispersion processes without any a priori knowledge of the character of the trajectories. Clusters based on the autocorrelation functions are associated to different inhomogeneous dispersion processes. Finally, we propose a new stochastic model capable of predicting the different forms of autocorrelations.

A Lagrangian Trajectory Analysis of Azimuthally Asymmetric Equivalent Potential Temperature in the Outer Core of Sheared Tropical Cyclones

A Lagrangian Trajectory Analysis of Azimuthally Asymmetric Equivalent Potential Temperature in the Outer Core of Sheared Tropical Cyclones

Implications of Emission Sources and Biosphere Exchange on Temporal Variations of CO2 and δ13C Using Continuous Atmospheric Measurements at Shadnagar (India)

AbstractDiurnal variation of atmospheric CO2 and its driving factors are studied using high‐precision in situ mixing ratio measurements and stable carbon isotopic CO2 (δ13C‐CO2) for the first time over Shadnagar, a suburban site in India, from November 2018 to October 2019. The annual mean mixing ratios of atmospheric CO2 and δ13C‐CO2 are observed to be 414.76 ± 4.26 ppm and −11.19 ‰ ± 1.63 ‰. Maximum diurnal variability of atmospheric CO2 was observed in summer monsoon (17.30 ± 9.29 ppm), and the minimum was noticed in winter (7.19 ± 0.11 ppm), indicating strong seasonality in diurnal variability of amplitude. To characterize the atmospheric CO2 sources, the Miller‐Tans model was implemented separately using the CO2 and its δ13C‐CO2 isotopic data during day and night. However, a strong source signature of δ13C‐CO2 was observed during the night‐time of summer monsoon with a slope of −37.42‰ ± 0.73‰, obtained using a reduced major axis regression. The identified source indicates possible emissions from fossil fuel combustion. Further, a Lagrangian back trajectory analysis was performed to study the influence of transport on the observed CO2 mixing ratios. The model trajectory confirms the influence of the Indian summer monsoon on the variations of atmospheric CO2 mixing ratios. Our study shows that fossil fuel emissions are one of the major contributors of CO2 in the study location (about ∼2 to 4 ppm) with biogenic fluxes adding a clear seasonality ranging from −8 to 4 ppm.

Large eddy simulations of the accumulation of buoyant material in oceanic wind-driven and convective turbulence

Buoyant material such as microplastics accumulate near the ocean surface in regions with convergent surface currents where they can be harmful to marine life. Here, we use large eddy simulations to investigate the transport and accumulation of buoyant material in a turbulent ocean mixed layer under combined wind and convection forcing. We model non-inertial buoyant particles with a combination of buoyant tracers and Lagrangian surface particles, which allows us to explore a wide range of particle buoyancies. Surface cooling drives convection, and under this regime persistent convective vortices form that trap buoyant particles, leading to large concentrations. Despite their small size, the convective vortices exhibit a bias towards cyclonic vorticity that has not been reported previously. Based on an analysis of Lagrangian trajectories, the average time that a particle spends inside a convective vortex is long enough for planetary vorticity to become important and further vortex stretching causes an exponential increase in vorticity. When wind forcing is included, there is a transition from convective cells to longitudinal wind rolls with three distinct flow patterns observed under weak, moderate and strong wind forcing. For sufficiently weak winds, convective vortices survive but are less effective at trapping buoyant material. Under strong wind forcing, convective vortices no longer exist, but some clustering occurs in regions of high speed associated with longitudinal wind rolls. We quantify the degree of clustering using the Gini coefficient and find that clustering is strongly influenced by the relative size of the friction and convective velocities and the particle buoyancy.

Evaluation of the distribution of COVID-19 particles in an Isolation room to reduce the possibility of transmission via CFD simulation

The outbreak and prolonged COVID-19 pandemic has caused a population decline as well as a profound impact on the global economy, the COVID virus spreads highly in the air through the process of sneezing, contact leads to many dangers to the health and safety of people around the world. Many simulation studies have been carried out to predict the risk of spread, as well as to find solutions to limit the infection when spreading sneeze droplets in the air. In this study, the motion and distribution of droplets containing coronaviruses emitted by coughing or sneezing in the isolation room at Ho Chi Minh City, Vietnam National University were investigated using ANSYS Fluent software. The airflow in the isolation room was simulated by a 3D turbulence model and energy equation using the finite volume method (FVM) with a domain of isolation room solved for appropriate boundary conditions. The effect of ventilation airflow speed and the size of droplets on the distribution of particles in the air were investigated by the Lagrangian particle trajectory analysis method. The CFD analysis result showed that the velocity distribution, turbulent kinetic energy, and flow dynamics had strongly affected the reducing rate of average droplet concentration in the isolation room. Specifically, the study focused on the dispersion of liquid droplets containing the virus under fixed operating conditions of ventilation systems and exhaust fans, with a flow rate of 840 m3/h. Under these conditions, the retention time of liquid droplets was determined to be 37.5 seconds, corresponding to droplet diameters ranging from 5 to 100 micrometres. The results indicate that the presence of particles in the room gradually becomes diluted over time due to the continuous circulation of air. The ability of air to diffuse within the vicinity of the occupant's position and the limited spread of small particles within the room demonstrate that the operating conditions are suitable.

Identifying Causes of Short-Range Forecast Errors in Maximum Temperature during Recent Central European Heatwaves Using the ECMWF-IFS Ensemble

Abstract In the last few years, central Europe faced a number of severe, record-breaking heatwaves. Previous studies focused on predictability of heatwaves on medium-range to subseasonal time scales (5–30 days). However, also short-range (3-day) forecasts of maximum temperature (Tmax) can exhibit substantial errors even on larger spatial scales. This study investigates the causes of short-range forecast errors in Tmax over central Europe for the summers of 2015–20 using the 50-member ensemble of the operational ECMWF-IFS (ECMWF-ENS). The 3-day forecast errors, individually calculated for each ensemble member with respect to a 0–18-h control forecast, are fed into a multivariate linear regression model to study the relative importance of different error sources. Outside of heatwaves, errors in Tmax forecasts are predominantly caused by incorrectly predicted downwelling shortwave radiation, mainly due to errors in low cloud cover. During heatwaves, ECMWF-ENS exhibits a systematic underestimation of Tmax (−0.4 K), which is exacerbated under clear-sky and low wind conditions, and other error sources gain importance: the second most important error source is over- or underestimation of nocturnal temperatures in the residual layer. Additional Lagrangian trajectory analysis for the years 2018–20 (due to limited data availability) suggests a link to accumulating errors in near-surface diabatic heating of air masses associated with forecast errors in residence time over land and cloud cover. Regionally, other physical processes can be of dominant importance during heatwaves. Coastal regions are influenced by errors in near-surface wind whereas errors in soil moisture are more important in southeastern parts of central Europe.

Multiscale wavelet analysis of 3D Lagrangian trajectories in a mechanically agitated vessel

Flow turbulence properties are of utmost importance for the optimization of mixing in stirred vessels. A new experimental-theoretical framework is developed to study such turbulence properties. A discrete wavelet transform is used to decompose Lagrangian flow trajectories measured by positron emission particle tracking into their mean and stochastic components representing different scales. The mean component represents low frequency scale motion or non-diffusive/background motion, while the stochastic component accounts for high frequency scale motion or diffusive motion of small eddies. Decomposed Lagrangian trajectories are used to construct maps of local mean and fluctuation flow velocity, turbulent kinetic energy and its dissipation rate, and, for the first time, turbulent diffusion coefficients. Particle image velocimetry measurements are utilised to independently validate results and tune the input parameters of the analysis. Such detailed information on local mixing scales is invaluable to aid equipment design and operation and facilitate heat/mass transfer and enhance reaction kinetics.

The Effect of Convective Injection of Ice on Stratospheric Water Vapor in a Changing Climate

AbstractStratospheric water vapor affects the Earth's radiative balance and stratospheric chemistry, yet its future changes are uncertain and not fully understood. The influence of deep convection on stratospheric water vapor remains subject to debate. This letter presents a detailed process‐based model study of the impact of convective ice sublimation on stratospheric water vapor in response to CO2 forced climate change. The influence of convective injection is found to be limited by the vertical profile of temperature and saturation vapor pressure in the tropical tropopause layer, not by the frequency of occurrence. Lagrangian trajectory analysis shows the relative contributions to stratospheric water vapor from sublimation and large‐scale transport are approximately unchanged when CO2 is increased. The results indicate the role of convective ice injection for stratospheric water vapor in a warmer climate remains constrained by large‐scale temperatures.

Wildfire Smoke Highlights Troposphere‐to‐Stratosphere Pathway

AbstractFollowing the 2020 wildfires in Australia, an extremely large amount of smoke entered the stratosphere and was dispersed throughout the southern hemisphere stratosphere. However, the pathway and entry point of the smoke into the stratosphere and the underlying mechanism remained unclear. Here, Lagrangian trajectory analysis is used to examine the flow downstream of the fires in the south Pacific, where the smoke was detected. We find that tropical cyclone Sarai merged with an extratropical cyclone to form a troposphere‐wide cyclonic system, with a deep potential vorticity cutoff above it. The smoke first traveled in the isentropic layer between 340 and 350 °K. Having reached the cyclone, the smoke circulated and entered the stratosphere through a dip in the tropopause height within the cutoff. The cyclone described in this case study is not uncommon in these regions, possibly underlining the importance of this mechanism for troposphere‐to‐stratosphere exchange.

Origin of water-soluble organic aerosols at the Maïdo high-altitude observatory, Réunion Island, in the tropical Indian Ocean

Abstract. The tropical and subtropical Indian Ocean (IO) is expected to be a significant source of water-soluble organic aerosols (WSOAs), which are important factors relevant to cloud formation of aerosol particles. Current atmospheric numerical models significantly underestimate the budget of organic aerosols and their precursors, especially over tropical oceans. This is primarily due to poor knowledge of sources and the paucity of observations of these parameters considering spatial and temporal variation over the tropical open ocean. To evaluate the contribution of sources to WSOA as well as their formation processes, submicrometer aerosol sampling was conducted at the high-altitude Maïdo observatory (21.1∘ S, 55.4∘ E; 2160 m a.s.l.), located on the remote island of La Réunion in the southwest IO. The aerosol samples were continuously collected during local daytime and nighttime, which corresponded to the ambient conditions of the marine boundary layer (MBL) and free troposphere (FT), respectively, from 15 March to 24 May 2018. Chemical analysis showed that organic matter was the dominant component of submicrometer water-soluble aerosol (∼ 45 ± 17 %) during the wet season (15 March–23 April). On the other hand, sulfate dominated (∼ 77 ± 17 %) during the dry season (24 April–24 May), most of which was attributable to the effect of volcanic eruption. Measurements of the stable carbon isotope ratio of water-soluble organic carbon (WSOC) suggested that marine sources contributed significantly to the observed WSOC mass in both the MBL and the FT in the wet season, whereas a mixture of marine and terrestrial sources contributed to WSOC in the dry season. The distinct seasonal changes in the dominant source of WSOC were also supported by Lagrangian trajectory analysis. Positive matrix factorization analysis suggested that marine secondary organic aerosol (OA) dominantly contributed to the observed WSOC mass (∼ 70 %) during the wet season, whereas mixtures of marine and terrestrial sources contributed during the dry season in both MBL and FT. Overall, this study demonstrates that the effect of marine secondary sources is likely important up to the FT in the wet season, which may affect cloud formation as well as direct radiative forcing over oceanic regions.

Magnitude, Scale, and Dynamics of the 2020 Mei-yu Rains and Floods over China

Large parts of East and South Asia were affected by heavy precipitation and flooding during early summer 2020. This study provides both a statistical and dynamical characterization of rains and floods affecting the Yangtze River Basin (YRB). By aggregating daily and monthly precipitation over river basins across Asia, it is shown that the YRB is one of the areas that was particularly affected. June and July 2020 rainfall was higher than in the previous 20 years, and the YRB experienced anomalously high rainfall across most of its sub-basins. YRB discharge also attained levels not seen since 1998/1999. An automated method detecting the daily position of the East Asian Summer Monsoon Front (EASMF) is applied to show that the anomalously high YRB precipitation was associated with a halted northward progression of the EASMF and prolonged mei-yu conditions over the YRB lasting more than one month. Two 5-day heavy-precipitation episodes (12−16 June and 4−8 July 2020) are selected from this period for dynamical characterization, including Lagrangian trajectory analysis. Particular attention is devoted to the dynamics of the airstreams converging at the EASMF. Both episodes display heavy precipitation and convergence of monsoonal and subtropical air masses. However, clear differences are identified in the upper-level flow pattern, substantially affecting the balance of airmass advection towards the EASMF. This study contextualizes heavy precipitation in Asia in summer 2020 and showcases several analysis tools developed by the authors for the study of such events.

COVID-19 spread in a classroom equipped with partition – A CFD approach

In this study, the motion and distribution of droplets containing coronaviruses emitted by coughing of an infected person in front of a classroom (e.g., a teacher) were investigated using CFD. A 3D turbulence model was used to simulate the airflow in the classroom, and a Lagrangian particle trajectory analysis method was used to track the droplets. The numerical model was validated and was used to study the effects of ventilation airflow speeds of 3, 5, and 7 m/s on the dispersion of droplets of different sizes. In particular, the effect of installing transparent barriers in front of the seats on reducing the average droplet concentration was examined. The results showed that using the seat partitions for individuals can prevent the infection to a certain extent. An increase in the ventilation air velocity increased the droplets’ velocities in the airflow direction, simultaneously reducing the trapping time of the droplets by solid barriers. As expected, in the absence of partitions, the closest seats to the infected person had the highest average droplet concentration (3.80 × 10−8 kg/m3 for the case of 3 m/s).

Probabilistic Forecasts of Sea Ice Trajectories in the Arctic: Impact of Uncertainties in Surface Wind and Ice Cohesion

We study the response of the Lagrangian sea ice model neXtSIM to the uncertainty in sea surface wind and sea ice cohesion. The ice mechanics in neXtSIM are based on a brittle-like rheological framework. The study considers short-term ensemble forecasts of Arctic sea ice from January to April 2008. Ensembles are generated by perturbing the wind inputs and ice cohesion field both separately and jointly. The resulting uncertainty in the probabilistic forecasts is evaluated statistically based on the analysis of Lagrangian sea ice trajectories as sampled by virtual drifters seeded in the model to cover the Arctic Ocean and using metrics borrowed from the search-and-rescue literature. The comparison among the different ensembles indicates that wind perturbations dominate the forecast uncertainty (i.e., the absolute spread of the ensemble), while the inhomogeneities in the ice cohesion field significantly increase the degree of anisotropy in the spread—i.e., trajectories drift divergently in different directions. We suggest that in order to obtain enough uncertainties in a sea ice model with brittle-like rheologies, to predict sea ice drift and trajectories, one should consider using ensemble-based simulations where at least wind forcing and sea ice cohesion are perturbed.

The effect of nasal airway obstruction on the dispersion and deposition of inhaled volatile droplets in the human nasal cavity: A numerical study

Nasal airway obstruction (NAO) is one of the main problems in the upper part of the human respiratory system. NAO may considerably affect the airflow and the behavior of droplets in the nasal cavity. In the present study, the effect of septal deviation as a special kind of NAO on the deposition and penetration of initially micron-sized inhaled droplets in the nasal cavities of two patients was numerically investigated. The geometries were constructed using CT scan images, and breathing zones were added to the models to make the inspiratory cycle more physically realistic. The motion of droplets was studied using the Lagrangian trajectory analysis approach, including the drag, Saffman's lift, and Brownian forces, as well as the evaporation process. The results showed that both unhealthy cases with obstruction had less heat transfer than the healthy nasal passage, which results in slower evaporation of droplets. On the other hand, due to the septal deviation, the deposition of droplets increased in the cases with nasal obstruction. Inertial impaction was the primary deposition mechanism, which was more critical than the diffusion in the region in which septal deviations diverted the airflow. The simulation results showed that due to less convoluted turbinate passages and smaller surface area to volume ratio (SAVR) of the nasal cavities with obstruction in comparison with a healthy nose, the size of droplets that escape from the human nasal cavity became smaller. As a result, for patients with septal deviations, small droplets could penetrate deep into the respiratory system and increase the risk of transmission of respiratory diseases.

A Case Study of the Physical Processes Associated with the Atmospheric River Initial-Condition Sensitivity from an Adjoint Model

Abstract Analysis of a strong landfalling atmospheric river is presented that compares the evolution of a control simulation with that of an adjoint-derived perturbed simulation using the Coupled Ocean–Atmosphere Mesoscale Prediction System. The initial-condition sensitivities are optimized for all state variables to maximize the accumulated precipitation within the majority of California. The water vapor transport is found to be substantially enhanced at the California coast in the perturbed simulation during the time of peak precipitation, demonstrating a strengthened role of the orographic precipitation forcing. Similarly, moisture convergence and vertical velocities derived from the transverse circulation are found to be substantially enhanced during the time of peak precipitation, also demonstrating a strengthened role of the dynamic component of the precipitation. Importantly, both components of precipitation are associated with enhanced latent heating by which (i) a stronger diabatically driven low-level potential vorticity anomaly strengthens the low-level wind (and thereby the orographic precipitation forcing), and (ii) greater moist diabatic forcing enhances the Sawyer–Eliassen transverse circulation and thereby increases ascent and dynamic precipitation. A Lagrangian parcel trajectory analysis demonstrates that a positive moisture perturbation within the atmospheric river increases the moisture transport into the warm conveyor belt offshore, which enhances latent heating in the perturbed simulation. These results suggest that the precipitation forecast in this case is particularly sensitive to the initial moisture content within the atmospheric river due to its role in enhancing both the orographic precipitation forcing and the dynamic component of precipitation.

Deposition fraction of ellipsoidal fibers in the human nasal cavity- Influence of non-creeping formulation of hydrodynamic forces and torques

In this study, the deposition of fibrous particles in a realistic 3D model of the right nasal cavity of a 24-years-old woman was simulated using the non-creeping formulations for hydrodynamic forces and torques. The Lagrangian trajectory analysis approach within the Ansys-Fluent software was used for these simulations. Several user-defined functions (UDFs) for solving the coupled translational and rotational motion of an ellipsoidal fiber and for evaluation of non-creeping forces and torques were developed and were incorporated in the Ansys-Fluent DPM. The passage included the main nasal cavity from the nostril to the beginning of the nasopharynx. Both laminar and turbulent steady inhalation breathing conditions were assumed, and for turbulence modeling, the Realizable k-ε model was employed. It was assumed that the airflow was incompressible. The breathing rates of 2.5, 5.0, 7.5, and 10 lit/min per nostril were considered for laminar airflow corresponding to the rest or light physical activity conditions. For turbulent airflow, the breathing rates of 15, 20, and 30 lit/min were assumed for high physical activities. The transport and deposition of fibers of different sizes and aspect ratios in the nasal cavity under laminar and turbulent airflow regimes were investigated.The simulation results showed that the increase of air flow rate, fiber diameter, and aspect ratio led to the increase of deposition in the human nasal cavity. In addition, the use of forces and torques estimated from the more accurate non-creeping flow estimation led to somewhat lower particle deposition in the nasal cavity compared to those obtained from the simplified creeping flow assumption.

Inertial impaction of particles on a circular cylinder for a wide range of Reynolds and P numbers: A comparative study

In this paper, particulate gas flows over a circular cylinder were studied numerically for wide ranges of flow Reynolds numbers (5 < Re < 5 × 106) and P numbers (0.025 < P < 5 × 104). P number is defined as 9Re/S and S is the particle-fluid density ratio. For Re ≤ 100, the laminar flow simulations were performed while the turbulent flow simulations were done for Re ≥ 103 using unsteady Reynolds-averaged Navier-Stokes (URANS) equations. The Reynolds stress model (RSM) was used to account for the anisotropic turbulent stresses around the cylinder. The computed drag was compared with the available experimental data and earlier numerical results. It was shown that the RSM could properly predict the drag-drop at the critical flow regime. Deposition of particles on the cylinder surface was also investigated using the Lagrangian trajectory analysis. Particle capture efficiencies were evaluated and compared with the available experimental data and theoretical models. The simulation results indicated that for P ≥ 102, the computed capture efficiencies obtained by the viscous flow analysis coincided with those obtained from the inviscid flows. For 1 ≤ P ≤ 10, differences between viscous and inviscid flow collection efficiencies, however, were more than 20% when Stk≤1. However, for P ≤ 0.1, differences between the collection efficiencies obtained by viscous and inviscid flows exceeded 20% when Stk≤2.2. In the case of Re = 103 and P = 10, the highest capture efficiency was obtained by impaction for Stk≥0.5.

Climatology and dynamics of the link between dry intrusions and cold fronts during winter. Part I: global climatology

Cold fronts are a primary feature of the day-to-day variability of weather in the midlatitudes, and feature in conceptual extratropical cyclone models alongside the dry intrusion airstream. Here the climatological frequency and spatial distribution of the co-occurrence of these two features are quantified, and the differences in cold front characteristics (intensity, size, and precipitation) when a dry intrusion is present or not are calculated. Fronts are objectively identified in the ECMWF ERA-Interim dataset for the winter seasons in each hemisphere and split into three sub-types: central fronts (within a cyclone area); trailing fronts (outwith the cyclone area but connected to a central front); and isolated fronts (not connected to a cyclone). These are then associated with dry intrusions identified using Lagrangian trajectory analysis. Trailing fronts are most likely to be associated with a DI in both hemispheres, and this occurs more frequently in the western parts of the major storm track regions. Isolated fronts are linked to DIs more frequently on the eastern ends of the storm tracks, and in the subtropics. All front types, when co-occurring with a DI, are stronger in terms of their temperature gradient, are much larger in area, and typically have higher average precipitation. Therefore, climatologically the link with DIs increases the impact of cold fronts. There are some differences in the statistics of the precipitation for trailing and isolated fronts that are further investigated in Part II of this study from the front-centred perspective.

FSLE analysis and validation of Lagrangian simulations based on satellite-derived GlobCurrent velocity data

We present an independent validation of the satellite surface velocity fields released by the ESA Data User Element GlobCurrent Project. The validation methodology is based on the analysis of Lagrangian numerical trajectories integrated from satellite-based sea surface currents. Two case studies were considered: Mediterranean Sea and North Atlantic Ocean.The Finite-Scale Lyapunov Exponents provide a rigorous, quantitative tool to evaluate Lagrangian simulations with respect to real drifter trajectories. An accuracy threshold scale can be identified as the scale above which the error size, propagating along a numerical trajectory, grows no faster than the relative separation between real drifters. Below this threshold, the error growth rate tends to diverge linearly as the error decreases. The mean error growth speed, at early stage, is found to be related to the kinetic energy of the missing scales of motion, not resolved by the GlobCurrent products. Established kinematic Lagrangian models are, also, exploited to compensate the energy gap between real and numerical trajectories in the unresolved scale range. Ultimately, GlobCurrent surface velocity fields are shown to have overall good ‘Lagrangian skills' for large-scale transport and dispersion numerical simulations.

Large eddy simulation of pressure and dilution-jet effects on soot formation in a model aircraft swirl combustor

Soot formation in a model aircraft engine configuration operating at elevated pressures is studied using large eddy simulation (LES) and detailed models for precursor and soot population evolution. Specifically, pressure and secondary oxidation air injection effects on soot formation are simulated. The configuration simulated is a dual-swirl ethylene/air combustor operating at pressures of 3 and 5 bars, with and without secondary oxidation air injection. The inflow conditions are chosen such that for the two different pressures, the only hydrodynamic change is the Reynolds number. Detailed comparisons with experimental data show that the simulation captures gas-phase statistics accurately. Although the spatial structure of soot formation is captured, including some of the trends for different operating conditions, the quantitative comparisons had significant differences. This could be attributed to the large distribution in the measurements or the chemical/physical models for soot formation. Detailed analysis showed that soot mass generation in such devices is driven by acetylene-based surface growth, with strong oxidation zones that significantly reduce net soot emissions. More importantly, soot formation occurs due to a spatially and temporally intermittent phenomena, where a small set of fluid trajectories that deposit fuel-rich pockets into the right gas-phase conditions is responsible for the bulk of soot mass generated. The occurrence of these relatively low-frequency trajectories is due to large scale unsteadiness caused by the strong swirl near the fuel jets. Lagrangian particle trajectory analysis revealed that lower pressure case without sidejet injection encourages entrainment of soot particles into the inner recirculation zone, increasing the residence time and leading to increased soot volume fraction. When pressure is increased from 3 to 5 bar, these particles move through a different mixture fraction-progress variable phase space. Consequently, there is a hydrodynamic scaling mode introduced, which can produce interesting variations from the nominal pressure scaling for soot production. These studies point to an intricate dependence of soot formation on large-scale turbulent flows, which is generally non-universal and not observed in canonical jet flames.