Recent laboratory experiments and in situ observations have produced results in broad agreement with respect to ice crystal habits in the atmosphere. These studies reveal that the ice crystal habit at −20°C is platelike, extending to −40°C, and not columnar as indicated in many habit diagrams found in atmospheric science journals and texts. These diagrams were typically derived decades ago from laboratory studies, some with inherent habit bias, or from combinations of laboratory and in situ observations at the ground, observations that often did not account for habit modification by precipitation from overlying clouds of varying temperatures. Habit predictions from these diagrams often disagreed with in situ observations at temperatures below −20°C. More recent laboratory and in situ studies have achieved a consensus on atmospheric ice crystal habits that differs from the traditional habit diagrams. These newer results can now be combined to give a comprehensive description of ice crystal habits ...

A Comprehensive Habit Diagram for Atmospheric Ice Crystals: Confirmation from the Laboratory, AIRS II, and Other Field Studies

Microphysical data were collected by the NCAR C-130 research aircraft during the First International Satellite Cloud Climatology Project (ISCCP) Regional Experiment Arctic Cloud Experiment (FIRE ACE). Boundary layer clouds 100 to 400 m thick were observed on 11 of the 16 missions. The all-water clouds varied from being adiabatic and homogeneous with monomodal drop spectra to subadiabatic and inhomogeneous with bimodal drop spectra and drizzle. The subadiabatic clouds were observed to be actively mixing near cloud top. The adiabatic clouds provided a test of the performance of the liquid water content (LWC) probes but only in low LWC conditions. A mixed-phase boundary layer cloud displayed striking variability in the hydrometeor fields on a horizontal scale of 10 km and a vertical scale of 100 m. Cloud Particle Imager (CPI) data showed separate regions with small supercooled cloud drops, supercooled drizzle (at −25°C) and graupel particles. A deep stratus cloud with its base at 2 km (+2°C) and top at 6 km (−25°C) contained drizzle near cloud top and (lower in the cloud) very high (2500 to 4000 L−1) concentrations of ice particles in conditions that did not meet all the Hallett-Mossop criteria. CPI data showed that an Arctic cirrus cloud was composed of very high (∼100,000 L−1) concentrations of small ice particles interspersed with single, large (mostly bullet rosette) crystals. The data showed that the cirrus cloud was inhomogeneous on scales down to tens of meters. The average ice particle concentrations measured in the cirrus by the FSSP and CPI probes were several hundred to a few thousand per liter, much higher than commonly found in the literature.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2000JD900789

An overview of microphysical properties of Arctic clouds observed in May and July 1998 during FIRE ACE

[1] The CALIOP depolarization measurements, combined with backscatter intensity measurements, are effective in discriminating between water clouds and ice clouds. The same depolarization measurements can also be used for estimating liquid water content information. Using cloud temperature information from the collocated infrared imaging radiometer measurements and cloud water paths from collocated MODIS measurements, this study compiles global statistics of the occurrence frequency, liquid water content, liquid water path, and their temperature dependence. For clouds with temperatures between −40°C and 0°C, the liquid phase fractions and liquid water paths are significantly higher than the ones from previous studies using passive remote sensing measurements. At midlatitudes, the occurrence of liquid phase clouds at temperatures between −40°C and 0°C depends jointly on both cloud height and cloud temperature. At high latitudes, more than 95% of low-level clouds with temperatures between −40°C and 0°C are water clouds. Supercooled water clouds are mostly observed over ocean near the storm-track regions and high-latitude regions. Supercooled water clouds over land are observed in the Northern Hemisphere over Europe, East Asia, and North America, and these are the supercooled water clouds with highest liquid water contents. The liquid water content of all supercooled water clouds is characterized by a Gamma (Γ) distribution. The mode values of liquid water content are around 0.06 g/m3 and are independent of cloud temperature. For temperatures warmer than −15°C, mean value of the liquid water content is around 0.14 g/m3. As the temperature decreases, the mean cloud liquid water content also decreases. These results will benefit cloud models and cloud parameterizations used in climate models in improving their ice-phase microphysics parameterizations and the aviation hazard forecast.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2009JD012384

Occurrence, liquid water content, and fraction of supercooled water clouds from combined CALIOP/IIR/MODIS measurements

This paper considers the theory of diffraction image formation of spherical particles and peculiarities of particle sizing by discrete imaging probes. The diffraction images of spherical water droplets are approximated by Fresnel diffraction by an opaque disc. The approach developed in the paper is applicable to all types of array and matrix imaging probes. The analysis measurement accuracy is performed for the PMS Optical Array Prove (OAP)-2D-C and OAP-2Dgray probes. It is shown that a 25-mm resolution PMS OAP-2D-C probe can both oversize and undersize droplets smaller than approximately 100 mm in diameter, and oversize droplets larger than approximately 100 mm. The errors in droplet sizing increase with decreasing size. The discrete manner of particle image registration also leads to losses of particles with sizes smaller than 100 mm. For the ideal case with zero photodiode response time, these losses reach 70% for 25-mm droplets. A nonzero response time will increase these losses. These findings help explain discrepancies observed in the overlap region of the PMS FSSP and OAP droplet spectra. A variety of calculated digital images for PMS OAP-2D-C and OAP-2Dgray probes is presented. Different methods of particle image sizing are discussed. Several methods of size correction of individual droplets and droplet ensembles are suggested. Correction algorithms for these effects are derived, and distortion and correction retrieval matrices are calculated. Several examples of actual and measured size distributions are presented.

https://journals.ametsoc.org/doi/pdf/10.1175/1520-0426%281998%29015%3C0708%3AEOTAOP%3E2.0.CO%3B2

Evaluation of the Accuracy of PMS Optical Array Probes

Clouds are a critical component of the Earth's coupled water and energy cycles. Poor understanding of cloud–radiation–dynamics feedbacks results in large uncertainties in forecasting human-induced climate changes. Better understanding of cloud microphysical and dynamical processes is critical to improving cloud parameterizations in climate models as well as in cloud-resolving models. Airborne in situ and remote sensing can make critical contributions to progress. Here, a new integrated cloud observation capability developed for the University of Wyoming King Air is described. The suite of instruments includes the Wyoming Cloud Lidar, a 183- GHz microwave radiometer, the Wyoming Cloud Radar, and in situ probes. Combined use of these remote sensor measurements yields more complete descriptions of the vertical structure of cloud microphysical properties and of cloud-scale dynamics than that attainable through ground-based remote sensing or in situ sampling alone. Together with detailed in situ data on aeroso...

/pdf/single-aircraft-integration-of-remote-sensing-and-in-situ-5bqga7c774.pdf

Single Aircraft Integration of Remote Sensing and In Situ Sampling for the Study of Cloud Microphysics and Dynamics

Statistical characteristics of 584 liquid water content (LWC) profiles collected mainly in midlatitude supercooled stratiform frontal clouds during five field campaigns are presented. It has been found that the majority (55%) of liquid layers have thickness less than 500 m and the depth of these layers decreases with decreasing temperature. LWC profiles for thin cloud layers are usually close to quasi-adiabatic, whereas for thick clouds they are approximately constant with an average LWC value close to 0.14 g m−3. Good agreement was observed between cumulative distributions for liquid water paths derived from in situ LWC profiles and those inferred in previous experiments from ground-based 37 GHz radiometers. Copyright © 2007 Crown in the right of Canada. Published by John Wiley & Sons, Ltd

http://radiometrics.com/data/uploads/2012/11/Korolev_QJRMS_07.pdf

J. W. Strapp

Papers

In situ measurements of liquid water content profiles in midlatitude stratiform clouds

Improved measurements of the drop size distribution of a freezing drizzle event