scholarly journals Impact of H<sub>2</sub>SO<sub>4</sub>/H<sub>2</sub>O coating and ice crystal size on radiative properties of sub-visible cirrus

2006 ◽  
Vol 6 (3) ◽  
pp. 5231-5250
Author(s):  
P. Räisänen ◽  
A. Bogdan ◽  
K. Sassen ◽  
M. Kulmala ◽  
M. J. Molina
Keyword(s):  
Cirrus Clouds ◽  
Radiative Properties ◽  
Ice Crystal ◽  
Radiative Effects ◽  
Ice Particles ◽  
Large Numbers ◽  
Tropopause Region ◽  
Cloud Radiative Effects ◽  
Ice Crystal Size ◽  
The Impact

Abstract. Recent laboratory experiments showed that at conditions resembling those near the tropopause region, small quasi-spherical ice particles can be coated by a liquid H2SO4/H2O over-layer formed after the freezing of diluted sulfuric acid/water aerosol drops. Here, idealized radiative transfer tests are conducted to evaluate the impact that such an over-layer would have on the radiative effects produced by sub-visible cirrus clouds (SVCs). The calculations show that the over-layer increases both the shortwave (SW) and longwave (LW) cloud radiative effects (CRE), but the impact is small: ~0.02 W m-2, or even less, for the total (LW+SW) CRE at the top of the atmosphere. For the smallest ice particles, for which the over-layer is thickest, the fractional change in CRE can, however, reach ~20% for the SW CRE and over 50% for the LW CRE. The dependence of LW and SW CRE on particle size is also considered in the paper. Calculations for spherical uncoated ice particles show that even for high, optically thin cirrus clouds, the total CRE can be negative, if the diameter of the particles is smaller than about 3–4 µm. Apart from the SVCs, this result could be relevant for contrail cirrus clouds, which are believed to consist of large numbers of very small ice particles.

scholarly journals Impact of H<sub>2</sub>SO<sub>4</sub>/H<sub>2</sub>O coating and ice crystal size on radiative properties of sub-visible cirrus

2006 ◽  
Vol 6 (12) ◽  
pp. 4659-4667 ◽  
Author(s):  
P. Räisänen ◽  
A. Bogdan ◽  
K. Sassen ◽  
M. Kulmala ◽  
M. J. Molina
Keyword(s):  
Cirrus Clouds ◽  
Radiative Properties ◽  
Ice Crystal ◽  
Radiative Effects ◽  
Ice Particles ◽  
Large Numbers ◽  
Tropopause Region ◽  
Cloud Radiative Effects ◽  
Ice Crystal Size ◽  
The Impact

Abstract. Recent laboratory experiments showed that at conditions resembling those near the tropopause region, small ice particles can be coated by a liquid H2SO4/H2O over-layer formed after the freezing of diluted sulfuric acid/water aerosol drops. Here, idealized radiative transfer tests are conducted to evaluate the impact that such an over-layer would have on the radiative effects produced by sub-visible cirrus clouds (SVCs). Spherical particle shape is assumed to keep the problem tractable. The calculations show that the over-layer increases both the shortwave (SW) and longwave (LW) cloud radiative effects (CRE), but the impact is small: ~0.02 W m−2, or even less, for the total (LW+SW) CRE at the top of the atmosphere. For the smallest ice particles, for which the over-layer is thickest, the fractional change in CRE can, however, reach ~20% for the SW CRE and over 50% for the LW CRE. The dependence of LW and SW CRE on particle size is also studied in the paper. Calculations for spherical and spheroidal uncoated ice particles show that even for high, optically thin cirrus, the total CRE can be negative, if the diameter of the particles is smaller than about 3–4 μm. Apart from the SVCs, this result could be relevant for contrail cirrus clouds, which are believed to consist of large numbers of very small ice particles.

scholarly journals Thin and subvisible cirrus and contrails in a subsaturated environment

2011 ◽  
Vol 11 (12) ◽  
pp. 5853-5865 ◽  
Author(s):  
M. Kübbeler ◽  
M. Hildebrandt ◽  
J. Meyer ◽  
C. Schiller ◽  
Th. Hamburger ◽  
...  
Keyword(s):  
Crystal Size ◽  
Life Time ◽  
Cirrus Clouds ◽  
Ice Crystals ◽  
Radiative Properties ◽  
Ice Crystal ◽  
Size Spectra ◽  
Ice Clouds ◽  
Frontal Systems ◽  
Ice Crystal Size

Abstract. The frequency of occurrence of cirrus clouds and contrails, their life time, ice crystal size spectra and thus their radiative properties depend strongly on the ambient distribution of the relative humidity with respect to ice (RHice). Ice clouds do not form below a certain supersaturation and both cirrus and contrails need at least saturation conditions to persist over a longer period. Under subsaturated conditions, cirrus and contrails should dissipate. During the mid-latitude aircraft experiment CONCERT 2008 (CONtrail and Cirrus ExpeRimenT), RHice and ice crystals were measured in cirrus and contrails. Here, we present results from 2.3/1.7 h of observation in cirrus/contrails during 6 flights. Thin and subvisible cirrus with contrails embedded therein have been detected frequently in a subsaturated environment. Nevertheless, ice crystals up to radii of 50 μm and larger, but with low number densities were often observed inside the contrails as well as in the cirrus. Analysis of the meteorological situation indicates that the crystals in the contrails were entrained from the thin/subvisible cirrus clouds, which emerged in frontal systems with low updrafts. From model simulations of cirrus evaporation times it follows that such thin/subvisible cirrus can exist for time periods of a couple of hours and longer in a subsaturated environment and thus may represent a considerable part of the cirrus coverage.

scholarly journals Thin and subvisible cirrus and contrails in a subsaturated environment

2010 ◽  
Vol 10 (12) ◽  
pp. 31153-31186 ◽  
Author(s):  
M. Kübbeler ◽  
M. Hildebrandt ◽  
J. Meyer ◽  
C. Schiller ◽  
T. Hamburger ◽  
...  
Keyword(s):  
Crystal Size ◽  
Life Time ◽  
Cirrus Clouds ◽  
Ice Crystals ◽  
Radiative Properties ◽  
Ice Crystal ◽  
Size Spectra ◽  
Ice Clouds ◽  
Frontal Systems ◽  
Ice Crystal Size

Abstract. The frequency of occurrence of cirrus clouds and contrails, their life time, ice crystal size spectra and thus their radiative properties depend strongly on the ambient distribution of the relative humidity with respect to ice (RHice). Ice clouds do not form below a certain supersaturation and both cirrus and contrails need at least saturation conditions to persist over a longer period. Under subsaturated conditions, cirrus and contrails should dissipate. During the mid-latitude aircraft experiment CONCERT 2008 (CONtrail and Cirrus ExpeRimenT), RHice and ice crystals were measured in cirrus and contrails. Here, we present results from 2.3/1.7 h of observation in cirrus/contrails during 6 flights. Thin and subvisible cirrus with contrails embedded therein have been detected frequently in a subsaturated environment. Nevertheless, ice crystals up to radii of 50 μm and larger, but with low number densities were often observed inside the contrails as well as in the cirrus. Analysis of the meteorological situation indicates that the crystals in the contrails were entrained from the thin/subvisible cirrus clouds, which emerged in frontal systems with low updrafts. From model simulations of cirrus evaporation times it follows that such thin/subvisible cirrus can exist for time periods of a couple of hours and longer in a subsaturated environment and thus may represent a considerable part of the cirrus coverage.

scholarly journals On the Occurrence of Hollow Bullet Rosette– and Column-Shaped Ice Crystals in Midlatitude Cirrus

2007 ◽  
Vol 64 (12) ◽  
pp. 4514-4519 ◽  
Author(s):  
C. G. Schmitt ◽  
A. J. Heymsfield
Keyword(s):  
Cirrus Clouds ◽  
Ice Crystals ◽  
Radiative Properties ◽  
Cirrus Cloud ◽  
Ice Crystal ◽  
Particle Size Distributions ◽  
Polyvinyl Formal ◽  
Ice Particles ◽  
Cloud Ice ◽  
Parameter Values

Abstract Cirrus clouds in mid- and high latitudes are frequently composed of bullet rosette– and column-shaped ice crystals, which can have hollow ends. Bullet rosette–shaped ice crystals are composed of a number of bullets radiating from a central point. Research has shown that the light-scattering properties of ice particles with hollow ends are different from the scattering properties of solid ice particles. Knowledge of the frequency of occurrence of hollow particles is important to more accurately calculate the radiative properties of cirrus clouds. This note presents the results of a survey of cirrus cloud ice crystal replicas imaged from balloon-borne Formvar (polyvinyl formal) replicators. Fifty percent to 80% of the replicated bullet rosette– and column-shaped particles had hollow ends. In bullets longer than 150 μm in length, the length of the hollows of the bullets averaged 88% of the total length of the bullet. The combined length of both hollow portions of column-shaped ice crystals varied from 50% of the length of the column for 30-μm-long columns to 80% of the length of the columns longer than 200 μm. Asymmetry parameter values estimated from cirrus cloud aircraft particle size distributions are higher by 0.014 when hollow crystals are considered. This difference leads to a 2.5 W m−2 increase for hollow crystals at the surface for a 0.5 optical depth cloud, demonstrating the importance of the incorporation of hollow particle scattering characteristics into radiative transfer calculations.

scholarly journals The origin of midlatitude ice clouds and the resulting influence on their microphysical properties

2015 ◽  
Vol 15 (23) ◽  
pp. 34243-34281 ◽  
Author(s):  
A. E. Luebke ◽  
A. Afchine ◽  
A. Costa ◽  
J. Meyer ◽  
C. Rolf ◽  
...  
Keyword(s):  
Bimodal Distribution ◽  
Cirrus Clouds ◽  
Ice Crystals ◽  
Radiative Properties ◽  
Ice Crystal ◽  
Ice Clouds ◽  
Microphysical Properties ◽  
Ice Crystal Size ◽  
Ice Water

Abstract. The radiative role of ice clouds in the atmosphere is known to be important, but uncertainties remain concerning the magnitude and net effects. However, through measurements of the microphysical properties of cirrus clouds, we can better characterize them, which can ultimately allow for their radiative properties to be more accurately ascertained. It has recently been proposed that there are two types of cirrus clouds – in situ and liquid origin. In this study, we present observational evidence to show that two distinct types of cirrus do exist. Airborne, in situ measurements of cloud ice water content (IWC), ice crystal concentration (Nice), and ice crystal size from the 2014 ML-CIRRUS campaign provide cloud samples that have been divided according to their origin type. The key features that set liquid origin cirrus apart from the in situ origin cirrus are a higher frequency of high IWC (> 100 ppmv), higher Nice values, and larger ice crystals. A vertical distribution of Nice shows that the in situ origin cirrus clouds exhibit a median value of around 0.1 cm−3, while the liquid origin concentrations are slightly, but notably higher. The median sizes of the crystals contributing the most mass are less than 200 μm for in situ origin cirrus, with some of the largest crystals reaching 550 μm in size. The liquid origin cirrus, on the other hand, were observed to have median diameters greater than 200 μm, and crystals that were up to 750 μm. An examination of these characteristics in relation to each other and their relationship to temperature provides strong evidence that these differences arise from the dynamics and conditions in which the ice crystals formed. Additionally, the existence of these two groups in cirrus cloud populations may explain why a bimodal distribution in the IWC-temperature relationship has been observed. We hypothesize that the low IWC mode is the result of in situ origin cirrus and the high IWC mode is the result of liquid origin cirrus.

scholarly journals The origin of midlatitude ice clouds and the resulting influence on their microphysical properties

2016 ◽  
Vol 16 (9) ◽  
pp. 5793-5809 ◽  
Author(s):  
Anna E. Luebke ◽  
Armin Afchine ◽  
Anja Costa ◽  
Jens-Uwe Grooß ◽  
Jessica Meyer ◽  
...  
Keyword(s):  
Bimodal Distribution ◽  
Cirrus Clouds ◽  
Ice Crystals ◽  
Radiative Properties ◽  
Ice Crystal ◽  
Ice Clouds ◽  
Microphysical Properties ◽  
Ice Crystal Size ◽  
Ice Water

Abstract. The radiative role of ice clouds in the atmosphere is known to be important, but uncertainties remain concerning the magnitude and net effects. However, through measurements of the microphysical properties of cirrus clouds, we can better characterize them, which can ultimately allow for their radiative properties to be more accurately ascertained. Recently, two types of cirrus clouds differing by formation mechanism and microphysical properties have been classified – in situ and liquid origin cirrus. In this study, we present observational evidence to show that two distinct types of cirrus do exist. Airborne, in situ measurements of cloud ice water content (IWC), ice crystal concentration (Nice), and ice crystal size from the 2014 ML-CIRRUS campaign provide cloud samples that have been divided according to their origin type. The key features that set liquid origin cirrus apart from the in situ origin cirrus are higher frequencies of high IWC ( > 100 ppmv), higher Nice values, and larger ice crystals. A vertical distribution of Nice shows that the in situ origin cirrus clouds exhibit a median value of around 0.1 cm−3, while the liquid origin concentrations are slightly, but notably higher. The median sizes of the crystals contributing the most mass are less than 200 µm for in situ origin cirrus, with some of the largest crystals reaching 550 µm in size. The liquid origin cirrus, on the other hand, were observed to have median diameters greater than 200 µm, and crystals that were up to 750 µm. An examination of these characteristics in relation to each other and their relationship to temperature provides strong evidence that these differences arise from the dynamics and conditions in which the ice crystals formed. Additionally, the existence of these two groups in cirrus cloud populations may explain why a bimodal distribution in the IWC-temperature relationship has been observed. We hypothesize that the low IWC mode is the result of in situ origin cirrus and the high IWC mode is the result of liquid origin cirrus.

Cirrus: The Future

Cirrus ◽  
2002 ◽  
Author(s):  
David K. Lynch ◽  
Kenneth Sassen
Keyword(s):  
Global Scale ◽  
Cirrus Clouds ◽  
Radiative Properties ◽  
Ice Crystal ◽  
Policy Makers ◽  
Temperature Changes ◽  
Remote Sensing Techniques ◽  
Ice Water ◽  
The Impact

The preceding 20 chapters reveal cirrus in considerable depth. Just as important, however, is what is not revealed. There are many things that we do not know or understand about cirrus. In this final chapter we present the outstanding scientific issues facing the cirrus research community. Our goal here is to produce a guide for students, scientists, policy makers, and funding organizations who wish to quickly grasp the direction and future needs of cirrus research. The impact of cirrus clouds on climate and how they interact with a climate perturbed by human enterprise is only dimly perceived. Do cirrus clouds, on a regional or global scale, act to cool or warm our planet? By reflecting incoming solar radiation to space, they can cool. Yet as an opacity source in the 10-μm window, they can radiate downward and warm the Earth. Which process dominates, and under what conditions does warming overtake cooling? Does the atmosphere react to cirrus globally or regionally (i.e., can cirrus increase pole-equator temperature differences or mute them)? Are there other mechanisms at work that defeat or amplify temperature changes by cirrus? We do not yet know. Programs such as SUCCESS, ICE, CRYSTAL, INCA, and FIRE/SHEBA will do much to answer questions about contrails and cirrus variability from one part of the world to another. They also will go a long way toward understanding one of the most difficult problems in meteorology: how convection and turbulence are related to cirrus formation and maintenance. In the meantime, existing capabilities are underused. For example, remote sensing techniques for estimating ice water path now exist but have not been assigned enough priority to achieve the necessary breakthroughs. Considerable progress could also be made in data analysis. As in other fields, analyzing existing data has a lower funding priority than designing and building new hardware and flight systems. Three fields of inquiry need more attention before we can claim a sufficient understanding of cirrus: physical properties, radiative properties, and modeling. These fields are interconnected in often subtle ways. Much of what we do not know about cirrus involves the range of properties and their evolution in time.

scholarly journals Monte Carlo-based subgrid parameterization of vertical velocity and stratiform cloud microphysics in ECHAM5.5-HAM2

2013 ◽  
Vol 13 (2) ◽  
pp. 5477-5507
Author(s):  
J. Tonttila ◽  
P. Räisänen ◽  
H. Järvinen
Keyword(s):  
Monte Carlo ◽  
Vertical Velocity ◽  
Cloud Droplet ◽  
Cloud Microphysics ◽  
Radiative Effects ◽  
Cloud Droplets ◽  
Microphysical Properties ◽  
Cloud Radiative Effects ◽  
Cloud Activation ◽  
The Impact

Abstract. A new method for parameterizing the subgrid variations of vertical velocity and cloud droplet number concentration (CDNC) is presented for GCMs. These parameterizations build on top of existing parameterizations that create stochastic subgrid cloud columns inside the GCM grid-cells, which can be employed by the Monte Carlo independent column approximation approach for radiative transfer. The new model version adds a description for vertical velocity in individual subgrid columns, which can be used to compute cloud activation and the subgrid distribution of the number of cloud droplets explicitly. This provides a consistent way for simulating the cloud radiative effects with two-moment cloud microphysical properties defined in subgrid-scale. The primary impact of the new parameterizations is to decrease the CDNC over polluted continents, while over the oceans the impact is smaller. This promotes changes in the global distribution of the cloud radiative effects and might thus have implications on model estimation of the indirect radiative effect of aerosols.

scholarly journals The efficacy of aerosol–cloud radiative perturbations from near-surface emissions in deep open-cell stratocumuli

2018 ◽  
Vol 18 (23) ◽  
pp. 17475-17488 ◽  
Author(s):  
Anna Possner ◽  
Hailong Wang ◽  
Robert Wood ◽  
Ken Caldeira ◽  
Thomas P. Ackerman
Keyword(s):  
Emission Line ◽  
Radiative Properties ◽  
Radiative Effect ◽  
Radiative Effects ◽  
Near Surface ◽  
Open Cell ◽  
Detection And Attribution ◽  
Cloud Radiative Effects ◽  
Ship Tracks ◽  
Cloud Radiative Properties

Abstract. Aerosol–cloud radiative effects are determined and quantified in simulations of deep open-cell stratocumuli observed during the VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) campaign off the west coast of Chile. The cloud deck forms in a boundary layer 1.5 km deep, with cell sizes reaching 50 km in diameter. Global databases of ship tracks suggest that these linear structures are seldom found in boundary layers this deep. Here, we quantify the changes in cloud radiative properties to a continuous aerosol point source moving along a fixed emission line releasing 1017 particles per second. We show that a spatially coherent cloud perturbation is not evident along the emission line. Yet our model simulates an increase in domain-mean all-sky albedo of 0.05, corresponding to a diurnally averaged cloud radiative effect of 20 W m−2, given the annual mean solar insolation at the VOCALS-REx site. Therefore, marked changes in cloud radiative properties in precipitating deep open cells may be driven by anthropogenic near-surface aerosol perturbations, such as those generated by ships. Furthermore, we demonstrate that these changes in cloud radiative properties are masked by the naturally occurring variability within the organised cloud field. A clear detection and attribution of cloud radiative effects to a perturbation in aerosol concentrations becomes possible when sub-filtering of the cloud field is applied, using the spatio-temporal distribution of the aerosol perturbation. Therefore, this work has implications for the detection and attribution of effective cloud radiative forcing in marine stratocumuli, which constitutes one of the major physical uncertainties within the climate system. Our results suggest that ships may sometimes have a substantial radiative effect on marine clouds and albedo, even when ship tracks are not readily visible.

Subtropical clouds stabilize near-Snowball Earth states

2020 ◽  
Author(s):  
Christoph Braun ◽  
Aiko Voigt ◽  
Johannes Hörner ◽  
Joaquim G. Pinto
Keyword(s):  
Sea Ice ◽  
General Circulation ◽  
General Circulation Models ◽  
Snowball Earth ◽  
Radiative Effects ◽  
Albedo Feedback ◽  
The Earth ◽  
Cloud Radiative Effects ◽  
Planetary Albedo ◽  
The Impact

&lt;p&gt;Atmospheric general circulation models developed for the Earth system include comprehensive parameterizations of clouds. Applying them to exoplanet atmospheres provides an opportunity to advance understanding of clouds, atmosphere dynamics, and their coupling in the context of planetary climate dynamics and habitability.&lt;/p&gt;&lt;p&gt;Here, we study a deep-time extreme climate of Earth as an example of the cold limit of the habitable zone. Geological evidence indicates near-global ice cover during the Neoproterozoic (1000 &amp;#8211; 541 Million years ago) associated with considerable hysteresis of atmospheric CO&lt;sub&gt;2&lt;/sub&gt;. The Snowball Earth hypothesis provides a straightforward interpretation of Neoproterozoic proxies based on a runaway of the sea-ice albedo feedback. However, the Snowball Earth hypothesis relies on the existence of local habitats to explain the survival of photosynthetic marine species on an entirely ice-covered planet. The Jormungand hypothesis may resolve this issue by considering a weakening of the sea-ice albedo feedback by exposure of dark bare sea ice when sea ice enters the subtropics. This potentially allows the Earth system to stabilize in a climate state - the Jormungand state - with near-global ice cover. Around the equator, a narrow strip of ocean remains ice-free, where life would have easily survived during the pan-glaciations.&lt;/p&gt;&lt;p&gt;The weakening of the sea-ice albedo feedback is based on the change of the meridional structure of planetary albedo with a moving sea-ice edge. While previous work focused on the contribution of surface albedo to planetary albedo, we here focus on the impact of subtropical and tropical cloudiness on planetary albedo. Enhanced cloudiness generally weakens the sea-ice albedo feedback and thus decreases the climate sensitivity of the Jormungand state, i.e. it stabilizes the Jormungand state. We analyze the impact of cloudiness on the stability of the Jormungand state in the general circulation models CAM3 and ICON-AES with idealized aquaplanet setups. While CAM3 shows significant CO&lt;sub&gt;2&lt;/sub&gt;-hysteresis of the Jormungand state, ICON-AES exhibits no stable Jormungand state. Consistently, CAM3 exhibits stronger cloudiness than ICON-AES, especially in the subtropics. An analysis with a one-dimensional energy balance model shows that the Jormungand hysteresis strongly depends on the sensitivity of the planetary albedo to an advance of sea ice into the subtropics. Accordingly, we demonstrate that the absence of cloud-radiative effects within vertical columns in the subtropics drastically decreases the Jormungand hysteresis in CAM3.&lt;/p&gt;&lt;p&gt;Overall, the magnitude of the Jormungand hysteresis is tightly linked to the representation of cloud-radiative effects in general circulation models. Our results highlight the important role of uncertainties associated with cloud-radiative effects for climate feedbacks on planet Earth in the context of extreme climates, such as they have occurred in Earth&amp;#8217;s deep past or might be found on Earth-like planets. In consequence, this also stresses the need and challenges of accounting for adequate cloud modeling for planetary climates.&lt;/p&gt;

Sign in / Sign up

Export Citation Format

Share Document