Gradient Drift Research Articles

Magnetic Flux Circulation in the Saturnian Magnetosphere as Constrained by Cassini Observations in the Inner Magnetosphere

AbstractIn steady state, magnetic flux conservation must be maintained in Saturn’s magnetosphere. The Enceladus plumes add mass to magnetic flux tubes in the inner magnetosphere, and centrifugal force pulls the mass‐loaded flux tubes outward. Those flux tubes are carried outward to the magnetotail where they deposit their mass and return to the mass loading region. It may take days for the magnetic flux to be carried outward to the tail, but the return of the nearly empty flux tubes can last only several hours, with speeds of inward motion around 200 km/s. Using time sequences of Cassini particle count rate, the difference in curvature drift and gradient drift is accounted for to determine the return speed, age, and starting dipole L‐shell of return flux tubes. Determination of this flux‐return process improves our understanding of the magnetic flux circulation at Saturn and provides insight into how other giant planets remove the mass added by their moons.

The Role of Mesoscale Plasma Sheet Dynamics in Ring Current Formation

During geomagnetically active periods ions are transported from the magnetotail into the inner magnetosphere and accelerated to energies of tens to hundreds of keV. These energetic ions, of mixed composition with the most important species being H+ and O+, become the dominant source of plasma pressure in the inner magnetosphere. Ion transport and acceleration can occur at different spatial and temporal scales ranging from global quasi-steady convection to localized impulsive injection events and may depend on the ion gyroradius. In this study we ascertain the relative importance of mesoscale flow structures and the effects of ion non-adiabaticity on the produced ring current. For this we use: global magnetohydrodynamic (MHD) simulations to generate self-consistent electromagnetic fields under typical driving conditions which exhibit bursty bulk flows (BBFs); and injected test particles, initialized to match the plasma moments of the MHD simulation, and subsequently evolved according to the kinetic equations of motion. We show that the BBFs produced by our simulation reproduce thermodynamic and magnetic statistics from in situ measurements and are numerically robust. Mining the simulation data we create a data set, over a billion points, connecting particle transport to characteristics of the MHD flow. From this we show that mesoscale bubbles, localized depleted entropy regions, and particle gradient drifts are critical for ion transport. Finally we show, using identical particle ensembles with varying mass, that O+ non-adiabaticity creates qualitative differences in energization and spatial distribution while H+ non-adiabaticity has non-negligible implications for loss timescales.

New Findings of the Sporadic E (Es) Layer Development Around the Magnetic Equator During a High‐Speed Solar (HSS) Wind Stream Event

AbstractThe equatorial (Esq) and blanketing (Esb) sporadic (Es) layers occur due to the Equatorial Electrojet Current (EEJ) plasma instabilities and tidal wind components, respectively. Both Esq and Esb layers can appear concurrently over some Brazilian equatorial regions due to the peculiar geomagnetic field configuration in this sector. Previous works indicate that the inclination angle limit for the Esq occurrence in ionograms is 7°. However, we found evidence that regions more distant can also experience such equatorial dynamics during disturbed periods. In this context, we deeply investigated this EEJ influence expansion effect by analyzing the Esq layers in regions not so close to the magnetic equator during a high‐speed solar wind stream event that occurred on May 05 and 06, 2018. To explain these atypical Esq layer occurrences, we considered the Es layer parameters obtained from digital ionosondes over the Brazilian regions, São Luís (dip: 9.5°), and Araguatins (dip: 10.5°). We use magnetometer data and a model named MIRE (E Region Ionospheric Model) to validate this mechanism. The results show that the eastward electric field of the Gradient Drift instability in the EEJ is effective during the magnetic storm main phase in the boundary equatorial magnetic sites, creating the Esq layers. Thus, the EEJ plasma irregularity superimposes the wind shear mechanism, changing the Es layer dynamics during disturbed periods over the magnetic equator boundary sites. Therefore, this work establishes new findings of the EEJ influence expansion dynamics in the Es layer formation over the Brazilian regions, which was considered in MIRE for the first time.

Interaction Between an EMSTID and an EPB in the EIA Crest Region Over China

AbstractFew observations investigated the interaction between an electrical medium‐scale traveling ionospheric disturbance (EMSTID) and an equatorial plasma bubble (EPB). This paper presents another interaction between a southwestward propagating EMSTID and an eastward drifting EPB in the equatorial ionization anomaly (EIA) crest region of China. When the EMSTID and the EPB touched each other, several depletions of the EMSTID (EPB) showed the eastward (westward) velocity disturbances of the EPB (EMSTID) depletions. Besides, phase elongations of the EPB depletions contrarotated as the EMSTID propagated southwestward. However, of important finding is that the interaction of the EMSTID and the EPB could have polarized one depletion of the postmidnight EPB that should have become a fossilized bubble. Inside that polarized EPB depletion were meter‐scale irregularities that caused activated radar echoes and enhanced ranged spread F (RSF). The interaction occurred in descending ionosphere and the lower density regions got filled up with an enhanced density plasma. We propose that the EMSTID and the EPB could have electrically coupled with each other, causing an enhanced polarization electric field (PEF) that polarized that EPB depletion; the E × B gradient drift instability (Kelley, 1989) could have caused the meter‐scale irregularities when that enhanced PEF was imposed on that reactivated EPB depletion surrounded by that enhanced density plasma. This study provides observational evidence that how an electrical couple of EMSTID and EPB events can activate a postmidnight EPB depletion that should become a fossilized structure.

Frequency drift in MR spectroscopy at 3T

PurposeHeating of gradient coils and passive shim components is a common cause of instability in the B0 field, especially when gradient intensive sequences are used. The aim of the study was to set a benchmark for typical drift encountered during MR spectroscopy (MRS) to assess the need for real-time field-frequency locking on MRI scanners by comparing field drift data from a large number of sites. MethodA standardized protocol was developed for 80 participating sites using 99 3T MR scanners from 3 major vendors. Phantom water signals were acquired before and after an EPI sequence. The protocol consisted of: minimal preparatory imaging; a short pre-fMRI PRESS; a ten-minute fMRI acquisition; and a long post-fMRI PRESS acquisition. Both pre- and post-fMRI PRESS were non-water suppressed. Real-time frequency stabilization/adjustment was switched off when appropriate. Sixty scanners repeated the protocol for a second dataset. In addition, a three-hour post-fMRI MRS acquisition was performed at one site to observe change of gradient temperature and drift rate. Spectral analysis was performed using MATLAB. Frequency drift in pre-fMRI PRESS data were compared with the first 5:20 minutes and the full 30:00 minutes of data after fMRI. Median (interquartile range) drifts were measured and showed in violin plot. Paired t-tests were performed to compare frequency drift pre- and post-fMRI. A simulated in vivo spectrum was generated using FID-A to visualize the effect of the observed frequency drifts. The simulated spectrum was convolved with the frequency trace for the most extreme cases. Impacts of frequency drifts on NAA and GABA were also simulated as a function of linear drift. Data from the repeated protocol were compared with the corresponding first dataset using Pearson's and intraclass correlation coefficients (ICC). ResultsOf the data collected from 99 scanners, 4 were excluded due to various reasons. Thus, data from 95 scanners were ultimately analyzed. For the first 5:20 min (64 transients), median (interquartile range) drift was 0.44 (1.29) Hz before fMRI and 0.83 (1.29) Hz after. This increased to 3.15 (4.02) Hz for the full 30 min (360 transients) run. Average drift rates were 0.29 Hz/min before fMRI and 0.43 Hz/min after. Paired t-tests indicated that drift increased after fMRI, as expected (p < 0.05). Simulated spectra convolved with the frequency drift showed that the intensity of the NAA singlet was reduced by up to 26%, 44 % and 18% for GE, Philips and Siemens scanners after fMRI, respectively. ICCs indicated good agreement between datasets acquired on separate days. The single site long acquisition showed drift rate was reduced to 0.03 Hz/min approximately three hours after fMRI. DiscussionThis study analyzed frequency drift data from 95 3T MRI scanners. Median levels of drift were relatively low (5-min average under 1 Hz), but the most extreme cases suffered from higher levels of drift. The extent of drift varied across scanners which both linear and nonlinear drifts were observed.

Instability Mechanisms for the F‐Region Plasma Irregularities Inside the Midlatitude Ionospheric Trough: Swarm Observations

AbstractThe midlatitude ionospheric trough (MIT) is a well‐known feature in the topside ionosphere. Previous MIT related studies mainly focused on the MIT structure itself, while few studies focused on irregularities inside the MIT region. In this study, we provided for the first time the magnetic latitude and magnetic local time distribution of irregularities within the MIT, by using the Swarm in situ plasma measurements. Orbital cases show that both the MIT equatorward and poleward walls are embedded with small‐scale irregularities. Further statistical analysis reveals that the particle precipitation is the dominant mechanism for the dayside MIT region irregularities, while nightside MIT region irregularities are strongly related with the temperature gradient drift instability. The Swarm observations show that the temperature gradient drift instability occur not only in MIT equatorward wall but also in MIT polarward wall, which is different to the theoretical prediction of Hudson and Kelley (1976,https://doi.org/10.1029/JA081i022p03913).

Direct evidence of gradient drift instability being the origin of a rotating spoke in a crossed field plasma

A plasma rotating spoke in a crossed field discharge is studied using 2D radial-azimuthal fully kinetic particle-in-cell Monte Carlo collision simulations. The kinetic model reveals the whole perturbation spectrum of the gradient drift instability in the linear stage: Simon–Hoh, lower hybrid, and ion sound modes, providing direct evidence of the spoke of gradient drift instability nature. The two-fluid dispersion relation of gradient drift instability was utilized to analyze the linear development of instabilities in the simulations. The charge separation effect was incorporated in the fluid linear theory and a super-resolution signal processing method (multiple signal classification) was applied to obtain the numerical frequency spectrum. The simulated spectrum and growth rate show excellent agreement with the theoretical dispersion relation (real frequency and imaginary frequency) in the investigated cases. The most linearly unstable mode was found to be the lower hybrid instability and the mode transition into the m = 1 macroscopic rotating structure after saturation of the linear phase is accompanied by an inverse energy cascade. In the nonlinear stage, pronounced spoke phenomena can occur when the heating of E θ × B electron flow channeled in the spoke front passage suffices to provide enhanced ionization.

Evolution of Mid‐latitude Density Irregularities and Scintillation in North America During the 7–8 September 2017 Storm

AbstractUsing the University Navstar Consortium (UNAVCO) Global Positioning System (GPS) receiver network in North America, we present 2‐D distributions of GPS radio signal scintillation in the mid‐latitude ionosphere during the 7–8 September 2017 storm. The mid‐latitude ionosphere showed a variety of density structures such as the storm enhanced density (SED) base and plume, main trough, secondary plume, and secondary trough during the storm main and early recovery phases. Enhanced phase and amplitude scintillation indices were observed at the density gradients of those structures. SuperDARN radar echoes were also enhanced at the density gradients. The collocation of the scintillation and HF radar echoes indicates that density irregularities developed across a wide range of wavelengths (tens of meters to tens of kilometers) in the mid‐latitude density structures. The density gradients and irregularities were also detected by Swarm and DMSP as in‐situ density structures that disturbed the GPS signals. The irregularities were a substantial fraction (∼10%–50%) of the background density. The density irregularity had a power law spectrum with slope of ∼ −1.8, suggesting that gradient drift instability (GDI) contributed to turbulence formation. Both high‐latitude and low‐latitude processes likely contributed to forming the mid‐latitude density structures, and the mid‐latitude scintillation occurred at the interface of high‐latitude and low‐latitude forcing.

Two-dimensional hybrid model of gradient drift instability and enhanced electron transport in a Hall thruster

An axial–azimuthal two-dimensional Hall thruster discharge model was developed for analyzing gradient drift instability (GDI) and cross field electron transport enhancement induced solely by the GDI. A hybrid particle-fluid model was used for the partially ionized plasma, where the inertialess electron fluid in the quasineutral plasma was assumed. A nonoscillatory numerical method was proposed for the potential solver in the electron fluid model to avoid numerical instability and analyze the physics of GDI accurately. A simulation is performed for a 1 kW-class anode-layer-type Hall thruster, and the flow field with plasma instability is presented. Plasma instability with vortex-like structures is observed in the acceleration and plume regions. The generated plasma instability enhances the cross field electron transport in the axial direction around the channel exit and in the plume region. Grid convergence is confirmed regarding the effect of electron transport enhancement, which indicates that cross field electron transport enhancement is based on the plasma instability. Furthermore, the comparison between the simulation results and linear perturbation analyses demonstrates that the simulated plasma instability reflects the theory of GDI. Thus, it is concluded that the hybrid model is useful for the analyses of GDI, and the GDI can enhance the cross field electron transport in Hall thrusters.

Quantifying Real-Time Sample Temperature Under the Gas Environment in the Transmission Electron Microscope Using a Novel MEMS Heater.

Accurate control and measurement of real-time sample temperature are critical for the understanding and interpretation of the experimental results from in situ heating experiments inside environmental transmission electron microscope (ETEM). However, quantifying the real-time sample temperature remains a challenging task for commercial in situ TEM heating devices, especially under gas conditions. In this work, we developed a home-made micro-electrical-mechanical-system (MEMS) heater with unprecedented small temperature gradient and thermal drift, which not only enables the temperature evolution caused by gas injection to be measured in real-time but also makes the key heat dissipation path easier to model to theoretically understand and predict the temperature decrease. A new parameter termed as “gas cooling ability (H)”, determined purely by the physical properties of the gas, can be used to compare and predict the gas-induced temperature decrease by different gases. Our findings can act as a reference for predicting the real temperature for in situ heating experiments without closed-loop temperature sensing capabilities in the gas environment, as well as all gas-related heating systems.

Global Positioning System (GPS) Scintillation Associated with a Polar Cap Patch

A Global Positioning System (GPS) network in the polar cap, along with ionosonde and SuperDARN radar measurements, are used to study GPS signal amplitude and phase scintillation associated with a polar cap patch. The patch was formed due to a north-to-south transition of the interplanetary magnetic field (IMF Bz). The patch moved antisunward with an average speed of ~600 m/s and lasted for ~2 h. Significant scintillation occurred on the leading edge of the patch, with smaller bursts of scintillation inside and on the trailing edge. As the patch moved, it maintained the integrity of the scintillation, producing irregularities (Fresnel scale) on the leading edge. There were no convection shears or changes in the direction of convection during scintillation events. Observations suggest that scintillation-producing Fresnel scale structures are generated through the non-linear evolution of the gradient drift instability mechanism.

Modeling the dominance of the gradient drift or Kelvin–Helmholtz instability in sheared ionospheric E × B flows

Studies have shown that in sheared E×B flows in an inhomogeneous ionospheric plasma, the gradient drift (GDI) or the Kelvin–Helmholtz (KHI) instability may grow. This work examines the conditions that cause one of these instabilities to dominate over the other using a novel model to study localized ionospheric instabilities. The effect of collisions with neutral particles plays an important role in the instability development. It is found that the KHI is dominant in low collisionality regimes, the GDI is dominant in high collisionality regimes, and there exists an intermediate region in which both instabilities exist in tandem. For low collisionality cases in which the velocity shear is sufficiently far from the density gradient, the GDI is found to grow as a secondary instability extending from the KHI vortices. The inclusion of a neutral wind-driven electric field in the direction of the velocity shear does not impact the dominance of either instability. Using data from empirical ionospheric models, two altitude limits are found. For altitudes above the higher limit, the KHI is dominant. For altitudes below the lower limit, the GDI is dominant. In the intermediate region, both instabilities grow together. Increasing the velocity shear causes both limits to be lower in altitude. This implies that for ionospheric phenomena whose density and velocity gradients span large altitude ranges, such as subauroral polarization streams, the instabilities observed by space-based and ground-based observation instruments could be significantly different.

Investigation of the Gradient Drift Instability as a Cause of Density Irregularities in Subauroral Polarization Streams

AbstractDensity irregularities have been observed in subauroral polarization streams (SAPS). One hypothesis of the cause of this ionospheric turbulence, based on the background morphology, is the gradient drift instability (GDI). This work models the GDI using a two‐dimensional electrostatic fluid model to determine if it is a viable cause of turbulence generation in SAPS. A statistical study of different velocity profiles, based on SuperDARN radar and Global Positioning System total electron content data, is used to prescribe parameters in the numerical model. The parameter space of different SAPS profiles is explored to study the effect on GDI development. As the velocity shear is initialized closer to the unstable density gradient, the GDI becomes increasingly damped. For these cases, the density and electric potential turbulence cascades obtained from the numerical model follow power laws of about −5/3 or −2, which is in agreement with observational data. If the region of sheared velocity overlaps the density gradient, the GDI becomes stabilized. The latitudinal location of maximum GDI growth depends on the density profile, the velocity profile, and the neutral wind direction. Using velocity profiles with regions of low velocity shear can cause instabilities that grow inside SAPS which have turbulence cascades with different behavior. In all parameter regimes considered, the GDI turbulence is precluded from extending through regions of velocity shear. Turbulence is generated for a variety of SAPS relevant conditions; therefore, the GDI has been shown to be a viable candidate for generating ionospheric irregularities in SAPS.

Nonlinear Simulation of Ionospheric Irregularities at Mars

Abstract Motivated by the observations and linear theory analysis of ionospheric irregularities at Mars, we performed numerical simulations of the nonlinear evolution of the electromagnetic gradient drift instability in the Martian ionospheric dynamo region. The seeding source of ionospheric irregularities is perturbation zonal neutral wind. We found that the perturbation electric fields induced by the gradient drift instability can convect lower density plasma into higher density plasma at higher altitudes. Then, the associated perturbation magnetic field and electric field can cause the velocity shear of the plasma, which induced the Kelvin–Helmholtz instability at higher altitude. The Kelvin–Helmholtz instabilities furthermore lead to smaller-scale irregularities in plasma density, magnetic field, and electric field in the Martial ionosphere. Key points: (1) Nonlinear simulation of small-scale ionospheric irregularities at Mars was present. (2) Ionospheric irregularities at Mars can be seeded by the perturbation neutral winds. (3) Model results are comparable to linear theory analysis and satellite observations.

Review of ionospheric irregularities and ionospheric electrodynamic coupling in the middle latitude region

This paper briefly reviews ionospheric irregularities that occur in the E and F regions at mid-latitudes. Sporadic E (ES) is a common ionospheric irregularity phenomenon that is first noticed in the E layer. ES mainly appears during daytime in summer hemispheres, and is formed primarily from neutral wind shear in the mesosphere and lower thermosphere (MLT) region. Field-aligned irregularity (FAI) in the E region is also observed by Very High Frequency (VHF) radar in mid-latitude regions. FAI frequently occurs after sunset in summer hemispheres, and spectrum features of E region FAI echoes suggest that type-2 irregularity is dominant in the nighttime ionosphere. A close relationship between ES and E region FAI implies that ES may be a possible source of E region FAI in the nighttime ionosphere. Strong neutral wind shear, steep ES plasma density gradient, and a polarized electric field are the significant factors affecting the formation of E region FAI. At mid-latitudes, joint observational experiments including ionosonde, VHF radar, Global Positioning System (GPS) stations, and all-sky optical images have revealed strong connections across different scales of ionospheric irregularities in the nighttime F region, such as spread F (SF), medium-scale traveling ionospheric disturbances (MSTID), and F region FAI. Observations suggest that different scales of ionospheric irregularities are generally attributed to the Perkins instability and subsequently excited gradient drift instability. Nighttime MSTID can further evolve into small-scale structures through a nonlinear cascade process when a steep plasma density gradient exists at the bottom of the F region. In addition, the effect of ionospheric electrodynamic coupling processes, including ionospheric E-F coupling and inter-hemispheric coupling on the generation of ionospheric irregularities, becomes more prominent due to the significant dip angle and equipotentiality of magnetic field lines in the mid-latitude ionosphere. Polarized electric fields can map to different ionospheric regions and excite plasma instabilities which form ionospheric irregularities. Nevertheless, the mapping efficiency of a polarized electric field depends on the ionospheric background and spatial scale of the field.

Study of the Electron Velocity Inside Sub‐Ion‐Scale Magnetic Holes in the Solar Wind by MMS Observations

AbstractElectron vortices are a key element in the sub‐ion magnetic hole. Here, we investigate the electron velocity inside two sub‐ion magnetic holes in the solar wind based on the Magnetospheric Multiscale (MMS) mission. We find that the observational electron velocities inside the magnetic holes are contributed by the combination of the electron diamagnetic (Ve,dia), E × B (Ve,E), magnetic gradient (Ve,▽B) and curvature (Ve,R) drifts. Ve,dia, Ve,▽B, and Ve,R are comparable, while Ve,E is very small inside the hole. The weak Ve,E could result from the electric field approximately perpendicular to the magnetic field inside the structure. The value of Ve,▽B + Ve,R is near 0; thus, Ve,dia is approximately equal to the observational electron velocity. The current density contributed by the electron diamagnetic, magnetic gradient and curvature drift motions is self‐consistent with the magnetic depression inside the hole, suggesting that these three electron drift motions play a crucial role in stabilizing the magnetic hole in the mirror‐stable astrophysical plasma environment.

Interaction Between a Southwestward Propagating MSTID and a Poleward Moving WSA‐Like Plasma Patch on a Magnetically Quiet Night at Midlatitude China Region

AbstractIn this paper, we first investigate the effects of a postevening Weddell Sea Anomaly (WSA)‐like plasma patch on a southwestward propagating medium‐scale traveling ionospheric disturbance (MSTID) over Xinglong, China (40.4°N, 117.6°E; Mlat. ~30.4°N). We found that some of this kind of WSA‐like plasma patches moved northward from the equatorial ionization anomaly (EIA) regions to midlatitudes, as they traveled westward into China. During 2012–2016, these plasma patches frequently occurred during the period of May–August with a monthly occurrence rate of over 20%, causing nighttime plasma density enhancements (NPDEs) in midlatitudes of China. Over 50% of these structures were accompanied by concurrent MSTID and Es. We propose that an intense polarization electric field (PEF) associated with an MSTID/Es from the more northern regions of EIA could frequently drive these plasma patches poleward. On the night of 27 June 2014 (Kp &lt; 2−), either an MSTID and an intense Es layer (the maximum foEs &gt;12 MHz) occurred at the onset of the poleward motion of a WSA‐like plasma patch, lending credence to this possibility. The observed plasma patch was pushed poleward to interact with the observed MSTID, causing some poleward extending C‐shaped airglow depletions/enhancements of the MSTID in a transition region where the ionosphere changed from a collapse region to an uplifted one. We attributed those poleward extending airglow depletions to the interaction between the MSTID and the plasma patch because of the secondary gradient drift instability and those of airglow enhancements to the redistribution of plasma.

Geomagnetic Effects in Spatial Distributions of Particle Precipitation in Terms of Particle Energy Channels

AbstractThis study examines the spatial distributions of precipitation during active and quiet times. Most previous studies commonly classified precipitation into different energy spectral types, but we utilized a classification according to particle energy channels. A general conclusion derived from these distributions suggests that regardless of active and quiet times, low‐energy (&lt;1 keV) and high‐energy precipitating particles are mostly on the dayside and nightside, respectively. A comparison with past results reveals that the high‐energy electron precipitation during quiet times is mostly due to wave scattering and that during active times is mainly produced by quasi‐static potential structures (QSPS) and Alfvénic acceleration, while low‐energy electron precipitation is mostly caused by QSPS and Alfvénic acceleration regardless of quiet and active times. For both high‐energy proton and electron precipitation, the nightside dawn‐dusk asymmetry of their distributions during active times is found to be opposite of that during quiet times. We infer that the distribution of high‐energy precipitation during quiet times is dominated by the curvature and gradient drifts, while during active times it is mainly due to the physical processes or phenomena related to substorms in the magnetotail. Empirical orthogonal function analysis has been applied in this study to derive where the flux has the maximum enhancement as the geomagnetic activity increases. The results further demonstrate that low‐energy and high‐energy protons mainly increase in the noon and postmidnight sectors, respectively. The highest enhancements of low‐energy and high‐energy electrons are in the prenoon and premidnight sectors, respectively.

Asymptotics of the three-dimensional Vlasov equation in the large magnetic field limit

We study the asymptotic behavior of solutions to the Vlasov equation in the presence of a strong external magnetic field. In particular we provide a mathematically rigorous derivation of the guiding-center approximation in the general three dimensional setting under the action of large inhomogeneous magnetic fields. First order corrections are computed and justified as well, including electric cross field, magnetic gradient and magnetic curvature drifts. We also treat long time behaviors on two specific examples, the two dimensional case in carte-sian coordinates and a poloidal axi-symmetric geometry, the former for expository purposes. Algebraic manipulations that underlie concrete computations make the most of the linearity of the stiffest part of the system of characteristics instead of relying on any particular variational structure.

Improved Discrete Random Walk Stochastic Model for Simulating Particle Dispersion and Deposition in Inhomogeneous Turbulent Flows

Abstract The performance of different versions of the discrete random walk models in turbulent flows with nonuniform normal root-mean-square (RMS) velocity fluctuations and turbulence time scales were carefully investigated. The OpenFOAM v2−f low Reynolds number turbulence model was used for evaluating the fully developed streamwise velocity and the wall-normal RMS velocity fluctuations profiles in a turbulent channel flow. The results were then used in an in-house matlab particle tracking code, including the drag and Brownian forces, and the trajectories of randomly injected point-particles with diameters ranging from 10 nm to 30 μm were evaluated under the one-way coupling assumption. The distributions and deposition velocities of fluid-tracer and finite-size particles were evaluated using the conventional-discrete random walk (DRW) model, the modified-DRW model including the velocity gradient drift correction, and the new improved-DRW model including the velocity and time gradient drift terms. It was shown that the conventional-DRW model leads to superfluous migration of fluid-point particles toward the wall and erroneous particle deposition rate. The concentration profiles of tracer particles obtained by using the modified-DRW model still are not uniform. However, it was shown that the new improved-DRW model with the velocity and time scale drift corrections leads to uniform distributions for fluid-point particles and reasonable concentration profiles for finite-size heavy particles. In addition, good agreement was found between the estimated deposition velocities of different size particles by the new improved-DRW model with the available data.