Distinct Contributions of Ice Nucleation, Large-Scale Environment, and Shallow Cumulus Detrainment to Cloud Phase Partitioning With NCAR CAM5

Abstract In this study, two parameterizations of ice nucleation rate on dust particles are used in a parcel model to simulate aircraft measurements of ice crystal number concentration Ni in the Arctic. The parcel model has detailed microphysics for droplet and ice nucleation, growth, and evaporation with prescribed vertical air velocities. Three dynamic regimes are considered, including large-scale ascent, cloud-top generating cells, and their combination. With observed meteorological conditions and aerosol concentrations, the parcel model predicts the number concentrations of size-resolved ice crystals, which may be compared to aircraft measurements. Model results show rapid changes with height/time in relative humidity, Ni, and thermodynamic phase partitioning, which is not resolved in current climate and weather forecasting models. Parameterizations for ice number and nucleation rate in mixed-phase stratus clouds are thus developed based on the parcel model results to represent the time-integrated effect of some microphysical processes in large-scale models.

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Dynamics of Subsiding Shells in Actively Growing Clouds with Vertical Updrafts

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-19-0018.1 ◽

2020 ◽

Vol 77 (4) ◽

pp. 1353-1369 ◽

Cited By ~ 2

Author(s):

Vishnu Nair ◽

Thijs Heus ◽

Maarten van Reeuwijk

Keyword(s):

Shell Thickness ◽

Large Scale ◽

Cloud Environment ◽

Initial State ◽

Cumulus Clouds ◽

Mean Velocity ◽

Flow Parameters ◽

Shallow Cumulus ◽

Order Of Magnitude ◽

Self Similar

Abstract The dynamics of a subsiding shell at the edges of actively growing shallow cumulus clouds with updrafts is analyzed using direct numerical simulation. The actively growing clouds have a fixed in-cloud buoyancy and velocity. Turbulent mixing and evaporative cooling at the cloud edges generate a subsiding shell that grows with time. A self-similar regime is observed for first- and second-order moments when normalized with respective maximum values. Internal scales derived from integral properties of the flow problem are identified. A self-similarity analysis using these scales reveals that contrary to classical self-similar flows, the turbulent kinetic energy budget terms and velocity moments scale according to the buoyancy and not with the mean velocity. The shell thickness is observed to increase linearly with time. The buoyancy scale remains time invariant and is set by the initial cloud–environment thermodynamics. The shell accelerates ballistically with a magnitude set by the saturation value of the buoyancy of the cloud–environment mixture. In this regime, the shell is buoyancy driven and independent of the in-cloud velocity. Relations are obtained for predicting the shell thickness and minimum velocities by linking the internal scales with external flow parameters. The values thus calculated are consistent with the thickness and velocities observed in typical shallow cumulus clouds. The entrainment coefficient is a function of the initial state of the cloud and the environment, and is shown to be on the same order of magnitude as fractional entrainment rates calculated for large-scale models.

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Responses of Shallow Cumulus Convection to Large-Scale Temperature and Moisture Perturbations: A Comparison of Large-Eddy Simulations and a Convective Parameterization Based on Stochastically Entraining Parcels

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-11-0279.1 ◽

2012 ◽

Vol 69 (6) ◽

pp. 1936-1956 ◽

Cited By ~ 29

Author(s):

Ji Nie ◽

Zhiming Kuang

Keyword(s):

Large Scale ◽

Potential Temperature ◽

Large Eddy Simulations ◽

Cumulus Parameterization ◽

Temperature Perturbation ◽

Cumulus Convection ◽

Positive Temperature ◽

Shallow Cumulus ◽

Scale Temperature ◽

Large Eddy

Abstract Responses of shallow cumuli to large-scale temperature/moisture perturbations are examined through diagnostics of large-eddy simulations (LESs) of the undisturbed Barbados Oceanographic and Meteorological Experiment (BOMEX) case and a stochastic parcel model. The perturbations are added instantaneously and allowed to evolve freely afterward. The parcel model reproduces most of the changes in the LES-simulated cloudy updraft statistics in response to the perturbations. Analyses of parcel histories show that a positive temperature perturbation forms a buoyancy barrier, which preferentially eliminates parcels that start with lower equivalent potential temperature or have experienced heavy entrainment. Besides the amount of entrainment, the height at which parcels entrain is also important in determining their fate. Parcels entraining at higher altitudes are more likely to overcome the buoyancy barrier than those entraining at lower altitudes. Stochastic entrainment is key for the parcel model to reproduce the LES results. Responses to environmental moisture perturbations are quite small compared to those to temperature perturbations because changing environmental moisture is ineffective in modifying buoyancy in the BOMEX shallow cumulus case. The second part of the paper further explores the feasibility of a stochastic parcel–based cumulus parameterization. Air parcels are released from the surface layer and temperature/moisture fluxes effected by the parcels are used to calculate heating/moistening tendencies due to both cumulus convection and boundary layer turbulence. Initial results show that this conceptually simple parameterization produces realistic convective tendencies and also reproduces the LES-simulated mean and variance of cloudy updraft properties, as well as the response of convection to temperature/moisture perturbations.

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Aerosol effects on shallow cumulus cloud fields in idealised and realistic simulations

10.5194/egusphere-egu2020-18231 ◽

2020 ◽

Author(s):

George Spill ◽

Philip Stier ◽

Paul Field ◽

Guy Dagan

Keyword(s):

Large Scale ◽

Trade Wind ◽

Quasi Equilibrium ◽

Cumulus Cloud ◽

Shallow Convection ◽

Shallow Cumulus ◽

Synoptic Conditions ◽

Large Eddy ◽

Transient Forcing ◽

Periodic Domains

Shallow cumulus clouds interact with their environment in myriad significant ways, and yet their behavour is still poorly understood, and is responsible for much uncertainty in climate models. Improving our understanding of these clouds is therefore an important part of improving our understanding of the climate system as a whole.Modelling studies of shallow convection have traditionally made use of highly idealised simulations using large-eddy models, which allow for high resolution, detailed simulations. However, this idealised nature, with periodic boundaries and constant forcing, and the quasi-equilibrium cloud fields produced, means that they do not capture the effect of transient forcing and conditions found in the real atmosphere, which contains shallow cumulus cloud fields unlikely to be in equilibrium.&#160;Simulations with more realistic nested domains and forcings have previously been shown to have significant persistent responses differently to aerosol perturbations, in contrast to many large eddy simulations in which perturbed runs tend to reach a similar quasi-equilibrium.&#160;Here, we further this investigation by using a single model to present a comparison of familiar idealised simulations of trade wind cumuli in periodic domains, and simulations with a nested domain, whose boundary conditions are provided by a global driving model, able to simulate transient synoptic conditions.&#160;The simulations are carried out using the Met Office Unified Model (UM), and are based on a case study from the Rain In Cumulus over the Ocean (RICO) field campaign. Large domains of 500km are chosen in order to capture large scale cloud field behaviour. A double-moment interactive microphysics scheme is used, along with prescribed aerosol profiles based on RICO observations, which are then perturbed.We find that the choice between realistic nested domains with transient forcing and idealised periodic domains with constant forcing does indeed affect the nature of the response to aerosol perturbations, with the realistic simulations displaying much larger persistent changes in domain mean fields such as liquid water path and precipitation rate.&#160;

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Sensitivity of CAM5-Simulated Arctic Clouds and Radiation to Ice Nucleation Parameterization

Journal of Climate ◽

10.1175/jcli-d-12-00517.1 ◽

2013 ◽

Vol 26 (16) ◽

pp. 5981-5999 ◽

Cited By ~ 55

Author(s):

Shaocheng Xie ◽

Xiaohong Liu ◽

Chuanfeng Zhao ◽

Yuying Zhang

Keyword(s):

Radiative Forcing ◽

Large Scale ◽

Arctic Region ◽

Atmospheric Model ◽

Ice Nucleation ◽

The Arctic ◽

Liquid Water Path ◽

Arctic Clouds ◽

Water Path ◽

Low Level

Abstract Sensitivity of Arctic clouds and radiation in the Community Atmospheric Model, version 5, to the ice nucleation process is examined by testing a new physically based ice nucleation scheme that links the variation of ice nuclei (IN) number concentration to aerosol properties. The default scheme parameterizes the IN concentration simply as a function of ice supersaturation. The new scheme leads to a significant reduction in simulated IN concentration at all latitudes while changes in cloud amounts and properties are mainly seen at high- and midlatitude storm tracks. In the Arctic, there is a considerable increase in midlevel clouds and a decrease in low-level clouds, which result from the complex interaction among the cloud macrophysics, microphysics, and large-scale environment. The smaller IN concentrations result in an increase in liquid water path and a decrease in ice water path caused by the slowdown of the Bergeron–Findeisen process in mixed-phase clouds. Overall, there is an increase in the optical depth of Arctic clouds, which leads to a stronger cloud radiative forcing (net cooling) at the top of the atmosphere. The comparison with satellite data shows that the new scheme slightly improves low-level cloud simulations over most of the Arctic but produces too many midlevel clouds. Considerable improvements are seen in the simulated low-level clouds and their properties when compared with Arctic ground-based measurements. Issues with the observations and the model–observation comparison in the Arctic region are discussed.

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Tropical tropopause ice clouds: a dynamic approach to the mystery of low crystal numbers

Atmospheric Chemistry and Physics ◽

10.5194/acp-13-9801-2013 ◽

2013 ◽

Vol 13 (19) ◽

pp. 9801-9818 ◽

Cited By ~ 53

Author(s):

P. Spichtinger ◽

M. Krämer

Keyword(s):

Gravity Waves ◽

Large Scale ◽

Full Range ◽

Ice Nucleation ◽

Ice Formation ◽

Ice Crystal ◽

Ice Clouds ◽

Tropical Tropopause Layer ◽

Tropical Tropopause ◽

Homogeneous Freezing

Abstract. The occurrence of high, persistent ice supersaturation inside and outside cold cirrus in the tropical tropopause layer (TTL) remains an enigma that is intensely debated as the "ice supersaturation puzzle". However, it was recently confirmed that observed supersaturations are consistent with very low ice crystal concentrations, which is incompatible with the idea that homogeneous freezing is the major method of ice formation in the TTL. Thus, the tropical tropopause "ice supersaturation puzzle" has become an "ice nucleation puzzle". To explain the low ice crystal concentrations, a number of mainly heterogeneous freezing methods have been proposed. Here, we reproduce in situ measurements of frequencies of occurrence of ice crystal concentrations by extensive model simulations, driven by the special dynamic conditions in the TTL, namely the superposition of slow large-scale updraughts with high-frequency short waves. From the simulations, it follows that the full range of observed ice crystal concentrations can be explained when the model results are composed from scenarios with consecutive heterogeneous and homogeneous ice formation and scenarios with pure homogeneous ice formation occurring in very slow (< 1 cm s−1) and faster (> 1 cm s−1) large-scale updraughts, respectively. This statistical analysis shows that about 80% of TTL cirrus can be explained by "classical" homogeneous ice nucleation, while the remaining 20% stem from heterogeneous and homogeneous freezing occurring within the same environment. The mechanism limiting ice crystal production via homogeneous freezing in an environment full of gravity waves is the shortness of the gravity waves, which stalls freezing events before a higher ice crystal concentration can be formed.

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Implications of Warm Rain in Shallow Cumulus and Congestus Clouds for Large-Scale Circulations

Surveys in Geophysics ◽

10.1007/s10712-017-9429-z ◽

2017 ◽

Vol 38 (6) ◽

pp. 1257-1282 ◽

Cited By ~ 4

Author(s):

Louise Nuijens ◽

Kerry Emanuel ◽

Hirohiko Masunaga ◽

Tristan L’Ecuyer

Keyword(s):

Large Scale ◽

Warm Rain ◽

Shallow Cumulus

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The Theory of Ice Nucleation by Heterogeneous Freezing of Deliquescent Mixed CCN. Part II: Parcel Model Simulation

Journal of the Atmospheric Sciences ◽

10.1175/jas-3367.1 ◽

2005 ◽

Vol 62 (2) ◽

pp. 261-285 ◽

Cited By ~ 39

Author(s):

Vitaly I. Khvorostyanov ◽

Judith A. Curry

Keyword(s):

Large Scale ◽

Model Simulation ◽

Cloud Condensation Nuclei ◽

Ice Nucleation ◽

Crystal Nucleation ◽

Ice Crystal ◽

Diffusional Growth ◽

Ice Nuclei ◽

Cloud Models ◽

Bin Microphysics

Abstract The new theory of ice nucleation by heterogeneous freezing of deliquescent mixed cloud condensation nuclei (CCN) presented in Part I is incorporated into a parcel model with explicit water and ice bin microphysics to simulate the process of ice nucleation under transient thermodynamic conditions. Simulations are conducted over the temperature range −4° to −60°C, with vertical velocities varying from 1 to 100 cm s−1, for varying initial relative humidities and aerosol characteristics. These simulations show that the same CCN that are responsible for the drop nucleation may initiate crystal nucleation and can be identified as ice nuclei (IN) when crystals form. The simulated nucleation rates and concentrations of nucleated crystals depend on temperature and supersaturation simultaneously, showing good agreement with observations but with noticeable differences when compared with classical temperature-only and supersaturation-only parameterizations. The kinetics of heterogeneous ice nucleation exhibits a negative feedback via water supersaturation, whereby ice nucleation depends on the water supersaturation that is diminished by ice crystal diffusional growth. This feedback is stronger than the corresponding feedback for drop nucleation, and may explain discrepancies between observed ice nuclei concentrations and ice crystal concentrations, the very small fraction of CCN that may serve as IN, and the much smaller crystal concentrations as compared to drop concentrations. The relative importance of heterogeneous versus homogeneous nucleation is examined for a variety of cloud conditions. Based on these calculations, a simple parameterization for ice crystal concentration is suggested for use in cloud models and large-scale models.

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Partitioning of microbial cells between clouds and precipitation

10.5194/egusphere-egu2020-2876 ◽

2020 ◽

Author(s):

Raphaëlle Péguilhan ◽

Ludovic Besaury ◽

Florent Rossi ◽

Jean-Luc Baray ◽

Thibaud Mas ◽

...

Keyword(s):

Flow Rate ◽

Metabolic Activity ◽

Chem Phys ◽

Ice Nucleation ◽

High Flow ◽

High Flow Rate ◽

Rrna Gene ◽

Phase Partitioning ◽

Nucleation Activity ◽

Ice Nucleation Activity

It is known that microorganisms are present in the outdoor atmosphere, in clouds and precipitation. These microorganisms originate from various local and distant sources and consist of very diverse and ephemeral communities. The most abundant bacterial taxa typically include Alpha-, Beta- and Gamma-Proteobacteria, with notably Pseudomonas and Sphingomonas among the dominant genera observed. Still, very little is known about their sources, metabolic activity, distribution, and their dynamics during their atmospheric life cycle. It was proposed in the past that bacteria with high ice nucleation activity are likely more efficiently precipitated than others [1]. Here, we extend this hypothesis and suggest more generally that different bacteria taxa could exhibit different phase partitioning between aerosol particles, cloud and rainwater, which may affect their atmospheric residence times. This implies that microorganisms are not equally distributed among the different atmospheric compartments (clouds, aerosols and precipitation).To investigate this hypothesis, cloud and rain samples were collected simultaneously from single precipitation events, from two meteorological stations located at different altitudes: the summit of puy de D&#244;me Mountain (1465 m above sea level; France), embedded in clouds, using cloud impactors and high-flow-rate impingers [2], and below the summit, at Opme Station (680 a.s.l.) where precipitation occurred, using automated precipitation collector. The bacterial biodiversity was examined by 16s rRNA gene amplicon MiSeq sequencing. Samples were also characterized for their chemical contents. We show that clouds and precipitation host distinct microbial communities. Clouds host communities from high altitude likely to be of distant origin, while precipitation also includes material originating from the air column underneath and from local origin. So, comparing the biodiversity hosted in clouds and precipitation within single air masses provides information on the relative contribution of local and distant sources to the microorganisms deposited at the surface with rainfalls, and provides very new information concerning the processing and fate of bacteria in the atmosphere.&#160;[1]&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160; M. Joly, P. Amato, L. Deguillaume, M. Monier, C. Hoose, and A. M. Delort, &#8220;Quantification of ice nuclei active at near 0 &#176;c temperatures in low-altitude clouds at the Puy de D&#244;me atmospheric station,&#8221; Atmos. Chem. Phys., vol. 14, no. 15, pp. 8185&#8211;8195, 2014.[2]&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160; T. &#352;antl-Temkiv et al., &#8220;High-Flow-Rate Impinger for the Study of Concentration, Viability, Metabolic Activity, and Ice-Nucleation Activity of Airborne Bacteria,&#8221; Environ. Sci. Technol., vol. 51, no. 19, pp. 11224&#8211;11234, 2017.

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Best practices for precipitation sample storage for offline studies of ice nucleation

10.5194/amt-2020-183 ◽

2020 ◽

Cited By ~ 1

Author(s):

Charlotte M. Beall ◽

Dolan Lucero ◽

Thomas C. Hill ◽

Paul J. DeMott ◽

M. Dale Stokes ◽

...

Keyword(s):

Room Temperature ◽

Storage Time ◽

Ice Nucleation ◽

Correction Factors ◽

Ice Crystal ◽

Phase Partitioning ◽

Cloud Properties ◽

Precipitation Sample ◽

Order Of Magnitude ◽

La Jolla

Abstract. Ice nucleating particles (INPs) are efficiently removed from clouds through precipitation, a convenience of nature for the study of these very rare particles that influence multiple climate-relevant cloud properties including ice crystal concentrations, size distributions, and phase-partitioning processes. INPs suspended in precipitation can be used to estimate in-cloud INP concentrations and to infer their original composition. Offline droplet assays are commonly used to measure INP concentrations in precipitation samples. Heat and filtration treatments are also used to probe INP composition and size ranges. Many previous studies report storing samples prior to INP analyses, but little is known about the effects of storage on INP concentration or their sensitivity to treatments. Here, through a study of 15 precipitation samples collected at a coastal location in La Jolla, CA, USA, we found significant changes caused by storage to concentrations of INPs with warm to moderate freezing temperatures (−7 to −19 ºC). We compared four conditions: 1.) storage at room temperature (+21–23 ºC), 2.) storage at +4 ºC 3.) storage at −20 ºC, and 4.) flash freezing samples with liquid nitrogen prior to storage at −20 ºC. Results demonstrate that storage can lead to both enhancements and losses of greater than one order of magnitude, with non-heat-labile INPs being generally less sensitive to storage regime, but significant losses of INPs smaller than 0.45 μm in all tested storage protocols. No correlation was found between total storage time (1–166 days) and changes in INP concentration. We provide the following recommendations for preservation of precipitation samples from coastal environments intended for INP analysis: that samples be stored at −20 ºC to minimize storage artifacts, that changes due to storage are likely and an additional uncertainty in INP concentrations, and that filtration treatments be applied only to fresh samples. Average INP losses of 72 %, 42 %, 25 % and 32 % were observed for untreated samples stored using the room temperature, +4 ºC, −20 ºC, and flash frozen protocols, respectively. Finally, correction factors are provided so that INP measurements obtained from stored samples may be used to estimate concentrations in fresh samples.

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