Cirrus Clouds

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.

Download Full-text

Freezing thresholds and cirrus cloud formation mechanisms inferred from in situ measurements of relative humidity

Atmospheric Chemistry and Physics ◽

10.5194/acp-3-1791-2003 ◽

2003 ◽

Vol 3 (5) ◽

pp. 1791-1806 ◽

Cited By ~ 108

Author(s):

W. Haag ◽

B. Kärcher ◽

J. Ström ◽

A. Minikin ◽

U. Lohmann ◽

...

Keyword(s):

Relative Humidity ◽

Large Scale ◽

Climate Model ◽

Global Climate Model ◽

In Situ Measurements ◽

Cirrus Clouds ◽

Formation Mechanisms ◽

Cirrus Cloud ◽

Homogeneous Freezing

Abstract. Factors controlling the microphysical link between distributions of relative humidity above ice saturation in the upper troposphere and lowermost stratosphere and cirrus clouds are examined with the help of microphysical trajectory simulations. Our findings are related to results from aircraft measurements and global model studies. We suggest that the relative humidities at which ice crystals form in the atmosphere can be inferred from in situ measurements of water vapor and temperature close to, but outside of, cirrus clouds. The comparison with concomitant measurements performed inside cirrus clouds provides a clue to freezing mechanisms active in cirrus. The analysis of field data taken at northern and southern midlatitudes in fall 2000 reveals distinct differences in cirrus cloud freezing thresholds. Homogeneous freezing is found to be the most likely mechanism by which cirrus form at southern hemisphere midlatitudes. The results provide evidence for the existence of heterogeneous freezing in cirrus in parts of the polluted northern hemisphere, but do not suggest that cirrus clouds in this region form exclusively on heterogeneous ice nuclei, thereby emphasizing the crucial importance of homogeneous freezing. The key features of distributions of upper tropospheric relative humidity simulated by a global climate model are shown to be in general agreement with both, microphysical simulations and field observations, delineating a feasible method to include and validate ice supersaturation in other large-scale atmospheric models, in particular chemistry-transport and weather forecast models.

Download Full-text

Improving our fundamental understanding of the role of aerosol−cloud interactions in the climate system

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1514043113 ◽

2016 ◽

Vol 113 (21) ◽

pp. 5781-5790 ◽

Cited By ~ 199

Author(s):

John H. Seinfeld ◽

Christopher Bretherton ◽

Kenneth S. Carslaw ◽

Hugh Coe ◽

Paul J. DeMott ◽

...

Keyword(s):

Remote Sensing ◽

Radiative Forcing ◽

General Circulation ◽

Climate Models ◽

Large Range ◽

General Circulation Models ◽

Radiative Properties ◽

Aerosol Cloud ◽

Aerosol Cloud Interactions

The effect of an increase in atmospheric aerosol concentrations on the distribution and radiative properties of Earth’s clouds is the most uncertain component of the overall global radiative forcing from preindustrial time. General circulation models (GCMs) are the tool for predicting future climate, but the treatment of aerosols, clouds, and aerosol−cloud radiative effects carries large uncertainties that directly affect GCM predictions, such as climate sensitivity. Predictions are hampered by the large range of scales of interaction between various components that need to be captured. Observation systems (remote sensing, in situ) are increasingly being used to constrain predictions, but significant challenges exist, to some extent because of the large range of scales and the fact that the various measuring systems tend to address different scales. Fine-scale models represent clouds, aerosols, and aerosol−cloud interactions with high fidelity but do not include interactions with the larger scale and are therefore limited from a climatic point of view. We suggest strategies for improving estimates of aerosol−cloud relationships in climate models, for new remote sensing and in situ measurements, and for quantifying and reducing model uncertainty.

Download Full-text

A microphysics guide to cirrus clouds – Part 1: Cirrus types

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-31537-2015 ◽

2015 ◽

Vol 15 (21) ◽

pp. 31537-31586 ◽

Cited By ~ 3

Author(s):

M. Krämer ◽

C. Rolf ◽

A. Luebke ◽

A. Afchine ◽

N. Spelten ◽

...

Keyword(s):

Parameter Space ◽

Field Measurements ◽

Cirrus Clouds ◽

Radiative Properties ◽

Formation Mechanisms ◽

Liquid Droplets ◽

Atmospheric Conditions ◽

Model Simulations ◽

Microphysical Properties

Abstract. The microphysical and radiative properties of cirrus clouds continue to be beyond understanding and thus still represent one of the largest uncertainties in the prediction of the Earth's climate (IPCC, 2013). Our study aims to provide a guide to cirrus microphysics, which is compiled from an extensive set of model simulations, covering the broad range of atmospheric conditions for cirrus formation and evolution. The model results are portrayed in the same parameter space as field measurements, i.e. in the Ice Water Content-Temperature (IWC-T) parameter space. We validate this cirrus analysis approach by evaluating cirrus data sets from seventeen aircraft campaigns, conducted in the last fifteen years, spending about 94 h in cirrus over Europe, Australia, Brazil as well as Southern and Northern America. Altogether, the approach of this study is to track cirrus IWC development with temperature by means of model simulations, compare with observations and then assign, to a certain degree, cirrus microphysics to the observations. Indeed, the field observations show characteristics expected from the simulated cirrus guide. For example, high/low IWCs are found together with high/low ice crystal concentrations Nice. An important finding from our study is the classification of two types of cirrus with differing formation mechanisms and microphysical properties: the first cirrus type is rather thin with lower IWCs and forms directly as ice (in-situ origin cirrus). The second type consists predominantly of thick cirrus originating from mixed phase clouds (i.e. via freezing of liquid droplets – liquid origin cirrus), which are completely glaciated while lifting to the cirrus formation temperature region (< 235 K). In the European field campaigns, in-situ origin cirrus occur frequently at slow updrafts in low and high pressure systems, but also in conjunction with faster updrafts. Also, liquid origin cirrus mostly related to warm conveyor belts are found. In the US and tropical campaigns, thick liquid origin cirrus which are formed in large convective systems are detected more frequently.

Download Full-text

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

10.5194/egusphere-egu21-285 ◽

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

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.&#160; There is likely a spatial and seasonal dependence here.&#160; 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.&#160; 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.&#160;This study takes a different approach by using CALIPSO satellite effective diameter (De) 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 De 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 De retrievals that depend on temperature (T), latitude, season and land fraction (land vs. ocean).&#160; The treatment of ice particle fall speeds was also revised.&#160; Two 40-year WACCM6 simulations were differenced to obtain the radiative contribution of hom; one based on the retrieved De and one based on retrieved De corresponding to het conditions (where retrieved N was minimal).&#160; The experimental design assumes hom-affected cirrus occur only outside the &#177; 30 &#176;latitude zone since cirrus within this zone exhibited the lowest N and were thus used to produce the De &#8211; T look-up tables corresponding to het conditions.&#160; These De &#8211; 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 De retrievals.&#160; CALCAL &#8211; HET differences in the cloud radiative effect (CRE) reveal the estimated CRE effect due to hom.&#160;The results show CALCAL &#8211; HET CRE differences of 2.4 and 2.5 W m-2 in the northern and southern hemispheres, respectively.&#160; These CRE differences are largely due to cirrus-induced changes in mixed phase clouds.&#160; However, top-of-model (TOM) CALCAL &#8211; 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-2 in the northern and southern hemispheres, respectively.&#160; Radiative contributions from hom were minimal during the summer months (JJA) since shortwave and longwave cloud forcing tends to cancel then.&#160; Other studies show this is true for the tropics (reinforcing the realism of our experimental design from a radiation purview).&#160; During non-summer months, the TOM CALCAL &#8211; HET difference in total net forcing was 2.4 W m-2 in both hemispheres.&#160;

Download Full-text

A Deep Learning Network to Retrieve Ocean Hydrographic Profiles from Combined Satellite and In Situ Measurements

Remote Sensing ◽

10.3390/rs12193151 ◽

2020 ◽

Vol 12 (19) ◽

pp. 3151

Author(s):

Bruno Buongiorno Nardelli

Keyword(s):

Deep Learning ◽

General Circulation ◽

Short Term Memory ◽

Learning Algorithm ◽

General Circulation Models ◽

Remotely Sensed ◽

In Situ Measurements ◽

Ocean Dynamics ◽

Vertical Profiles

An efficient combination of remotely-sensed data and in situ measurements is needed to obtain accurate 3D ocean state estimates, representing a fundamental step to describe ocean dynamics and its role in the Earth climate system and marine ecosystems. Observations can either be assimilated in ocean general circulation models or used to feed data-driven reconstructions and diagnostic models. Here we describe an innovative deep learning algorithm that projects sea surface satellite data at depth after training with sparse co-located in situ vertical profiles. The technique is based on a stacked Long Short-Term Memory neural network, coupled to a Monte-Carlo dropout approach, and is applied here to the measurements collected between 2010 and 2018 over the North Atlantic Ocean. The model provides hydrographic vertical profiles and associated uncertainties from corresponding remotely sensed surface estimates, outperforming similar reconstructions from simpler statistical algorithms and feed-forward networks.

Download Full-text

A microphysics guide to cirrus clouds – Part 1: Cirrus types

Atmospheric Chemistry and Physics ◽

10.5194/acp-16-3463-2016 ◽

2016 ◽

Vol 16 (5) ◽

pp. 3463-3483 ◽

Cited By ~ 78

Author(s):

Martina Krämer ◽

Christian Rolf ◽

Anna Luebke ◽

Armin Afchine ◽

Nicole Spelten ◽

...

Keyword(s):

Parameter Space ◽

Field Measurements ◽

Cirrus Clouds ◽

Radiative Properties ◽

Formation Mechanisms ◽

Atmospheric Conditions ◽

Jet Streams ◽

Model Simulations ◽

Microphysical Properties

Abstract. The microphysical and radiative properties of cirrus clouds continue to be beyond understanding and thus still represent one of the largest uncertainties in the prediction of the Earth's climate (IPCC, 2013). Our study aims to provide a guide to cirrus microphysics, which is compiled from an extensive set of model simulations, covering the broad range of atmospheric conditions for cirrus formation and evolution. The model results are portrayed in the same parameter space as field measurements, i.e., in the Ice Water Content-Temperature (IWC-T) parameter space. We validate this cirrus analysis approach by evaluating cirrus data sets from 17 aircraft campaigns, conducted in the last 15 years, spending about 94 h in cirrus over Europe, Australia, Brazil as well as South and North America. Altogether, the approach of this study is to track cirrus IWC development with temperature by means of model simulations, compare with observations and then assign, to a certain degree, cirrus microphysics to the observations. Indeed, the field observations show characteristics expected from the simulated Cirrus Guide. For example, high (low) IWCs are found together with high (low) ice crystal concentrations Nice. An important finding from our study is the classification of two types of cirrus with differing formation mechanisms and microphysical properties: the first cirrus type forms directly as ice (in situ origin cirrus) and splits in two subclasses, depending on the prevailing strength of the updraft: in slow updrafts these cirrus are rather thin with lower IWCs, while in fast updrafts thicker cirrus with higher IWCs can form. The second type consists predominantly of thick cirrus originating from mixed phase clouds (i.e., via freezing of liquid droplets – liquid origin cirrus), which are completely glaciated while lifting to the cirrus formation temperature region (< 235 K). In the European field campaigns, slow updraft in situ origin cirrus occur frequently in low- and high-pressure systems, while fast updraft in situ cirrus appear in conjunction with jet streams or gravity waves. Also, liquid origin cirrus mostly related to warm conveyor belts are found. In the US and tropical campaigns, thick liquid origin cirrus which are formed in large convective systems are detected more frequently.

Download Full-text

Freezing thresholds and cirrus cloud formation mechanisms inferred from in situ measurements of relative humidity

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-3-3267-2003 ◽

2003 ◽

Vol 3 (3) ◽

pp. 3267-3299 ◽

Cited By ~ 4

Author(s):

W. Haag ◽

B. Kärcher ◽

J. Ström ◽

A. Minikin ◽

U. Lohmann ◽

...

Keyword(s):

Relative Humidity ◽

Large Scale ◽

Climate Model ◽

Global Climate Model ◽

In Situ Measurements ◽

Cirrus Clouds ◽

Cloud Formation ◽

Formation Mechanisms ◽

Cirrus Cloud

Abstract. Factors controlling the distribution of relative humidity above ice saturation in the upper troposphere and lower stratosphere in the presence of cirrus clouds are examined with the help of microphysical trajectory simulations using a box model. Our findings are related to results from recent field campaigns and global model studies. We suggest that the relative humidities at which ice crystals form in the atmosphere can be inferred from in situ measurements of water vapor and temperature close to, but outside of, cirrus clouds. The comparison with similar measurements performed inside cirrus clouds provides a clue to freezing mechanisms active in cirrus. The comparison with field data reveals distinct interhemispheric differences in cirrus cloud freezing thresholds. Combining the present findings with recent results addressing the frequency distributions of updraft speeds and cirrus ice crystal number densities (Kärcher and Ström, 2993} provides evidence for the existence of complex heterogeneous freezing mechanisms in cirrus, at least in the polluted northern hemisphere, and further emphasizes the key role of gravity wave-induced dynamical variability in vertical air motion at the mesoscale. The key features of distributions of upper tropospheric relative humidity simulated by a global climate model are shown to be in general agreement with both, microphysical simulations and field observations, delineating a feasible method to include and validate ice supersaturation in other large-scale models of the atmosphere, in particular chemistry-transport and weather forecast models.

Download Full-text

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

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-34243-2015 ◽

2015 ◽

Vol 15 (23) ◽

pp. 34243-34281 ◽

Cited By ~ 2

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.

Download Full-text

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

Atmospheric Chemistry and Physics ◽

10.5194/acp-16-5793-2016 ◽

2016 ◽

Vol 16 (9) ◽

pp. 5793-5809 ◽

Cited By ~ 41

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.

Download Full-text

Cirrus Cloud Properties as Seen by the CALIPSO Satellite and ECHAM-HAM Global Climate Model

Journal of Climate ◽

10.1175/jcli-d-16-0608.1 ◽

2018 ◽

Vol 31 (5) ◽

pp. 1983-2003 ◽

Cited By ~ 13

Author(s):

B. Gasparini ◽

A. Meyer ◽

D. Neubauer ◽

S. Münch ◽

U. Lohmann

Keyword(s):

Water Content ◽

Cirrus Clouds ◽

Ice Crystals ◽

Water Vapor Transport ◽

Formation Mechanisms ◽

Ice Crystal ◽

Extinction Coefficients ◽

Ice Water Content ◽

Ice Water

Cirrus clouds impact the planetary energy balance and upper-tropospheric water vapor transport and are therefore relevant for climate. In this study cirrus clouds at temperatures colder than −40°C simulated by the ECHAM–Hamburg Aerosol Module (ECHAM-HAM) general circulation model are compared to Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations ( CALIPSO) satellite data. The model captures the general cloud cover pattern and reproduces the observed median ice water content within a factor of 2, while extinction is overestimated by about a factor of 3 as revealed by temperature-dependent frequency histograms. Two distinct types of cirrus clouds are found: in situ–formed cirrus dominating at temperatures colder than −55°C and liquid-origin cirrus dominating at temperatures warmer than −55°C. The latter cirrus form in anvils of deep convective clouds or by glaciation of mixed-phase clouds, leading to high ice crystal number concentrations. They are associated with extinction coefficients and ice water content of up to 1 km−1 and 0.1 g m−3, respectively, while the in situ–formed cirrus are associated with smaller extinction coefficients and ice water content. In situ–formed cirrus are nucleated either heterogeneously or homogeneously. The simulated homogeneous ice crystals are similar to liquid-origin cirrus, which are associated with high ice crystal number concentrations. On the contrary, heterogeneously nucleated ice crystals appear in smaller number concentrations. However, ice crystal aggregation and depositional growth smooth the differences between several formation mechanisms, making the attribution to a specific ice nucleation mechanism challenging.

Download Full-text