scholarly journals Dual Lidar Observations at 10.6 μm and 532 nm for Retrieving Semitransparent Cirrus Cloud Properties

2006 ◽  
Vol 45 (4) ◽  
pp. 537-555 ◽  
Author(s):  
M. Chiriaco ◽  
H. Chepfer ◽  
V. Noel ◽  
M. Haeffelin ◽  
P. Drobinski
Keyword(s):  
Absorption Efficiency ◽  
Cloud Base ◽  
Ice Clouds ◽  
Ice Cloud ◽  
Cloud Properties ◽  
Combining Data ◽  
Remote Sensing Techniques ◽  
Infrared Radiances ◽  
Lidar Observations ◽  
532 Nm

Abstract To improve the estimation of the infrared radiances in cirrus clouds, one needs to consider the vertical inhomogeneities of the cloud properties. The position of the maximum of absorption within an ice cloud is potentially important to the improvement of the split-window techniques for retrieving particle size and for understanding the radiative effect of the cloud in the infrared spectrum. Current remote sensing techniques used for inferring ice clouds hardly reach the level of accuracy required to resolve the vertical inhomogeneities of a cloud and to determine the position of absorption. This study explores the possibility of retrieving the vertical structures of ice clouds by combining data from two lidar measurements acquired at the wavelengths of 532 nm and 10.6 μm. A method is proposed to retrieve the variability of ice crystal absorption efficiency at 10.6 μm, the particle concentration weighted by the crystal area, and the attenuation by absorption at 10.6 μm. The method is tested against observations collected at Site Instrumental de Recherche en Télédétection Atmosphérique (SIRTA) in Palaiseau, France. Observations and simulations both show that lidar observations collected simultaneously at those two wavelengths can be used to determine the level within the ice cloud where maximum attenuation of infrared radiation occurs. The maximum attenuation may occur near the cloud base or the cloud top, depending on the case studied.

scholarly journals The variability of tropical ice cloud properties as a function of the large-scale context from ground-based radar-lidar observations over Darwin, Australia

2011 ◽  
Vol 11 (16) ◽  
pp. 8363-8384 ◽  
Author(s):  
A. Protat ◽  
J. Delanoë ◽  
P. T. May ◽  
J. Haynes ◽  
C. Jakob ◽  
...  
Keyword(s):  
Large Scale ◽  
Effective Radius ◽  
Ice Clouds ◽  
Ice Cloud ◽  
Microphysical Properties ◽  
Cloud Properties ◽  
Ice Water Content ◽  
Mean Differences ◽  
Ice Water ◽  
Lidar Observations

Abstract. The high complexity of cloud parameterizations now held in models puts more pressure on observational studies to provide useful means to evaluate them. One approach to the problem put forth in the modelling community is to evaluate under what atmospheric conditions the parameterizations fail to simulate the cloud properties and under what conditions they do a good job. It is the ambition of this paper to characterize the variability of the statistical properties of tropical ice clouds in different tropical "regimes" recently identified in the literature to aid the development of better process-oriented parameterizations in models. For this purpose, the statistical properties of non-precipitating tropical ice clouds over Darwin, Australia are characterized using ground-based radar-lidar observations from the Atmospheric Radiation Measurement (ARM) Program. The ice cloud properties analysed are the frequency of ice cloud occurrence, the morphological properties (cloud top height and thickness), and the microphysical and radiative properties (ice water content, visible extinction, effective radius, and total concentration). The variability of these tropical ice cloud properties is then studied as a function of the large-scale cloud regimes derived from the International Satellite Cloud Climatology Project (ISCCP), the amplitude and phase of the Madden-Julian Oscillation (MJO), and the large-scale atmospheric regime as derived from a long-term record of radiosonde observations over Darwin. The vertical variability of ice cloud occurrence and microphysical properties is largest in all regimes (1.5 order of magnitude for ice water content and extinction, a factor 3 in effective radius, and three orders of magnitude in concentration, typically). 98 % of ice clouds in our dataset are characterized by either a small cloud fraction (smaller than 0.3) or a very large cloud fraction (larger than 0.9). In the ice part of the troposphere three distinct layers characterized by different statistically-dominant microphysical processes are identified. The variability of the ice cloud properties as a function of the large-scale atmospheric regime, cloud regime, and MJO phase is large, producing mean differences of up to a factor 8 in the frequency of ice cloud occurrence between large-scale atmospheric regimes and mean differences of a factor 2 typically in all microphysical properties. Finally, the diurnal cycle of the frequency of occurrence of ice clouds is also very different between regimes and MJO phases, with diurnal amplitudes of the vertically-integrated frequency of ice cloud occurrence ranging from as low as 0.2 (weak diurnal amplitude) to values in excess of 2.0 (very large diurnal amplitude). Modellers should now use these results to check if their model cloud parameterizations are capable of translating a given atmospheric forcing into the correct statistical ice cloud properties.

scholarly journals The variability of tropical ice cloud properties as a function of the large-scale context from ground-based radar-lidar observations over Darwin, Australia

2010 ◽  
Vol 10 (8) ◽  
pp. 20069-20124
Author(s):  
A. Protat ◽  
J. Delanoë ◽  
P. T. May ◽  
J. Haynes ◽  
C. Jakob ◽  
...  
Keyword(s):  
Large Scale ◽  
Cloud Fraction ◽  
Ice Clouds ◽  
Ice Cloud ◽  
Microphysical Properties ◽  
Cloud Properties ◽  
Ice Water Content ◽  
Mean Differences ◽  
Ice Water ◽  
Lidar Observations

Abstract. The statistical properties of non-precipitating tropical ice clouds over Darwin, Australia are characterized using ground-based radar-lidar observations from the Atmospheric Radiation Measurement (ARM) Program. The ice cloud properties analysed are the frequency of ice cloud occurrence, the morphological properties (cloud top height and thickness, cloud fraction as derived considering a typical large-scale model grid box), and the microphysical and radiative properties (ice water content, visible extinction, effective radius, terminal fall speed, and total concentration). The variability of these tropical ice cloud properties is then studied as a function of the large-scale cloud regimes derived from the International Satellite Cloud Climatology Project (ISCCP), the amplitude and phase of the Madden–Julian Oscillation (MJO), and the large-scale atmospheric regime as derived from a long-term record of radiosonde observations over Darwin. The rationale for characterizing this variability is to provide an observational basis to which model outputs can be compared for the different regimes or large-scale characteristics and from which new parameterizations accounting for the large-scale context can be derived. The mean vertical variability of ice cloud occurrence and microphysical properties is large (1.5 order of magnitude for ice water content and extinction, a factor 3 in effective radius, and three orders of magnitude in concentration, typically). 98% of ice clouds in our dataset are characterized by either a small cloud fraction (smaller than 0.3) or a very large cloud fraction (larger than 0.9). Our results also indicate that, at least in the northern Australian region, the upper part of the troposphere can be split into three distinct layers characterized by different statistically-dominant microphysical processes. The variability of the ice cloud properties as a function of the large-scale atmospheric regime, cloud regime, and MJO phase is found to be large, producing mean differences of up to a factor of 8 in the frequency of ice cloud occurrence between large-scale atmospheric regimes, a factor of 3 to 4 for the ISCCP regimes and the MJO phases, and mean differences of a factor of 2 typically in all microphysical properties analysed in the present paper between large-scale atmospheric regimes or MJO phases. Large differences in occurrence (up to 60–80%) are also found in the main patterns of the cloud fraction distribution of ice clouds (fractions smaller than 0.3 and larger than 0.9). Finally, the diurnal cycle of the frequency of occurrence of ice clouds is also very different between regimes and MJO phases, with diurnal amplitudes of the vertically-integrated frequency of ice cloud occurrence ranging from as low as 0.2 (almost no detectable diurnal cycle) to values in excess of 2.0 (very large diurnal amplitude).

scholarly journals On the origin of subvisible cirrus clouds in the tropical upper troposphere

2012 ◽  
Vol 12 (6) ◽  
pp. 14875-14926 ◽  
Author(s):  
M. Reverdy ◽  
V. Noel ◽  
H. Chepfer ◽  
B. Legras
Keyword(s):  
Cloud Formation ◽  
Formation Processes ◽  
Ice Clouds ◽  
Back Trajectories ◽  
Air Masses ◽  
Ice Cloud ◽  
And Behavior ◽  
Atmospheric Phenomena ◽  
Mean Variance ◽  
Lidar Observations

Abstract. Spaceborne lidar observations have recently revealed a previously undetected significant population of SubVisible Cirrus (SVC). We show them to be colder than −74 °C, with an optical depth below 0.0015 on average. The formation and persistence over time of this new cloud population could be related to several atmospheric phenomena. In this paper, we investigate the importance of external processes in the creation of this cloud population, vs. the traditional ice cloud formation theory through convection. The importance of three scenarios in the formation of the global SVC population is investigated through different approaches that include comparisons with data imaging from several spaceborne instruments and back-trajectories that document the history and behavior of air masses leading to a point in time and space where subvisible cirrus were detected. In order simplify the study of cloud formation processes, we singled out SVC with coherent temperature histories (mean variance lower than 4 K) according to back-trajectories along 5, 10 or 15 days (respectively 58, 25 and 11% of SVC). Our results suggest that external processes, including local increases in liquid and hygroscopic aerosol concentration (either through biomass burning or volcanic injection forming sulfate-based aerosols in the troposphere or the stratosphere) have no noticeable short-term or mid-term impact on the SVC population. On the other hand, we find that ~60% of air masses interacted with convective activity in the days before they led to cloud formation and detection, which correspond to 37 to 65% of SVC. These results put forward the important influence of classical cloud formation processes compared to external influences in forming SVC. They support the view that the SVC population observed by CALIOP is an extension of the general upper tropospheric ice clouds population with its extreme thinness as its only differentiating factor.

scholarly journals Investigation of ice particle habits to be used for ice cloud remote sensing for the GCOM-C satellite mission

2016 ◽  
Vol 16 (18) ◽  
pp. 12287-12303 ◽  
Author(s):  
Husi Letu ◽  
Hiroshi Ishimoto ◽  
Jerome Riedi ◽  
Takashi Y. Nakajima ◽  
Laurent C.-Labonnote ◽  
...  
Keyword(s):  
Optical Thickness ◽  
Single Scattering ◽  
Single Scattering Albedo ◽  
Asymmetry Factor ◽  
Size Parameter ◽  
Geometric Optics ◽  
Ice Clouds ◽  
Extinction Efficiency ◽  
Ice Cloud ◽  
Cloud Properties

Abstract. In this study, various ice particle habits are investigated in conjunction with inferring the optical properties of ice clouds for use in the Global Change Observation Mission-Climate (GCOM-C) satellite programme. We develop a database of the single-scattering properties of five ice habit models: plates, columns, droxtals, bullet rosettes, and Voronoi. The database is based on the specification of the Second Generation Global Imager (SGLI) sensor on board the GCOM-C satellite, which is scheduled to be launched in 2017 by the Japan Aerospace Exploration Agency. A combination of the finite-difference time-domain method, the geometric optics integral equation technique, and the geometric optics method is applied to compute the single-scattering properties of the selected ice particle habits at 36 wavelengths, from the visible to the infrared spectral regions. This covers the SGLI channels for the size parameter, which is defined as a single-particle radius of an equivalent volume sphere, ranging between 6 and 9000 µm. The database includes the extinction efficiency, absorption efficiency, average geometrical cross section, single-scattering albedo, asymmetry factor, size parameter of a volume-equivalent sphere, maximum distance from the centre of mass, particle volume, and six nonzero elements of the scattering phase matrix. The characteristics of calculated extinction efficiency, single-scattering albedo, and asymmetry factor of the five ice particle habits are compared. Furthermore, size-integrated bulk scattering properties for the five ice particle habit models are calculated from the single-scattering database and microphysical data. Using the five ice particle habit models, the optical thickness and spherical albedo of ice clouds are retrieved from the Polarization and Directionality of the Earth's Reflectances-3 (POLDER-3) measurements, recorded on board the Polarization and Anisotropy of Reflectances for Atmospheric Sciences coupled with Observations from a Lidar (PARASOL) satellite. The optimal ice particle habit for retrieving the SGLI ice cloud properties is investigated by adopting the spherical albedo difference (SAD) method. It is found that the SAD is distributed stably due to the scattering angle increases for bullet rosettes with an effective diameter (Deff) of 10 µm and Voronoi particles with Deff values of 10, 60, and 100 µm. It is confirmed that the SAD of small bullet-rosette particles and all sizes of Voronoi particles has a low angular dependence, indicating that a combination of the bullet-rosette and Voronoi models is sufficient for retrieval of the ice cloud's spherical albedo and optical thickness as effective habit models for the SGLI sensor. Finally, SAD analysis based on the Voronoi habit model with moderate particle size (Deff = 60 µm) is compared with the conventional general habit mixture model, inhomogeneous hexagonal monocrystal model, five-plate aggregate model, and ensemble ice particle model. The Voronoi habit model is found to have an effect similar to that found in some conventional models for the retrieval of ice cloud properties from space-borne radiometric observations.

scholarly journals Ice crystal number concentration estimates from lidar-radar satellite retrievals. Part 2: Controls on the ice crystal number concentration

2018 ◽  
Author(s):  
Edward Gryspeerdt ◽  
Odran Sourdeval ◽  
Johannes Quaas ◽  
Julien Delanoë ◽  
Philipp Kühne
Keyword(s):  
Global Scale ◽  
Number Concentration ◽  
Ice Crystal ◽  
Ice Clouds ◽  
Ice Cloud ◽  
Cloud Properties ◽  
Radar Satellite ◽  
Mixed Phase Clouds

Abstract. The ice crystal number concentration (Ni) is a key property of ice clouds, both radiatively and microphysically. However, due to sparse in-situ measurements of ice cloud properties, the controls on the Ni have remained difficult to determine. As more advanced treatments of ice clouds are included in global models, it is becoming increasingly necessary to develop strong observational constraints on the processes involved. This work uses the DARDAR-LIM Ni retrieval described in part one to investigate the controls of the Ni at a global scale. The retrieved clouds are separated by type. The effects of temperature, proxies for in-cloud updraught and aerosol concentrations are investigated. Variations in the cloud top Ni (Ni(top)) consistent with both homogeneous and heterogeneous nucleation are observed and along with a possible role of aerosol both increasing and decreasing the Ni(top) depending on the prevailing meteorological situation. Away from the cloud top, the Ni displays a different sensitivity to these controlling factors, providing a possible explanation to the low Ni sensitivity to temperature and INP observed in previous in-situ studies. This satellite dataset provides a new way of investigating the response of cloud properties to meteorological and aerosol controls. The results presented in this work increase our confidence in the retrieved Ni and will form the basis for further study into the processes influencing ice and mixed phase clouds.

scholarly journals Use of spectral cloud emissivities and their related uncertainties to infer ice cloud boundaries: methodology and assessment using CALIPSO cloud products

2019 ◽  
Vol 12 (9) ◽  
pp. 5039-5054
Author(s):  
Hye-Sil Kim ◽  
Bryan A. Baum ◽  
Yong-Sang Choi
Keyword(s):  
North Pacific Ocean ◽  
Weather Prediction ◽  
Radiation Budget ◽  
Cloud Base ◽  
Ice Clouds ◽  
Ice Cloud ◽  
New Information ◽  
Infrared Imager ◽  
Cloud Temperature ◽  
Cloud Regimes

Abstract. Satellite-imager-based operational cloud property retrievals generally assume that a cloudy pixel can be treated as being plane-parallel with horizontally homogeneous properties. This assumption can lead to high uncertainties in cloud heights, particularly for the case of optically thin, but geometrically thick, clouds composed of ice particles. This study demonstrates that ice cloud emissivity uncertainties can be used to provide a reasonable range of ice cloud layer boundaries, i.e., the minimum to maximum heights. Here ice cloud emissivity uncertainties are obtained for three IR channels centered at 11, 12, and 13.3 µm. The range of cloud emissivities is used to infer a range of ice cloud temperature and heights, rather than a single value per pixel as provided by operational cloud retrievals. Our methodology is tested using MODIS observations over the western North Pacific Ocean during August 2015. We estimate minimum–maximum heights for three cloud regimes, i.e., single-layered optically thin ice clouds, single-layered optically thick ice clouds, and multilayered clouds. Our results are assessed through comparison with CALIOP version 4 cloud products for a total of 11873 pixels. The cloud boundary heights for single-layered optically thin clouds show good agreement with those from CALIOP; biases for maximum (minimum) heights versus the cloud-top (base) heights of CALIOP are 0.13 km (−1.01 km). For optically thick and multilayered clouds, the biases of the estimated cloud heights from the cloud top or cloud base become larger (0.30/−1.71 km, 1.41/−4.64 km). The vertically resolved boundaries for ice clouds can contribute new information for data assimilation efforts for weather prediction and radiation budget studies. Our method is applicable to measurements provided by most geostationary weather satellites including the GK-2A advanced multichannel infrared imager.

scholarly journals Thermodynamic Phase and Ice Cloud Properties in Northern Hemisphere Winter Extratropical Cyclones Observed by Aqua AIRS

2015 ◽  
Vol 54 (11) ◽  
pp. 2283-2303 ◽  
Author(s):  
Catherine M. Naud ◽  
Brian H. Kahn
Keyword(s):  
Northern Hemisphere ◽  
Cloud Cover ◽  
Frontal Region ◽  
Extratropical Cyclones ◽  
Ice Clouds ◽  
Ice Cloud ◽  
Cloud Properties ◽  
Hemisphere Winter ◽  
Thermodynamic Phase ◽  
Northern Hemisphere Winter

AbstractIce cloud properties in Northern Hemisphere winter extratropical cyclones are examined using the Atmospheric Infrared Sounder (AIRS), version 6, cloud products. The cloud thermodynamic phase product indicates that warm frontal clouds are dominated by ice, liquid-phase clouds occur outside of the warm frontal region, and supercooled or mixed-phase clouds are found in the southwestern quadrant of the cyclones. Stratiform ice clouds populate the warm frontal region and portions of the cold sector while convective ice clouds populate southeastern portions of the warm front and the southeastern quadrant. Total cloud cover is smaller in land cyclones than in ocean cyclones, especially in the southwestern quadrant and the warm frontal region. Ice cloud cover is less over land in the warm frontal region, because land cyclones are generally weaker and drier than ocean cyclones. The impact of cyclone average precipitable water (PW) and the magnitude of 850-hPa vertical ascent ω850 on the thermodynamic phase, occurrence of stratiform or convective ice cloud, ice particle effective diameter, optical thickness, and cloud-top temperature are discussed. When comparing land and ocean cyclones with similar PW and ω850, ice cloud coverage is found to be greater over land. Convective ice cloud occurs more often and is deeper over land. Supercooled cloud appears to persist to colder temperatures over ocean than over land, especially in the warm frontal region. These results suggest that, over land, ice cloud formation in warm fronts is possibly more efficient because of a greater aerosol amount from local or regional sources.

scholarly journals Developing and bounding ice particle mass- and area-dimension expressions for use in atmospheric models and remote sensing

2016 ◽  
Vol 16 (7) ◽  
pp. 4379-4400 ◽  
Author(s):  
Ehsan Erfani ◽  
David L. Mitchell
Keyword(s):  
Remote Sensing ◽  
Power Laws ◽  
Field Studies ◽  
Particle Mass ◽  
Atmospheric Models ◽  
Cloud Particle ◽  
Ice Clouds ◽  
Ice Cloud ◽  
Cloud Properties ◽  
Probe Measurements

Abstract. Ice particle mass- and projected area-dimension (m-D and A-D) power laws are commonly used in the treatment of ice cloud microphysical and optical properties and the remote sensing of ice cloud properties. Although there has long been evidence that a single m-D or A-D power law is often not valid over all ice particle sizes, few studies have addressed this fact. This study develops self-consistent m-D and A-D expressions that are not power laws but can easily be reduced to power laws for the ice particle size (maximum dimension or D) range of interest, and they are valid over a much larger D range than power laws. This was done by combining ground measurements of individual ice particle m and D formed at temperature T  <  −20 °C during a cloud seeding field campaign with 2-D stereo (2D-S) and cloud particle imager (CPI) probe measurements of D and A, and estimates of m, in synoptic and anvil ice clouds at similar temperatures. The resulting m-D and A-D expressions are functions of temperature and cloud type (synoptic vs. anvil), and are in good agreement with m-D power laws developed from recent field studies considering the same temperature range (−60 °C  <  T  <  −20 °C).

scholarly journals Ice crystal number concentration estimates from lidar–radar satellite remote sensing – Part 2: Controls on the ice crystal number concentration

2018 ◽  
Vol 18 (19) ◽  
pp. 14351-14370 ◽  
Author(s):  
Edward Gryspeerdt ◽  
Odran Sourdeval ◽  
Johannes Quaas ◽  
Julien Delanoë ◽  
Martina Krämer ◽  
...  
Keyword(s):  
Global Scale ◽  
Number Concentration ◽  
Ice Crystal ◽  
Ice Clouds ◽  
Ice Cloud ◽  
Cloud Properties ◽  
Effects Of Temperature ◽  
Radar Satellite ◽  
Mixed Phase Clouds

Abstract. The ice crystal number concentration (Ni) is a key property of ice clouds, both radiatively and microphysically. Due to sparse in situ measurements of ice cloud properties, the controls on the Ni have remained difficult to determine. As more advanced treatments of ice clouds are included in global models, it is becoming increasingly necessary to develop strong observational constraints on the processes involved. This work uses the DARDAR-Nice Ni retrieval described in Part 1 to investigate the controls on the Ni at a global scale. The retrieved clouds are separated by type. The effects of temperature, proxies for in-cloud updraft and aerosol concentrations are investigated. Variations in the cloud top Ni (Ni(top)) consistent with both homogeneous and heterogeneous nucleation are observed along with differing relationships between aerosol and Ni(top) depending on the prevailing meteorological situation and aerosol type. Away from the cloud top, the Ni displays a different sensitivity to these controlling factors, providing a possible explanation for the low Ni sensitivity to temperature and ice nucleating particles (INP) observed in previous in situ studies. This satellite dataset provides a new way of investigating the response of cloud properties to meteorological and aerosol controls. The results presented in this work increase our confidence in the retrieved Ni and will form the basis for further study into the processes influencing ice and mixed phase clouds.

scholarly journals Objective Assessment of the Information Content of Visible and Infrared Radiance Measurements for Cloud Microphysical Property Retrievals over the Global Oceans. Part II: Ice Clouds

2006 ◽  
Vol 45 (1) ◽  
pp. 42-62 ◽  
Author(s):  
Steven J. Cooper ◽  
Tristan S. L’Ecuyer ◽  
Philip Gabriel ◽  
Anthony J. Baran ◽  
Graeme L. Stephens
Keyword(s):  
Information Content ◽  
Near Infrared ◽  
Objective Assessment ◽  
Ice Clouds ◽  
Ice Cloud ◽  
Cloud Properties ◽  
Microphysical Property ◽  
Retrieval Scheme ◽  
Retrieval Problem ◽  
Moderate Resolution Imaging Spectroradiometer

Abstract Cirrus clouds play an important yet poorly determined role in the earth’s climate system and its various feedback mechanisms. As such, a significant amount of work has been accomplished both in understanding the physics of the ice clouds and in using this knowledge to estimate global distributions of ice cloud properties from satellite-based instruments. This work seeks to build on these past efforts by offering a reexamination of the ice cloud retrieval problem in context of recent advancements in the understanding of optical properties for a variety of realistic ice crystal shapes. In this work, the formal information content analysis outlined in Part I is used to objectively select the optimal combination of measurements for an ice cloud microphysical property retrieval scheme given a realistic assessment of the uncertainties that govern the ice cloud retrieval problem. Although this analysis is for a theoretical retrieval combining simulated measurements from the Moderate Resolution Imaging Spectroradiometer (MODIS) with the CloudSat Cloud Profiling Radar (CPR) above an ocean surface, the general methodology is applicable to any instrument package. Channel selection via information content is determined through a realistic characterization of not only the sensitivity of top-of-the-atmosphere radiances to desired retrieval parameters but also to the uncertainties resulting from both the measurements themselves and from the forward model assumptions used in relating observational and retrieval space. Results suggest that the channels that maximize retrieval information are strongly dependent upon the state of the atmosphere, meaning that no combination of two or three channels will always ensure an accurate retrieval. Because of the complexities of this state-dependent nature and the need for a consistent retrieval scheme for an operational retrieval, a five-channel retrieval approach consisting of a combination of error-weighted visible, near-infrared, and infrared channels is suggested. Such an approach ensures high information content regardless of cloud and atmospheric properties through use of the inherent sensitivities in each of these spectral regions.

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