scholarly journals Transport of dust particles from the Bodélé region to the monsoon layer – AMMA case study of the 9–14 June 2006 period

2011 ◽  
Vol 11 (2) ◽  
pp. 479-494 ◽  
Author(s):  
S. Crumeyrolle ◽  
P. Tulet ◽  
L. Gomes ◽  
L. Garcia-Carreras ◽  
C. Flamant ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Dust Particle ◽  
Particle Concentration ◽  
Strong Relationship ◽  
Atmospheric Model ◽  
Dust Particles ◽  
Particle Sedimentation ◽  
Dynamical Mechanism ◽  
Surface Cover ◽  
The Impact

Abstract. Aerosol properties were measured during an airborne campaign experiment that took place in June 2006 in West Africa within the framework of the African Monsoon Multidisciplinary Analyses (AMMA). The goal of the present study was to investigate a dynamical mechanism able to facilitate the sedimentation of dust particles from the Saharan Air Layer (SAL) into the boundary layer. A significant change in the dust particle concentration measured along the meridian between Niamey (Niger) and Cotonou (Benin) was found in the boundary layer (~700 m), where the dust particle concentration increased in a zone where local emission is not possible. Moreover, the boundary layer top observed with the dropsondes launched with the F-F20 shows a strong relationship with the surface cover anomalies, with higher Boundary Layer (BL) tops over the warmer surfaces, such as croplands, as opposed to adjacent forest. A mesoscale atmospheric model with a new on-line dust parameterization, resulting from the Alfaro and Gomes (2001) parametrisation and AMMA observations, was used to interpret the impact of vegetation anomalies on dust particle sedimentation. The results of the simulation are consistent with the observations, with higher dust concentration over the warm surface cover anomalies.

scholarly journals Transport of dust particles from the Bodélé region to the monsoon layer: AMMA case study of the 9–14 June 2006 period

2010 ◽  
Vol 10 (2) ◽  
pp. 5051-5090 ◽  
Author(s):  
S. Crumeyrolle ◽  
P. Tulet ◽  
L. Garcia-Carreras ◽  
C. Flamant ◽  
D. J. Parker ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Dust Particle ◽  
Particle Concentration ◽  
Strong Relationship ◽  
Atmospheric Model ◽  
Dust Particles ◽  
Particle Sedimentation ◽  
Surface Cover ◽  
Mesoscale Atmospheric Model ◽  
The Impact

Abstract. Aerosol properties were measured during an airborne campaign experiment that took place in June 2006 in West Africa within the framework of the African Monsoon Multidisciplinary Analyses (AMMA). The goal of the present study was to determine the process that facilitates the sedimentation of dust particles from the Saharan Air Layer (SAL) to the boundary layer. A significant change in the dust particle concentration measured along the meridian between Niamey (Niger) and Cotonou (Benin) was found in the boundary layer (~700 m), where the dust particle concentration increased in a zone where local emission is not possible. Moreover, the boundary layer top observed with the dropsondes launched with the F-F20 shows a strong relationship with the surface cover anomalies, with higher Boundary Layer (BL) tops over the warmer surfaces, such as croplands, as opposed to adjacent forest. A mesoscale atmospheric model with a new on-line dust parameterization, resulting from the Alfaro and Gomes (2001) parametrisation and AMMA observations, was used to interpret the impact of vegetation anomalies on dust particle sedimentation. The results of the simulation are consistent with the observations, with higher dust over the warm surface cover anomalies.

scholarly journals Chemical aging of atmospheric mineral dust during transatlantic transport

2016 ◽  
Author(s):  
Mohamed Abdelkader ◽  
Swen Metzger ◽  
Benedikt Steil ◽  
Klaus Klingmüller ◽  
Holger Tost ◽  
...  
Keyword(s):  
Atlantic Ocean ◽  
Direct Effect ◽  
Dust Particles ◽  
Hygroscopic Growth ◽  
Aging Effects ◽  
Particle Sedimentation ◽  
Inter Tropical Convergence Zone ◽  
Dust Transport ◽  
Dust Fraction ◽  
The Impact

Abstract. Transatlantic dust transport has many implications for the atmosphere, ocean and climate. We present a modeling study on the impact of the key processes (dust emissions flux, convection and dust aging parameterizations) that control the transatlantic dust transport. Typically, the Inter-Tropical Convergence Zone (ITCZ) acts as a barrier for the meridional dust transport. To characterize the dust outflow over the Atlantic Ocean, we address two regional phenomena: (i) dust interactions with the ITCZ (DIZ) and (ii) the adjacent dust transport over the Atlantic Ocean (DTA). In the DTA zone, the dust loading shows a steep and linear gradient westward over the Atlantic Ocean where particle sedimentation is the dominant removal process, whereas in the DIZ zone cloud interactions and wet deposition predominate. To study the different impacts of aging, we present two case studies that exclude condensation and coagulation, and include dust aging at various levels of complexity. For dust aging, we consider the uptake of inorganic acids on the surface of mineral particles that form salt compounds. Calcium, used as a proxy for the overall chemically reactive dust fraction, drives the dust-related neutralization reactions leading to higher dust aerosol optical depth (AOD). The aged dust particles are transferred to the soluble aerosol modes in the model and are mixed with other species that originate from anthropogenic and natural sources. The neutralization products (salts) take up water vapor from the atmosphere and increase the dust AOD under subsaturated conditions. We define the "direct effect of dust aging" to refer to the increase in AOD as a result of hygroscopic growth. On the other hand, the aged dust is more efficiently removed (wet and dry) because of the increase in particle size and hygroscopicity. This more efficient removal reduces the dust AOD over the DIZ zone. We define this as the "indirect effect of dust aging", complementary to the direct effect that is dominant in the DTA zone. Distinction of the two aging effects helps develop insight into the regional importance of dust–air-pollution interactions.

scholarly journals 67P/Churyumov–Gerasimenko’s dust activity from pre- to post-perihelion as detected by Rosetta/GIADA

2020 ◽  
Vol 496 (1) ◽  
pp. 125-137
Author(s):  
A Longobardo ◽  
V Della Corte ◽  
A Rotundi ◽  
M Fulle ◽  
G Rinaldi ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Thermal Properties ◽  
Dust Particle ◽  
Particle Velocity ◽  
Particle Concentration ◽  
Dust Particles ◽  
Data Set ◽  
Trace Back ◽  
Dust Distribution ◽  
Cometary Activity

ABSTRACT We characterized the 67P/Churyumov–Gerasimenko’s dust activity, by analysing individual dust particle velocity and momentum measurements of Grain Impact Analyser and Dust Accumulator (GIADA), the dust detector onboard the ESA/Rosetta spacecraft, collecting dust from tens to hundreds of kilometres from the nucleus. Specifically, we developed a procedure to trace back the motion of dust particles down to the nucleus, identifying the surface’s region ejecting each dust particle. This procedure has been developed and validated for the first part of the mission by Longobardo et al. and was extended to the entire GIADA data set in this work. The results based on this technique allowed us to investigate the link between the dust porosity (fluffy/compact) and the morphology of the ejecting surface (rough/smooth). We found that fluffy and compact particles, despite the lack of correlation in their coma spatial distribution (at large nucleocentric distances) induced by their different velocities, have common ejection regions. In particular, the correlation between the distributions of fluffy and compact particles is maintained up to an altitude of about 10 km. Fluffy particles are more abundant in rough terrains. This could be the result of past cometary activity that resurfaced the smooth terrains and/or of the comet formation process that stored the fluffy particles inside the voids between the pebbles. The variation of fluffy particle concentration between rough and smooth terrains agrees with predictions of comet formation models. Finally, no correlation between dust distribution on the nucleus and surface thermal properties was found.

scholarly journals Laboratory experiments on the dynamics of powder-snow avalanches in the run-out zone

1991 ◽  
Vol 37 (126) ◽  
pp. 281-295 ◽  
Author(s):  
Felix Hermann ◽  
Kolumban Hutter
Keyword(s):  
Boundary Layer ◽  
Laboratory Experiments ◽  
Particle Concentration ◽  
Dynamic Pressure ◽  
Considerable Reduction ◽  
Snow Avalanches ◽  
Boundary Layer Flows ◽  
Ensemble Averaging ◽  
Particle Sedimentation ◽  
Turbulence Effects

AbstractWe report on laboratory experiments on the motion of powder-snow avalanches along a bent chute. The avalanches are simulated as turbulent boundary-layer flows of polystyrene particles in still water along a chute consisting of a straight inclined part, a curved part and a second, possibly inclined, run-out zone. An ultrasonic measuring technique is used to determine mean particle speeds (via the Doppler shift of the reflected signal) and the particle concentration (via the attenuation of the echoes). By ensemble averaging, individual turbulence effects are eliminated. As measuring procedures,profileswere determined for particle velocity and density across the boundary layer; these were taken (i) for the avalanche tail along the entire track, i.e. in the steep part and the run-out zone, and (ii) for the avalanche head in the run-out zone below the kink in the terrain. Moreover,time sectionsof velocity and density (i.e. time series at fixed positions along a line through the boundary layer) were recorded and the particle mass deposited in the various zones of the track was measured.The analysis of the data reveals the following results: a concave change in the terrain topography acts as a very efficient mechanism for particle sedimentation, thus affecting particle concentration and velocity, and considerable reduction close to the ground, whereas the density is reduced throughout the depth, thus leading to a considerable reduction of dynamic pressure close to the ground and leaving it somewhat greater at higher altitudes. We conclude with practical considerations for the field glaciologist.

Assessing the Turbulence Kinetic Energy Budget in the Boundary Layer Using WRF-LES: Impact of Momentum Perturbation

2021 ◽  
Author(s):  
Mukesh Kumar ◽  
Tirtha Banerjee ◽  
Alex Jonko ◽  
Jeff Mirocha ◽  
William Lassman
Keyword(s):  
Boundary Layer ◽  
Kinetic Energy ◽  
Wind Farm ◽  
Initial Conditions ◽  
Random Perturbation ◽  
Turbulent Transport ◽  
Atmospheric Model ◽  
Turbulence Kinetic Energy ◽  
Convective Boundary ◽  
The Impact

<p>Mesoscale-to-Large Eddy Simulation (LES) grid nesting is an important tool for many atmospheric model applications, ranging from wind energy to wildfire spread studies. Different techniques are used in such applications to accelerate the development of turbulence in the LES domain. Here, we explore the impact of a simple and computationally efficient Stochastic Cell Perturbation method (SCPM) to accelerate the generation of turbulence in the Weather Research and Forecasting (WRF) LES model on the Turbulence Kinetic Energy (TKE) budget. In a convective boundary layer, we study the variation of TKE budget terms under the initial conditions of the Scaled Wind Farm Technology (SWiFT) facility located in West Texas. In this study, WRF LES is used with a horizontal grid resolution of 12 m, and is one-way nested within an idealized mesoscale domain. It is crucial to understand how forced perturbation shifts the balance between the terms of the TKE budget. Here, we quantify the shear production, and buoyant production in an unstable case. Since additional production terms are introduced in the SCPM method, we investigate the dissipation term of TKE. In addition, we also study the generation of turbulent transport. Generally, it integrates over height to null in a planar homogeneous case without subsidence, indicating it is positive over some heights and negative over other heights. Furthermore, we also study the variation of the TKE transport term after extending the random perturbation up to a certain height. The findings of this study will provide a better understanding of the contribution of different budget terms in a forced LES simulation.</p>

scholarly journals Increase of the aerosol hygroscopicity by cloud processing in a mesoscale convective system: a case study from the AMMA campaign

2008 ◽  
Vol 8 (23) ◽  
pp. 6907-6924 ◽  
Author(s):  
S. Crumeyrolle ◽  
L. Gomes ◽  
P. Tulet ◽  
A. Matsuki ◽  
A. Schwarzenboeck ◽  
...  
Keyword(s):  
Cloud Condensation Nuclei ◽  
Mesoscale Convective System ◽  
Atmospheric Model ◽  
Dust Particles ◽  
Convective System ◽  
Cloud Processing ◽  
Before And After ◽  
Mesoscale Convective ◽  
The Impact ◽  
Aerosol Properties

Abstract. Aerosol properties were measured during an airborne campaign experiment that took place in July 2006 in West Africa within the framework of the African Monsoon Multidisciplinary Analyses (AMMA). The goal of the present study was to determine the main microphysical processes that affect the aerosols during the passage of a mesoscale convective system (MCS) over the region of Niamey in Niger. A significant change in the aerosol profiles measured before and after the passage of the MCS was found in a layer located between 1300 and 3000 m, where the aerosol concentration drastically decreased after the passage of the MCS. Concurrently, a significant increase in the cloud condensation nuclei (CCN) fraction was also observed during the post-MCS period in the same layer. Moreover, the results of the elemental composition analyses of individual particles collected in this layer after the MCS passage have shown higher contributions of sulfate, nitrate and chloride to the total aerosol mass. A mesoscale atmospheric model with on-line dust parameterization and Lagrangian backtrajectories was used to interpret the impact of the MCS on the aerosol properties. The results of the simulation show that the MCS 1) generates dust particles at the surface in the gust front of the system and washout of particles during the system precipitation, 2) modifies the aerosol mixing state (intensive aerosol property) through cloud processing, and 3) enhances CCN activity of particles through coating by soluble material.

scholarly journals Measurement of Dust Electric Charges by the Ulysses and Galileo Dust Detectors

1996 ◽  
Vol 150 ◽  
pp. 481-484 ◽  
Author(s):  
J. Svestka ◽  
S. Auer ◽  
M. Baguhl ◽  
E. Grün
Keyword(s):  
Electric Field ◽  
Dust Particle ◽  
Time Of Flight ◽  
Opposite Polarity ◽  
Dust Particles ◽  
Impact Speed ◽  
The Impact

The Galileo and Ulysses dust detectors can detect electric charges of dust particles. Dust particles entering the sensor (see, e.g., Grün et al. 1992) may be detected by the charge Qp that they induce to the charge grid. All suitably massive dust particles - charged or uncharged - are then detected by the cloud of ions and electrons they produce during the impact on the hemispherical target after the time of flight between the charge grid and the target. After separation in the electric field, ions and electrons are collected by separate electrodes and produce two pulses of opposite polarity. From the two pulse heights and the rise times, the mass and impact speed of the dust particle are derived.

scholarly journals Laboratory experiments on the dynamics of powder-snow avalanches in the run-out zone

1991 ◽  
Vol 37 (126) ◽  
pp. 281-295 ◽  
Author(s):  
Felix Hermann ◽  
Kolumban Hutter
Keyword(s):  
Boundary Layer ◽  
Laboratory Experiments ◽  
Particle Concentration ◽  
Dynamic Pressure ◽  
Considerable Reduction ◽  
Snow Avalanches ◽  
Boundary Layer Flows ◽  
Ensemble Averaging ◽  
Particle Sedimentation ◽  
Turbulence Effects

AbstractWe report on laboratory experiments on the motion of powder-snow avalanches along a bent chute. The avalanches are simulated as turbulent boundary-layer flows of polystyrene particles in still water along a chute consisting of a straight inclined part, a curved part and a second, possibly inclined, run-out zone. An ultrasonic measuring technique is used to determine mean particle speeds (via the Doppler shift of the reflected signal) and the particle concentration (via the attenuation of the echoes). By ensemble averaging, individual turbulence effects are eliminated. As measuring procedures, profiles were determined for particle velocity and density across the boundary layer; these were taken (i) for the avalanche tail along the entire track, i.e. in the steep part and the run-out zone, and (ii) for the avalanche head in the run-out zone below the kink in the terrain. Moreover, time sections of velocity and density (i.e. time series at fixed positions along a line through the boundary layer) were recorded and the particle mass deposited in the various zones of the track was measured.The analysis of the data reveals the following results: a concave change in the terrain topography acts as a very efficient mechanism for particle sedimentation, thus affecting particle concentration and velocity, and considerable reduction close to the ground, whereas the density is reduced throughout the depth, thus leading to a considerable reduction of dynamic pressure close to the ground and leaving it somewhat greater at higher altitudes. We conclude with practical considerations for the field glaciologist.

Saltating particles in a turbulent boundary layer: experiment and theory

2009 ◽  
Vol 625 ◽  
pp. 47-74 ◽  
Author(s):  
M. CREYSSELS ◽  
P. DUPONT ◽  
A. OULD EL MOCTAR ◽  
A. VALANCE ◽  
I. CANTAT ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Wind Speed ◽  
Turbulent Boundary Layer ◽  
Particle Concentration ◽  
Low Velocity ◽  
Wind Speeds ◽  
Image Velocimetry ◽  
The University ◽  
Velocity Moments ◽  
The Impact

The work presented here focuses on the analysis of a turbulent boundary layer saturated with saltating particles. Experiments were carried out in a wind tunnel 15m long and 0.6m wide at the University of Aarhus in Denmark with sand grains 242 μm in size for wind speeds ranging from the threshold speed to twice its value. The saltating particles were analysed using particle image velocimetry (PIV) and particle-tracking velocimetry (PTV), and vertical profiles of particle concentration and velocity were extracted. The particle concentration was found to decrease exponentially with the height above the bed, and the characteristic decay height was independent of the wind speed. In contrast with the logarithmic profile of the wind speed, the grain velocity was found to vary linearly with the height. In addition, the measurements indicated that the grain velocity profile depended only slightly on the wind speed. These results are shown to be closely related to the features of the splash function that characterizes the impact of the saltating particles on a sandbed. A numerical simulation is developed that explicitly incorporates low-velocity moments of the splash function in a calculation of the boundary conditions that apply at the bed. The overall features of the experimental measurements are reproduced by simulation.

scholarly journals Increase of the aerosol hygroscopicity by aqueous mixing in a mesoscale convective system: a case study from the AMMA campaign

2008 ◽  
Vol 8 (3) ◽  
pp. 10057-10103 ◽  
Author(s):  
S. Crumeyrolle ◽  
L. Gomes ◽  
P. Tulet ◽  
A. Matsuki ◽  
A. Schwarzenboeck ◽  
...  
Keyword(s):  
Cloud Condensation Nuclei ◽  
Mesoscale Convective System ◽  
Atmospheric Model ◽  
Dust Particles ◽  
Convective System ◽  
Before And After ◽  
Mesoscale Convective ◽  
Microphysical Processes ◽  
The Impact ◽  
Aerosol Properties

Abstract. Aerosol properties were measured during an airborne campaign experiment that took place in July 2006 in West Africa within the framework of the African Monsoon Multidisciplinary Analyses (AMMA). The goal of the present study was to determine the main microphysical processes that affect the aerosols during the passage of a mesoscale convective system (MCS) over the region of Niamey in Niger. A main difference in the aerosol profiles measured before and after the passage of the MCS was found for a layer located between 1300 and 3000 m where the aerosol concentration has drastically decreased after the passage of the MCS. Concurrently, a significant increase of the cloud condensation nuclei fraction was also observed during the post-MCS period in the same layer. Moreover, the results of the elemental composition analyses of individual particles collected in this layer after the MCS passage have shown higher contributions of sulfate, nitrate and chloride to the total aerosol. A mesoscale atmospheric model with on-line dust parameterization and Lagrangian backtrajectories was used to interpret the impact of the MCS on the aerosol properties. The results of the simulation show that the MCS 1) generates dust particles at the surface in front of the system and washout particles behind, 2) modifies the aerosol mixing state through cloud processing, and 3) enhances CCN activity of particles through the coating of soluble material.

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