Microphysical  Characteristics  of  Frozen  Droplet  Aggregates 
from Deep Convective Clouds

Um, Junshik; McFarquhar, Greg M.; Stith, Jeffrey L.; Jung, Chang Hoon; Lee, Seoung Soo; Lee, Ji Yi; Shin, Younghwan; Lee, Yun Gon

doi:10.5194/acp-2018-5

Cited by 2 publications

(8 citation statements)

References 56 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Examples of CPI images, mostly frozen drops in a highly electrified anvil sampled by a GV during DC3, adapted from (a) Um et al () and (b) Stith et al (). Arrows in b point to small faceted crystals.…”

Section: Results From Field Campaignsmentioning

confidence: 99%

“…Tropical maritime anvils contain more faceted ice, with aggregates of faceted ice, but fewer aggregates overall and fewer rimed aggregates. Higher concentrations of small drops (up to hundreds per cubic centimeters) are carried to colder levels in midlatitude continental updrafts and support the production of rimed aggregates and homogeneous freezing of the small drops (Stith et al, ; Um et al, ; Um & McFarquhar, ). Midlatitude anvils that have high electrical charge often contain chains of frozen drops and small ice particles. Chains of frozen drops and small ice particles appear much less frequently in tropical maritime anvils, except perhaps in highly electrified tropical maritime anvils (Connolly et al, ; Um & McFarquhar, ) Tropical convective anvils that originate over land, or are somewhat continental in nature, may exhibit some of the characteristics of midlatitude continental anvils, such as higher than average concentrations of small ice and aggregates (Gallagher et al, , ; Um & McFarquhar, ). The total concentration of ice particles drops off with distance from active convection in both tropical maritime (Woods et al, ) and midlatitude anvils (Lawson et al, ). Relatively high concentration (1 to 10 per cm −3 ) of small, quasi‐spherical ice can be observed downwind of in situ cirrus formed orographically, which may or may not form rosette shaped particles (Figure ).…”

Section: Summary and Discussionmentioning

confidence: 99%

“…On the other hand, chains are rarely observed in Maritime Tropical anvils (Figure ), unless the anvil is highly electrified, which is not typical. The chains of frozen drops and small crystals observed in midlatitude continental anvils have been attributed to high electric fields (Connolly et al, ; Gallagher et al, ; Lawson et al, ; Stith et al, ; Um et al, ), implied from the laboratory work of Saunders and Wahab (). This is supported by the correlation between the degree of aggregation and the in‐anvil concentration of lightning‐produced NO x , suggesting that the aggregation and electrification occurred in the same regions of the cloud (Stith et al, ).…”

Section: Overview Of Particle Shapes In Anvil and In Situ Cirrusmentioning

confidence: 99%

“…The shapes of cirrus ice particles have been shown to have significant influence on the Earth's radiation budget (Baran, ; Feng et al, ; Hartmann, ; Hartmann & Berry, ; Jensen et al, ; Lawson et al, ; Loeb et al, ; McFarquhar et al, ; Mishchenko et al, ; Stephens, ; Stephens et al, ; Um et al, ; Yang et al, , ). According to Baran (), “space‐based measurements reveal that cirrus covers about 30% of the midlatitudes at any given time, while in the tropics, the coverage can be 60–80% at any given time.” Guignard et al () report that about 25% of the Earth is covered by subvisible cirrus (SVC), which is found mostly in the Tropical Tropopause Layer (TTL).…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

A Review of Ice Particle Shapes in Cirrus formed In Situ and in Anvils

et al. 2019

Self Cite

View full text Add to dashboard Cite

Results from 22 airborne field campaigns, including more than 10 million high-resolution particle images collected in cirrus formed in situ and in convective anvils, are interpreted in terms of particle shapes and their potential impact on radiative transfer. Emphasis is placed on characterizing ice particle shapes in tropical maritime and midlatitude continental anvil cirrus, as well as in cirrus formed in situ in the upper troposphere, and subvisible cirrus in the upper tropical troposphere layer. There is a distinctive difference in cirrus ice particle shapes formed in situ compared to those in anvils that are generated in close proximity to convection. More than half the mass in cirrus formed in situ are rosette shapes (polycrystals and bullet rosettes). Cirrus formed from fresh convective anvils is mostly devoid of rosette-shaped particles. However, small frozen drops may experience regrowth downwind of an aged anvil in a regime with RH ice >~120% and then grow into rosette shapes. Identifiable particle shapes in tropical maritime anvils that have not been impacted by continental influences typically contain mostly single plate-like and columnar crystals and aggregates. Midlatitude continental anvils contain single-rimed particles, more and larger aggregates with riming, and chains of small ice particles when in a highly electrified environment. The particles in subvisible cirrus are <~100 μm and quasi-spherical with some plates and rare trigonal shapes. Percentages of particle shapes and power laws relating mean particle area and mass to dimension are provided to improve parameterization of remote retrievals and numerical simulations.

show abstract

Section: Results From Field Campaignsmentioning

confidence: 99%

Section: Summary and Discussionmentioning

confidence: 99%

Section: Overview Of Particle Shapes In Anvil and In Situ Cirrusmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

A Review of Ice Particle Shapes in Cirrus formed In Situ and in Anvils

et al. 2019

Self Cite

View full text Add to dashboard Cite

show abstract

“…This is complicated by a couple of issues. First, several idealized crystal models representing shapes of small crystals have been proposed (McFarquhar et al, 2002;Yang et al, 2003;Nousiainen and McFarquhar, 2004;Nousiainen et al, 2011;Um andMcFarquhar, 2011, 2013;Järvinen et al, 2016), but it is not known which best characterizes the shapes. Second, few in situ aircraft observations of continental convective clouds have been made due to their high altitudes and the difficulty of flying through or near strong updrafts.…”

Section: Introductionmentioning

confidence: 99%

Microphysical characteristics of frozen droplet aggregates from deep convective clouds

McFarquhar

Stith

et al. 2018

Atmos. Chem. Phys.

Self Cite

View full text Add to dashboard Cite

Abstract. During the 2012 Deep Convective Clouds and Chemistry (DC3) experiment the National Science Foundation/National Center for Atmospheric Research Gulfstream V (GV) aircraft sampled the upper anvils of two storms that developed in eastern Colorado on 6 June 2012. A cloud particle imager (CPI) mounted on the GV aircraft recorded images of ice crystals at altitudes of 12.0 to 12.4 km and temperatures (T) from −61 to −55 ∘C. A total of 22 393 CPI crystal images were analyzed, all with maximum dimension (Dmax⁡)<433 µm and with an average Dmax⁡ of 80.7±45.4 µm. The occurrence of well-defined pristine crystals (e.g., columns and plates) was less than 0.04 % by number. Single frozen droplets and frozen droplet aggregates (FDAs) were the dominant habits with fractions of 73.0 % (by number) and 46.3 % (by projected area), respectively. The relative frequency of occurrence of single frozen droplets and FDAs depended on temperature and position within the anvil cloud. A new algorithm that uses the circle Hough transform technique was developed to automatically identify the number, size, and relative position of element frozen droplets within FDAs. Of the FDAs, 42.0 % had two element frozen droplets with an average of 4.7±5.0 element frozen droplets. The frequency of occurrence gradually decreased with the number of element frozen droplets. Based on the number, size, and relative position of the element frozen droplets within the FDAs, possible three-dimensional (3-D) realizations of FDAs were generated and characterized by two different shape parameters, the aggregation index (AI) and the fractal dimension (Df), that describe 3-D shapes and link to scattering properties with an assumption of spherical shape of element frozen droplets. The AI of FDAs decreased with an increase in the number of element frozen droplets, with larger FDAs with more element frozen droplets having more compact shapes. The Df of FDAs was about 1.20–1.43 smaller than that of black carbon (BC) aggregates (1.53–1.85) determined in previous studies. Such a smaller Df of FDAs indicates that FDAs have more linear chain-like branched shapes than the compact shapes of BC aggregates. Determined morphological characteristics of FDAs along with the proposed reconstructed 3-D representations of FDAs in this study have important implications for improving the calculations of the microphysical (e.g., fall velocity) and radiative (e.g., asymmetry parameter) properties of ice crystals in upper anvil clouds.

show abstract

Microphysical Characteristics of Frozen Droplet Aggregates from Deep Convective Clouds

Cited by 2 publications

References 56 publications

A Review of Ice Particle Shapes in Cirrus formed In Situ and in Anvils

A Review of Ice Particle Shapes in Cirrus formed In Situ and in Anvils

Microphysical characteristics of frozen droplet aggregates from deep convective clouds

Contact Info

Product

Resources

About