Is increasing ice crystal sedimentation velocity in geoengineering simulations a good proxy for cirrus cloud seeding?

Gasparini, Blaž; Münch, Steffen; Poncet, Laure; Feldmann, Monika; Lohmann, Ulrike

doi:10.5194/acp-2016-1109

Cited by 4 publications

(17 citation statements)

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“…Also, cautions should be taken in interpreting results from CCT simulations via increasing the falling speed of ice particles. It is found that to increase the falling speed of cirrus ice crystals might not be a good proxy for cirrus cloud seeding since an increase in ice particle falling speed cannot explicitly represent the competition between homogeneous and heterogeneous ice particle nucleation [ Gasparini et al ., ]. Furthermore, in our simulations additional sulfate aerosols are prescribed in the upper stratosphere.…”

Section: Discussionmentioning

confidence: 98%

Simultaneous stabilization of global temperature and precipitation through cocktail geoengineering

Cao

Duan

Bala

et al. 2017

Geophysical Research Letters

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Solar geoengineering has been proposed as a backup plan to offset some aspects of anthropogenic climate change if timely CO2 emission reductions fail to materialize. Modeling studies have shown that there are trade‐offs between changes in temperature and hydrological cycle in response to solar geoengineering. Here we investigate the possibility of stabilizing both global mean temperature and precipitation simultaneously by combining two geoengineering approaches: stratospheric sulfate aerosol increase (SAI) that deflects sunlight to space and cirrus cloud thinning (CCT) that enables more longwave radiation to escape to space. Using the slab ocean configuration of National Center for Atmospheric Research Community Earth System Model, we simulate SAI by uniformly adding sulfate aerosol in the upper stratosphere and CCT by uniformly increasing cirrus cloud ice particle falling speed. Under an idealized warming scenario of abrupt quadrupling of atmospheric CO2, we show that by combining appropriate amounts of SAI and CCT geoengineering, global mean (or land mean) temperature and precipitation can be restored simultaneously to preindustrial levels. However, compared to SAI, cocktail geoengineering by mixing SAI and CCT does not markedly improve the overall similarity between geoengineered climate and preindustrial climate on regional scales. Some optimal spatially nonuniform mixture of SAI with CCT might have the potential to better mitigate climate change at both the global and regional scales.

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Section: Discussionmentioning

confidence: 98%

Simultaneous stabilization of global temperature and precipitation through cocktail geoengineering

Cao

Duan

Bala

et al. 2017

Geophysical Research Letters

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“…Furthermore, it should be nontoxic and affordable. Several studies assumed seeding scenarios with such a perfect substance (e.g., Gasparini et al, ; Storelvmo et al, ), hence disregarding methods of deployment but rather assuming that the aerosol particles were in place in necessary concentrations. Suitable agents could be Bismuth tri‐iodide (BiI 3 ; Mitchell & Finnegan, ) and mineral dust (Lohmann & Gasparini, ).…”

Section: Influence Of Seedingmentioning

confidence: 99%

“…Another type of studies used a prescribed increased sedimentation velocity of ice crystals as proxy for seeding (Crook et al, ; Jackson et al, ; Muri et al, ). This approach can reproduce surface climate responses to seeding but is unable to capture the changes in cloud microphysical processes that occur when considering seeding aerosol in a cirrus formation parameterization (Gasparini et al, ). Applying the latter approach, a large fraction of the seeding effect is outweighed by a reduction in liquid clouds in response to increased convective activity.…”

Section: Introductionmentioning

confidence: 99%

“…The effects of seeding aerosol with nucleating properties like mineral dust injected in various scenarios into the atmosphere are explored. Furthermore, due to the high resolution, the impact of cirrus seeding on lower‐lying mixed‐phase clouds can be investigated, as the effect of seeding here has been proposed to outweigh much of the desired outcome (Gasparini et al, ).…”

Section: Introductionmentioning

confidence: 99%

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A Process Study on Thinning of Arctic Winter Cirrus Clouds With High‐Resolution ICON‐ART Simulations

et al. 2019

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In this study, cloud‐resolving simulations of a case study for a limited area of the hibernal Arctic were performed with the atmospheric modeling system ICON‐ART (ICOsahedral Nonhydrostatic‐Aerosol and Reactive Trace gases). A thorough comparison with data both from satellite as well as aircraft measurement is presented to validate the simulations. In addition, the model is applied to clarify the microphysical processes occurring when introducing artificial aerosol particles into the upper troposphere with the aim of modifying cirrus clouds in the framework of climate engineering. Former modeling studies investigating the climate effect of this method were performed with simplifying assumptions and much coarser resolution, reaching partly contradicting conclusions concerning the method's effectiveness. The primary effect of seeding is found to be a reduction of ice crystal number concentrations in cirrus clouds, leading to increased outgoing longwave radiative fluxes at the top of the atmosphere, thereby creating a cooling effect. Furthermore, a secondary effect is found, as ice crystals formed from the injected seeding aerosol particles lead to enhanced riming of cloud droplets within the planetary boundary layer. This effectively reduces the coverage of mixed‐phase clouds, thus generating additional cooling by increased upward longwave radiative fluxes at the surface. The efficacy of seeding cirrus clouds proves to be relatively independent from the atmospheric background conditions, scales with the number concentrations of seeding particles, and is highest for large aerosol particles.

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“…After the initial ascent (14:32-14:34 UTC), the cloud top slopes from over 10 km down to under 9 km at the northern edge, corresponding to a vertical velocity of about −30 cm s −1 . Sedimentation may contribute to this, but sub-10 µm particles are rather associated with fall speeds of under 2 cm s −1 (Gasparini et al, 2016, their Fig. 1).…”

Section: Classifying Evolution Stagesmentioning

confidence: 99%

Determining stages of cirrus evolution: a cloud classification scheme

et al. 2017

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Abstract. Cirrus clouds impose high uncertainties on climate prediction, as knowledge on important processes is still incomplete. For instance it remains unclear how cloud microphysical and radiative properties change as the cirrus evolves. Recent studies classify cirrus clouds into categories including in situ, orographic, convective and liquid origin clouds and investigate their specific impact. Following this line, we present a novel scheme for the classification of cirrus clouds that addresses the need to determine specific stages of cirrus evolution. Our classification scheme is based on airborne Differential Absorption and High Spectral Resolution Lidar measurements of atmospheric water vapor, aerosol depolarization, and backscatter, together with model temperature fields and simplified parameterizations of freezing onset conditions. It identifies regions of supersaturation with respect to ice (ice-supersaturated regions, ISSRs), heterogeneous and homogeneous nucleation, depositional growth, and ice sublimation and sedimentation with high spatial resolution. Thus, all relevant stages of cirrus evolution can be classified and characterized. In a case study of a gravity leewave-influenced cirrus cloud, encountered during the ML-CIRRUS flight campaign, the applicability of our classification is demonstrated. Revealing the structure of cirrus clouds, this valuable tool might help to examine the influence of evolution stages on the cloud's net radiative effect and to investigate the specific variability of optical and microphysical cloud properties in upcoming research.

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Is increasing ice crystal sedimentation velocity in geoengineering simulations a good proxy for cirrus cloud seeding?

Cited by 4 publications

References 0 publications

Simultaneous stabilization of global temperature and precipitation through cocktail geoengineering

Simultaneous stabilization of global temperature and precipitation through cocktail geoengineering

A Process Study on Thinning of Arctic Winter Cirrus Clouds With High‐Resolution ICON‐ART Simulations

Determining stages of cirrus evolution: a cloud classification scheme

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