A comprehensive estimate of the global cooling effect from hindering homogeneous ice nucleation under cirrus conditions with CAM5

2020 ◽  
Author(s):  
Jiaojiao Liu ◽  
Xiangjun Shi
Keyword(s):  
Climate Modeling ◽  
Ice Nucleation ◽  
Fixed Number ◽  
Cirrus Clouds ◽  
Ice Crystals ◽  
Cooling Effect ◽  
Minimum Concentration ◽  
Community Atmosphere Model ◽  
Global Cooling ◽  
Cooling Effects

<p>The warming effect of cirrus clouds is well-known. In recent years, in order to mitigate global warming, cirrus cloud thinning as a newly emerging method of geoengineering has been studied based on climate modeling. Adding a few (~10 L<sup>–1</sup>) INPs (ice nucleating particles including ice crystals) might hinder homogeneous ice nucleation, which can produce a large number of ice crystals (~1000 L<sup>–1</sup>), and then reduce cirrus clouds. On the other hand, the cirrus clouds might increase if too much INPs were added. Therefore, the effectiveness of cirrus seeding on cooling our earth is still in debate. In this study, we developed a method (optimal seeding scheme) to calculate the minimum concentration of seeding INPs, which is just enough to prevent homogeneous nucleation from happening. Simulation with the Community Atmosphere Model version 5(CAM5) using the optimal seeding scheme shows a significant cooling effect (–1.4 W/m<sup>2</sup>), which is equal to two-thirds of the cooling potential (–2.1 W/m<sup>2</sup>) derived from the pure heterogeneous simulation (i.e., homogeneous ice nucleation is artificially switched off). Seeding fixed 20 L<sup>-1</sup> and 200 L<sup>-1</sup> concentrations of INPs show the global average radiative effect at –0.5 W m<sup>-2</sup> (cooling) and 0.1 W m<sup>-2</sup> (warming), respectively. The cooling effect of seeding fixed number concentration of INPs is not obvious, which is consistent with previous studies. Furthermore, using the optimal seeding scheme, the sensitivities of cooling effects to seeding area, ice nucleation parameterizations and homogeneous ice nucleation occurrence frequency are also investigated.</p>

scholarly journals Estimating the potential cooling effect of cirrus thinning achieved via the seeding approach

2021 ◽  
Vol 21 (13) ◽  
pp. 10609-10624
Author(s):  
Jiaojiao Liu ◽  
Xiangjun Shi
Keyword(s):  
Ice Nucleation ◽  
Cooling Effect ◽  
Low Latitude ◽  
Sensitivity Experiment ◽  
Ice Nuclei ◽  
Community Atmosphere Model ◽  
Seeding Method ◽  
Global Cooling ◽  
Solar Noon ◽  
Mixed Phase Clouds

Abstract. Cirrus thinning is a newly emerging geoengineering approach to mitigate global warming. To sufficiently exploit the potential cooling effect of cirrus thinning with the seeding approach, a flexible seeding method is used to calculate the optimal seeding number concentration, which is just enough to prevent homogeneous ice nucleation from occurring. A simulation using the Community Atmosphere Model version 5 (CAM5) with the flexible seeding method shows a global cooling effect of -1.36±0.18 W m−2, which is approximately two-thirds of that from artificially turning off homogeneous nucleation (-1.98±0.26 W m−2). However, simulations with fixed seeding ice nuclei particle number concentrations of 20 and 200 L−1 show a weak cooling effect of -0.27±0.26 W m−2 and warming effect of 0.35±0.28 W m−2, respectively. Further analysis shows that cirrus seeding leads to a significant warming effect of liquid and mixed-phase clouds, which counteracts the cooling effect of cirrus clouds. This counteraction is more prominent at low latitudes and leads to a pronounced net warming effect over some low-latitude regions. The sensitivity experiment shows that cirrus seeding carried out at latitudes with solar noon zenith angles greater than 12∘ could yield a stronger global cooling effect of −2.00 ± 0.25 W m−2. Overall, the potential cooling effect of cirrus thinning is considerable, and the flexible seeding method is essential.

scholarly journals Estimating the potential cooling effect of cirrus thinning achieved via the seeding approach

2021 ◽  
Author(s):  
Jiaojiao Liu ◽  
Xiangjun Shi
Keyword(s):  
Ice Nucleation ◽  
Cooling Effect ◽  
Low Latitude ◽  
Sensitivity Experiment ◽  
Ice Nuclei ◽  
Community Atmosphere Model ◽  
Seeding Method ◽  
Global Cooling ◽  
Solar Noon ◽  
Mixed Phase Clouds

Abstract. Cirrus thinning is a newly emerging geoengineering approach to mitigate global warming. To sufficiently exploit the potential cooling effect of cirrus thinning with the seeding approach, a flexible seeding method is used to calculate the optimal seeding number concentration, which is just enough to prevent homogeneous ice nucleation from occurring. A simulation using the Community Atmosphere Model version 5 (CAM5) with the flexible seeding method shows a global cooling effect of 1.36 ± 0.18 W m−2, which is approximately two-thirds of that from artificially turning off homogeneous nucleation (−1.98 ± 0.26 W m−2). However, simulations with fixed seeding ice nuclei particle number concentrations of 20 and 200 L−1 show a weak cooling effect of −0.27 ± 0.26 W m−2 and warming effect of 0.35 ± 0.28 W m−2, respectively. Further analysis shows that cirrus seeding leads to a significant warming effect of liquid and mixed-phase clouds, which counteracts the cooling effect of cirrus clouds. This counteraction is more prominent at low latitudes and leads to a pronounced net warm effect over some low latitude regions. The sensitivity experiment shows that cirrus seeding carried out at latitudes with solar noon zenith angles greater than 12° could yields a stronger global cooling effect of −2.00 ± 0.25 W m−2. Overall, the potential cooling effect of cirrus thinning is considerable, and the flexible seeding method is essential.

scholarly journals Effects of pre-existing ice crystals on cirrus clouds and comparison between different ice nucleation parameterizations with the Community Atmosphere Model (CAM5)

2015 ◽  
Vol 15 (3) ◽  
pp. 1503-1520 ◽  
Author(s):  
X. Shi ◽  
X. Liu ◽  
K. Zhang
Keyword(s):  
Ice Nucleation ◽  
Number Concentration ◽  
Cirrus Clouds ◽  
Ice Crystals ◽  
Cirrus Cloud ◽  
Ice Crystal ◽  
Anthropogenic Aerosol ◽  
Community Atmosphere Model ◽  
Atmosphere Model ◽  
Heterogeneous Ice Nucleation

Abstract. In order to improve the treatment of ice nucleation in a more realistic manner in the Community Atmosphere Model version 5.3 (CAM5.3), the effects of pre-existing ice crystals on ice nucleation in cirrus clouds are considered. In addition, by considering the in-cloud variability in ice saturation ratio, homogeneous nucleation takes place spatially only in a portion of the cirrus cloud rather than in the whole area of the cirrus cloud. Compared to observations, the ice number concentrations and the probability distributions of ice number concentration are both improved with the updated treatment. The pre-existing ice crystals significantly reduce ice number concentrations in cirrus clouds, especially at mid- to high latitudes in the upper troposphere (by a factor of ~10). Furthermore, the contribution of heterogeneous ice nucleation to cirrus ice crystal number increases considerably. Besides the default ice nucleation parameterization of Liu and Penner (2005, hereafter LP) in CAM5.3, two other ice nucleation parameterizations of Barahona and Nenes (2009, hereafter BN) and Kärcher et al. (2006, hereafter KL) are implemented in CAM5.3 for the comparison. In-cloud ice crystal number concentration, percentage contribution from heterogeneous ice nucleation to total ice crystal number, and pre-existing ice effects simulated by the three ice nucleation parameterizations have similar patterns in the simulations with present-day aerosol emissions. However, the change (present-day minus pre-industrial times) in global annual mean column ice number concentration from the KL parameterization (3.24 × 106 m−2) is less than that from the LP (8.46 × 106 m−2) and BN (5.62 × 106 m−2) parameterizations. As a result, the experiment using the KL parameterization predicts a much smaller anthropogenic aerosol long-wave indirect forcing (0.24 W m−2) than that using the LP (0.46 W m−2) and BN (0.39 W m−2) parameterizations.

scholarly journals Implementation of a comprehensive ice crystal formation parameterization for cirrus and mixed-phase clouds in the EMAC model (based on MESSy 2.53)

2018 ◽  
Vol 11 (10) ◽  
pp. 4021-4041 ◽  
Author(s):  
Sara Bacer ◽  
Sylvia C. Sullivan ◽  
Vlassis A. Karydis ◽  
Donifan Barahona ◽  
Martina Krämer ◽  
...  
Keyword(s):  
Climate Model ◽  
Ice Nucleation ◽  
Cirrus Clouds ◽  
Mixed Phase ◽  
Ice Crystals ◽  
Dust Particles ◽  
Crystal Formation ◽  
Ice Crystal ◽  
Upper Troposphere ◽  
Mixed Phase Clouds

Abstract. A comprehensive ice nucleation parameterization has been implemented in the global chemistry-climate model EMAC to improve the representation of ice crystal number concentrations (ICNCs). The parameterization of Barahona and Nenes (2009, hereafter BN09) allows for the treatment of ice nucleation taking into account the competition for water vapour between homogeneous and heterogeneous nucleation in cirrus clouds. Furthermore, the influence of chemically heterogeneous, polydisperse aerosols is considered by applying one of the multiple ice nucleating particle parameterizations which are included in BN09 to compute the heterogeneously formed ice crystals. BN09 has been modified in order to consider the pre-existing ice crystal effect and implemented to operate both in the cirrus and in the mixed-phase regimes. Compared to the standard EMAC parameterizations, BN09 produces fewer ice crystals in the upper troposphere but higher ICNCs in the middle troposphere, especially in the Northern Hemisphere where ice nucleating mineral dust particles are relatively abundant. Overall, ICNCs agree well with the observations, especially in cold cirrus clouds (at temperatures below 205 K), although they are underestimated between 200 and 220 K. As BN09 takes into account processes which were previously neglected by the standard version of the model, it is recommended for future EMAC simulations.

Combining cirrus cloud CALIPSO (IIR-CALIOP) and aircraft measurements with climate modeling to evaluate the spatial and seasonal radiative impact of homogeneous ice nucleation

2021 ◽  
Author(s):  
David L. Mitchell ◽  
John F. Mejia ◽  
Anne Garnier ◽  
Yuta Tomii ◽  
Martina Krämer ◽  
...  
Keyword(s):  
Experimental Design ◽  
Climate Modeling ◽  
Cloud Microphysics ◽  
Ice Nucleation ◽  
Cirrus Clouds ◽  
Radiative Properties ◽  
Cirrus Cloud ◽  
Modeling Studies ◽  
Northern And Southern Hemispheres

<p>Many global climate modeling studies over the last decade have attempted to evaluate the relative contributions of homo- and heterogeneous ice nucleation (henceforth hom and het) in cirrus clouds, and the radiative contribution of hom relative to het.  There is likely a spatial and seasonal dependence here.  Since the microphysical and radiative properties of hom- and het-dominated cirrus clouds are likely very different, the outcome of such studies may be important to climate science.  But since the physics determining the competition between hom and het is very complex, involving poorly constrained variables, results from such modeling studies have often contradicted each other.</p><p> </p><p>This study takes a different approach by using CALIPSO satellite effective diameter (D<sub>e</sub>) retrievals from cirrus clouds, validated by recent in situ measurements (obtained from 24 field campaigns consisting of 150 flights), to constrain the cloud microphysics module (i.e., version 2 of the Morrison-Gettelman scheme or MG2) in the Whole Atmosphere Community Climate Model version 6 (WACCM6). [As a side-note, the ice particle number concentration N was calculated from the retrieved D<sub>e</sub> and the in situ climatological ice water content and shown to be consistent with N retrievals based on a CloudSat-CALIPSO lidar-radar method]. The MG2 cirrus cloud ice particle size distribution was constrained to conform with these D<sub>e</sub> retrievals that depend on temperature (T), latitude, season and land fraction (land vs. ocean).  The treatment of ice particle fall speeds was also revised.  Two 40-year WACCM6 simulations were differenced to obtain the radiative contribution of hom; one based on the retrieved D<sub>e</sub> and one based on retrieved D<sub>e</sub> corresponding to het conditions (where retrieved N was minimal).  The experimental design assumes hom-affected cirrus occur only outside the ± 30 °latitude zone since cirrus within this zone exhibited the lowest N and were thus used to produce the D<sub>e</sub> – T look-up tables corresponding to het conditions.  These D<sub>e</sub> – T relationships for het conditions were applied to the entire planet in one simulation (labeled HET) while the other simulation (labeled CALCAL for CALIPSO-calibrated) is based on the actual D<sub>e</sub> retrievals.  CALCAL – HET differences in the cloud radiative effect (CRE) reveal the estimated CRE effect due to hom.</p><p> </p><p>The results show CALCAL – HET CRE differences of 2.4 and 2.5 W m<sup>-2</sup> in the northern and southern hemispheres, respectively.  These CRE differences are largely due to cirrus-induced changes in mixed phase clouds.  However, top-of-model (TOM) CALCAL – HET differences in total net forcing did not match these CRE differences due to mid-level increases in relative humidity in HET relative to CALCAL, so that these TOM differences were 1.8 and 2.0 W m<sup>-2</sup> in the northern and southern hemispheres, respectively.  Radiative contributions from hom were minimal during the summer months (JJA) since shortwave and longwave cloud forcing tends to cancel then.  Other studies show this is true for the tropics (reinforcing the realism of our experimental design from a radiation purview).  During non-summer months, the TOM CALCAL – HET difference in total net forcing was 2.4 W m<sup>-2</sup> in both hemispheres.</p><p> </p>

scholarly journals Cirrus Clouds

2017 ◽  
Vol 58 ◽  
pp. 2.1-2.26 ◽  
Author(s):  
Andrew J. Heymsfield ◽  
Martina Krämer ◽  
Anna Luebke ◽  
Phil Brown ◽  
Daniel J. Cziczo ◽  
...  
Keyword(s):  
General Circulation ◽  
General Circulation Models ◽  
Ice Nucleation ◽  
In Situ Measurements ◽  
Cirrus Clouds ◽  
Ice Crystals ◽  
Radiative Properties ◽  
Formation Mechanisms ◽  
Wide Range

Abstract The goal of this chapter is to synthesize information about what is now known about one of the three main types of clouds, cirrus, and to identify areas where more knowledge is needed. Cirrus clouds, composed of ice particles, form in the upper troposphere, where temperatures are generally below −30°C. Satellite observations show that the maximum-occurrence frequency of cirrus is near the tropics, with a large latitudinal movement seasonally. In situ measurements obtained over a wide range of cirrus types, formation mechanisms, temperatures, and geographical locations indicate that the ice water content and particle size generally decrease with decreasing temperature, whereas the ice particle concentration is nearly constant or increases slightly with decreasing temperature. High ice concentrations, sometimes observed in strong updrafts, result from homogeneous nucleation. The satellite-based and in situ measurements indicate that cirrus ice crystals typically differ from the simple, idealized geometry for smooth hexagonal shapes, indicating complexity and/or surface roughness. Their shapes significantly impact cirrus radiative properties and feedbacks to climate. Cirrus clouds, one of the most uncertain components of general circulation models (GCM), pose one of the greatest challenges in predicting the rate and geographical pattern of climate change. Improved measurements of the properties and size distributions and surface structure of small ice crystals (about 20 μm) and identifying the dominant ice nucleation process (heterogeneous versus homogeneous ice nucleation) under different cloud dynamical forcings will lead to a better representation of their properties in GCM and in modeling their current and future effects on climate.

scholarly journals Effects of preexisting ice crystals on cirrus clouds and comparison between different ice nucleation parameterizations with the Community Atmosphere Model (CAM5)

2014 ◽  
Vol 14 (12) ◽  
pp. 17635-17679 ◽  
Author(s):  
X. Shi ◽  
X. Liu ◽  
K. Zhang
Keyword(s):  
Probability Distributions ◽  
Atmospheric Model ◽  
Ice Nucleation ◽  
Number Concentration ◽  
Cirrus Clouds ◽  
Ice Crystals ◽  
Cirrus Cloud ◽  
Ice Crystal ◽  
Anthropogenic Aerosol ◽  
Heterogeneous Ice Nucleation

Abstract. In order to improve the treatment of ice nucleation in a more realistic manner in the Community Atmospheric Model version 5.3 (CAM5.3), the effects of preexisting ice crystals on ice nucleation in cirrus clouds are considered. In addition, by considering the in-cloud variability in ice saturation ratio, homogeneous nucleation takes place spatially only in a portion of cirrus cloud rather than in the whole area of cirrus cloud. With these improvements, the two unphysical limiters used in the representation of ice nucleation are removed. Compared to observations, the ice number concentrations and the probability distributions of ice number concentration are both improved with the updated treatment. The preexisting ice crystals significantly reduce ice number concentrations in cirrus clouds, especially at mid- to high latitudes in the upper troposphere (by a factor of ~10). Furthermore, the contribution of heterogeneous ice nucleation to cirrus ice crystal number increases considerably. Besides the default ice nucleation parameterization of Liu and Penner (2005, hereafter LP) in CAM5.3, two other ice nucleation parameterizations of Barahona and Nenes (2009, hereafter BN) and Kärcher et al. (2006, hereafter KL) are implemented in CAM5.3 for the comparison. In-cloud ice crystal number concentration, percentage contribution from heterogeneous ice nucleation to total ice crystal number, and preexisting ice effects simulated by the three ice nucleation parameterizations have similar patterns in the simulations with present-day aerosol emissions. However, the change (present-day minus pre-industrial times) in global annual mean column ice number concentration from the KL parameterization (3.24 × 106 m−2) is obviously less than that from the LP (8.46 × 106 m−2) and BN (5.62 × 106 m−2) parameterizations. As a result, experiment using the KL parameterization predicts a much smaller anthropogenic aerosol longwave indirect forcing (0.24 W m−2) than that using the LP (0.46 W m−2) and BN (0.39 W m−2) parameterizations.

scholarly journals Aerosol effects on ice clouds: can the traditional concept of aerosol indirect effects be applied to aerosol-cloud interactions in cirrus clouds?

2010 ◽  
Vol 10 (21) ◽  
pp. 10345-10358 ◽  
Author(s):  
S. S. Lee ◽  
J. E. Penner
Keyword(s):  
Radiative Forcing ◽  
Critical Role ◽  
Cloud Microphysics ◽  
Cirrus Clouds ◽  
Ice Crystals ◽  
Radiation Budget ◽  
Traditional Concept ◽  
Substantial Impact ◽  
Double Moment ◽  
Aerosol Cloud Interactions

Abstract. Cirrus clouds cover approximately 20–25% of the globe and thus play an important role in the Earth's radiation budget. Therefore the effect of aerosols on cirrus clouds can have a substantial impact on global radiative forcing if either the ice-water path (IWP) and/or the cloud ice number concentration (CINC) changes. This study examines the aerosol indirect effect (AIE) through changes in the CINC and IWP for a cirrus cloud case. We use a cloud-system resolving model (CSRM) coupled with a double-moment representation of cloud microphysics. Intensified interactions among CINC, deposition and dynamics play a critical role in increasing the IWP as aerosols increase. Increased IWP leads to a smaller change in the outgoing LW radiation relative to that for the SW radiation for increasing aerosols. Increased aerosols lead to increased CINC, providing increased surface area for water vapor deposition. The increased deposition causes depositional heating which produces stronger updrafts, and leads to the increased IWP. The conversion of ice crystals to aggregates through autoconversion and accretion plays a negligible role in the IWP response to aerosols, and the sedimentation of aggregates is negligible. The sedimentation of ice crystals plays a more important role in the IWP response to aerosol increases than the sedimentation of aggregates, but not more than the interactions among the CINC, deposition and dynamics.

scholarly journals Simulating the influence of primary biological aerosol particles on clouds by heterogeneous ice nucleation

2018 ◽  
Vol 18 (20) ◽  
pp. 15437-15450 ◽  
Author(s):  
Matthias Hummel ◽  
Corinna Hoose ◽  
Bernhard Pummer ◽  
Caroline Schaupp ◽  
Janine Fröhlich-Nowoisky ◽  
...  
Keyword(s):  
Pseudomonas Syringae ◽  
Aerosol Particles ◽  
Fungal Spores ◽  
Ice Nucleation ◽  
Ice Crystals ◽  
Atmospheric Measurements ◽  
Cloud Ice ◽  
Biological Aerosol Particles ◽  
Ice Phase ◽  
Heterogeneous Ice Nucleation

Abstract. Primary ice formation, which is an important process for mixed-phase clouds with an impact on their lifetime, radiative balance, and hence the climate, strongly depends on the availability of ice-nucleating particles (INPs). Supercooled droplets within these clouds remain liquid until an INP immersed in or colliding with the droplet reaches its activation temperature. Only a few aerosol particles are acting as INPs and the freezing efficiency varies among them. Thus, the fraction of supercooled water in the cloud depends on the specific properties and concentrations of the INPs. Primary biological aerosol particles (PBAPs) have been identified as very efficient INPs at high subzero temperatures, but their very low atmospheric concentrations make it difficult to quantify their impact on clouds. Here we use the regional atmospheric model COSMO–ART to simulate the heterogeneous ice nucleation by PBAPs during a 1-week case study on a domain covering Europe. We focus on three highly ice-nucleation-active PBAP species, Pseudomonas syringae bacteria cells and spores from the fungi Cladosporium sp. and Mortierella alpina. PBAP emissions are parameterized in order to represent the entirety of bacteria and fungal spores in the atmosphere. Thus, only parts of the simulated PBAPs are assumed to act as INPs. The ice nucleation parameterizations are specific for the three selected species and are based on a deterministic approach. The PBAP concentrations simulated in this study are within the range of previously reported results from other modeling studies and atmospheric measurements. Two regimes of PBAP INP concentrations are identified: a temperature-limited and a PBAP-limited regime, which occur at temperatures above and below a maximal concentration at around −10 ∘C, respectively. In an ensemble of control and disturbed simulations, the change in the average ice crystal concentration by biological INPs is not statistically significant, suggesting that PBAPs have no significant influence on the average state of the cloud ice phase. However, if the cloud top temperature is below −15 ∘C, PBAP can influence the cloud ice phase and produce ice crystals in the absence of other INPs. Nevertheless, the number of produced ice crystals is very low and it has no influence on the modeled number of cloud droplets and hence the cloud structure.

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