scholarly journals Explicit simulation of aerosol physics in a cloud-resolving model

2004 ◽  
Vol 4 (1) ◽  
pp. 753-803 ◽  
Author(s):  
A. M. L. Ekman ◽  
C. Wang ◽  
J. Wilson ◽  
J. Ström
Keyword(s):  
Chemical Species ◽  
Convective Cloud ◽  
Substantial Part ◽  
Cloud Droplets ◽  
Upper Troposphere ◽  
Aerosol Mass ◽  
Cloud Resolving Model ◽  
Long Time ◽  
Nucleation Scavenging ◽  
Aitken Mode

Abstract. The role of convection in introducing aerosols and promoting the formation of new particles to the upper troposphere has been examined using a cloud-resolving model coupled with an interactive explicit aerosol module. A baseline simulation suggests good agreement in the upper troposphere between modeled and observed results including concentrations of aerosols in different size ranges, mole fractions of key chemical species, and concentrations of ice particles. In addition, a set of 34 sensitivity simulations has been carried out to investigate the sensitivity of modeled results to the treatment of various aerosol physical and chemical processes in the model. The size distribution of aerosols is proved to be an important factor in determining the aerosols' fate within the convective cloud. Nucleation mode aerosols (0<−d<−5.84 nm) are quickly transferred to the larger modes as they grow through coagulation and condensation of H2SO4. Accumulation mode aerosols (d>−31.0 nm) are almost completely removed by nucleation (activation of cloud droplets) and impact scavenging. However, a substantial part (up to 10% of the boundary layer concentration) of the Aitken mode aerosol population (5.84 nm<−d<−31.0 nm) reaches the top of the cloud and the free troposphere. These particles may continually survive in the upper troposphere, or over time form ice crystals, both that could impact the atmospheric radiative budget. The sensitivity simulations performed indicate that critical processes in the model causing a substantial change in the upper tropospheric Aitken mode number concentration are coagulation, condensation, nucleation scavenging, nucleation of aerosols and the transfer of aerosol mass and number between different aerosol bins. In particular, for aerosols in the Aitken mode to grow to CCN size, coagulation appears to be more important than condensation. Less important processes are dry deposition, impact scavenging and the initial vertical distribution and concentration of aerosols. It is interesting to note that in order to sustain a vigorous storm cloud, the supply of CCN must be continuous over a considerably long time period of the simulation. Hence, the treatment of the growth of particles is in general much more important than the initial aerosol concentration itself.

scholarly journals Explicit simulations of aerosol physics in a cloud-resolving model: a sensitivity study based on an observed convective cloud

2004 ◽  
Vol 4 (3) ◽  
pp. 773-791 ◽  
Author(s):  
A. M. L. Ekman ◽  
C. Wang ◽  
J. Wilson ◽  
J. Ström
Keyword(s):  
Chemical Species ◽  
Convective Cloud ◽  
Sensitivity Study ◽  
Substantial Part ◽  
Cloud Droplets ◽  
Upper Troposphere ◽  
Cloud Resolving Model ◽  
Long Time ◽  
Nucleation Scavenging ◽  
Aitken Mode

Abstract. The role of convection in introducing aerosols and promoting the formation of new particles to the upper troposphere has been examined using a cloud-resolving model coupled with an interactive explicit aerosol module. A baseline simulation suggests good agreement in the upper troposphere between modeled and observed results including concentrations of aerosols in different size ranges, mole fractions of key chemical species, and concentrations of ice particles. In addition, a set of 34 sensitivity simulations has been carried out to investigate the sensitivity of modeled results to the treatment of various aerosol physical and chemical processes in the model. The size distribution of aerosols is proved to be an important factor in determining the aerosols' fate within the convective cloud. Nucleation mode aerosols (here defined by 0≤d≤5.84 nm) are quickly transferred to the larger modes as they grow through coagulation of aerosols and condensation of H2SO4. Accumulation mode aerosols (here defined by d≥31.0 nm) are almost completely removed by nucleation (activation of cloud droplets) and impact scavenging. However, a substantial part (up to 10% of the boundary layer concentration) of the Aitken mode aerosol population (here defined by 5.84 nm≤d≤31.0 nm) reaches the top of the cloud and the free troposphere. These particles may continually survive in the upper troposphere, or over time form ice crystals, both that could impact on the atmospheric radiative budget. The sensitivity simulations performed indicate that critical processes in the model causing a substantial change in the upper tropospheric number concentration of Aitken mode aerosols are coagulation of aerosols, condensation of H2SO4, nucleation scavenging, nucleation of aerosols and the transfer of aerosol mass and number between different aerosol bins. In particular, for aerosols in the Aitken mode to grow to CCN size, coagulation of aerosols appears to be more important than condensation of H2SO4. Less important processes are dry deposition, impact scavenging and the initial vertical distribution and concentration of aerosols. It is interesting to note that in order to sustain a vigorous storm cloud, the supply of CCN must be continuous over a considerably long time period of the simulation. Hence, the treatment of the growth of particles is in general much more important than the initial aerosol concentration itself.

scholarly journals Explicit Simulation of Aerosol Physics in a Cloud-Resolving Model: Aerosol Transport and Processing in the Free Troposphere

2006 ◽  
Vol 63 (2) ◽  
pp. 682-696 ◽  
Author(s):  
Annica M. L. Ekman ◽  
Chien Wang ◽  
Johan Ström ◽  
Radovan Krejci
Keyword(s):  
Convective Cloud ◽  
Number Concentration ◽  
Box Model ◽  
Sulfate Aerosols ◽  
Accumulation Mode ◽  
Nucleation Mode ◽  
Cloud Resolving Model ◽  
Aerosol Module ◽  
Carbon Aerosols ◽  
Aitken Mode

Abstract Large concentrations of small aerosols have been previously observed in the vicinity of anvils of convective clouds. A 3D cloud-resolving model (CRM) including an explicit size-resolving aerosol module has been used to examine the origin of these aerosols. Five different types of aerosols are considered: nucleation mode sulfate aerosols (here defined by 0 ≤ d ≤5.84 nm), Aitken mode sulfate aerosols (here defined by 5.84 nm ≤ d ≤ 31.0 nm), accumulation mode sulfate aerosols (here defined by d ≥ 31.0 nm), mixed aerosols, and black carbon aerosols. The model results suggest that approximately 10% of the initial boundary layer number concentration of Aitken mode aerosols and black carbon aerosols are present at the top of the convective cloud as the cloud reaches its decaying state. The simulated average number concentration of Aitken mode aerosols in the cloud anvil (∼1.6 × 104 cm−3) is in the same order of magnitude as observations. Thus, the model results strongly suggest that vertical convective transport, particularly during the active period of the convection, is responsible for a major part of the appearance of high concentrations of small aerosols (corresponding to the Aitken mode in the model) observed in the vicinity of cloud anvils. There is some formation of new aerosols within the cloud, but the formation is small. Nucleation mode aerosols are also efficiently scavenged through impaction scavenging by precipitation. Accumulation mode and mixed mode aerosols are efficiently scavenged through nucleation scavenging and their concentrations in the cloud anvil are either very low (mixed mode) or practically zero (accumulation mode). In addition to the 3D CRM, a box model, including important features of the aerosol module of the 3D model, has been used to study the formation of new aerosols after the cloud has evaporated. The possibility of these aerosols to grow to suitable cloud condensation or ice nuclei size is also examined. Concentrations of nucleation mode aerosols up to 3 × 104 cm−3 are obtained. The box model simulations thus suggest that new particle formation is a substantial source of small aerosols in the upper troposphere during and after the dissipation of the convective cloud. Nucleation mode and Aitken mode aerosols grow due to coagulation and condensation of H2SO4 on the aerosols, but the growth rate is low. Provided that there is enough OH available to oxidize SO2, parts of the aerosol population (∼400 cm−3) can reach the accumulation mode size bin of the box model after 46 h of simulation.

scholarly journals What do we learn on bromoform transport and chemistry in deep convection from fine scale modelling?

2011 ◽  
Vol 11 (11) ◽  
pp. 29561-29600 ◽  
Author(s):  
V. Marécal ◽  
M. Pirre ◽  
G. Krysztofiak ◽  
B. Josse
Keyword(s):  
Boundary Layer ◽  
Transport Model ◽  
Deep Convection ◽  
Chemical Species ◽  
Convective Cloud ◽  
Initial Boundary ◽  
Mixing Ratio ◽  
Atmospheric Conditions ◽  
Upper Troposphere ◽  
Soluble Species

Abstract. Bromoform is one of the main sources of halogenated Very Short-Lived Species (VSLS) that possibly contributes when degradated to the inorganic halogen loading in the stratosphere. Because of its short lifetime of about four weeks, its pathway to the stratosphere is mainly the transport by convection up to the tropical tropopause layer (TTL) and then by radiative ascent in the low stratosphere. Some of its degradation product gases (PGs) that are soluble can be scavenged and not reach the TTL. In this paper we present a detailed modelling study of the transport and the degradation of bromoform and its PGs in convection. We use a 3-D-cloud resolving model coupled with a chemistry model including gaseous and aqueous chemistry. We run idealised simulations up to 10 days, initialised using a tropical radiosounding for atmospheric conditions and using outputs from a global chemistry-transport model for chemical species. Bromoform is initialised only in the low levels. The first simulation is run with stable atmospheric conditions. It shows that the sum of the bromoform and its PGs significantly decreases with time because of dry deposition and that PGs are mainly in the form of HBr after 2 days of simulation. The other simulation is similar to the first simulation but includes perturbations of temperature and of moisture leading to the development of a convective cloud reaching the TTL. Results of this simulation show an efficient vertical transport of the bromoform from the boundary layer in the upper troposphere and TTL (mixing ratio up to 45% of the initial boundary layer mixing ratio). The organic PGs, which are for the most abundant of them not very soluble, are also uplifted efficiently. For the inorganic PGs, which are more abundant than organic PGs, their mixing ratios in the upper troposphere and in the TTL depend on the partitioning between inorganic soluble and inorganic non soluble species in the convective cloud. Important soluble species such as HBr and HOBr are efficiently scavenged by rain. This removal is reduced by the production of Br2 (not soluble) in the gas phase from aqueous processes in the cloud droplets. This Br2 production process is therefore important for the PG budget in the upper troposphere and in the TTL. We also showed that this process is favoured by acidic conditions in the coud droplets, i.e. polluted conditions.

scholarly journals Modelling the reversible uptake of chemical species in the gas phase by ice particles formed in a convective cloud

2009 ◽  
Vol 9 (6) ◽  
pp. 24361-24410 ◽  
Author(s):  
V. Marécal ◽  
M. Pirre ◽  
E. D. Rivière ◽  
N. Pouvesle ◽  
J. N. Crowley ◽  
...  
Keyword(s):  
Cloud Model ◽  
Laboratory Data ◽  
Chemical Species ◽  
Convective Cloud ◽  
Trace Gas ◽  
Limiting Factor ◽  
Mixing Ratios ◽  
Ice Particles ◽  
Cloud Resolving Model ◽  
Single Moment

Abstract. The present paper is a preliminary study preparing the introduction of reversible trace gas uptake by ice particles into a 3-D cloud resolving model. For this a 3-D simulation of a tropical deep convection cloud was run with the BRAMS cloud resolving model using a two-moment bulk microphysical parameterization. Trajectories encountering the convective clouds were computed from these simulation outputs along which the variations of the pristine ice, snow and aggregate mixing ratios and size distributions were extracted. The reversible uptake of 11 trace gases by ice was examined assuming applicability of Langmuir isotherms using recently evaluated (IUPAC) laboratory data. The results show that ice uptake is only significant for HNO3, HCl, CH3COOH and HCOOH. For H2O2, using new results for the partition coefficient results in significant partitioning to the ice phase for this trace gas also. It was also shown that the uptake is largely dependent on the temperature for some species. The adsorption saturation at the ice surface for large gas concentrations is generally not a limiting factor except for HNO3 and HCl for gas concentration greater than 1 ppbv. For HNO3, results were also obtained using a trapping theory, resulting in a similar order of magnitude of uptake, although the two approaches are based on different assumptions. The results were compared to those obtained using a BRAMS cloud simulation based on a single-moment microphysical scheme instead of the two moment scheme. We found similar results with a slightly more important uptake when using the single-moment scheme which is related to slightly higher ice mixing ratios in this simulation. The way to introduce these results in the 3-D cloud model is discussed.

scholarly journals What do we learn about bromoform transport and chemistry in deep convection from fine scale modelling?

2012 ◽  
Vol 12 (14) ◽  
pp. 6073-6093 ◽  
Author(s):  
V. Marécal ◽  
M. Pirre ◽  
G. Krysztofiak ◽  
P. D. Hamer ◽  
B. Josse
Keyword(s):  
Boundary Layer ◽  
Production Process ◽  
Gas Phase ◽  
Aqueous Phase ◽  
Convective Cloud ◽  
Mixing Ratio ◽  
Atmospheric Conditions ◽  
Cloud Droplets ◽  
Upper Troposphere ◽  
Mixing Ratios

Abstract. Bromoform is one of the most abundant halogenated Very Short-Lived Substances (VSLS) that possibly contributes, when degradated, to the inorganic halogen loading in the stratosphere. In this paper we present a detailed modelling study of the transport and the photochemical degradation of bromoform and its product gases (PGs) in a tropical convective cloud. The aim was to explore the transport and chemistry of bromoform under idealised conditions at the cloud scale. We used a 3-D cloud-resolving model coupled with a chemistry model including gaseous and aqueous chemistry. In particular, our model features explicit partitioning of the PGs between the gas phase and the aqueous phase based on newly calculated Henry's law coefficients using theoretical methods. We ran idealised simulations for up to 10 days that were initialised using a tropical radiosounding of atmospheric conditions and using outputs from a global chemistry-transport model for chemical species. Two simulations were run with stable atmospheric conditions with a bromoform initial mixing ratio of 40 pptv (part per trillion by volume) and 1.6 pptv up to 1 km altitude. The first simulation corresponds to high bromoform mixing ratios that are representative of real values found near strong localised sources (e.g. tropical coastal margins) and the second to the global tropical mean mixing ratio from observations. Both of these simulations show that the sum of bromoform and its PGs significantly decreases with time because of dry deposition, and that PGs are mainly in the form of HBr after 2 days of simulation. Two further simulations are conducted; these are similar to the first two simulations but include perturbations of temperature and moisture leading to the development of a convective cloud reaching the tropical tropopause layer (TTL). Results of these simulations show an efficient vertical transport of the bromoform from the boundary layer to the upper troposphere and the TTL. The bromoform mixing ratio in the TTL is up to 45% of the initial boundary layer mixing ratio. The most abundant organic PGs, which are not very soluble, are also uplifted efficiently in both simulations featuring the convective perturbation. The inorganic PGs are more abundant than the organic PGs, and their mixing ratios in the upper troposphere and in the TTL depend on the partitioning between inorganic soluble and insoluble species in the convective cloud. Important soluble species such as HBr and HOBr are efficiently scavenged by rain. This removal of Bry by rain is reduced by the release of Br2 (relatively insoluble) to the gas phase due to aqueous chemistry processes in the cloud droplets. The formation of Br2 in the aqueous phase and its subsequent release to the gas phase makes a non negligible contribution to the high altitude bromine budget in the case of the large bromoform (40 pptv) initial mixing ratios. In this specific, yet realistic case, this Br2 production process is important for the PG budget in the upper troposphere and in the TTL above convective systems. This process is favoured by acidic conditions in the cloud droplets, i.e. polluted conditions. In the case of low bromoform initial mixing ratios, which are more representative of the mean distribution in the tropics, this Br2 production process is shown to be less important. These conclusions could nevertheless be revisited if the knowledge of chlorine and bromine chemistry in the cloud droplets was improved in the future.

scholarly journals A New Parameterization of the Accretion of Cloud Water by Graupel and Its Evaluation through Cloud and Precipitation Simulations

2019 ◽  
Vol 76 (2) ◽  
pp. 381-400 ◽  
Author(s):  
Han-Gyul Jin ◽  
Hyunho Lee ◽  
Jong-Jin Baik
Keyword(s):  
Collection Efficiency ◽  
Precipitation Amount ◽  
Cloud Droplet ◽  
Convective Cloud ◽  
Heavy Precipitation ◽  
Cloud Water ◽  
The Other ◽  
Precipitation Event ◽  
Cloud Droplets ◽  
Cloud Resolving Model

Abstract A new parameterization of the accretion of cloud water by graupel for use in bulk microphysics schemes is derived by analytically integrating the stochastic collection equation (SCE). In this parameterization, the collection efficiency between graupel particles and cloud droplets is expressed in a functional form using the data obtained from a particle trajectory model by a previous study. The new accretion parameterization is evaluated through box model simulations in comparison with a bin-based direct SCE solver and two previously developed accretion parameterizations that employ the continuous collection equation and a simplified SCE, respectively. Changes in cloud water and graupel mass contents via the accretion process predicted by the new parameterization are closest to those predicted by the direct SCE solver. Furthermore, the new parameterization predicts a decrease in the cloud droplet number concentration that is smaller than the decreases predicted by the other accretion parameterizations, consistent with the direct SCE solver. The new and the other accretion parameterizations are implemented into a cloud-resolving model. Idealized deep convective cloud simulations show that among the accretion parameterizations, the new parameterization predicts the largest rate of accretion by graupel and the smallest rate of accretion by snow, which overall enhances rainfall through the largest rate of melting of graupel. Real-case simulations for a precipitation event over the southern Korean Peninsula show that among the examined accretion parameterizations, the new parameterization simulates precipitation closest to observations. Compared to the other accretion parameterizations, the new parameterization decreases the fractions of light and moderate precipitation amounts and increases the fraction of heavy precipitation amount.

scholarly journals The Relative Importance of Scavenging, Oxidation, and Ice-Phase Processes in the Production and Wet Deposition of Sulfate

2005 ◽  
Vol 62 (7) ◽  
pp. 2118-2135 ◽  
Author(s):  
Vlado Spiridonov ◽  
Mladjen Curic
Keyword(s):  
Wet Deposition ◽  
Lower Percentage ◽  
Relative Importance ◽  
Total Sulfur ◽  
Sulfate Production ◽  
Relative Contribution ◽  
Cloud Resolving Model ◽  
Cloud Scavenging ◽  
Nucleation Scavenging ◽  
Ice Phase

Abstract The relative importance of various processes to sulfate production and wet deposition is examined by using a cloud-resolving model coupled with a sulfate chemistry submodel. Results using different versions of the model are then compared and principal differences with respect to their dynamics, microphysics, and chemistry are carefully discussed. The results imply that the dominant microphysical and chemical conversions of sulfate in the 3D run are nucleation, scavenging, and oxidation. Due to the lower cloud water and rainwater pH, oxidation does not contribute as significantly to the sulfate mass in the 2D run as the 3D. Sensitivity tests have revealed that in-cloud scavenging in the 2D run for continental nonpolluted and continental polluted clouds accounted for 29.4% and 31.5% of the total sulfur deposited, respectively. The 3D run shows a lower percentage contribution to sulfur deposition for about 28.2% and 29.6%. In addition, subcloud scavenging for the 2D run contributed about 32.7% and 38.2%. In-cloud oxidation in the 2D run accounted for about 24.5% to 30.4% of the total sulfur mass deposited. Subcloud oxidation contributed from 21.0% to 20.6% of the total sulfur mass removed by wet deposition. In-cloud oxidation for the 3D run shows slightly lower percentage values when compared to those from the 2D run. The relative contribution of subcloud oxidation for continental nonpolluted and polluted clouds exceeds those values in the 2D run by approximately 7% and 10%, respectively. Ignoring the ice phase and considering those types of convective clouds in the 2D run may lead to a higher value of the total sulfur mass removed by the wet deposition of about 33.9% to 39.2% for the continental nonpolluted and 36.2% to 45.6% for the continental polluted distributions relative to the base runs.

scholarly journals Upper Tropospheric Water Vapor Transport from Indian to Sahelian Regions

Atmosphere ◽  
2018 ◽  
Vol 9 (10) ◽  
pp. 403 ◽  
Author(s):  
Abdoulaye Sy ◽  
Bouya Diop ◽  
Joël Van Baelen ◽  
Christophe Duroure ◽  
Yahya Gour ◽  
...  
Keyword(s):  
Water Vapor ◽  
Indian Monsoon ◽  
Water Vapor Transport ◽  
Substantial Part ◽  
Monsoon Region ◽  
Direct Role ◽  
Air Masses ◽  
Upper Troposphere ◽  
Tropical Easterly Jet

We present a study of upper tropospheric westward transport of air masses coming from the Indian monsoon zone over the period 1998–2008. The objective is to characterize upper tropospheric transport of water vapor from the Indian to Sahelian regions, and to improve the understanding of the dynamical mechanisms that govern water vapor variations in West Africa and the interconnections between India and the Sahel, focusing on the direct role of the Indian monsoon region on Sahel tropospheric water vapor and precipitation. The calculations of forward trajectories with LACYTRAJ (LACY TRAJectory code) and humidity fluxes show that a substantial part (40 to 70% at 300 hPa) of trajectories coming from the upper troposphere of the monsoon region crossed the Sahelian region in a few days (3–14 days), and water vapor fluxes connecting these two regions are established when the Indian monsoon begins at latitudes higher than 15° N in its south–north migration. The intensity and orientation of water vapor fluxes are related to the tropical easterly jet, but they are from the east above the high convection zones. Between 1998 and 2008, these fluxes between the 500–300 hPa pressure levels are associated with precipitation in Sahel only if they are from the east and with an intensity exceeding 8 kg·(m·s)−1.

scholarly journals On the contribution of Aitken mode particles to cloud droplet populations at continental background areas – a parametric sensitivity study

2007 ◽  
Vol 7 (3) ◽  
pp. 6077-6112
Author(s):  
T. Anttila ◽  
V.-M. Kerminen
Keyword(s):  
Surface Tension ◽  
Particle Size ◽  
Chemical Composition ◽  
Pure Water ◽  
Particle Surface ◽  
Chemical Properties ◽  
Sensitivity Study ◽  
Geometric Standard Deviation ◽  
Cloud Droplets ◽  
Aitken Mode

Abstract. Aitken mode particles are potentially an important source of cloud droplets in continental background areas. In order to find out which physico-chemical properties of Aitken mode particles are most important regarding their cloud-nucleating ability, we applied a global sensitivity method to an adiabatic air parcel model simulating the number of cloud droplets formed on Aitken mode particles, CD2. The technique propagates uncertainties in the parameters describing the properties of Aitken mode to CD2. The results show that if the Aitken mode particles do not contain molecules that are able to reduce the particle surface tension more than 30% and/or decrease the mass accommodation coefficient of water, α, below 10−2, the chemical composition and modal properties may have roughly an equal importance at low updraft velocities characterized by maximum supersaturations <0.1%. For larger updraft velocities, however, the particle size distribution is clearly more important than the chemical composition. In general, CD2 exhibits largest sensitivity to the particle number concentration, followed by the particle size. Also the shape of the particle mode, characterized by the geometric standard deviation (GSD), can be as important as the mode mean size at low updraft velocities. Finally, the performed sensitivity analysis revealed also that the chemistry may dominate the total sensitivity of CD2 to the considered parameters if: 1) the value of α varies at least one order of magnitude more than what is expected for pure water surfaces (10−2–1), or 2) the particle surface tension varies more than roughly 30% under conditions close to reaching supersaturation.

scholarly journals A mass-conserving and multi-tracer efficient transport scheme in the online integrated Enviro-HIRLAM model

2013 ◽  
Vol 6 (4) ◽  
pp. 1029-1042 ◽  
Author(s):  
B. Sørensen ◽  
E. Kaas ◽  
U. S. Korsholm
Keyword(s):  
Prediction Model ◽  
Weather Prediction ◽  
Three Dimensional ◽  
Chemical Species ◽  
Numerical Weather Prediction Model ◽  
Computationally Efficient ◽  
Long Time ◽  
Dimensional Version ◽  
The Stability ◽  
Lagrangian Scheme

Abstract. In this paper a new advection scheme for the online coupled chemical–weather prediction model Enviro-HIRLAM is presented. The new scheme is based on the locally mass-conserving semi-Lagrangian method (LMCSL), where the original two-dimensional scheme has been extended to a fully three-dimensional version. This means that the three-dimensional semi-implicit semi-Lagrangian scheme which is currently used in Enviro-HIRLAM is largely unchanged. The HIRLAM model is a computationally efficient hydrostatic operational short-term numerical weather prediction model, which is used as the base for the online integrated Enviro-HIRLAM. The new scheme is shown to be efficient, mass conserving, and shape preserving, while only requiring minor alterations to the original code. It still retains the stability at long time steps, which the semi-Lagrangian schemes are known for, while handling the emissions of chemical species accurately. Several mass-conserving filters have been tested to assess the optimal balance of accuracy vs. efficiency.

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