scholarly journals Parameterization of the nitric acid effect on CCN activation

2005 ◽  
Vol 5 (4) ◽  
pp. 879-885 ◽  
Author(s):  
S. Romakkaniemi ◽  
H. Kokkola ◽  
A. Laaksonen
Keyword(s):  
Nitric Acid ◽  
Aerosol Particle ◽  
Large Scale ◽  
Nitric Acid Concentration ◽  
Cloud Droplet ◽  
Cloud Drop ◽  
Cloud Droplets ◽  
Radiative Balance ◽  
Model Simulations ◽  
Acid Effect

Abstract. In this paper we present a parameterization of the nitric acid effect on cloud droplet formation. The new parameterization is intended to be used in large scale models in order to obtain regional and global estimates of the effect of nitric acid on cloud drop concentrations and the radiative balance. The parameterization is based on numerical air parcel model simulations and can be applied for unimodal and bimodal lognormal aerosol particle size distributions in a large variety of different conditions. In addition to the aerosol particle distribution and gas-phase HNO3 concentration, the parameterization requires temperature, total pressure, updraft velocity, and the number concentration of cloud droplets formed at zero nitric acid concentration, as input parameters. The parameterization is also suitable for describing the effect of hydrochloric acid on the cloud drop concentrations, and in practice, the HNO3 and HCl concentrations can be summed up to yield the total effect. The comparison between the parameterization and the results from numerical air parcel model simulations show good consistency.

scholarly journals Parameterization of the nitric acid effect on CCN activation

2004 ◽  
Vol 4 (6) ◽  
pp. 7859-7879
Author(s):  
S. Romakkaniemi ◽  
H. Kokkola ◽  
A. Laaksonen
Keyword(s):  
Nitric Acid ◽  
Aerosol Particle ◽  
Large Scale ◽  
Nitric Acid Concentration ◽  
Cloud Droplet ◽  
Cloud Drop ◽  
Cloud Droplets ◽  
Radiative Balance ◽  
Model Simulations ◽  
Acid Effect

Abstract. In this paper we present a parameterization of the nitric acid effect on cloud droplet formation. The new parameterization is intended to be used in large scale models in order to obtain regional and global estimates of the effect of nitric acid on cloud drop concentrations and the radiative balance. The parameterization is based on numerical air parcel model simulations and can be applied for unimodal and bimodal lognormal aerosol particle size distributions in a large variety of different conditions. In addition to the aerosol particle distribution and gas-phase HNO3 concentration, the parameterization requires temperature, total pressure, updraft velocity, and the number concentration of cloud droplets formed at zero nitric acid concentration, as input parameters. The parametrization is also suitable for describing the effect of hydrochloric acid on the cloud drop concentrations, and in practice, the HNO3 and HCl concentrations can be summed up to yield the total effect. The comparison between the parameterization and the results from numerical air parcel model simulations show good consistency.

scholarly journals An investigation into the performance of four cloud droplet activation parameterisations

2014 ◽  
Vol 7 (4) ◽  
pp. 1535-1542 ◽  
Author(s):  
E. Simpson ◽  
P. Connolly ◽  
G. McFiggans
Keyword(s):  
Aerosol Particle ◽  
Large Scale ◽  
Aerosol Particles ◽  
Cloud Droplet ◽  
Particle Growth ◽  
Systematic Evaluation ◽  
Climate Modelling ◽  
Median Diameter ◽  
Droplet Activation ◽  
Simulation Time

Abstract. Cloud droplet number concentration prediction is central to large-scale weather and climate modelling. The benchmark cloud parcel model calculation of aerosol particle growth and activation, by diffusion of vapour to aerosol particles in a rising parcel of air experiencing adiabatic expansion, is too computationally expensive for use in large-scale global models. Therefore the process of activation of aerosol particles into cloud droplets is parameterised with an aim to strike the optimum balance between numerical expense and accuracy. We present a detailed systematic evaluation of three cloud droplet activation parameterisations that are widely used in large-scale models and one recent update. In all cases, it is found that there is a tendency to overestimate the fraction of activated aerosol particles when the aerosol particle "median diameter" is large (between 250 and 2000 nm) in a single lognormal mode simulation. This is due to an infinite "effective simulation time" of the parameterisations compared to a prescribed simulation time in the parcel model. This problem arises in the parameterisations because it is assumed that a parcel of air rises to the altitude where maximum supersaturation occurs, regardless of whether this altitude is above the cloud top. Such behaviour is problematic because, in some cases, large aerosol can completely suppress the activation of drops. In some cases when the "median diameter" is small (between 5 and 250 nm) in a single lognormal mode the fraction of activated drops is underestimated by the parameterisations. Secondly, it is found that in dual-mode cases there is a systematic tendency towards underestimation of the fraction of activated drops, which is due to the methods used by the parameterisations to approximate the sink of water vapour.

A Study of Aerosol Impacts on Clouds and Precipitation Development in a Large Winter Cyclone

2014 ◽  
Vol 71 (10) ◽  
pp. 3636-3658 ◽  
Author(s):  
Gregory Thompson ◽  
Trude Eidhammer
Keyword(s):  
Radiation Effects ◽  
Large Scale ◽  
Forecast Error ◽  
Longwave Radiation ◽  
Cloud Droplet ◽  
Aircraft Icing ◽  
Cloud Droplets ◽  
Surface Precipitation ◽  
Continental Scale ◽  
Observational Uncertainty

Abstract Aerosols influence cloud and precipitation development in complex ways due to myriad feedbacks at a variety of scales from individual clouds through entire storm systems. This paper describes the implementation, testing, and results of a newly modified bulk microphysical parameterization with explicit cloud droplet nucleation and ice activation by aerosols. Idealized tests and a high-resolution, convection-permitting, continental-scale, 72-h simulation with five sensitivity experiments showed that increased aerosol number concentration results in more numerous cloud droplets of overall smaller size and delays precipitation development. Furthermore, the smaller droplet sizes cause the expected increased cloud albedo effect and more subtle longwave radiation effects. Although increased aerosols generally hindered the warm-rain processes, regions of mixed-phase clouds were impacted in slightly unexpected ways with more precipitation falling north of a synoptic-scale warm front. Aerosol impacts to regions of light precipitation, less than approximately 2.5 mm h−1, were far greater than impacts to regions with higher precipitation rates. Comparisons of model forecasts with five different aerosol states versus surface precipitation measurements revealed that even a large-scale storm system with nearly a thousand observing locations did not indicate which experiment produced a more correct final forecast, indicating a need for far longer-duration simulations due to the magnitude of both model forecast error and observational uncertainty. Last, since aerosols affect cloud and precipitation phase and amount, there are resulting implications to a variety of end-user applications such as surface sensible weather and aircraft icing.

scholarly journals The influence of nitric acid on the cloud processing of aerosol particles

2006 ◽  
Vol 6 (6) ◽  
pp. 1627-1634 ◽  
Author(s):  
S. Romakkaniemi ◽  
H. Kokkola ◽  
K. E. J. Lehtinen ◽  
A. Laaksonen
Keyword(s):  
Sulfuric Acid ◽  
Nitric Acid ◽  
Aerosol Particles ◽  
Cloud Droplet ◽  
Number Concentration ◽  
Radiative Properties ◽  
Aerosol Size Distribution ◽  
Cloud Droplets ◽  
Cloud Processing ◽  
Cloud Droplet Number Concentration

Abstract. In this paper we present simulations of the effect of nitric acid (HNO3) on cloud processing of aerosol particles. Sulfuric acid (H2SO4) production and incloud coagulation are both affected by condensed nitric acid as nitric acid increases the number of cloud droplets, which will lead to smaller mean size and higher total surface area of droplets. As a result of increased cloud droplet number concentration (CDNC), the incloud coagulation rate is enhanced by a factor of 1–1.3, so that the number of interstitial particles reduces faster. In addition, sulfuric acid production occurs in smaller particles and so the cloud processed aerosol size distribution is dependent on the HNO3 concentration. This affects both radiative properties of aerosol particles and the formation of cloud droplets during a sequence of cloud formation-evaporation events. It is shown that although the condensation of HNO3 increases the number of cloud droplets during the single updraft, it is possible that presence of HNO3 can actually decrease the cloud droplet number concentration after several cloud cycles when also H2SO4 production is taken into account.

scholarly journals An investigation into the performance of three cloud droplet activation parameterisations

2014 ◽  
Vol 7 (1) ◽  
pp. 1317-1336
Author(s):  
E. Simpson ◽  
P. Connolly ◽  
G. McFiggans
Keyword(s):  
Aerosol Particle ◽  
Large Scale ◽  
Aerosol Particles ◽  
Cloud Droplet ◽  
Particle Growth ◽  
Systematic Evaluation ◽  
Climate Modelling ◽  
Median Diameter ◽  
Droplet Activation ◽  
Simulation Time

Abstract. Cloud droplet number concentration prediction is central to large scale weather and climate modelling. The benchmark cloud parcel model calculation of aerosol particle growth and activation, by diffusion of vapour to aerosol particles in a rising parcel of air experiencing adiabatic expansion, is too computationally expensive for use in large scale global models. Therefore the process of activation of aerosol particles into cloud droplets is parameterised with an aim to strike the optimum balance between numerical expense and accuracy. We present the first systematic evaluation of three cloud droplet activation parameterisations that are widely used in large-scale models. In all cases, it is found that there is a tendency to overestimate the fraction activated aerosol particles when the aerosol particle "median diameter" is large in a single lognormal mode simulations. This is due to an infinite "effective simulation time" of the parameterisations compared to a prescribed simulation time in the parcel model. In some cases when the "median diameter" is small in a single lognormal mode the fraction of activated drops is underestimated by the parameterisations. Secondly it is found that in dual-mode cases there is a systematic tendency towards underestimation of the fraction of activated drops, which is due the methods used by the parameterisations to approximate the maximum supersaturation with respect to water vapour.

scholarly journals CCN activation and cloud processing in sectional aerosol models with low size resolution

2005 ◽  
Vol 5 (9) ◽  
pp. 2561-2570 ◽  
Author(s):  
H. Korhonen ◽  
V.-M. Kerminen ◽  
K. E. J. Lehtinen ◽  
M. Kulmala
Keyword(s):  
Size Distribution ◽  
Large Scale ◽  
Reference Model ◽  
Cloud Model ◽  
Cloud Droplet ◽  
Anthropogenic Sources ◽  
Aerosol Size Distribution ◽  
Droplet Growth ◽  
Cloud Droplets ◽  
Cloud Processing

Abstract. We investigate the influence of low size resolution, typical to sectional aerosol models in large scale applications, on cloud droplet activation and cloud processing of aerosol particles. A simplified cloud model with five approaches to determine the fraction of activated particles is compared with a detailed reference model under different atmospheric conditions. In general, activation approaches which assume a distribution profile within the critical model size sections predict the cloud droplet concentration most accurately under clean and moderately polluted conditions. In such cases, the deviation from the reference simulations is below 15% except for very low updraft velocities. In highly polluted cases, the concentration of cloud droplets is significantly overestimated due to the inability of the simplified model to account for the kinetic limitations of the droplet growth. Of the profiles examined, taking into account the local shape of the particle size distribution is the most accurate although in most cases the shape of the profile has little relevance. While the low resolution cloud model cannot reproduce the details of the out-of-the-cloud aerosol size distribution, it captures well the amount of sulphate produced in aqueous-phase reactions as well as the distribution of the sulphate between the cloud droplets. Overall, the simplified cloud model with low size resolution performs well for clean and moderately polluted regions that cover most of the Earth's surface and is therefore suitable for large scale models. It can, however, show uncertainties in areas with strong pollution from anthropogenic sources.

scholarly journals CCN activation and cloud processing in simplified sectional aerosol models with low size resolution

2005 ◽  
Vol 5 (4) ◽  
pp. 4871-4892
Author(s):  
H. Korhonen ◽  
V.-M. Kerminen ◽  
K. E. J. Lehtinen ◽  
M. Kulmala
Keyword(s):  
Size Distribution ◽  
Large Scale ◽  
Reference Model ◽  
Cloud Model ◽  
Cloud Droplet ◽  
Aerosol Size Distribution ◽  
Droplet Growth ◽  
Distribution Profile ◽  
Cloud Droplets ◽  
Cloud Processing

Abstract. We investigate the influence of low size resolution, typical to sectional aerosol models in large scale applications, on cloud droplet activation and cloud processing of aerosol particles. A simplified cloud scheme with five approaches to determine the fraction of activated particles is compared with a detailed reference model under different atmospheric conditions. In general, activation approaches which assume a distribution profile within the critical model size sections predict the cloud droplet concentration most accurately under clean and moderately polluted conditions. In such cases, the deviation from the reference simulations is below 15% except for very low updraft velocities. In highly polluted cases, the concentration of cloud droplets is significantly overestimated due to the inability of the simplified scheme to account for the kinetic limitations of the droplet growth. Of the profiles examined, taking into account the local shape of the particle size distribution is the most accurate although in most cases the shape of the profile has little relevance. While the low resolution cloud model cannot reproduce the details of the out-of-the-cloud aerosol size distribution, it captures well the amount of sulphate produced in aqueous-phase reactions as well as the distribution of the sulphate between the cloud droplets. Overall, the simplified cloud scheme with low size resolution performs well for clean and moderately polluted regions that cover most of the Earth's surface and is therefore suitable for large scale models.

scholarly journals Brightening of the global cloud field by nitric acid and the associated radiative forcing

2012 ◽  
Vol 12 (16) ◽  
pp. 7625-7633 ◽  
Author(s):  
R. Makkonen ◽  
S. Romakkaniemi ◽  
H. Kokkola ◽  
P. Stier ◽  
P. Räisänen ◽  
...  
Keyword(s):  
Nitric Acid ◽  
Indirect Effect ◽  
Radiative Forcing ◽  
Climate Model ◽  
Cloud Condensation Nuclei ◽  
Cloud Droplet ◽  
So2 Emissions ◽  
Cloud Droplets ◽  
Cloud Albedo ◽  
Albedo Effect

Abstract. Clouds cool Earth's climate by reflecting 20% of the incoming solar energy, while also trapping part of the outgoing radiation. The effect of human activities on clouds is poorly understood, but the present-day anthropogenic cooling via changes of cloud albedo and lifetime could be of the same order as warming from anthropogenic addition in CO2. Soluble trace gases can increase water condensation to particles, possibly leading to activation of smaller aerosols and more numerous cloud droplets. We have studied the effect of nitric acid on the aerosol indirect effect with the global aerosol-climate model ECHAM5.5-HAM2. Including the nitric acid effect in the model increases cloud droplet number concentrations globally by 7%. The nitric acid contribution to the present-day cloud albedo effect was found to be −0.32 W m−2 and to the total indirect effect −0.46 W m−2. The contribution to the cloud albedo effect is shown to increase to −0.37 W m−2 by the year 2100, if considering only the reductions in available cloud condensation nuclei. Overall, the effect of nitric acid can play a large part in aerosol cooling during the following decades with decreasing SO2 emissions and increasing NOx and greenhouse gases.

scholarly journals The influence of nitric acid on the cloud processing of aerosol particles

2005 ◽  
Vol 5 (5) ◽  
pp. 10197-10216 ◽  
Author(s):  
S. Romakkaniemi ◽  
H. Kokkola ◽  
K. E. J. Lehtinen ◽  
A. Laaksonen
Keyword(s):  
Sulfuric Acid ◽  
Nitric Acid ◽  
Aerosol Particles ◽  
Cloud Droplet ◽  
Total Surface Area ◽  
Coagulation Rate ◽  
Cloud Droplets ◽  
Sulfuric Acid Production ◽  
Cloud Processing ◽  
Mean Size

Abstract. In this paper we present simulations of the effect of nitric acid (HNO3) on cloud processing of aerosol particles. Sulfuric acid (H2SO4) production and incloud coagulation are both affected by condensed nitric acid as nitric acid increases the number of cloud droplets, which will lead to smaller mean size and higher total surface area of droplets. Increased acidity due to HNO3 affects the H2SO4 production. As a result of increased cloud droplet number concentration (CDNC), the incloud coagulation rate is enhanced, so that the number of interstitial particles reduces faster. In addition, sulfuric acid production occurs in smaller particles and this will lead to higher number of particles in the accumulation mode.

scholarly journals Constraints on interactions between aerosols and clouds on a global scale from a combination of MODIS-CERES satellite data and climate simulations

2010 ◽  
Vol 10 (20) ◽  
pp. 9851-9861 ◽  
Author(s):  
X. Ma ◽  
K. von Salzen ◽  
J. Cole
Keyword(s):  
Liquid Water ◽  
Negative Relationship ◽  
Cloud Droplet ◽  
Global Scale ◽  
Effective Radius ◽  
Liquid Water Path ◽  
Cloud Droplets ◽  
Cloud Liquid Water ◽  
Albedo Effect ◽  
Cloud Liquid Water Path

Abstract. Satellite-based cloud top effective radius retrieved by the CERES Science Team were combined with simulated aerosol concentrations from CCCma CanAM4 to examine relationships between aerosol and cloud that underlie the first aerosol indirect (cloud albedo) effect. Evidence of a strong negative relationship between sulphate, and organic aerosols, with cloud top effective radius was found for low clouds, indicating both aerosol types are contributing to the first indirect effect on a global scale. Furthermore, effects of aerosol on the cloud droplet effective radius are more pronounced for larger cloud liquid water paths. While CanAM4 broadly reproduces the observed relationship between sulphate aerosols and cloud droplets, it does not reproduce the dependency of cloud top droplet size on organic aerosol concentrations nor the dependency on cloud liquid water path. Simulations with a modified version of the model yield a more realistic dependency of cloud droplets on organic carbon. The robustness of the methods used in the study are investigated by repeating the analysis using aerosol simulated by the GOCART model and cloud top effective radii derived from the MODIS Science Team.

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