Model investigation into rain enhancement by hygroscopic seeding in mixed-phase convective clouds

2020 ◽  
Author(s):  
Juha Tonttila ◽  
Harri Kokkola ◽  
Tomi Raatikainen ◽  
Jaakko Ahola ◽  
Hannele Korhonen ◽  
...  
Keyword(s):  
Field Experiments ◽  
Cloud Microphysics ◽  
Phase Region ◽  
Mixed Phase ◽  
Moderate Intensity ◽  
Precipitation Process ◽  
Ambient Conditions ◽  
Convective Clouds ◽  
The Impact ◽  
Mixed Phase Region

<p>Intentional release of large hygroscopic particles in a cloud, i.e. cloud seeding, is potentially capable of increasing rain formation. In this work, we focus on convective clouds of moderate intensity observed over the United Arab Emirates, where we use a large eddy simulator coupled with detailed bin aerosol-cloud microphysics module (UCLALES-SALSA) to study the processes controlling the seeding efficacy. Despite numerous field experiments, the conditions that favor efficient seeding induced rain enhancement are not well characterized. Models such as UCLALES-SALSA provide the means to study the microphysical effects in varying ambient conditions in a controlled setting. The clouds targeted by our simulations have a mixed-phase component and rain is primarily produced by the cold precipitation process. The results show that the fast growing droplets formed by the relatively large hygroscopic seeding aerosol affect the riming process in the mixed-phase region inside the clouds. The collision rate between the hydrometeors in the mixed-phase region is enhanced, producing larger frozen particles. Consequently, the ice tends to get more heavily rimed, as indicated by the fraction of rimed ice from the total ice mass, which promotes increased particle fall velocities.</p><p> </p><p>However, the impact of seeding on the riming process depends on the state of the cloud and its environment. In conditions already favoring high rime fraction, often associated with relatively strong surface precipitation events, the effect of seeding is hindered, at least in terms of relative difference. Nevertheless, even if the effect of seeding on the total precipitation yield is small, it may still affect the timing of the precipitation onset, a topic currently under investigation. Work is also in progress to characterize the dependence between ambient conditions (in terms of aerosol and the thermodynamic properties of the atmospheric column) and the susceptibility of the mixed-phase clouds to seeding injection.</p>

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.

scholarly journals Spin excitations in [La[sub 1−x]Ca[sub x]MnO[sub 3]] in the mixed-phase region

2002 ◽  
Vol 91 (10) ◽  
pp. 7511 ◽  
Author(s):  
L. Stumpe ◽  
B. Kirby ◽  
H. Kaiser ◽  
J. J. Rhyne ◽  
J. F. Mitchell
Keyword(s):  
Phase Region ◽  
Mixed Phase ◽  
Spin Excitations ◽  
Mixed Phase Region

Phase diagrams for impurity-doped VO2

1976 ◽  
Vol 54 (1) ◽  
pp. 1-8 ◽  
Author(s):  
J. M. Reyes ◽  
S. L. Segel ◽  
M. Sayer
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Phase Diagrams ◽  
Phase Region ◽  
Mixed Phase ◽  
Phase Boundaries ◽  
Temperature Changes ◽  
Impurity Doped ◽  
T Phase ◽  
Mixed Phase Region

The general form of the phase diagrams for impurity-doped VO2 is considered and shown to include mixed phase boundary regions. Phase diagrams for Cr and Al-doped VO2 are established on the basis of the temperature dependence of the 51V nuclear magnetic resonance (NMR) signal. In Cr-doped VO2, the (M2) phase is shown to exist over a smaller temperature–concentration range than reported previously and in Al-doped VO2, two intermediate single phases (M2) and (M3) are found. The (T) phase which has been previously suggested to be a definite phase having triclinic symmetry is shown to be a mixed phase region in which the contributions from the components change with temperature. Changes in NMR signal intensity at the phase boundaries show that half the V sites have paired spins in both the(M2) and (M3) phases.

Nucleation Processes in Deep Convection Simulated by a Cloud-System-Resolving Model with Double-Moment Bulk Microphysics

2007 ◽  
Vol 64 (3) ◽  
pp. 738-761 ◽  
Author(s):  
Vaughan T. J. Phillips ◽  
Leo J. Donner ◽  
Stephen T. Garner
Keyword(s):  
Deep Convection ◽  
Phase Region ◽  
Mixed Phase ◽  
Cloud Droplets ◽  
Ice Concentration ◽  
Double Moment ◽  
Preferential Evaporation ◽  
Cloud Ice ◽  
Homogeneous Freezing ◽  
Mixed Phase Region

Abstract A novel type of limited double-moment scheme for bulk microphysics is presented here for cloud-system-resolving models (CSRMs). It predicts the average size of cloud droplets and crystals, which is important for representing the radiative impact of clouds on the climate system. In this new scheme, there are interactive components for ice nuclei (IN) and cloud condensation nuclei (CCN). For cloud ice, the processes of primary ice nucleation, Hallett–Mossop (HM) multiplication of ice particles (secondary ice production), and homogeneous freezing of aerosols and droplets provide the source of ice number. The preferential evaporation of smaller droplets during homogeneous freezing of cloud liquid is represented for the first time. Primary and secondary (i.e., in cloud) droplet nucleation are also represented, by predicting the supersaturation as a function of the vertical velocity and local properties of cloud liquid. A linearized scheme predicts the supersaturation, explicitly predicting rates of condensation and vapor deposition onto liquid (cloud liquid, rain) and ice (cloud ice, snow, graupel) species. The predicted supersaturation becomes the input for most nucleation processes, including homogeneous aerosol freezing and secondary droplet activation. Comparison of the scheme with available aircraft and satellite data is performed for two cases of deep convection over the tropical western Pacific Ocean. Sensitivity tests are performed with respect to a range of nucleation processes. The HM process of ice particle multiplication has an important impact on the domain-wide ice concentration in the lower half of the mixed-phase region, especially when a lack of upper-level cirrus suppresses homogeneous freezing. Homogeneous freezing of droplets and, especially, aerosols is found to be the key control on number and sizes of cloud particles in the simulated cloud ensemble. Preferential evaporation of smaller droplets during homogeneous freezing produces a major impact on ice concentrations aloft. Aerosols originating from the remote free troposphere become activated in deep convective updrafts and produce most of the supercooled cloud droplets that freeze homogeneously aloft. Homogeneous aerosol freezing is found to occur only in widespread regions of weak ascent while homogeneous droplet freezing is restricted to deep convective updrafts. This means that homogeneous aerosol freezing can produce many more crystals than homogeneous droplet freezing, if conditions in the upper troposphere are favorable. These competing mechanisms of homogeneous freezing determine the overall response of the ice concentration to environmental CCN concentrations in the simulated cloud ensemble. The corresponding sensitivity with respect to environmental IN concentrations is much lower. Nevertheless, when extremely high concentrations of IN are applied, that are typical for plumes of desert dust, the supercooled cloud liquid is completely eliminated in the upper half of the mixed phase region. This shuts down the process of homogeneous droplet freezing.

scholarly journals Comparison between Low-Flash and Non-Lightning-Producing Convective Areas within a Mature Mesoscale Convective System

2011 ◽  
Vol 26 (4) ◽  
pp. 468-486 ◽  
Author(s):  
Jennifer L. Palucki ◽  
Michael I. Biggerstaff ◽  
Donald R. MacGorman ◽  
Terry Schuur
Keyword(s):  
Vertical Motion ◽  
Mesoscale Convective System ◽  
Phase Region ◽  
Life Cycles ◽  
Radar Reflectivity ◽  
Mixed Phase ◽  
Convective System ◽  
Lightning Flash ◽  
Mesoscale Convective ◽  
Mixed Phase Region

Abstract Two small multicellular convective areas within a larger mesoscale convective system that occurred on 20 June 2004 were examined to assess vertical motion, radar reflectivity, and dual-polarimetric signatures between flash and non-flash-producing convection. Both of the convective areas had similar life cycles and general structures. Yet, one case produced two flashes, one of which may have been a cloud-to-ground flash, while the other convective area produced no flashes. The non-lightning-producing case had a higher peak reflectivity up to 6 km. Hence, if a reflectivity-based threshold were used as a precursor to lightning, it would have yielded misleading results. The peak upward motion in the mixed-phase region for both cases was 8 m s−1 or less. However, the lightning-producing storm contained a wider region where the updraft exceeded 5 m s−1. Consistent with the broader updraft region, the lightning-producing case exhibited a distinct graupel signature over a broader region than the non-lightning-producing convection. Slight differences in vertical velocity affected the quantity of graupel present in the mixed-phase region, thereby providing the subtle differences in polarimetric signatures that were associated with lightning activity. If the results here are generally applicable, then graupel volume may be a better precursor to a lightning flash than radar reflectivity. With the dual-polarimetric upgrade to the national observing radar network, it should be possible to better distinguish between lightning- and non-lightning-producing areas in weak convective systems that pose a potential safety hazard to the public.

scholarly journals Sensitivity of cirrus and mixed-phase clouds to the ice nuclei spectra in McRAS-AC: single column model simulations

2012 ◽  
Vol 12 (6) ◽  
pp. 14927-14957
Author(s):  
R. Morales Betancourt ◽  
D. Lee ◽  
L. Oreopoulos ◽  
Y. C. Sud ◽  
D. Barahona ◽  
...  
Keyword(s):  
Cloud Microphysics ◽  
Ice Nucleation ◽  
Mixed Phase ◽  
Cloud Particle ◽  
Water Path ◽  
Ice Water Path ◽  
Single Column ◽  
Mixed Phase Clouds ◽  
Ice Water ◽  
The Impact

Abstract. The salient features of mixed-phase and ice clouds in a GCM cloud scheme are examined using the ice formation parameterizations of Liu and Penner (LP) and Barahona and Nenes (BN). The performance of LP and BN ice nucleation parameterizations were assessed in the GEOS-5 AGCM using the McRAS-AC cloud microphysics framework in single column mode. Four dimensional assimilated data from the intensive observation period of ARM TWP-ICE campaign was used to drive the fluxes and lateral forcing. Simulation experiments where established to test the impact of each parameterization in the resulting cloud fields. Three commonly used IN spectra were utilized in the BN parameterization to described the availability of IN for heterogeneous ice nucleation. The results show large similarities in the cirrus cloud regime between all the schemes tested, in which ice crystal concentrations were within a factor of 10 regardless of the parameterization used. In mixed-phase clouds there are some persistent differences in cloud particle number concentration and size, as well as in cloud fraction, ice water mixing ratio, and ice water path. Contact freezing in the simulated mixed-phase clouds contributed to transfer liquid to ice efficiently, so that on average, the clouds were fully glaciated at T~260 K, irrespective of the ice nucleation parameterization used. Comparison of simulated ice water path to available satellite derived observations were also performed, finding that all the schemes tested with the BN parameterization predicted average values of IWP within ±15% of the observations.

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