scholarly journals Mineral dust indirect effects and cloud radiative feedbacks of a simulated idealized nocturnal squall line

2013 ◽  
Vol 13 (8) ◽  
pp. 4467-4485 ◽  
Author(s):  
R. B. Seigel ◽  
S. C. van den Heever ◽  
S. M. Saleeby
Keyword(s):  
Indirect Effects ◽  
Mineral Dust ◽  
Synergistic Effects ◽  
Atmospheric Modeling ◽  
Dust Particles ◽  
Squall Line ◽  
Cold Pool ◽  
Freezing Level ◽  
Warm Rain Process ◽  
The Individual

Abstract. Mineral dust is arguably the most abundant aerosol species in the world and as such potentially plays a large role in aerosol indirect effects (AIEs). This study assesses and isolates the individual responses in a squall line that arise (1) from radiation, (2) from dust altering the microphysics, as well as (3) from the synergistic effects between (1) and (2). To accomplish these tasks, we use the Regional Atmospheric Modeling System (RAMS) set up as a cloud-resolving model (CRM). The CRM contains aerosol and microphysical schemes that allow mineral dust particles to nucleate as cloud drops and ice crystals, replenish upon evaporation and sublimation, be tracked throughout hydrometeor transition, and be scavenged by precipitation and dry sedimentation. Factor separation is used on four simulations of the squall line in order to isolate the individual roles of radiation (RADIATION), microphysically active dust (DUST MICRO), and the nonlinear interactions of those factors (SYNERGY). Results indicate that RADIATION acts to increase precipitation, intensify the cold pool, and enhance the mesoscale organization of the squall line due to changes in microphysics originating from cloud top cooling. Conversely, DUST MICRO decreases precipitation, weakens the cold pool, and weakens the mesoscale organization of the squall line due to an enhancement of the warm rain process. SYNERGY shows little impact on the squall line, except near the freezing level, where an increase in mesoscale organization takes place. The combined effect of the mineral dust AIE due to both DUST MICRO and SYNERGY is to weaken the squall line.

scholarly journals Assessing the mineral dust indirect effects and radiation impacts on a simulated idealized nocturnal squall line

2012 ◽  
Vol 12 (11) ◽  
pp. 29607-29655 ◽  
Author(s):  
R. B. Seigel ◽  
S. C. van den Heever ◽  
S. M. Saleeby
Keyword(s):  
Indirect Effects ◽  
Mineral Dust ◽  
Synergistic Effects ◽  
Atmospheric Modeling ◽  
Dust Particles ◽  
Squall Line ◽  
Cold Pool ◽  
Freezing Level ◽  
Warm Rain Process ◽  
The Individual

Abstract. Mineral dust is arguably the most abundant aerosol species in the world and it plays a large role in aerosol indirect effects (AIEs). This study assesses and isolates the individual responses in a squall line that arise (1) from radiation, (2) from dust altering the microphysics, as well as (3) from the synergistic effects between (1) and (2). To accomplish these tasks, we use the Regional Atmospheric Modeling System (RAMS) set up as a cloud-resolving model (CRM). The CRM contains aerosol and microphysical schemes that allow mineral dust particles to nucleate as cloud drops and ice crystals, replenish upon evaporation and sublimation, be tracked throughout hydrometeor transition, and scavenge by precipitation and dry sedimentation. Factor separation is used on four simulations of the squall line in order to isolate the individual roles of radiation (RADIATION), microphysically active dust (DUST MICRO), and the nonlinear interactions of those factors (SYNERGY). Results indicate that RADIATION acts to increase precipitation, intensify the cold pool, and enhance the mesoscale organization of the squall line due to changes in microphysics beginning from cloud top cooling. Conversely, DUST MICRO decreases precipitation, weakens the cold pool, and weakens the mesoscale organization of the squall line due to an enhancement of the warm rain process. SYNERGY shows little impact on the squall line, except near the freezing level, where an increase in mesoscale organization takes place. The combined effect of the mineral dust AIE due to both DUST MICRO and SYNERGY is to weaken the squall line.

Squall-Line Intensification via Hydrometeor Recirculation

2013 ◽  
Vol 70 (7) ◽  
pp. 2012-2031 ◽  
Author(s):  
Robert B. Seigel ◽  
Susan C. van den Heever
Keyword(s):  
Line Strength ◽  
Atmospheric Modeling ◽  
Squall Line ◽  
Cold Pool ◽  
Latent Heating ◽  
Moist Convection ◽  
Freezing Level ◽  
Squall Lines ◽  
Deep Moist Convection ◽  
Inflow Jet

Abstract Many studies have demonstrated the intimate connection between microphysics and deep moist convection, especially for squall lines via cold pool pathways. The present study examines four numerically simulated idealized squall lines using the Regional Atmospheric Modeling System (RAMS) and includes a control simulation that uses full two-moment microphysics and three sensitivity experiments that vary the mean diameter of the hail hydrometeor size distribution. Results suggest that a circulation centered at the freezing level supports midlevel convective updraft invigoration through increased latent heating. The circulation begins with hail hydrometeors that initiate within the convective updraft above the freezing level and are then ejected upshear because of the front-to-rear flow of the squall line. As the hail falls below the freezing level, the rear-inflow jet (RIJ) advects the hail hydrometeors downshear and into the upshear flank of the midlevel convective updraft. Because the advection occurs below the freezing level, some of the hail melts and sheds raindrops. The addition of hail and rain to the updraft increases latent heating owing to both an enhancement in riming and vapor deposition onto hail and rain. The increase in latent heating enhances buoyancy within the updraft, which leads to an increase in precipitation and cold pool intensity that promote a positive feedback on squall-line strength. The upshear-tilted simulated squall lines in this study indicate that as hail size is decreased, squall lines are invigorated through the recirculation mechanism.

scholarly journals Direct observations of the atmospheric processing of Asian mineral dust

2007 ◽  
Vol 7 (5) ◽  
pp. 1213-1236 ◽  
Author(s):  
R. C. Sullivan ◽  
S. A. Guazzotti ◽  
D. A. Sodeman ◽  
K. A. Prather
Keyword(s):  
Mineral Dust ◽  
Heterogeneous Reaction ◽  
Field Studies ◽  
Dust Particles ◽  
Reaction Products ◽  
Transport Pathway ◽  
Air Masses ◽  
Atmospheric Processing ◽  
Acid Reaction ◽  
The Individual

Abstract. The accumulation of secondary acids and ammonium on individual mineral dust particles during ACE-Asia has been measured with an online single-particle mass spectrometer, the ATOFMS. Changes in the amounts of sulphate, nitrate, and chloride mixed with dust particles correlate with air masses from different source regions. The uptake of secondary acids depended on the individual dust particle mineralogy; high amounts of nitrate accumulated on calcium-rich dust while high amounts of sulphate accumulated on aluminosilicate-rich dust. Oxidation of S(IV) to S(VI) by iron in the aluminosilicate dust is a possible explanation for this enrichment of sulphate, which has important consequences for the fertilization of remote oceans by soluble iron. This study shows the segregation of sulphate from nitrate and chloride in individual aged dust particles for the first time. A transport and aging timeline provides an explanation for the observed segregation. Our data suggests that sulphate became mixed with the dust first. This implies that the transport pathway is more important than the reaction kinetics in determining which species accumulate on mineral dust. Early in the study, dust particles in volcanically influenced air masses were mixed predominately with sulphate. Dust mixed with chloride then dominated over sulphate and nitrate when a major dust front reached the R. V. Ronald Brown. We hypothesize that the rapid increase in chloride on dust was due to mixing with HCl(g) released from acidified sea salt particles induced by heterogeneous reaction with volcanic SO2(g), prior to the arrival of the dust front. The amount of ammonium mixed with dust correlated strongly with the total amount of secondary acid reaction products in the dust. Submicron dust and ammonium sulphate were internally mixed, contrary to frequent reports that they exist as external mixtures. The size distribution of the mixing state of dust with these secondary species validates previous mechanisms of the atmospheric processing of dust and generally agrees with simulated aerosol chemistry from the STEM-2K3 model. This series of novel results has important implications for improving the treatment of dust in global chemistry models and highlights a number of key processes that merit further investigation through laboratory and field studies.

scholarly journals An integrated modeling study on the effects of mineral dust and sea salt particles on clouds and precipitation

2010 ◽  
Vol 10 (10) ◽  
pp. 23959-24014 ◽  
Author(s):  
S. Solomos ◽  
G. Kallos ◽  
J. Kushta ◽  
M. Astitha ◽  
C. Tremback ◽  
...  
Keyword(s):  
Air Quality ◽  
Mineral Dust ◽  
Eastern Mediterranean ◽  
Atmospheric Modeling ◽  
Sea Salt ◽  
Cloud Formation ◽  
Dust Particles ◽  
Limited Area ◽  
Aerosol Cloud ◽  
Climate Interactions

Abstract. The amount of airborne particles that will nucleate and form cloud droplets under specific atmospheric conditions, depends on their number concentration, size distribution and chemical composition. Aerosol is affected by primary particle emissions, gas-phase precursors, their transformation and interaction with atmospheric constituents, clouds and dynamics. A comprehensive assessment of these interactions requires an integrated approach; most studies however decouple aerosol processes from cloud and atmospheric dynamics and cannot account for all the feedbacks involved in aerosol-cloud-climate interactions. This study addresses aerosol-cloud-climate interactions with the Integrated Community Limited Area Modeling System (ICLAMS) that includes online parameterization of the physical and chemical processes between air quality and meteorology. ICLAMS is an extended version of the Regional Atmospheric Modeling System (RAMS) and it has been designed for coupled air quality – meteorology studies. Model sensitivity tests for a single-cloud study as well as for a case study over the Eastern Mediterranean illustrate the importance of aerosol properties in cloud formation and precipitation. Mineral dust particles are often coated with soluble material such as sea-salt, thus exhibiting increased CCN efficiency. Increasing the percentage of salt-coated dust particles by 15% in the model resulted in more vigorous convection and more intense updrafts. The clouds that were formed extended about 3 km higher and the initiation of precipitation was delayed by one hour. Including on-line parameterization of the aerosol effects improved the model bias for the twenty-four hour accumulated precipitation by 7%. However, the spatial distribution and the amounts of precipitation varied greatly between the different aerosol scenarios. These results indicate the large portion of uncertainty that remains unresolved and the need for more accurate description of aerosol feedbacks in atmospheric models and climate change predictions.

Dust Lofting and Ingestion by Supercell Storms

2012 ◽  
Vol 69 (5) ◽  
pp. 1453-1473 ◽  
Author(s):  
Robert B. Seigel ◽  
Susan C. van den Heever
Keyword(s):  
Mineral Dust ◽  
Ambient Air ◽  
Cloud Microphysics ◽  
Atmospheric Modeling ◽  
Cold Pool ◽  
Moist Convection ◽  
Surface Emission ◽  
Supercell Storms ◽  
Outflow Boundary ◽  
Regional Atmospheric Modeling

Abstract Recent research pertaining to aerosol impacts on cloud microphysics has shown a need for understanding mineral dust entrainment into moist convection. The goal of this study is to examine the pathways in which nonmicrophysically active mineral dust is entrained into supercell storms within three commonly observed dust regimes. The Regional Atmospheric Modeling System (RAMS) with an interactive dust model that allows for surface emission was used to achieve this goal. First, a supercell is simulated within an already dusty environment (EXP-BACKGROUND) to investigate ingestion purely from a background source. Second, the supercell is simulated within a clean background environment and lofts its own dust via the interactive dust model (EXP-STORM) to investigate the regime in which the only source of dust in the atmosphere is due to the storm itself. Finally, the supercell is simulated with a low-level convergence boundary introduced ahead of the supercell to investigate dust lofting by outflow boundary interactions (EXP-BOUNDARY). Results indicate that the supercell in EXP-BACKGROUND ingests large dust concentrations ahead of the rear flank downdraft (RFD) cold pool. Conversely, dust lofted by the cold pool in EXP-STORM is ingested by the supercell in relatively small amounts via a narrow corridor generated by turbulent mixing of the RFD cold pool and ambient air. The addition of a convergence boundary in EXP-BOUNDARY is found to act as an additional source of dust for the supercell. Results demonstrate the importance of an appropriate dust representation for numerical modeling.

The Sensitivity of a Numerically Simulated Idealized Squall Line to the Vertical Distribution of Aerosols

2014 ◽  
Vol 71 (12) ◽  
pp. 4581-4596 ◽  
Author(s):  
Zachary J. Lebo
Keyword(s):  
Vertical Distribution ◽  
Number Concentration ◽  
Squall Line ◽  
Cold Pool ◽  
Heating Rates ◽  
Low Level ◽  
Freezing Level ◽  
Cold Pools ◽  
Raindrop Size ◽  
The Vertical Distribution

Abstract Changes in the aerosol number concentration are reflected by changes in raindrop size and number concentration that ultimately affect the strength of cold pools via evaporation. Therefore, aerosol perturbations can potentially alter the balance between cold pool–induced and low-level wind shear–induced circulations. In the present work, simulations with increased aerosol loadings below approximately 3 km, between approximately 3 and 10 km, and at all vertical levels are performed to specifically address both the overall sensitivity of a squall line to the vertical distribution of aerosols and the extent to which low-level aerosols can affect the convective strength of the system. The results suggest that low-level aerosol perturbations have a negligible effect on the overall storm strength even though they act to enhance low-level latent heating rates. A tracer analysis shows that the low-level aerosols are either predominantly detrained at or below the freezing level or are rapidly lifted to the top of the troposphere or the lower stratosphere within the strongest convective cores. Moreover, it is shown that midlevel aerosol perturbations have nearly the same effect as perturbing the entire domain, increasing the convective updraft mass flux by more than 10%. These changes in strength are driven by a complex chain of events caused by smaller supercooled droplets, larger graupel, and larger raindrops. Combined, these changes tend to reduce the low-level bulk evaporation rate, thus weakening the cold pool and enhancing updraft strength. The results presented herein suggest that midlevel aerosol perturbations may exhibit a much larger effect on squall lines, at least in the context of this idealized framework.

scholarly journals Advances in understanding mineral dust and boundary layer processes over the Sahara from Fennec aircraft observations

2015 ◽  
Vol 15 (1) ◽  
pp. 199-290 ◽  
Author(s):  
C. L. Ryder ◽  
J. B. McQuaid ◽  
C. Flamant ◽  
R. Washington ◽  
H. E. Brindley ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Mineral Dust ◽  
Deep Convection ◽  
Dust Particles ◽  
Cold Pool ◽  
Boundary Layer Processes ◽  
Airborne Measurement ◽  
Aircraft Observations ◽  
Scientific Results ◽  
The Uk

Abstract. The Fennec climate program aims to improve understanding of the Saharan climate system through a synergy of observations and modelling. We present a description of the Fennec airborne observations during 2011 and 2012 over the remote Sahara (Mauritania and Mali) and the advances in the understanding of mineral dust and boundary layer processes they have provided. Aircraft instrumentation aboard the UK FAAM BAe146 and French SAFIRE Falcon 20 is described, with specific focus on instrumentation specially developed and relevant to Saharan meteorology and dust. Flight locations, aims and associated meteorology are described. Examples and applications of aircraft measurements from the Fennec flights are presented, highlighting new scientific results delivered using a synergy of different instruments and aircraft. These include: (1) the first airborne measurement of dust particles sized up to 300 microns and associated dust fluxes in the Saharan atmospheric boundary layer (SABL), (2) dust uplift from the breakdown of the nocturnal low-level jet before becoming visible in SEVIRI satellite imagery, (3) vertical profiles of the unique vertical structure of turbulent fluxes in the SABL, (4) in-situ observations of processes in SABL clouds showing dust acting as CCN and IN at −15 °C, (5) dual-aircraft observations of the SABL dynamics, thermodynamics and composition in the Saharan heat low region (SHL), (6) airborne observations of a dust storm associated with a cold-pool (haboob) issued from deep convection over the Atlas, (7) the first airborne chemical composition measurements of dust in the SHL region with differing composition, sources (determined using Lagrangian backward trajectory calculations) and absorption properties between 2011 and 2012, (8) coincident ozone and dust surface area measurements suggest coarser particles provide a route for ozone depletion, (9) discrepancies between airborne coarse mode size distributions and AERONET sunphotometer retrievals under light dust loadings. These results provide insights into boundary layer and dust processes in the SHL region – a region of substantial global climatic importance.

scholarly journals Direct observations of the atmospheric processing of Asian mineral dust

2006 ◽  
Vol 6 (3) ◽  
pp. 4109-4170 ◽  
Author(s):  
R. C. Sullivan ◽  
S. A. Guazzotti ◽  
D. A. Sodeman ◽  
K. A. Prather
Keyword(s):  
Urban Areas ◽  
Mineral Dust ◽  
Field Studies ◽  
Dust Particles ◽  
Reaction Products ◽  
Mass Source ◽  
Atmospheric Processing ◽  
Acid Reaction ◽  
The Individual ◽  
High Degree

Abstract. The accumulation of secondary acid products and ammonium on individual mineral dust particles during ACE-Asia has been measured in real-time using ATOFMS. Changes in the amounts of sulphate, nitrate, and chloride mixed with dust particles corresponded to different air mass source regions. During volcanically influenced periods, dust mixed with sulphate dominated. This rapidly switched to dust predominantly mixed with chloride when the first Asian dust front reached the R/V Ronald Brown. We hypothesise that the high degree of mixing of dust with chloride was caused by the prior reaction of NOy(g) and volcanic SO2(g) with sea salt particles, reducing the availability of nitrate and sulphate precursors while releasing HCl(g), which then reacted with the incoming dust front. The segregation of sulphate from nitrate and chloride in individual dust particles is demonstrated for the first time. This is likely caused by the dust plume encountering elevated SO2(g) in the Chinese interior before reaching coastal urban areas polluted by both SO2(g) and NOx(g). This caused the fractions of dust mixed with nitrate and/or chloride to be strongly dependent on the total dust loadings, whereas dust mixed with sulphate did not show this same dust concentration dependence. Ammonium was also significantly mixed with dust and the amount correlated strongly with the total amount of secondary acid reaction products in the dust. Submicron dust and ammonium sulphate were internally mixed, contrary to frequent statements that they exist as an external mixture. The size distribution of the mixing state of dust with these secondary species validates previous models and mechanisms of the atmospheric processing of dust. The uptake of secondary acids was also dependent on the individual dust particle mineralogy; nitrate accumulated on calcium-rich dust while sulphate accumulated on aluminosilicate-rich dust. Oxidation of S(IV) to S(VI) by iron in the aluminosilicate-rich dust is a probable explanation for this result, with important consequences for dust as a vector for the fertilization of remote oceans by soluble iron. This series of novel results has important implications for improving the treatment of dust in global chemistry models and highlights several key processes requiring further investigation through laboratory and field studies.

scholarly journals Advances in understanding mineral dust and boundary layer processes over the Sahara from Fennec aircraft observations

2015 ◽  
Vol 15 (14) ◽  
pp. 8479-8520 ◽  
Author(s):  
C. L. Ryder ◽  
J. B. McQuaid ◽  
C. Flamant ◽  
P. D. Rosenberg ◽  
R. Washington ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Mineral Dust ◽  
Cloud Condensation Nuclei ◽  
Deep Convection ◽  
Dust Particles ◽  
Cold Pool ◽  
Boundary Layer Processes ◽  
Aircraft Observations ◽  
Scientific Results ◽  
The Uk

Abstract. The Fennec climate programme aims to improve understanding of the Saharan climate system through a synergy of observations and modelling. We present a description of the Fennec airborne observations during 2011 and 2012 over the remote Sahara (Mauritania and Mali) and the advances in the understanding of mineral dust and boundary layer processes they have provided. Aircraft instrumentation aboard the UK FAAM BAe146 and French SAFIRE (Service des Avions Français Instrumentés pour la Recherche en Environnement) Falcon 20 is described, with specific focus on instrumentation specially developed for and relevant to Saharan meteorology and dust. Flight locations, aims and associated meteorology are described. Examples and applications of aircraft measurements from the Fennec flights are presented, highlighting new scientific results delivered using a synergy of different instruments and aircraft. These include (1) the first airborne measurement of dust particles sizes of up to 300 microns and associated dust fluxes in the Saharan atmospheric boundary layer (SABL), (2) dust uplift from the breakdown of the nocturnal low-level jet before becoming visible in SEVIRI (Spinning Enhanced Visible Infra-Red Imager) satellite imagery, (3) vertical profiles of the unique vertical structure of turbulent fluxes in the SABL, (4) in situ observations of processes in SABL clouds showing dust acting as cloud condensation nuclei (CCN) and ice nuclei (IN) at −15 °C, (5) dual-aircraft observations of the SABL dynamics, thermodynamics and composition in the Saharan heat low region (SHL), (6) airborne observations of a dust storm associated with a cold pool (haboob) issued from deep convection over the Atlas Mountains, (7) the first airborne chemical composition measurements of dust in the SHL region with differing composition, sources (determined using Lagrangian backward trajectory calculations) and absorption properties between 2011 and 2012, (8) coincident ozone and dust surface area measurements suggest coarser particles provide a route for ozone depletion, (9) discrepancies between airborne coarse-mode size distributions and AERONET (AERosol Robotic NETwork) sunphotometer retrievals under light dust loadings. These results provide insights into boundary layer and dust processes in the SHL region – a region of substantial global climatic importance.

scholarly journals Aerosol optical depth retrievals at the Izaña Atmospheric Observatory from 1941 to 2013 by using artificial neural networks

2016 ◽  
Vol 9 (1) ◽  
pp. 53-62 ◽  
Author(s):  
R. D. García ◽  
O. E. García ◽  
E. Cuevas ◽  
V. E. Cachorro ◽  
A. Barreto ◽  
...  
Keyword(s):  
Neural Networks ◽  
Time Series ◽  
Artificial Neural Networks ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Mineral Dust ◽  
Dust Particles ◽  
Filter Radiometer ◽  
Artificial Neural

Abstract. This paper presents the reconstruction of a 73-year time series of the aerosol optical depth (AOD) at 500 nm at the subtropical high-mountain Izaña Atmospheric Observatory (IZO) located in Tenerife (Canary Islands, Spain). For this purpose, we have combined AOD estimates from artificial neural networks (ANNs) from 1941 to 2001 and AOD measurements directly obtained with a Precision Filter Radiometer (PFR) between 2003 and 2013. The analysis is limited to summer months (July–August–September), when the largest aerosol load is observed at IZO (Saharan mineral dust particles). The ANN AOD time series has been comprehensively validated against coincident AOD measurements performed with a solar spectrometer Mark-I (1984–2009) and AERONET (AErosol RObotic NETwork) CIMEL photometers (2004–2009) at IZO, obtaining a rather good agreement on a daily basis: Pearson coefficient, R, of 0.97 between AERONET and ANN AOD, and 0.93 between Mark-I and ANN AOD estimates. In addition, we have analysed the long-term consistency between ANN AOD time series and long-term meteorological records identifying Saharan mineral dust events at IZO (synoptical observations and local wind records). Both analyses provide consistent results, with correlations  >  85 %. Therefore, we can conclude that the reconstructed AOD time series captures well the AOD variations and dust-laden Saharan air mass outbreaks on short-term and long-term timescales and, thus, it is suitable to be used in climate analysis.

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