Top PDF Cloud-Aerosol-Radiation (CAR) ensemble modeling system

Cloud-Aerosol-Radiation (CAR) ensemble modeling system

Cloud-Aerosol-Radiation (CAR) ensemble modeling system

Fig. 1. Schematic of the interactive Cloud-Aerosol-Radiation ensemble model (CAR), illustrat- ing all key groups of parameterizations currently available (each with a number of schemes listed in parenthesis) and their links with directional data flow by arrows. Shown also are petas- cale computing optimization against in situ and satellite observations for ensemble size reduc- tion, as well as the full coupling with CWRF for integration of impacts to and feedbacks from climate variations over the US, where the interactive system evaluation is presented in this study.
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Dust aerosol impact on North Africa climate: a GCM investigation of aerosol-cloud-radiation interactions using A-Train satellite data

Dust aerosol impact on North Africa climate: a GCM investigation of aerosol-cloud-radiation interactions using A-Train satellite data

crease to the west (Fig. 5d). Differences between the sensi- tivity experiment IND and CTRL are statistically significant at the confidence level typically exceeds 95 % corresponding to the major changes in the OLR, precipitation, and cloud cover fields in North Africa. Anomalies are shown to be sig- nificant in all areas at above 70 % level. Note that the aerosol 2nd indirect effect, which is on the precipitation rate, is not included. Change in precipitation is through the interactions among aerosol, cloud, radiation, and dynamical processes in the model. Mahowald and Kiehl (2003) found a negative cor- relation between high cloud amount and dust along the equa- tor across North Africa and the Atlantic in a region of rela- tively large ice cloud amount. They also indicated that there was a positive anomalies to the west, indicating a shift in the location of ice clouds although there might be a net increase in ice cloud cover. Our simulation results appear to be in line with this observation. However, they also indicated that since there are no long-term ground measurements for dust and high clouds in these areas, and because it has been dif- ficult to map these high clouds using satellite observations, making a firm conclusion regarding high clouds, precipita- tion, and ice forming around dust kernels is not a straight- forward task. Further in-depth studies are needed from both observational and modeling approaches.
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Systematic variations of cloud top temperature and precipitation rate with aerosols over the global tropics

Systematic variations of cloud top temperature and precipitation rate with aerosols over the global tropics

Abstract. Aerosols may modify cloud properties and precip- itation via a variety of mechanisms with varying and con- tradicting consequences. Using a large ensemble of satellite data acquired by the Moderate Resolution Imaging Spec- troradiometer onboard the Earth Observing System’s Aqua platform, the CloudSat cloud profiling radar and the Cloud- Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite over the tropical oceans, we identified two distinct correlations of clouds and precipitation with aerosol loading. Cloud-top temperatures are significantly negatively correlated with increasing aerosol index (AI) over oceans and aerosol optical depth (AOT) over land for deep mixed-phase clouds with liquid droplets near the warm bases and ice crystals near the cold tops; no significant changes were found for uniformly liquid clouds. Precipitation rates are positively correlated with the AI for mixed-phase clouds, but negatively correlated for liquid clouds. These distinct cor- relations might be a manifestation of two potential mech- anisms: the invigoration effect (which enhances convection and precipitation) and the microphysical effect (which sup- presses precipitation). We note that the highly limited in- formation garnered from satellite products cannot unequiv- ocally support the causal relationships between cloud-top temperature/precipitation rate and aerosol loading. But if aerosols are indeed the causes for the observed relationships, they may change the overall distribution of precipitation, leading to a more extreme and unfavorable rainfall pattern of suppressing light rains and fostering heavy rains.
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Assessing regional scale predictions of aerosols, marine stratocumulus, and their interactions during VOCALS-REx using WRF-Chem

Assessing regional scale predictions of aerosols, marine stratocumulus, and their interactions during VOCALS-REx using WRF-Chem

Reproducing CCN gradients and including coupled cloud- aerosol-radiation processes are important to properly sim- ulate the marine stratocumulus over the SEP. This pa- per shows the improvement gained in using an interactive aerosol-cloud-radiation module in the chemistry version of the Weather Research and Forecasting (WRF-Chem) model (Grell et al., 2005; Fast et al., 2006). Specifically, a new cou- pling between the double-moment Morrison microphysics scheme (Morrison et al., 2005, 2009) and the aerosol mod- ules is used; we implemented this coupling in the April 2011 v3.3 release of WRF-Chem. The VAMOS Ocean-Cloud- Atmosphere-Land Study Regional Experiment (VOCALS- REx) was a field campaign during October and November 2008 designed to improve the scientific understanding of model simulations and predictions of the coupled climate system over the SEP (Wood et al., 2011b). The campaign provided extensive measurements for evaluating the capabil- ity of our model with the aforementioned new coupling in predicting aerosol and marine stratus clouds over this region. A recent modeling exercise by Abel et al. (2010) using the UK Met Office Unified Model (MetUM) is parallel to this model evaluation study. MetUM simulated a good rep- resentation of synoptically induced variability in cloud cover and boundary layer depth during the VOCALS-REx (Abel et al., 2010). However, the exclusion of cloud-aerosol interac- tions and the model’s relatively simple parameterization of cloud-microphysical effects (Toniazzo et al., 2011) are likely to preclude better agreement with field observations.
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Importance of tropospheric volcanic aerosol for indirect radiative forcing of climate

Importance of tropospheric volcanic aerosol for indirect radiative forcing of climate

L., Bidlot, J., Bormann, N., Delsol, C., Dragani, R., Fuentes, M., Geer, A. J., Haimberger, L., Healy, S., Hersbach, H., H ´olm, E. V., Isaksen, L., K ˚allberg, P., K ¨ohler, M., Matricardi, M., McNally, A. P., Monge-Sanz, B. M., Morcrette, J.-J., Peubey, C., de Rosnay, P., Tavolato, C., Th ´epaut, J.-N., and Vitart, F.: The ERA-Interim reanalysis: Configuration and performance of the data assimilation system, Q. J. Roy. Meteorol. Soc., 133, 1972–1990, doi:10.1002/qj.828,

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Aerosol-cloud interaction inferred from MODIS satellite data and global aerosol models

Aerosol-cloud interaction inferred from MODIS satellite data and global aerosol models

Several possibilities exist for aerosols and clouds to be in- terlinked through processes other than physical aerosol-cloud interactions. One possibility is that meteorological situations with clouds nearby influence the AOD. Relative humidity in- creases the AOD due to more water uptake by the particles. Since relative humidity is usually higher in the vicinity of clouds than in completely clear sky regions, an increase in cloud fraction with AOD may be strongly influenced by this effect. Further, larger scale meteorological conditions may influence both AOD and cloud parameters and it is not intu- itive to which extent and even in which direction this will impact the AOD – cloud relationships. Two examples il- lustrate this; 1) sea salt particles are generated under windy conditions, e.g. during frontal passages, when clouds are fre- quent, 2) over industrialized regions high pressure systems with weak winds will normally allow aerosol to build up, but in this case clear sky conditions are most usual. Fi- nally, cloud contamination in the AOD retrieval may be a problem, causing an apparent increase in cloud fraction with AOD (Kaufman et al., 2005c; Zhang et al., 2005).
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Chemical composition of ambient aerosol, ice residues and cloud droplet residues in mixed-phase clouds: single particle analysis during the Cloud and Aerosol Characterization Experiment (CLACE 6)

Chemical composition of ambient aerosol, ice residues and cloud droplet residues in mixed-phase clouds: single particle analysis during the Cloud and Aerosol Characterization Experiment (CLACE 6)

ertheless, the exact determination whether an individual ice residue (IR) (or droplet residue (DR)) is really just the origi- nal IN (CCN) or an IN (CCN) plus some additional material or not an IN (CCN) at all is a complex issue that merits fur- ther investigation but is beyond the scope of this paper. Fur- thermore, note that we have no information about the sam- pling location within the cloud, i.e. cloud base, cloud top, cloud edge or cloud core. Moreover, it is not known which heterogeneous nucleation processes were active (deposition, immersion, contact freezing etc.). The small primary ice par- ticles sampled by the Ice-CVI are those that formed most re- cently, thus, we may usually do not sample the most efficient IN which form ice particles first. In some sampling situations however, when ice particles just start to form in the cloud, the most efficient ice nuclei are activated and sampled, and in these situations we miss the less efficient ones. Therefore, we can only state that the sampled primary ice particles had to be quite young. Assuming measured ice particle growth rates between 0.4 and 0.9 µm s −1 (Mertes et al., 2001) result in ice particles “life times” before sampling between 22 and 50 seconds.
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Impact of cloud-borne aerosol representation on aerosol direct and indirect effects

Impact of cloud-borne aerosol representation on aerosol direct and indirect effects

Abstract. Aerosol particles attached to cloud droplets are much more likely to be removed from the atmosphere and are much less efficient at scattering sunlight than if unattached. Models used to estimate direct and indirect effects of aerosols employ a variety of representations of such cloud-borne par- ticles. Here we use a global aerosol model with a relatively complete treatment of cloud-borne particles to estimate the sensitivity of simulated aerosol, cloud and radiation fields to various approximations to the representation of cloud-borne particles. We find that neglecting transport of cloud-borne particles introduces little error, but that diagnosing cloud- borne particles produces global mean biases of 20% and lo- cal errors of up to 40% for aerosol, droplet number, and di- rect and indirect radiative forcing. Aerosol number, aerosol optical depth and droplet number are significantly underesti- mated in regions and seasons where and when wet removal is primarily by stratiform rather than convective clouds (po- lar regions during winter), but direct and indirect effects are less biased because of the limited sunlight there and then. A treatment that predicts the total mass concentration of cloud- borne particles for each mode yields smaller errors and runs 20% faster than the complete treatment. The errors are much smaller than current estimates of uncertainty in direct and in- direct effects of aerosols, which suggests that the treatment of cloud-borne aerosol is not a significant source of uncer- tainty in estimates of direct and indirect effects.
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Retrieving aerosol in a cloudy environment: aerosol product availability as a function of spatial resolution

Retrieving aerosol in a cloudy environment: aerosol product availability as a function of spatial resolution

Abstract. The challenge of using satellite observations to re- trieve aerosol properties in a cloudy environment is to pre- vent contamination of the aerosol signal from clouds, while maintaining sufficient aerosol product yield to satisfy spe- cific applications. We investigate aerosol retrieval availabil- ity at different instrument pixel resolutions using the standard MODIS aerosol cloud mask applied to MODIS data and sup- plemented with a new GOES-R cloud mask applied to GOES data for a domain covering North America and surround- ing oceans. Aerosol product availability is not the same as the cloud free fraction and takes into account the techniques used in the MODIS algorithm to avoid clouds, reduce noise and maintain sufficient numbers of aerosol retrievals. The in- herent spatial resolution of each instrument, 0.5 × 0.5 km for MODIS and 1 × 1 km for GOES, is systematically degraded to 1 × 1, 2 × 2, 1 × 4, 4 × 4 and 8 × 8 km resolutions and then analyzed as to how that degradation would affect the avail- ability of an aerosol retrieval, assuming an aerosol product resolution at 8 × 8 km. The analysis is repeated, separately, for near-nadir pixels and those at larger view angles to inves- tigate the effect of pixel growth at oblique angles on aerosol retrieval availability. The results show that as nominal pixel size increases, availability decreases until at 8 × 8 km 70 % to 85 % of the retrievals available at 0.5 km, nadir, have been lost. The effect at oblique angles is to further decrease avail- ability over land but increase availability over ocean, because sun glint is found at near-nadir view angles. Finer resolu- tion sensors (i.e., 1 × 1, 2 × 2 or even 1 × 4 km) will retrieve aerosols in partly cloudy scenes significantly more often than
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Influences of in-cloud aerosol scavenging parameterizations on aerosol concentrations and wet deposition in ECHAM5-HAM

Influences of in-cloud aerosol scavenging parameterizations on aerosol concentrations and wet deposition in ECHAM5-HAM

to the larger aerosol modes leads to an increase in new particle formation. The annual and global mean new particle nucleation rate was nearly three times greater for the F100 simulation as compared to the DIAG-FULL simulation. For the PROG-AP sim- ulation, the interstial coarse mode is reduced by up to half over the southern oceans. This occurs since the in-droplet and in-crystal modes (not shown here) contain these

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Estimation of aerosol water and chemical composition from AERONET at Cabauw, the Netherlands

Estimation of aerosol water and chemical composition from AERONET at Cabauw, the Netherlands

guess (x) to calculate aerosol water uptake, as well as a parameter (RH prior , in y) which is used in the optimization. It can be adjusted by the model if this leads to a better fit with the AERONET aerosol parameters, but changing RH from its prior value will also contribute to the cost function. The variance of the sounding RH in a layer of 2 km thick- ness near the ground is used as an uncertainty estimate, and is generally in the order

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A method based on neural networks for generating solar radiation map

A method based on neural networks for generating solar radiation map

Estimation of global solar radiation (GSR) is important in most solar energy applications, particularly in design methods, in system characterization and in decision making for energy management. In this paper, a new methodology based on artificial neural networks (ANN) for generating daily GSR data is presented. By modeling GSR in regions where historical records are available, solar potential map for other sites that GSR have not been recorded was generated. In order to examine the ANN models, meteorological data throughout the year 2008 belonging to Karaj city in Alborz province of Iran were used to develop GSR predictors. Input parameters were maximum temperature, relative sunshine duration and extraterrestrial solar radiation while the output parameter was the solar radiation. Various networks were designed and tested and the most accurate model was selected. The best network was found as one hidden layer network with 3-4-1 topology, i.e., a network having four neurons in its hidden layer. To estimate the differences between the measured and predicted values, root mean square error (RMSE), mean absolute error (MAE), mean absolute percentage error (MAPE) and coefficient of determination (R 2 ) were computed as0.66, 0.52, 4.46% and 0.978, respectively. The optimum ANN model was then used to predict GSR in other cities in the province. Data from three stations located in Hashtgerd, Taleghan and Chitgar cities were used as production set. The GSR values for production sites of Hashtgerd, Taleghan and Chigrar were calculated as 4.93, 4.35 and 5.08 kWh m -2 day -1 , respectively. Finally, the predicted solar potential values in all stations were integrated and represented in the form of a map. While results are site-specific, the methodology introduced here is general and provides an inexpensive means for GSR prediction based on readily available data.
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Chemical composition of ambient aerosol, ice residues and cloud droplet residues in mixed-phase clouds: single particle analysis during the Cloud and Aerosol Characterization Experiment (CLACE 6)

Chemical composition of ambient aerosol, ice residues and cloud droplet residues in mixed-phase clouds: single particle analysis during the Cloud and Aerosol Characterization Experiment (CLACE 6)

nuclei cannot be investigated as easily with chamber experiments due to the low, ∼10’s per liter, number density of IN in the atmosphere (DeMott et al., 2003). To analyze the chemical composition and ice nucleating ability of ambient aerosol, several field studies have applied a CFDC in combination with mass spectrometric analysis, mainly on sin- gle particle basis (DeMott et al., 2003). A CVI (counterflow virtual impactor) was used

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Characterization of aerosol and cloud water at a mountain site during WACS 2010: secondary organic aerosol formation through oxidative cloud processing

Characterization of aerosol and cloud water at a mountain site during WACS 2010: secondary organic aerosol formation through oxidative cloud processing

Oxalic acid, a highly oxidized organic formed via in-cloud processing (e.g., Ervens et al., 2004; Sorooshian et al., 2006, 2007), has been experimentally identified as an important aqueous oxidation product of many potential precursors un- der cloud-relevant concentrations (Perri et al., 2009; Tan et al., 2009, 2010, 2012). On the basis of aircraft measure- ments, Sorooshian et al. (2007) suggested that the source of oxalic acid in aerosol particles above cloud was a result of aqueous-phase processing, in which oxalic acid forma- tion was shown to be enhanced with increasing amounts of both liquid water content and pH in droplets. A recent model- ing study also concluded that in-cloud processing could ex- plain the observed oxalate concentration in both rural and remote locations (Myriokefalitakis et al., 2011). SOA forma- tion in aerosol water is also possible. Hennigan et al. (2008) measured both gas-phase and particulate WSOC during the summertime of Atlanta and observed a sharp increase of WSOC in particulate fraction at elevated relative humidity, suggesting a positive correlation with aerosol liquid water. Because of the limited water content in fine particles, Henry’s law partitioning alone cannot explain the SOA enhancement observed by Hennigan et al. (2008), and thus subsequent aqueous chemistry of dissolved organics that further drives the Henry’s law partitioning in aerosol particles likely took place. Furthermore, Kaul et al. (2011) recently reported that aqueous-phase processing likely enhanced the production of SOA in foggy periods in Kanpur, India. To explain a missing sink of glyoxal in Mexico City, .Volkamer et al. (2007) sug- gested that SOA formation from glyoxal in aqueous particles could contribute up to 15 % of total organic aerosol mass.
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Validation of aerosol and cloud layer structures from the space-borne lidar CALIOP using a ground-based lidar in Seoul, Korea

Validation of aerosol and cloud layer structures from the space-borne lidar CALIOP using a ground-based lidar in Seoul, Korea

For the CALIPSO mission, validation is defined as an as- sessment of the accuracy and precision of the derived sci- ence products by independent airborne or ground-based mea- surements (Kovacs and McCormick, 2006). Although a large number of ground-based lidar systems could potentially be involved in CALIOP validation efforts (e.g. MPL-NET, EARLINET, AD-NET), coincidence opportunities for direct comparisons between CALIOP observations and ground- based lidars are not as straight forward. Spatial and tem- poral variability of aerosol and cloud constraint greatly com- plicate the validation of CALIOP products by direct compar- ison with instruments at ground stations. Especially, clouds have relatively short lifetimes and even shorter correlation spatial scales (a few hundred meters to tens of kilometers). Indeed, CALIOP has a very narrow swath and carries out measurements over a significant horizontal distance during a short period of time, while ground-based lidar (e.g. SNU- L used in this study) with a narrow field-of-view is local-
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Putting the clouds back in aerosol–cloud interactions

Putting the clouds back in aerosol–cloud interactions

The second experiment used the MG2 configuration to reduce the efficiency of the vapor deposition onto ice (Bergeron–Findeisen process) by a factor of 10. This sim- ulates inhomogeneity in cloud liquid and ice (or effectively inhomogeneity for in-cloud supersaturation or vertical ve- locity) that does not effectively mix liquid and ice. Korolev (2008) noted uncertainties of at least a factor of 2 in vapor deposition rates based on small-scale cloud dynamics, and Lawson and Gettelman (2014) found better agreement with Antarctic mixed phase clouds when vapor deposition was re- duced by a factor of 100. We picked a value between these limits for a sensitivity test. The reduction of vapor deposition increases the mean LWP and slightly decreases 1LWP (Ta- ble 3). The stronger long-wave and shortwave components with more liquid likely lead to an increased magnitude in ACI (Table 2) of +45 %, but the exact mechanism is unclear.
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Microphysical process rates and global aerosol-cloud interactions

Microphysical process rates and global aerosol-cloud interactions

ing the rain mixing ratio (reducing LWP) and decreasing autoconversion to increase it again: the overall effect is to decrease LWP from the base case. The dT/4 case has 10 % higher LWP than the base simulation: this is expected since a shorter time step means less time for large amounts of cloud water to build up after macrophysics but before microphysics, thus microphysical process rates (sinks) are smaller, explaining

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A numerical study of aerosol influence on mixed-phase stratiform clouds through modulation of the liquid phase

A numerical study of aerosol influence on mixed-phase stratiform clouds through modulation of the liquid phase

structure via several pathways. An example of a positive local feedback involves the influence of aerosol soluble mass frac- tion on liquid condensational growth. This enhanced liquid condensational growth results in an increase in cloud liq- uid water, subsequently increasing cloud top radiative cool- ing rates. This increased cooling results in enhanced mix- ing via buoyant instability, increasing vertical motion. With this enhanced vertical motion comes increased supersatura- tion in the updrafts, further supporting additional conden- sational growth and production of cloud liquid water. Fig- ure 8 demonstrates that this feedback does not dominate the production of liquid water however, since both the Kaoli- nite and Soot simulations have lower LWP with increased soluble mass fraction. This is because of the interplay be- tween feedback mechanisms. In addition to positive feedback mechanisms as mentioned above, several negative local feed- backs are also initiated. One example includes the increase in ice depositional growth that occurs in conjunction with the elevated supersaturation occurring within stronger updrafts. This increased ice depositional growth will reduce local hu- midity and supersaturation, thereby reducing the amount of liquid growth in that portion of the cloud. These local feed- backs are only presented as examples, and many more in- teractions can be brought out of the internal connections be- tween system components. While beyond the scope of the current work, a thorough analysis of these interactions and their magnitudes will likely result in invaluable insight into these complex cloud structures. The magnitudes of processes involved govern the system’s ability to either achieve equilib- rium or be pushed into an alternative (i.e. glaciated) state and may help to shed light on the resiliency issues discussed in more detail in Morrison et al. (2012).
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Microphysical processing of aerosol particles in orographic clouds

Microphysical processing of aerosol particles in orographic clouds

During their residence time in the atmosphere, aerosol par- ticles undergo various modifications which may affect their ability to serve as CCN and IN. Thereby, aerosol processing within clouds plays a crucial role, as the aerosol mass, com- position and mixing state can be altered. Due to activation, nucleation and collision–coalescence processes aerosol par- ticles are incorporated into hydrometeors. Processes like au- toconversion, accretion, aggregation, freezing, melting, rim- ing and self-collection transfer aerosol mass and number between the different hydrometeor classes. Aqueous-phase chemistry within droplets can lead to the formation of new aerosol mass. Finally, wet deposition, sedimentation and scavenging processes lead to a removal of aerosol mass from the atmosphere. However, a substantial fraction of hydrom- eteors evaporate/sublimate, releasing newly formed aerosol particles to the atmosphere with different size, composi- tion and mixing state compared to the original ones. Re- cent investigations concerning the impact of aerosol solubil- ity and recycled aerosol particles on orographic cloud forma- tion have been conducted by Xue et al. (2010, 2012). They explicitly account for the release of aerosol particles upon droplet and rain evaporation, replenishing between one-third and two-thirds of the scavenged aerosol particles. In their model configuration, the CCN number concentration explic- itly depends on the number concentration and properties of the background and regenerated aerosol particles. In ideal- ized 2-D simulations of warm-phase clouds over two bell- shaped mountains, recycled aerosol particles enhance the cloud droplet number concentration and thus reduce precipi- tation formation at the second mountain (Xue et al., 2010). In mixed-phase clouds, regenerated aerosol particles were found to inhibit the riming process by changing the droplet size distribution (Xue et al., 2012).
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Cold and transition season cloud condensation nuclei measurements in western Colorado

Cold and transition season cloud condensation nuclei measurements in western Colorado

This result suggests that variability of CCN in this region may be less important than originally thought. This has implications for studies of aerosol effects on orographic clouds in this region. CCN flowing in to the San Juan Mountains and other locations along the Western Slope can be estimated by the available measurements from north- western Colorado, at least for particular wind regimes and seasons. This may also

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