scholarly journals Non-Monotonic Dependencies of Cloud Microphysics and Precipitation on Aerosol Loading in Deep Convective Clouds: A Case Study Using the WRF Model with Bin Microphysics

Atmosphere ◽  
2018 ◽  
Vol 9 (11) ◽  
pp. 434 ◽  
Author(s):  
Ye-Lim Jeon ◽  
Sungju Moon ◽  
Hyunho Lee ◽  
Jong-Jin Baik ◽  
Jambajamts Lkhamjav
Keyword(s):  
Precipitation Amount ◽  
Cloud Microphysics ◽  
Ice Crystals ◽  
Precipitation Event ◽  
Cold Pool ◽  
Convective Clouds ◽  
Aerosol Loading ◽  
Optimal Value ◽  
Deep Convective Clouds ◽  
Bin Microphysics

Aerosol-cloud-precipitation interactions in deep convective clouds are investigated through numerical simulations of a heavy precipitation event over South Korea on 15–16 July 2017. The Weather Research and Forecasting model with a bin microphysics scheme is used, and various aerosol number concentrations in the range N0 = 50–12,800 cm−3 are considered. Precipitation amount changes non-monotonically with increasing aerosol loading, with a maximum near a moderate aerosol loading (N0 = 800 cm−3). Up to this optimal value, an increase in aerosol number concentration results in a greater quantity of small droplets formed by nucleation, increasing the number of ice crystals. Ice crystals grow into snow particles through deposition and riming, leading to enhanced melting and precipitation. Beyond the optimal value, a greater aerosol loading enhances generation of ice crystals while the overall growth of ice hydrometeors through deposition stagnates. Subsequently, the riming rate decreases because of the smaller size of snow particles and supercooled drops, leading to a decrease in ice melting and a slight suppression of precipitation. As aerosol loading increases, cold pool and low-level convergence strengthen monotonically, but cloud development is more strongly affected by latent heating and convection within the system that is non-monotonically reinforced.

scholarly journals Theoretical basis for convective invigoration due to increased aerosol concentration

2011 ◽  
Vol 11 (1) ◽  
pp. 2773-2842 ◽  
Author(s):  
Z. J. Lebo ◽  
J. H. Seinfeld
Keyword(s):  
Cloud Microphysics ◽  
Number Concentration ◽  
Latent Heating ◽  
Microphysics Scheme ◽  
Convective Clouds ◽  
Aerosol Loading ◽  
Significant Difference ◽  
Deep Convective Clouds ◽  
Bin Microphysics ◽  
Cumulative Precipitation

Abstract. The potential effects of increased aerosol loading on the development of deep convective clouds and resulting precipitation amounts are studied by employing the Weather Research and Forecasting (WRF) model as a detailed high-resolution cloud resolving model (CRM) with both detailed bulk and bin microphysics schemes. The bulk microphysics scheme incorporates a physically based parameterization of cloud droplet activation as well as homogeneous and heterogeneous freezing in order to explicitly resolve the possible aerosol-induced effects on the cloud microphysics. These parameterizations allow one to segregate the effects of an increase in the aerosol number concentration into enhanced cloud condensation nuclei (CCN) and/or ice nuclei (IN) concentrations using bulk microphysics. The bin microphysics scheme, with its explicit calculations of cloud particle collisions, is shown to better predict cumulative precipitation. Increases in the CCN number concentration may not have a monotonic influence on the cumulative precipitation resulting from deep convective clouds. We demonstrate that the aerosol-induced effect is controlled by the balance between latent heating and the increase in condensed water aloft, each having opposing effects on buoyancy. It is also shown that under polluted conditions and in relatively dry environments, increases in the CCN number concentration reduce the cumulative precipitation due to the competition between the sedimentation and evaporation/sublimation timescales. The effect of an increase in the IN number concentration on the dynamics of deep convective clouds is small, but may act to suppress precipitation. A comparison of the predictions using the bin and bulk microphysics schemes demonstrate a significant difference between the predicted precipitation and the influence of aerosol perturbations on updraft velocity within the convective core. The bulk microphysics scheme is shown to be unable to capture the changes in latent heating that occur as a result of changes in the CCN number concentration, while the bin microphysics scheme demonstrates significant increases in the latent heating aloft with increasing CCN number concentration. This suggests that a detailed two-bulk microphysics scheme, which is more computationally efficient than bin microphysics schemes, may not be sufficient, even when coupled to a detailed activation scheme, to predict small changes that result from perturbations in aerosol loading.

scholarly journals Theoretical basis for convective invigoration due to increased aerosol concentration

2011 ◽  
Vol 11 (11) ◽  
pp. 5407-5429 ◽  
Author(s):  
Z. J. Lebo ◽  
J. H. Seinfeld
Keyword(s):  
Number Concentration ◽  
Latent Heating ◽  
Heating Rates ◽  
Microphysics Scheme ◽  
Convective Clouds ◽  
Aerosol Loading ◽  
Significant Difference ◽  
Deep Convective Clouds ◽  
Bin Microphysics ◽  
Cumulative Precipitation

Abstract. The potential effects of increased aerosol loading on the development of deep convective clouds and resulting precipitation amounts are studied by employing the Weather Research and Forecasting (WRF) model as a detailed high-resolution cloud resolving model (CRM) with both detailed bulk and bin microphysics schemes. Both models include a physically-based activation scheme that incorporates a size-resolved aerosol population. We demonstrate that the aerosol-induced effect is controlled by the balance between latent heating and the increase in condensed water aloft, each having opposing effects on buoyancy. It is also shown that under polluted conditions, increases in the CCN number concentration reduce the cumulative precipitation due to the competition between the sedimentation and evaporation/sublimation timescales. The effect of an increase in the IN number concentration on the dynamics of deep convective clouds is small and the resulting decrease in domain-averaged cumulative precipitation is shown not to be statistically significant, but may act to suppress precipitation. It is also shown that even in the presence of a decrease in the domain-averaged cumulative precipitation, an increase in the precipitation variance, or in other words, andincrease in rainfall intensity, may be expected in more polluted environments, especially in moist environments. A significant difference exists between the predictions based on the bin and bulk microphysics schemes of precipitation and the influence of aerosol perturbations on updraft velocity within the convective core. The bulk microphysics scheme shows little change in the latent heating rates due to an increase in the CCN number concentration, while the bin microphysics scheme demonstrates significant increases in the latent heating aloft with increasing CCN number concentration. This suggests that even a detailed two-bulk microphysics scheme, coupled to a detailed activation scheme, may not be sufficient to predict small changes that result from perturbations in aerosol loading.

scholarly journals Are simulated aerosol-induced effects on deep convective clouds strongly dependent on saturation adjustment?

2012 ◽  
Vol 12 (4) ◽  
pp. 10059-10114 ◽  
Author(s):  
Z. J. Lebo ◽  
H. Morrison ◽  
J. H. Seinfeld
Keyword(s):  
Mass Flux ◽  
Cold Pool ◽  
Latent Heating ◽  
Time Step ◽  
Microphysics Scheme ◽  
Surface Precipitation ◽  
Convective Clouds ◽  
Aerosol Loading ◽  
Deep Convective Clouds ◽  
Bulk Model

Abstract. Three configurations of a bulk microphysics scheme in conjunction with a detailed bin scheme are implemented in the Weather Research and Forecasting (WRF) model to specifically address the role of the saturation adjustment assumption (i.e., condensing/evaporating the surplus/deficit water vapor relative to saturation in one time step) on aerosol-induced invigoration of deep convective clouds. The bulk model configurations are designed to treat cloud droplet condensation/evaporation using either saturation adjustment, as employed in most bulk models, or an explicit representation of supersaturation over a time step, as used in bin models. Results demonstrate that the use of saturation adjustment artificially enhances condensation and latent heating at low levels and limits the potential for an increase in aerosol concentration to increase buoyancy at mid to upper levels. This leads to a small weakening of the time- and domain-averaged convective mass flux (~ -3%) in polluted compared to clean conditions. In contrast, the bin model and bulk scheme with explicit prediction of supersaturation simulate an increase in latent heating aloft and the convective updraft mass flux is weakly invigorated (~5%). The bin model also produces a large increase in domain-mean cumulative surface precipitation in polluted conditions (~18%), while all of the bulk model configurations simulate little change in precipitation. Finally, it is shown that the cold pool weakens substantially with increased aerosol loading when saturation adjustment is applied, which acts to reduce the low-level convergence and weaken the convective dynamics. With an explicit treatment of supersaturation in the bulk and bin models there is little change in cold pool strength, so that the convective response to polluted conditions is influenced more by changes in latent heating aloft. It is concluded that the use of saturation adjustment can explain differences in the response of cold pool evolution and convective dynamics with aerosol loading simulated by the bulk and bin models, but cannot explain large differences in the response of surface precipitation between these models.

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.

scholarly journals Are simulated aerosol-induced effects on deep convective clouds strongly dependent on saturation adjustment?

2012 ◽  
Vol 12 (20) ◽  
pp. 9941-9964 ◽  
Author(s):  
Z. J. Lebo ◽  
H. Morrison ◽  
J. H. Seinfeld
Keyword(s):  
Mass Flux ◽  
Cold Pool ◽  
Latent Heating ◽  
Time Step ◽  
Microphysics Scheme ◽  
Surface Precipitation ◽  
Convective Clouds ◽  
Aerosol Loading ◽  
Deep Convective Clouds ◽  
Bulk Model

Abstract. Three configurations of a bulk microphysics scheme in conjunction with a detailed bin scheme are implemented in the Weather Research and Forecasting (WRF) model to specifically address the role of the saturation adjustment assumption (i.e., condensing/evaporating the surplus/deficit water vapor relative to saturation in one time step) on aerosol-induced invigoration of deep convective clouds. The bulk model configurations are designed to treat cloud droplet condensation/evaporation using either saturation adjustment, as employed in most bulk models, or an explicit representation of supersaturation over a time step, as used in bin models. Results demonstrate that the use of saturation adjustment artificially enhances condensation and latent heating at low levels and limits the potential for an increase in aerosol concentration to increase buoyancy at mid to upper levels. This leads to a small weakening of the time- and domain-averaged convective mass flux (~-3%) in polluted compared to clean conditions. In contrast, the bin model and bulk scheme with explicit prediction of supersaturation simulate an increase in latent heating aloft and the convective updraft mass flux is weakly invigorated (~5%). The bin model also produces a large increase in domain-mean cumulative surface precipitation in polluted conditions (~18%), while all of the bulk model configurations simulate little change in precipitation. Finally, it is shown that the cold pool weakens substantially with increased aerosol loading when saturation adjustment is applied, which acts to reduce the low-level convergence and weaken the convective dynamics. With an explicit treatment of supersaturation in the bulk and bin models there is little change in cold pool strength, so that the convective response to polluted conditions is influenced more by changes in latent heating aloft. It is concluded that the use of saturation adjustment can explain differences in the response of cold pool evolution and convective dynamics with aerosol loading simulated by the bulk and bin models, but cannot explain large differences in the response of surface precipitation between these models.

scholarly journals Tropical deep convective life cycle: Cb-anvil cloud microphysics from high-altitude aircraft observations

2014 ◽  
Vol 14 (23) ◽  
pp. 13223-13240 ◽  
Author(s):  
W. Frey ◽  
S. Borrmann ◽  
F. Fierli ◽  
R. Weigel ◽  
V. Mitev ◽  
...  
Keyword(s):  
Life Cycle ◽  
High Altitude ◽  
Potential Temperature ◽  
Cloud Microphysics ◽  
Mature Stage ◽  
Convective System ◽  
Ice Crystal ◽  
Convective Clouds ◽  
Tropical Tropopause ◽  
Deep Convective Clouds

Abstract. The case study presented here focuses on the life cycle of clouds in the anvil region of a tropical deep convective system. During the SCOUT-O3 campaign from Darwin, Northern Australia, the Hector storm system has been probed by the Geophysica high-altitude aircraft. Clouds were observed by in situ particle probes, a backscatter sonde, and a miniature lidar. Additionally, aerosol number concentrations have been measured. On 30 November 2005 a double flight took place and Hector was probed throughout its life cycle in its developing, mature, and dissipating stage. The two flights were four hours apart and focused on the anvil region of Hector in altitudes between 10.5 and 18.8 km (i.e. above 350 K potential temperature). Trajectory calculations, satellite imagery, and ozone measurements have been used to ensure that the same cloud air masses have been probed in both flights. The size distributions derived from the measurements show a change not only with increasing altitude but also with the evolution of Hector. Clearly different cloud to aerosol particle ratios as well as varying ice crystal morphology have been found for the different development stages of Hector, indicating different freezing mechanisms. The development phase exhibits the smallest ice particles (up to 300 μm) with a rather uniform morphology. This is indicative for rapid glaciation during Hector's development. Sizes of ice crystals are largest in the mature stage (larger than 1.6 mm) and even exceed those of some continental tropical deep convective clouds, also in their number concentrations. The backscatter properties and particle images show a change in ice crystal shape from the developing phase to rimed and aggregated particles in the mature and dissipating stages; the specific shape of particles in the developing phase cannot be distinguished from the measurements. Although optically thin, the clouds in the dissipating stage have a large vertical extent (roughly 6 km) and persist for at least 6 h. Thus, the anvils of these high-reaching deep convective clouds have a high potential for affecting the tropical tropopause layer by modifying the humidity and radiative budget, as well as for providing favourable conditions for subvisible cirrus formation. The involved processes may also influence the amount of water vapour that ultimately reaches the stratosphere in the tropics.

scholarly journals Microphysical Characteristics of Frozen Droplet Aggregates from Deep Convective Clouds

2018 ◽  
Author(s):  
Junshik Um ◽  
Greg M. McFarquhar ◽  
Jeffrey L. Stith ◽  
Chang Hoon Jung ◽  
Seoung Soo Lee ◽  
...  
Keyword(s):  
National Science Foundation ◽  
Ice Crystals ◽  
Maximum Dimension ◽  
Cloud Particle ◽  
Atmospheric Research ◽  
Convective Clouds ◽  
National Science ◽  
Deep Convective Clouds

Abstract. During the 2012 Deep Convective Clouds and Chemistry (DC3) experiment the National Science Foundation/National Center for Atmospheric Research Gulfstream-V (G-V) aircraft sampled the upper anvils of two storms that developed in eastern Colorado on 6 June 2012. A cloud particle imager (CPI) mounted on the G-V aircraft recorded images of ice crystals at altitudes of 12.0–12.4 km and T = −61– −55 °C. A total of 22,393 CPI crystal images were analyzed, all with maximum dimension Dmax 

scholarly journals Comparing the impact of environmental conditions and microphysics on the forecast uncertainty of deep convective clouds and hail

2020 ◽  
Vol 20 (4) ◽  
pp. 2201-2219
Author(s):  
Constanze Wellmann ◽  
Andrew I. Barrett ◽  
Jill S. Johnson ◽  
Michael Kunz ◽  
Bernhard Vogel ◽  
...  
Keyword(s):  
Sensitivity Analysis ◽  
Environmental Conditions ◽  
Vertical Wind Shear ◽  
Environmental Parameters ◽  
Cloud Microphysics ◽  
Heating Rates ◽  
Dimensional Parameter ◽  
Convective Clouds ◽  
Deep Convective Clouds ◽  
The Impact

Abstract. Severe hailstorms have the potential to damage buildings and crops. However, important processes for the prediction of hailstorms are insufficiently represented in operational weather forecast models. Therefore, our goal is to identify model input parameters describing environmental conditions and cloud microphysics, such as the vertical wind shear and strength of ice multiplication, which lead to large uncertainties in the prediction of deep convective clouds and precipitation. We conduct a comprehensive sensitivity analysis simulating deep convective clouds in an idealized setup of a cloud-resolving model. We use statistical emulation and variance-based sensitivity analysis to enable a Monte Carlo sampling of the model outputs across the multi-dimensional parameter space. The results show that the model dynamical and microphysical properties are sensitive to both the environmental and microphysical uncertainties in the model. The microphysical parameters lead to larger uncertainties in the output of integrated hydrometeor mass contents and precipitation variables. In particular, the uncertainty in the fall velocities of graupel and hail account for more than 65 % of the variance of all considered precipitation variables and for 30 %–90 % of the variance of the integrated hydrometeor mass contents. In contrast, variations in the environmental parameters – the range of which is limited to represent model uncertainty – mainly affect the vertical profiles of the diabatic heating rates.

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