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(top right) Ice seeding of altocumulus clouds above the dust layer observed in the morning of 3 June 2006. (bottom right) Respective depolarization ratio. Radiosonde profiles of (top left) horizontal wind speed and direction and (bottom left) humidity and temperature. Horizontal lines in the depolarization plot indicate the À10°C, À20°C, and À30°C temperature height levels as measured with radiosonde launched at 1115 UTC (profile 828).
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1] Multiwavelength lidar, Sun photometer, and radiosonde observations were conducted at Ouarzazate (30.9°N, 6.9°W, 1133 m above sea level, asl), Morocco, in the framework of the Saharan Mineral Dust Experiment (SAMUM) in May–June 2006. The field site is close to the Saharan desert. Information on the depolarization ratio, backscatter and extinction...
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Cloud seeding; aerosol research; precipitation enhancement; Istanbul; drought; water supply; airborne seeding; silver iodide
Citations
... In a wider sense, ice crystals falling into a lower part of the same cloud can be understood as an internal seeder-feeder process (Hobbs et al., 1980). Natural cloud seeding by ice crystals has been inferred from remote sensing and observed during aircraft campaigns (Dennis, 1954;Hobbs et al., 1980Hobbs et al., , 1981Locatelli et al., 1983;Hobbs et al., 2001;Pinto et al., 2001;Fleishauer et al., 2002;Ansmann et al., 2008;Creamean et al., 2013;Ramelli et al., 2021). It requires multi-layer clouds, between which seeding ice crystals do not sublimate completely. ...
The ice phase impacts many cloud properties as well as cloud lifetime. Ice particles that sediment into a lower cloud from an upper cloud (external seeder–feeder process) or into the mixed-phase region of a deep cloud from cirrus levels (internal seeder–feeder process) can influence the ice phase of the lower cloud, amplify cloud glaciation and enhance surface precipitation. Recently, numerical weather prediction modeling studies have aimed at representing the ice crystal number concentration in mixed-phase clouds more accurately by including secondary ice formation processes. The increase in the ice crystal number concentration can impact the number of ice particles that sediment into the lower cloud and alter its composition and precipitation formation. In the Swiss Alps, the orography permits the formation of orographic clouds, making it ideal for studying the occurrence of multi-layered clouds and the seeder–feeder process. We present results from a case study on 18 May 2016, showing the occurrence frequency of multi-layered clouds and the seeder–feeder process. About half of all observed clouds were categorized as multi-layered, and the external seeder–feeder process occurred in 10 % of these clouds. Between cloud layers, ≈60 % of the ice particle mass was lost due to sublimation or melting. The external seeder–feeder process was found to be more important than the internal seeder–feeder process with regard to the impact on precipitation. In the case where the external seeder–feeder process was inhibited, the average surface precipitation and riming rate over the domain were both reduced by 8.5 % and 3.9 %, respectively. When ice–graupel collisions were allowed, further large reductions were seen in the liquid water fraction and riming rate. Inhibiting the internal seeder–feeder process enhanced the liquid water fraction by 6 % compared to a reduction of 5.8 % in the cloud condensate, therefore pointing towards the de-amplification in cloud glaciation and a reduction in surface precipitation. Adding to the observational evidence of frequent seeder–feeder situations, at least over Switzerland, our study highlights the extensive influence of sedimenting ice particles on the properties of feeder clouds as well as on precipitation formation.
... However, over the dust belt, dust has been found to initiate freezing in midlevel supercooled stratiform clouds at temperatures of −10°C and below (Liu et al., 2008;Zhang et al., 2012). These are warmer temperatures than those reported by Ansmann et al. (2008) who found no evidence of ice formation in supercooled stratiform clouds with cloud-top 355 temperatures above −18°C, but colder temperatures than those found by Sassen et al. (2003), who attributed the glaciation of altocumulus clouds at −5°C to African dust. Although mineral dust can act as INPPBAP are important at low altitudes between 40°S and 90°N with concentrations >10 L -1 at -16 o C. ...
Aerosol-cloud interactions, and particularly ice crystals in mixed-phase clouds (MPC), stand as a key source of uncertainty in climate change assessments. State-of-the-art laboratory-based parameterizations were introduced into a global chemistry-transport model to investigate the contribution of mineral dust, marine primary organic aerosol (MPOA), and terrestrial primary biological aerosol particles (PBAP) to ice nucleating particles (INP) in MPC. INP originating from PBAP (INPPBAP) are found to be the primary source of INP at low altitudes between -10 °C and -20 °C, particularly in the tropics, with a pronounced peak in the Northern Hemisphere (NH) during boreal summer. INPPBAP contributes about 27 % (in the NH) and 30 % (in the SH) of the INP population. Dust-derived INP (INPD) show a prominent presence at high altitudes in all seasons, dominating at temperatures below -25 °C, constituting 68 % of the INP average column burden. MPOA-derived INP (INPMPOA) dominate in the Southern Hemisphere (SH), particularly at subpolar and polar latitudes at low altitudes for temperatures below -16 °C, representing approximately 46 % of INP population in the SH. When evaluated against available global observational INP data, the model achieves its highest predictability across all temperature ranges when both INPD and INPMPOA are included. The additional introduction of INPPBAP slightly reduces model skills for temperatures lower than -16 oC; however, INPPBAP are the main contributors to warm-temperature ice nucleation events. Therefore, consideration of dust and marine and terrestrial bioaerosol as IPN precursors is required to simulate ice nucleation in climate models. In this respect, emissions, ice-nucleating activity of each particle type and its evolution during atmospheric transport require further investigations.
... Therefore, clouds are a key component of the climate system playing an important role in the radiative balance (Ramanathan et al., 1989;DeMott et al., 2010;Huang et al., 2021). Furthermore, since between 60% and 70% of the total precipitation is initiated by cold clouds, these clouds substantially control the exchange of water between oceans and continents, as well as between the planetary surface and the atmosphere (Ansmann et al., 2008;Burrows et al., 2013;Lohmann et al., 2016). ...
... Heterogeneous ice nucleation takes place through four different pathways: deposition ice nucleation, contact freezing, immersion freezing, and condensation freezing (Lohmann et al., 2016;Kanji et al., 2017;Ramachandran, 2018). Immersion freezing is considered to be the most important pathway for MPC and it occurs when an INP is immersed in a liquid droplet and upon cooling below 0 • C, it triggers drop freezing (Ansmann et al., 2008;Lohmann et al., 2016;Tobo, 2016;Kanji et al., 2017). ...
... They, therefore, mark a natural laboratory for studies of heterogeneous glaciation in environments where efficient INPs are present. Polarization lidar measurements can be used to investigate the effect of mineral dust (Ansmann et al., 2005(Ansmann et al., , 2008(Ansmann et al., , 2009(Ansmann et al., , 2019, volcanic ash , or other aerosol particle types (Kanitz et al., 2011;Seifert et al., 2015;Cheng and Yi, 2020;Radenz et al., 2021;Yi et al., 2021) acting as INPs in the heterogeneous glaciation of altocumulus clouds. ...
Mid-level altocumulus clouds (Ac) and high cirrus clouds (Ci) can be considered natural laboratories for studying cloud glaciation in the atmosphere. While their altitude makes them difficult to access with in situ instruments, they can be conveniently observed from the ground with active remote-sensing instruments such as lidar and radar. However, active remote sensing of Ac and Ci at visible wavelengths with lidar requires a clear line of sight between the instrument and the target cloud. It is therefore advisable to carefully assess potential locations for deploying ground-based lidar instruments in field experiments or for long-term observations that are focused on mid- or high-level clouds. Here, observations of clouds with two spaceborne lidars are used to assess where ground-based lidar measurements of mid- and high-level clouds are least affected by the light-attenuating effect of low-level clouds. It is found that cirrus can be best observed in the tropics, the Tibetan Plateau, the western part of North America, the Atacama region, the southern tip of South America, Greenland, Antarctica, and parts of western Europe. For the observation of altocumulus, a ground-based lidar is best placed at Greenland, Antarctica, the western flank of the Andes and Rocky Mountains, the Amazon, central Asia, Siberia, western Australia, or the southern half of Africa.
... 11 I. 5 Summary of aerosols sources and sinks in the atmosphere . . . 12 I. 6 Summary of INP concentrations from field measurements conducted globally . . Table III ven though water represents only a small fraction of the total mass of the atmosphere (about 0.25%, Trenberth et al. 2005), it has tremendous effects on the Earth's climate and biosphere. ...
... Immersion freezing is thought to be the most important ice nucleation pathway in mixed phase clouds (e.g. Ansmann et al. 2008;Boer et al. 2011;Murray et al. 2012), and is also the most studied mode as it is the easiest to reproduce experimentally (see Section I.2.3). In this thesis, immersion freezing is the only mode we will study. ...
... Marine aerosols, or sea spray aerosols (SSA) are generated from the breaking of bubbles at the air-water interface. The process for their formation is shown in Fig A small number of studies have attempted to link the biogeochemical state of the ocean to the properties of marine INPs (Table III. 4 NaCl concentration in the SSA 5 NaCl concentration in the SW (salinity) 6 INP concentration per aerosols in the SSA 7 Particulate organic carbon in the SW 8 Organic carbon in the SSA 9 Water insoluble organic carbon in the SSA Figure As already discussed in Chapter I, the ability of models to predict INP numbers and the development of new empirical parameterizations is one of the key areas of research of INP studies, and marine INPs are no exception to this need, with the added difficulty of taking into account the differences in oceanic regions, particularly with variable biological specificities. McCluskey et al. (2017) noted that finding predictors for marine INPs was of a primary importance. ...
Understanding how aerosol particles interact with atmospheric water is critical to understanding their impact on climate and precipitations. Ice Nuclei Particles (INPs) trigger the formation of atmospheric ice crystals. They are challenging to characterize because of their scarceness in the atmosphere and their variability. This variability depends partly on the different INP sources but also on the temperature at which they are activated. Considerably more variability being observed at warm temperatures (T > -20 °C), where biogenic particles have been identified as a key contributor. This is especially the case in marine regions, where the impact of ocean activity on the atmosphere is still largely unknown. The influence of atmospheric transport and aging on the IN properties of the ambient aerosols is another uncertainty in ice nucleation research. This thesis focused on the measurement and characterization of INPs in mountainous and oceanic regions, at T > -20 °C in the immersion freezing mode. Additional treatment of the samples allowed the retrieval of the concentration of biological INPs.The first half of this thesis focused on characterizing INP populations in the Southern Hemisphere waters sampled during two cruise campaigns: One in tropical waters near the Tonga volcanic arc, and the other in poor oligotrophic waters south of New Zealand. The concentrations of sea spray (SSA) INPs and seawater (SW) INPs measured in both campaigns were lower than in other marine environments, but similar to other studies in the Southern Oceans. The best correlations were observed between INPs and organic matter, bacteria and photosynthetic pigments, highlighting the strong link between biological activity and INP concentrations. Parametrizations for predicting SW and SSA INPs were developed, showing that the transfer from SW INP to SSA INPs can be calculated based on the relationship between SW INPs and a SW organic carbon.In order to understand the effect of atmospheric transport and aging on the IN properties of the aerosols, we measured INP concentrations at a continental site that is influenced by different air masses types. Two consecutive field campaigns took place at the Puy de Dôme station in Central France: the intensive, one-month long PICNIC campaign, and the long term WINS campaign. We measured concentrations between 0.001 and 0.1 INP/Lair, depending on the temperature. We also observed a majority of heat labile, potentially biogenic INPs at T>-12 °C. INP concentrations were at a minimum in winter and at a maximum in autumn and spring. Lower ratios of biogenic INPs were observed in the winter, explained by a decrease in vegetation cover and biogenic aerosols emissions. A parameterization for predicting warm INPs using the total aerosol concentrations as a predictor was successfully developed and tested.In summary, this thesis provides new information of ice nuclei particles properties in various remote sites. We were also able to develop empirical parameterizations for predicting INPs for each of these environments.
... Many recent studies addressing the mixed-phase cloud regime focus on immersion freezing, on the assumption that in mixed-phase clouds, particles that can serve as INPs are initially activated into cloud droplets. This therefore suggests that mixed-phase clouds are primarily affected by the immersion freezing mode, with deposition freezing playing a minor role, and the role of contact freezing still poorly understood (Ansmann et al., 2008;Kanji et al., 2017). As an example, Simpson et al. (2018) Another critical pathway by which INPs impact cloud phase and precipitation is through ice-growth processes, which occur through both vapor deposition and the collection and riming of cloud droplets onto primary ice. ...
Atmospheric ice‐nucleating particles (INPs) play a critical role in cloud freezing processes, with important implications for precipitation formation and cloud radiative properties, and thus for weather and climate. Additionally, INP emissions respond to changes in the Earth System and climate, for example, desertification, agricultural practices, and fires, and therefore may introduce climate feedbacks that are still poorly understood. As knowledge of the nature and origins of INPs has advanced, regional and global weather, climate, and Earth system models have increasingly begun to link cloud ice processes to model‐simulated aerosol abundance and types. While these recent advances are exciting, coupling cloud processes to simulated aerosol also makes cloud physics simulations increasingly susceptible to uncertainties in simulation of INPs, which are still poorly constrained by observations. Advancing the predictability of INP abundance with reasonable spatiotemporal resolution will require an increased focus on research that bridges the measurement and modeling communities. This review summarizes the current state of knowledge and identifies critical knowledge gaps from both observational and modeling perspectives. In particular, we emphasize needs in two key areas: (a) observational closure between aerosol and INP quantities and (b) skillful simulation of INPs within existing weather and climate models. We discuss the state of knowledge on various INP particle types and briefly discuss the challenges faced in understanding the cloud impacts of INPs with present‐day models. Finally, we identify priority research directions for both observations and models to improve understanding of INPs and their interactions with the Earth System.
... Laboratory and field data indicate that mineral dusts often dominate the INP population relevant for mixed-phase clouds below around −15 • C (O' Sullivan et al., 2014;Murray et al., 2012;Ansmann et al., 2008;Niemand et al., 2012;Ullrich et al., 2017). Potassium-rich feldspars (K-feldspars) are considered to be the most important ice-nucleating mineral commonly present in airborne mineral dust (Atkinson et al., 2013;Harrison et al., 2019;Zolles et al., 2015;Augustin-Bauditz et al., 2014;Kaufmann et al., 2016), with immersion mode nucleation observed at temperatures warmer than −5 • C in laboratory experiments (Harrison et al., 2016;Kaufmann et al., 2016;Whale et al., 2017). ...
Ice-nucleating particles (INPs) are atmospheric aerosol particles
that can strongly influence the radiative properties and precipitation onset
in mixed-phase clouds by triggering ice formation in supercooled cloud water
droplets. The ability to distinguish between INPs of mineral and biological
origin in samples collected from the environment is needed to better
understand their distribution and sources. A common method for assessing the
relative contributions of mineral and biogenic INPs in samples collected
from the environment (e.g. aerosol, rainwater, soil) is to determine the
ice-nucleating ability (INA) before and after heating, where heat is
expected to denature proteins associated with some biological ice nucleants.
The key assumption is that the ice nucleation sites of biological origin are
denatured by heat, while those associated with mineral surfaces remain
unaffected; we test this assumption here. We exposed atmospherically
relevant mineral samples to wet heat (INP suspensions warmed to above 90 ∘C) or dry heat (dry samples heated up to 250 ∘C) and
assessed the effects on their immersion mode INA using a droplet freezing
assay. K-feldspar, thought to be the dominant mineral-based atmospheric INP
type where present, was not significantly affected by wet heating, while
quartz, plagioclase feldspars and Arizona Test Dust (ATD) lost INA when
heated in this mode. We argue that these reductions in INA in the aqueous
phase result from direct alteration of the mineral particle surfaces by heat
treatment rather than from biological or organic contamination. We
hypothesise that degradation of active sites by dissolution of mineral
surfaces is the mechanism in all cases due to the correlation between
mineral INA deactivation magnitudes and their dissolution rates. Dry heating
produced minor but repeatable deactivations in K-feldspar particles but was
generally less likely to deactivate minerals compared to wet heating. We
also heat-tested biogenic INP proxy materials and found that cellulose and
pollen washings were relatively resistant to wet heat. In contrast,
bacterially and fungally derived ice-nucleating samples were highly sensitive to
wet heat as expected, although their activity remained non-negligible after
wet heating. Dry heating at 250 ∘C leads to deactivation of all
biogenic INPs. However, the use of dry heat at 250 ∘C for the
detection of biological INPs is limited since K-feldspar's activity is also
reduced under these conditions. Future work should focus on finding a set of
dry heat conditions where all biological material is deactivated, but key
mineral types are not. We conclude that, while wet INP heat tests at (>90 ∘C) have the potential to produce false positives, i.e. deactivation of a mineral INA that could be misconstrued as the presence of biogenic INPs, they are still a valid method for qualitatively detecting very heat-sensitive biogenic INPs in ambient samples
if the mineral-based INA is controlled by K-feldspar.
... These uncertainties are attributed to the larger spatial-temporal variability of aerosol dust and its complex interaction with atmosphere constituents, radiation, and clouds [2]. Besides, dust particles can participate in cloud formation as Cloud Condensation Nuclei (CCNs) and Ice-Nucleating Particles (INPs), and these clouds can redistribute solar radiation [3][4][5][6][7][8]. Furthermore, dust plumes can modify cloud microphysics and may even change precipitation distributions [9,10]. ...
The evolution and the properties of a Saharan dust plume were studied near the city of Karlsruhe in southwest Germany (8.4298°E, 49.0953°N) from 7 to 9 April 2018, combining a scanning LiDAR (90°, 30°), a vertically pointing LiDAR (90°), a sun photometer, and the transport model ICON-ART. Based on this Saharan dust case, we discuss the advantages of a scanning aerosol LiDAR and validate a method to determine LiDAR ratios independently. The LiDAR measurements at 355 nm showed that the dust particles had backscatter coefficients of 0.86 ± 0.14 Mm−1 sr−1, extinction coefficients of 40 ± 0.8 Mm−1, a LiDAR ratio of 46 ± 5 sr, and a linear particle depolarisation ratio of 0.27 ± 0.023. These values are in good agreement with those obtained in previous studies of Saharan dust plumes in Western Europe. Compared to the remote sensing measurements, the transport model predicted the plume arrival time, its layer height, and its structure quite well. The comparison of dust plume backscatter values from the ICON-ART model and observations for two days showed a correlation with a slope of 0.9 ± 0.1 at 355 nm. This work will be useful for future studies to characterise aerosol particles employing scanning LiDARs.
... These cloud-top temperatures for feeder clouds partly overlap with those observed over Cape Verde (15.0°N, 23.5°W) by Ansmann et al. (2009), who identified numerous feeder clouds with cloud-top temperatures of -5℃--20℃. In southern Morocco, Ansmann et al. (2008) observed that liquid clouds with temperatures of -12℃--15℃ produced strong ice virgae due to cloud seeding from another cloud several kilometers above. Fleishauer et al. (2002) even observed that ice particles existed at temperatures of -0.9℃--4.1℃ ...
Natural seeder‐feeder processes play an essential role in the formation and enhancement of precipitation. However, the cloud‐seeding process from mixed‐phase clouds is still not well understood due to the lack of sufficient observations. Natural seeder‐feeder processes from mixed‐phase clouds (seeder clouds) to lower‐lying liquid clouds (feeder clouds) were observed on 19 occasions using ground‐based polarization lidar and radiosonde measurements from June 2018 to June 2020 at a mid‐latitude plain observatory in Wuhan (30.5°N, 114.4°E), China. Ice crystals originating from seeder clouds fell into feeder clouds located 0.2–2.2 km below. During the sedimentation between seeder and feeder clouds, ice crystals partly underwent sublimation when passing through the in‐between dry air layers. The feeder clouds inhibited those ice crystals from complete sublimation and grew them larger by riming or vapor deposition from a favorable liquid water supply. Subsequently, ice crystals were observed afresh falling from feeder clouds, forming ice virgae descending toward the surface. Owing to cloud seeding, feeder clouds with cloud‐top temperatures (CTTs) as warm as −0.2°C to −14.5°C could produce ice virgae, although these CTTs are generally considered somewhat insufficient to initiate primary ice nucleation. The observed optically thin feeder clouds prolonged the survival time/distance of falling ice crystals, indicating that denser feeder clouds may induce enhanced precipitation.
... Complementing radar retrievals with size information from a collocated lidar improves the accuracy of cloud property retrieval further (Delanoë et al., 2013). In previous studies, remote sensing was used 100 to study (primary) ice nucleation in the atmosphere (see e.g., Sakai et al., 2003;Ansmann et al., 2008;Eidhammer et al., 2010;Seifert et al., , 2011Ansmann et al., 2019a;Engelmann et al., 2021) and to estimate SIP (see e.g., Auer et al., 1969;Luke et al., 2021;Sotiropoulou et al., 2021). The identification of a specific SIP process from atmospheric in situ and remote sensing observations is a challenge. ...
Understanding the evolution of the ice phase within mixed-phase clouds (MPCs) is necessary to reduce uncertainties related to the cloud radiative feedback in climate projections and precipitation initiation. Both primary ice formation via ice nucleating particles (INPs) and secondary ice production (SIP) within MPCs are unconstrained, not least because of the lack of atmospheric observations. In the past decades, advanced remote sensing methods have emerged which provide high resolution data of aerosol and cloud properties and could be key in understanding microphysical processes on a global scale. In this study, we retrieved INP concentrations, and ice multiplication factors (IMFs) in wintertime orographic clouds using active remote sensing and in situ observations obtained during the RACLETS campaign in the Swiss Alps. INP concentrations in air masses dominated by Saharan dust and continental aerosol were retrieved from a polarization Raman lidar and validated with aerosol and INP in situ observations on a mountaintop. A calibration factor of 0.0204 for the global INP parameterization by DeMott et al. (2010) is derived by comparing in situ aerosol and INP measurements improving the INP concentration retrieval for continental aerosols. Based on combined lidar and radar measurements, the ice crystal number concentration and ice water content were retrieved and validated with balloon-borne in situ observations, which agreed with the balloon-borne in situ observations within an order of magnitude. For seven cloud cases the ice multiplication factors (IMFs), defined as the quotient of the ice crystal number concentration to the INP concentration, were calculated. The median IMF was around 80 and SIP was active (defined as IMFs > 1) nearly 85 % of the time. SIP was found to be active at all observed temperatures (−30 °C to −5 °C) with highest IMFs between −20 °C and −5 °C. The introduced methodology could be extended to larger datasets to better understand the impact of SIP not only over the Alps but also at other locations and for other cloud types.
