scholarly journals 3-D model simulations of dynamical and microphysical interactions in pyro-convective clouds under idealized conditions

2013 ◽  
Vol 13 (7) ◽  
pp. 19527-19557 ◽  
Author(s):  
P. Reutter ◽  
J. Trentmann ◽  
A. Seifert ◽  
P. Neis ◽  
H. Su ◽  
...  
Keyword(s):  
Forest Fires ◽  
Aerosol Particles ◽  
Three Dimensional ◽  
Convective Cloud ◽  
Atmospheric Model ◽  
Cloud Microphysics ◽  
Aerosol Concentration ◽  
Activation Process ◽  
Cloud Droplets ◽  
Convective Clouds

Abstract. Pyro-convective clouds, i.e. convective clouds forming over wildland fires due to high sensible heat, play an important role for the transport of aerosol particles and trace gases into the upper troposphere and lower stratosphere. Additionally, due to the emission of a large number of aerosol particles from forest fires, the microphysical structure of a pyro-convective cloud is clearly different from that of ordinary convective clouds. A crucial step in the microphysical evolution of a (pyro-) convective cloud is the activation of aerosol particles to form cloud droplets. The activation process affects the initial number and size of cloud droplets and can thus influence the evolution of the convective cloud and the formation of precipitation. Building upon a realistic parameterization of CCN activation, the model ATHAM is used to investigate the dynamical and microphysical processes of idealized three-dimensional pyro-convective clouds in mid-latitudes. A state-of-the-art two-moment microphysical scheme has been implemented in order to study the influence of the aerosol concentration on the cloud development. The results show that the aerosol concentration influences the formation of precipitation. For low aerosol concentrations (NCN=1000 cm−3), rain droplets are rapidly formed by autoconversion of cloud droplets. This also triggers the formation of large graupel and hail particles resulting in an early and strong onset of precipitation. With increasing aerosol concentration (NCN=20 000 cm−3 and NCN=60 000 cm−3) the formation of rain droplets is delayed due to more but smaller cloud droplets. Therefore, the formation of ice crystals and snowflakes becomes more important for the eventual formation of graupel and hail. However, this causes a delay of the onset of precipitation and its intensity for increasing aerosol concentration. This work shows the first detailed investigation of the interaction between cloud microphysics and dynamics of a pyro-convective cloud using the combination of a high resolution atmospheric model and a detailed microphysical scheme.

scholarly journals 3-D model simulations of dynamical and microphysical interactions in pyroconvective clouds under idealized conditions

2014 ◽  
Vol 14 (14) ◽  
pp. 7573-7583 ◽  
Author(s):  
P. Reutter ◽  
J. Trentmann ◽  
A. Seifert ◽  
P. Neis ◽  
H. Su ◽  
...  
Keyword(s):  
High Resolution ◽  
Cloud Condensation Nuclei ◽  
Three Dimensional ◽  
Atmospheric Model ◽  
Cloud Microphysics ◽  
Aerosol Concentration ◽  
Cloud Droplets ◽  
Cloud Development ◽  
Microphysical Processes ◽  
D Model

Abstract. Dynamical and microphysical processes in pyroconvective clouds in mid-latitude conditions are investigated using idealized three-dimensional simulations with the Active Tracer High resolution Atmospheric Model (ATHAM). A state-of-the-art two-moment microphysical scheme building upon a realistic parameterization of cloud condensation nuclei (CCN) activation has been implemented in order to study the influence of aerosol concentration on cloud development. The results show that aerosol concentration influences the formation of precipitation. For low aerosol concentrations (NCN = 200 cm−3), rain droplets are rapidly formed by autoconversion of cloud droplets. This also triggers the formation of large graupel and hail particles, resulting in an early onset of precipitation. With increasing aerosol concentration (NCN = 1000 cm−3 and NCN = 20 000 cm−3) the formation of rain droplets is delayed due to more but smaller cloud droplets. Therefore, the formation of ice crystals and snowflakes becomes more important for the eventual formation of graupel and hail, which is delayed at higher aerosol concentrations. This results in a delay of the onset of precipitation and a reduction of its intensity with increasing aerosol concentration. This study is the first detailed investigation of the interaction between cloud microphysics and the dynamics of a pyroconvective cloud using the combination of a high-resolution atmospheric model and a detailed microphysical scheme.

scholarly journals A Satellite-Based Parameter to Monitor the Aerosol Impact on Convective Clouds

2007 ◽  
Vol 46 (5) ◽  
pp. 660-666 ◽  
Author(s):  
Itamar M. Lensky ◽  
Ron Drori
Keyword(s):  
Forest Fires ◽  
Land Surface ◽  
Cloud Condensation Nuclei ◽  
Urban Air Pollution ◽  
Sensible Heat Flux ◽  
Urban Pollution ◽  
Convective Cloud ◽  
Cloud Base ◽  
Suppression Effect ◽  
Convective Clouds

Abstract A method to monitor the aerosol impact on convective clouds using satellite data is presented. The impacts of forest fires and highly polluting megacities on cloud precipitation formation processes are quantified by the vertical extent above cloud base to which convective cloud tops have to develop for onset of precipitation in terms of temperature difference D15. Large D15 is a manifestation of the precipitation suppression effect of small cloud condensation nuclei aerosols that elevate the altitude where effective precipitation processes are initiated. A warmer land surface with a greater sensible heat flux that increases the updraft velocity at cloud base may also contribute to the same effect. Therefore, D15 is greater for clouds that develop over more polluted and/or warmer surfaces that result from smoke and urban pollution and/or urban heat island, respectively. The precipitation suppression effects of both smoke from forest fires and urban effects can be vividly seen in a case study over Southeast Asia. Typical values of D15 are 1°–6°C for tropical maritime clouds, 8°–15°C for tropical clouds over land, 16°–26°C for urban air pollution, and 18°–39°C for clouds ingesting smoke from forest fires.

scholarly journals Strong sensitivity of aerosol concentrations to convective wet scavenging parameterizations in a global model

2012 ◽  
Vol 12 (1) ◽  
pp. 1687-1732 ◽  
Author(s):  
B. Croft ◽  
J. R. Pierce ◽  
R. V. Martin ◽  
C. Hoose ◽  
U. Lohmann
Keyword(s):  
Cloud Droplet ◽  
Convective Cloud ◽  
Cloud Base ◽  
Ice Crystal ◽  
Cloud Droplets ◽  
Convective Clouds ◽  
The Standard Model ◽  
Wet Scavenging ◽  
Limiting Case ◽  
Precipitation Formation

Abstract. This study examines the influences of assumptions in convective wet scavenging parameterizations on global climate model simulations of aerosol concentrations and wet deposition. To facilitate this study, an explicit representation of the uptake of aerosol mass and number into convective cloud droplets and ice crystals by the processes of activation, collisions, freezing and evaporation is introduced into the ECHAM5-HAM model. This development replaces the prescribed aerosol cloud-droplet-borne/ice-crystal-borne fractions of the standard model. Relative to the standard model, the more consistent treatment between convective aerosol-cloud microphysical processes yields a reduction of aerosol wet removal in mixed liquid and ice phase convective clouds by at least a factor of two, and the global, annual mean aerosol burdens are increased by at least 20%. Two limiting cases regarding the wet scavenging of entrained aerosols are considered. In the first case, aerosols entering convective clouds at their bases are the only aerosols that are scavenged into cloud droplets, and are susceptible to removal by convective precipitation formation. In the second case, aerosols that are entrained into the cloud above the cloud base layer can activate, can collide with existing cloud droplets and ice crystals, and can subsequently be removed by precipitation formation. The limiting case that allows aerosols entrained above cloud base to become cloud-droplet-borne and ice-crystal-borne reduces the annual and global mean aerosol burdens by 30% relative to the other limiting case, and yields the closest agreement with global aerosol optical depth retrievals, and black carbon vertical profiles from aircraft campaigns (changes of about one order of magntiude in the upper troposphere). Predicted convective cloud droplet number concentrations are doubled in the tropical middle troposphere when aerosols entrained above cloud base are allowed to activate. These results show that aerosol concentrations and wet deposition predicted in a global model are strongly sensitive to the assumptions made regarding the wet scavenging of aerosols in convective clouds.

scholarly journals The effects of mineral dust particles, aerosol regeneration and ice nucleation parameterizations on clouds and precipitation

2012 ◽  
Vol 12 (19) ◽  
pp. 9303-9320 ◽  
Author(s):  
A. Teller ◽  
L. Xue ◽  
Z. Levin
Keyword(s):  
Mineral Dust ◽  
Cloud Microphysics ◽  
Ice Nucleation ◽  
Aerosol Concentration ◽  
Ice Crystals ◽  
Dust Particles ◽  
Cloud Base ◽  
Minor Effect ◽  
Total Precipitation ◽  
Cloud Droplets

Abstract. This study focuses on the effects of aerosol particles on the formation of convective clouds and precipitation in the Eastern Mediterranean Sea, with a special emphasis on the role of mineral dust particles in these processes. We used a new detailed numerical cloud microphysics scheme that has been implemented in the Weather Research and Forecast (WRF) model in order to study aerosol–cloud interaction in 3-D configuration based on 1° × 1° resolution reanalysis meteorological data. Using a number of sensitivity studies, we tested the contribution of mineral dust particles and different ice nucleation parameterizations to precipitation development. In this study we also investigated the importance of recycled (regenerated) aerosols that had been released to the atmosphere following the evaporation of cloud droplets. The results showed that increased aerosol concentration due to the presence of mineral dust enhanced the formation of ice crystals. The dynamic evolution of the cloud system sets the time periods and regions in which heavy or light precipitation occurred in the domain. The precipitation rate, the time and duration of precipitation were affected by the aerosol properties only at small spatial scales (with areas of about 20 km2). Changes of the ice nucleation scheme from ice supersaturation-dependent parameterization to a recent approach of aerosol concentration and temperature-dependent parameterization modified the ice crystals concentrations but did not affect the total precipitation in the domain. Aerosol regeneration modified the concentration of cloud droplets at cloud base by dynamic recirculation of the aerosols but also had only a minor effect on precipitation. The major conclusion from this study is that the effect of mineral dust particles on clouds and total precipitation is limited by the properties of the atmospheric dynamics and the only effect of aerosol on precipitation may come from significant increase in the concentration of accumulation mode aerosols. In addition, the presence of mineral dust had a much smaller effect on the total precipitation than on its spatial distribution.

scholarly journals Secondary Ice Formation in Idealised Deep Convection—Source of Primary Ice and Impact on Glaciation

Atmosphere ◽  
2020 ◽  
Vol 11 (5) ◽  
pp. 542
Author(s):  
Annette K. Miltenberger ◽  
Tim Lüttmer ◽  
Christoph Siewert
Keyword(s):  
Deep Convection ◽  
Three Dimensional ◽  
Convective Cloud ◽  
Cloud Formation ◽  
Ice Formation ◽  
Ice Crystal ◽  
Lagrangian Analysis ◽  
Vertical Coupling ◽  
Convective Clouds ◽  
Ice Production

Secondary ice production via rime-splintering is considered to be an important process for rapid glaciation and high ice crystal numbers observed in mixed-phase convective clouds. An open question is how rime-splintering is triggered in the relatively short time between cloud formation and observations of high ice crystal numbers. We use idealised simulations of a deep convective cloud system to investigate the thermodynamic and cloud microphysical evolution of air parcels, in which the model predicts secondary ice formation. The Lagrangian analysis suggests that the “in-situ” formation of rimers either by growth of primary ice or rain freezing does not play a major role in triggering secondary ice formation. Instead, rimers are predominantly imported into air parcels through sedimentation form higher altitudes. While ice nucleating particles (INPs) initiating heterogeneous freezing of cloud droplets at temperatures warmer than −10 °C have no discernible impact of the occurrence of secondary ice formation, in a scenario with rain freezing secondary ice production is initiated slightly earlier in the cloud evolution and at slightly different places, although with no major impact on the abundance or spatial distribution of secondary ice in the cloud as a whole. These results suggest that for interpreting and analysing observational data and model experiments regarding cloud glaciation and ice formation it is vital to consider the complex vertical coupling of cloud microphysical processes in deep convective clouds via three-dimensional transport and sedimentation.

Influence of Saharan Dust and Other Aerosols on Hurricane Nadine (2012) as Revealed by the Comparison of Ensemble Model Results and NASA HS3 Data

2020 ◽  
Author(s):  
Jainn Shi ◽  
Scott Braun ◽  
Zhining Tao ◽  
Jason Sippel
Keyword(s):  
Forest Fires ◽  
Cloud Microphysics ◽  
Saharan Dust ◽  
Weather Research And Forecasting ◽  
Radiation Physics ◽  
Convective Clouds ◽  
Ensemble Simulations ◽  
Goddard Space Flight Center ◽  
Core Simulation ◽  
Aerosol Effects

<p>This presentation will focus on simulations of the early stages of Hurricane Nadine (2012), which interacted with the SAL and never intensified beyond a minimal hurricane. Given the complexity of aerosol effects on cloud microphysics and radiation and their subsequent effects on deep convective clouds, there is a need to assess the combined microphysical and radiative effects of aerosols. We use the Goddard Space Flight Center version of the Weather Research and Forecasting model with interactive aerosol-cloud-radiation physics to study the influence of the SAL and other aerosols (sea salt and black/organic carbon) on Nadine via a series of model sensitivity runs. The results from the control experiment with all aerosols will be compared to the dropsonde and CPL aerosol lidar backscatter data collected during the NASA Hurricane and Severe Storm Sentinel (HS3) field campaign. Comparison of model results and dropsonde data shows evidence of the intrusion of Saharan air into the storm core. Simulation results also show the possible intrusion of biomass-burning aerosols that originated from forest fires in the Northwestern United States a few days before Nadine reached hurricane strength. In addition, we will also present results from three sets of 30-member ensemble simulations: 1) without aerosol coupling, 2) with all aerosols, and 3) with only dust aerosol, to study the aerosol impact on Nadine.</p>

scholarly journals Core and margin in warm convective clouds. Part II: aerosol effects on core properties

2018 ◽  
Author(s):  
Reuven H. Heiblum ◽  
Lital Pinto ◽  
Orit Altaratz ◽  
Guy Dagan ◽  
Ilan Koren
Keyword(s):  
Volume Fraction ◽  
Convective Cloud ◽  
Aerosol Concentration ◽  
Slow Evaporation ◽  
Core Mass ◽  
Convective Clouds ◽  
The Core ◽  
Aerosol Effect ◽  
Cloud Cores ◽  
Aerosol Effects

Abstract. The effects of aerosol on warm convective cloud cores are evaluated using single cloud and cloud field simulations. As presented in Part I, the Bcore ⊆ RHcore ⊆ Wcore property is seen during growth of warm convective clouds. We show that this property is kept irrespective of aerosol concentration. During dissipation core fractions generally decrease with less overlap between cores. However, for clouds that develop in low aerosol concentrations capable of producing precipitation, Bcore and subsequently Wcore volume fractions may increase during dissipation (i.e. loss of cloud mass). The RHcore volume fraction decreases during cloud lifetime and shows minor sensitivity to aerosol concentration. It is shown that a Bcore forms due to two processes: (i) Convection – condensation within supersaturated updrafts and release of latent heat, (ii) Adiabatic heating due to weak downdrafts. The former process occurs during cloud growth for all aerosol concentrations. The latter process only occurs for low aerosol concentrations during dissipation and precipitation stages where large mean drop sizes permit slow evaporation rates. The aerosol effect on the diffusion efficiencies play a crucial role in the development of the cloud and its partition to core and margin. Using the RHcore definition, it is shown that the total cloud mass is mostly dictated by core processes, while the total cloud volume is mostly dictated by margin processes. Increase in aerosol concentration increases the core (mass and volume) due to enhanced condensation but also decreases the margin due to evaporation. In clean clouds larger droplets evaporate much slower, enabling preservation of cloud volume and even increase by dilution (detrainment while losing mass). This explains how despite having smaller cores and less mass, cleaner clouds may live longer and grow to larger sizes.

Cloud-Resolving Model Applied to Nowcasting: An Evaluation of Radar Data Assimilation and Microphysics Parameterization

2020 ◽  
Vol 35 (6) ◽  
pp. 2345-2365
Author(s):  
Eder P. Vendrasco ◽  
Luiz A. T. Machado ◽  
Bruno Z. Ribeiro ◽  
Edmilson D. Freitas ◽  
Rute C. Ferreira ◽  
...  
Keyword(s):  
Data Assimilation ◽  
Three Dimensional ◽  
Convective Cloud ◽  
Radar Data ◽  
Precipitation Forecast ◽  
Southeastern Brazil ◽  
Convective Clouds ◽  
Cloud Resolving Model ◽  
Cycling Frequency ◽  
Radar Data Assimilation

AbstractThis research explores the benefits of radar data assimilation for short-range weather forecasts in southeastern Brazil using the Weather Research and Forecasting (WRF) Model’s three-dimensional variational data assimilation (3DVAR) system. Different data assimilation options are explored, including the cycling frequency, the number of outer loops, and the use of null-echo assimilation. Initially, four microphysics parameterizations are evaluated (Thompson, Morrison, WSM6, and WDM6). The Thompson parameterization produces the best results, while the other parameterizations generally overestimate the precipitation forecast, especially WDSM6. Additionally, the Thompson scheme tends to overestimate snow, while the Morrison scheme overestimates graupel. Regarding the data assimilation options, the results deteriorate and more spurious convection occurs when using a higher cycling frequency (i.e., 30 min instead of 60 min). The use of two outer loops produces worse precipitation forecasts than the use of one outer loop, and the null-echo assimilation is shown to be an effective way to suppress spurious convection. However, in some cases, the null-echo assimilation also removes convective clouds that are not observed by the radar and/or are still not producing rain, but have the potential to grow into an intense convective cloud with heavy rainfall. Finally, a cloud convective mask was implemented using ancillary satellite data to prevent null-echo assimilation from removing potential convective clouds. The mask was demonstrated to be beneficial in some circumstances, but it needs to be carefully evaluated in more cases to have a more robust conclusion regarding its use.

scholarly journals Reconstruction of cloud geometry using a scanning cloud radar

2015 ◽  
Vol 8 (6) ◽  
pp. 2491-2508 ◽  
Author(s):  
F. Ewald ◽  
C. Winkler ◽  
T. Zinner
Keyword(s):  
Remote Sensing ◽  
Radiative Transfer ◽  
Interpolation Method ◽  
Three Dimensional ◽  
Convective Cloud ◽  
Cloud Microphysics ◽  
Reconstruction Method ◽  
Cloud Radar ◽  
Barycentric Interpolation ◽  
Microphysical Parameters

Abstract. Clouds are one of the main reasons of uncertainties in the forecasts of weather and climate. In part, this is due to limitations of remote sensing of cloud microphysics. Present approaches often use passive spectral measurements for the remote sensing of cloud microphysical parameters. Large uncertainties are introduced by three-dimensional (3-D) radiative transfer effects and cloud inhomogeneities. Such effects are largely caused by unknown orientation of cloud sides or by shadowed areas on the cloud. Passive ground-based remote sensing of cloud properties at high spatial resolution could be crucially improved with this kind of additional knowledge of cloud geometry. To this end, a method for the accurate reconstruction of 3-D cloud geometry from cloud radar measurements is developed in this work. Using a radar simulator and simulated passive measurements of model clouds based on a large eddy simulation (LES), the effects of different radar scan resolutions and varying interpolation methods are evaluated. In reality, a trade-off between scan resolution and scan duration has to be found as clouds change quickly. A reasonable choice is a scan resolution of 1 to 2\\degree. The most suitable interpolation procedure identified is the barycentric interpolation method. The 3-D reconstruction method is demonstrated using radar scans of convective cloud cases with the Munich miraMACS, a 35 GHz scanning cloud radar. As a successful proof of concept, camera imagery collected at the radar location is reproduced for the observed cloud cases via 3-D volume reconstruction and 3-D radiative transfer simulation. Data sets provided by the presented reconstruction method will aid passive spectral ground-based measurements of cloud sides to retrieve microphysical parameters.

scholarly journals Sensitivity study of the aerosol effects on a supercell storm throughout its lifetime

2014 ◽  
Vol 14 (17) ◽  
pp. 24087-24118 ◽  
Author(s):  
A. Takeishi ◽  
T. Storelvmo
Keyword(s):  
Droplet Size ◽  
Cloud Condensation Nuclei ◽  
Wrf Model ◽  
Convective Cloud ◽  
Sensitivity Study ◽  
Cloud Microphysics ◽  
Microphysics Scheme ◽  
Convective Clouds ◽  
Aerosol Loading ◽  
Deep Convective Clouds

Abstract. An increase in atmospheric aerosol loading could alter the microphysics, dynamics, and radiative characteristics of deep convective clouds. Earlier modeling studies have shown that the effects of increased aerosols on the amount of precipitation from deep convective clouds are model-dependent. This study aims to understand the effects of increased aerosol loading on a deep convective cloud throughout its lifetime with the use of the Weather Research and Forecasting (WRF) model as a cloud-resolving model (CRM). It simulates an idealized supercell thunderstorm with 8 different aerosol loadings, for three different cloud microphysics schemes. Variation in aerosol concentration is mimicked by varying either cloud droplet number concentration or the number of activated cloud condensation nuclei. We show that the sensitivity to aerosol loading is dependent on the choice of microphysics scheme. For the schemes that are sensitive to aerosols loading, the production of graupel via riming of snow is the key factor determining the precipitation response. The formulation of snow riming depends on the microphysics scheme and is usually a function of two competing effects, the size effect and the number effect. In many simulations, a decrease in riming is seen with increased aerosol loading, due to the decreased droplet size that lowers the riming efficiency drastically. This decrease in droplet size also results in a delay in the onset of precipitation, as well as so-called warm rain suppression. Although these characteristics of convective invigoration (Rosenfeld et al., 2008) are seen in the first few hours of the simulations, variation in the accumulated precipitation mainly stems from graupel production rather than convective invigoration. These results emphasize the importance of accurate representations of graupel formation in microphysics schemes.

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