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.

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

2019 ◽  
Author(s):  
Constanze Wellmann ◽  
Andrew I. Barrett ◽  
Jill S. Johnson ◽  
Michael Kunz ◽  
Bernhard Vogel ◽  
...  
Keyword(s):  
Sensitivity Analysis ◽  
Environmental Conditions ◽  
Vertical Wind Shear ◽  
Cloud Microphysics ◽  
Heating Rates ◽  
Fall Velocity ◽  
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 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, especially the fall velocity of hail, lead to larger uncertainties in the output of integrated hydrometeor masses and precipitation variables. In contrast, variations in the environmental conditions mainly affect the vertical profiles of the diabatic heating rates.

scholarly journals The response of precipitation to aerosol through riming and melting in deep convective clouds

2010 ◽  
Vol 10 (11) ◽  
pp. 29007-29050
Author(s):  
Z. Cui ◽  
S. Davies ◽  
K. S. Carslaw ◽  
A. M. Blyth
Keyword(s):  
Cloud Model ◽  
Cloud Microphysics ◽  
Mixed Phase ◽  
Cloud Base ◽  
Spatial And Temporal Variability ◽  
Convective Clouds ◽  
Ice Particles ◽  
Wide Range ◽  
Deep Convective Clouds ◽  
The Impact

Abstract. We have used a 2-D axisymmetric, non-hydrostatic, bin-resolved cloud model to examine the impact of aerosol changes on the development of mixed-phase convective clouds. We have simulated convective clouds from four different sites (three continental and one tropical marine) with a wide range of realistic aerosol loadings and initial thermodynamic conditions (a total of 93 different clouds). It is found that the accumulated precipitation responds very differently to changing aerosol in the marine and continental environments. For the continental clouds, the scaled total precipitation reaches a maximum for aerosol that produce drop numbers at cloud base between 180–430 cm−3 when other conditions are the same. In contrast, all the tropical marine clouds show an increase in accumulated precipitation and deeper convection with increasing aerosol loading. For continental clouds, drops are rapidly depleted by ice particles shortly after the onset of precipitation. The precipitation is dominantly produced by melting ice particles. The riming rate increases with aerosol when the loading is very low, and decreases when the loading is high. Peak precipitation intensities tend to increase with aerosol up to drop concentrations (at cloud base) of ~500 cm−3 then decrease with further aerosol increases. This behaviour is caused by the initial transition from warm to mixed-phase rain followed by reduced efficiency of mixed-phase rain at very high drop concentrations. The response of tropical marine clouds to increasing aerosol is different to, and larger than, that of continental clouds. In the more humid tropical marine environment with low cloud bases we find that accumulated precipitation increases with increasing aerosol. The increase is driven by the transition from warm to mixed-phase rain. Our study suggests that the response of deep convective clouds to aerosol will be an important contribution to the spatial and temporal variability in cloud microphysics and precipitation.

scholarly journals The response of precipitation to aerosol through riming and melting in deep convective clouds

2011 ◽  
Vol 11 (7) ◽  
pp. 3495-3510 ◽  
Author(s):  
Z. Cui ◽  
S. Davies ◽  
K. S. Carslaw ◽  
A. M. Blyth
Keyword(s):  
Cloud Model ◽  
Cloud Microphysics ◽  
Mixed Phase ◽  
Cloud Base ◽  
Spatial And Temporal Variability ◽  
Convective Clouds ◽  
Ice Particles ◽  
Wide Range ◽  
Deep Convective Clouds ◽  
The Impact

Abstract. We have used a 2-D axisymmetric, non-hydrostatic, bin-resolved cloud model to examine the impact of aerosol changes on the development of mixed-phase convective clouds. We have simulated convective clouds from four different sites (three continental and one tropical marine) with a wide range of realistic aerosol loadings and initial thermodynamic conditions (a total of 93 different clouds). It is found that the accumulated precipitation responds very differently to changing aerosol in the marine and continental environments. For the continental clouds, the scaled total precipitation reaches a maximum for aerosol that produce drop numbers at cloud base between 180–430 cm−3 when other conditions are the same. In contrast, all the tropical marine clouds show an increase in accumulated precipitation and deeper convection with increasing aerosol loading. For continental clouds, drops are rapidly depleted by ice particles shortly after the onset of precipitation. The precipitation is dominantly produced by melting ice particles. The riming rate increases with aerosol when the loading is very low, and decreases when the loading is high. Peak precipitation intensities tend to increase with aerosol up to drop concentrations (at cloud base) of ~500 cm−3 then decrease with further aerosol increases. This behaviour is caused by the initial transition from warm to mixed-phase rain followed by reduced efficiency of mixed-phase rain at very high drop concentrations. The response of tropical marine clouds to increasing aerosol is different to, and larger than, that of continental clouds. In the more humid tropical marine environment with low cloud bases we find that accumulated precipitation increases with increasing aerosol. The increase is driven by the transition from warm to mixed-phase rain. Our study suggests that the response of deep convective clouds to aerosol will be an important contribution to the spatial and temporal variability in cloud microphysics and precipitation.

Regimes of Dry Convection above Wildfires: Sensitivity to Fire Line Details

2010 ◽  
Vol 67 (3) ◽  
pp. 611-632 ◽  
Author(s):  
Michael T. Kiefer ◽  
Matthew D. Parker ◽  
Joseph J. Charney
Keyword(s):  
Line Shape ◽  
3D Model ◽  
Three Dimensional ◽  
Vertical Wind Shear ◽  
Heating Rates ◽  
3D Simulations ◽  
Complex Phenomena ◽  
2D And 3D ◽  
The Impact ◽  
Dry Convection

Abstract Fire lines are complex phenomena with a broad range of scales of cross-line dimension, undulations, and along-line variation in heating rates. While some earlier studies have examined parcel processes in two-dimensional simulations, the complexity of fire lines in nature motivates a study in which the impact of three-dimensional fire line details on parcel processes is examined systematically. This numerical modeling study aims to understand how fundamental processes identified in 2D simulations operate in 3D simulations where the fire line is neither straight nor uniform in intensity. The first step is to perform simulations in a 3D model, with no fire line undulations or inhomogeneity. In general, convective modes simulated in the 2D model are reproduced in the 3D model. In one particular case with strong vertical wind shear, new convection develops separate from the main line of convection as a result of local changes to parcel speed and heating. However, in general the processes in the 2D and 3D simulations are identical. The second step is to examine 3D experiments wherein fire line shape and along-line inhomogeneity are varied. Parcel heating, as well as convective mode, is shown to exhibit sensitivity to fire line shape and along-line inhomogeneity.

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 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.

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