Icing of aircraft engines in ice crystal clouds: A case study

Abstract. The ability to run a global climate model in single-column mode is very useful for testing model improvements because single-column models (SCMs) are inexpensive to run and easy to interpret. A major breakthrough in Version 5 of the Community Atmosphere Model (CAM5) is the inclusion of prognostic aerosol. Unfortunately, this improvement was not coordinated with the SCM version of CAM5 and as a result CAM5-SCM initializes aerosols to zero. In this study we explore the impact of running CAM5-SCM with aerosol initialized to zero (hereafter named Default) and test three potential fixes. The first fix is to use CAM5's prescribed aerosol capability, which specifies aerosols at monthly climatological values. The second method is to prescribe aerosols at observed values. The third approach is to fix droplet and ice crystal numbers at prescribed values. We test our fixes in four different cloud regimes to ensure representativeness: subtropical drizzling stratocumulus (based on the DYCOMS RF02 case study), mixed-phase Arctic stratocumulus (using the MPACE-B case study), tropical shallow convection (using the RICO case study), and summertime mid-latitude continental convection (using the ARM95 case study). Stratiform cloud cases (DYCOMS RF02 and MPACE-B) were found to have a strong dependence on aerosol concentration, while convective cases (RICO and ARM95) were relatively insensitive to aerosol specification. This is perhaps expected because convective schemes in CAM5 do not currently use aerosol information. Adequate liquid water content in the MPACE-B case was only maintained when ice crystal number concentration was specified because the Meyers et al. (1992) deposition/condensation ice nucleation scheme used by CAM5 greatly overpredicts ice nucleation rates, causing clouds to rapidly glaciate. Surprisingly, predicted droplet concentrations for the ARM95 region in both SCM and global runs were around 25 cm−3, which is much lower than observed. This finding suggests that CAM5 has problems capturing aerosol effects in this climate regime.

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Seasonal variability in ice crystal properties at NorthGRIP: a case study around 301 m depth

Annals of Glaciology ◽

10.3189/172756403781815582 ◽

2003 ◽

Vol 37 ◽

pp. 119-122 ◽

Cited By ~ 6

Author(s):

Anders Svensson ◽

Pauli Baadsager ◽

Asbjørn Persson ◽

Christine Schøtt Hvidberg ◽

Marie-Louise Siggaard-Andersen

Keyword(s):

Seasonal Variability ◽

Ice Core ◽

Ice Crystal ◽

Axis Orientation ◽

Annual Cycles ◽

Average Value ◽

The North ◽

Chemical Impurities ◽

Crystal Properties

AbstractThe aim of this case study is to quantify the seasonal variability in crystal properties and to discuss the reason for the variability. A continuous 1.10 m long vertical thin-section profile covering approximately five annual cycles has been obtained from the North Greenland Icecore Project (NorthGRIP) ice core at around 301 m depth. The crystal outline and the c-axis orientation of more than 13000 crystals in the profile have been measured on a new Australian automated ice-crystal analyzer. In 2.5 cm resolution we observe a strong seasonal variability in crystal areas of >30%deviation from the average value of 6.7 mm2. Each year, a band of smaller crystals is observed in ice deposited during spring. The area distribution function is found to be close to a lognormal distribution. The crystal areas are compared to the concentration of chemical impurities in the ice; at a 5 cm resolution, the best correlation is found with the concentration of Ca2+. Our results show no seasonal variability of the average c-axis orientation of ice crystals.

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Ice crystal properties of amber ice and strain enhancement at the base of cold Antarctic glaciers

Annals of Glaciology ◽

10.3189/172756405781813618 ◽

2005 ◽

Vol 40 ◽

pp. 185-190 ◽

Cited By ~ 11

Author(s):

Denis Samyn ◽

Anders Svensson ◽

Sean J. Fitzsimons ◽

Reginald D. Lorrain

Keyword(s):

Impurity Content ◽

Ice Crystal ◽

Fine Grained ◽

Automated Method ◽

Lattice Preferred Orientation ◽

High Impurity ◽

Deformation Properties ◽

Crystal Properties ◽

Analytical Accuracy

AbstractTo improve our understanding of the deformation properties of cold-based polar glaciers, we examine here some of the factors leading to the localization of strain within the amber ice facies. We present a crystallographic case study of amber ice (a fine-grained bubbly ice containing a relatively high impurity content) sampled at the base of two Antarctic glaciers. The crystal fabrics and textures of amber ice were computed by application of a recently developed automated method. To date, it was tedious and awkward to determine amber ice facies accurately because of the sub-millimetric crystal size and relatively high debris content of this facies. The authomatic analytical method applied in this study allows not only for improving analytical accuracy in this task but also for considerably reducing the time of analysis. Our investigations reveal highly homogeneous crystallographic properties for the studied amber ice. The ice crystals are mainly polygonal, equant and sub-millimetric, and show a strong lattice-preferred orientation. These properties, beside the relatively high impurity content, are likely to exert a major control on strain enhancement in amber ice when this facies is present at the base of cold glaciers.

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Scattering of VHF radio waves from within the top 700 m of the Antarctic ice sheet and its relation to the depositional environment: a case-study along the Syowa–Mizuho–Dome Fuji traverse

Annals of Glaciology ◽

10.3189/172756402781817888 ◽

2002 ◽

Vol 34 ◽

pp. 157-164 ◽

Cited By ~ 11

Author(s):

Shuji Fujita ◽

Hideo Maeno ◽

Teruo Furukawa ◽

Kenichi Matsuoka

Keyword(s):

Accumulation Rate ◽

Ice Sheet ◽

Density Fluctuations ◽

Radio Waves ◽

Ice Crystal ◽

Local Conditions ◽

Short Pulses ◽

Scattered Power ◽

The Antarctic

AbstractRadio-wave scattering is a convenient method to image the properties of large internal regions of ice sheets. We used a ground-based radar system with short pulses of 60 and 179MHz frequencies to scatter off internal strata within 100–700 m of the surface in the ice sheet of East Antarctica. Data were examined along an 1150 kmlong traverse line that was approximately along the ice flowline from inland of Dome Fuji station to the coast. The scattered waves are from strata, and the dominant cause of the scattering was changes in dielectric permittivity across the strata. Therefore, density fluctuations primarily cause the scattering, although variations in ice-crystal fabrics and acidity could also have effects. The power scattered from the same depths varied by > 15 dB from one location to another. These variations correlate with the accumulation rate, changes in the surface slope, and subglacial bedrock undulations. Variations of the scattered power suggest that density contrasts in the strata are highly variable depending on these interdependent local conditions. The distribution of strata along the route allowed estimates of the ice-flow trajectories to depths of about 250 m.

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Lidar/radar approach to quantify the dust impact on ice nucleation in mid and high level clouds

E3S Web of Conferences ◽

10.1051/e3sconf/20199904003 ◽

2019 ◽

Vol 99 ◽

pp. 04003

Author(s):

Albert Ansmann ◽

Rodanthi-Elisavet Mamouri ◽

Johannes Bühl ◽

Patric Seifert ◽

Ronny Engelmann ◽

...

Keyword(s):

Particle Concentration ◽

Eastern Mediterranean ◽

Ice Nucleation ◽

Saharan Dust ◽

Ice Crystal ◽

Cloud Radar ◽

Field Campaigns ◽

High Level ◽

The Relationship

We present the first attempt of a closure experiment regarding the relationship between ice nucleating particle concentration (INPC) and ice crystal number concentration (ICNC), solely based on active remote sensing. The approach combines aerosol and cloud observations with polarization lidar, Doppler lidar, and cloud radar. Several field campaigns were conducted on the island of Cyprus in the Eastern Mediterranean from 2015-2018 to study heterogeneous ice formation in altocumulus and cirrus layers embedded in Saharan dust. A case study observed on 10 April 2017 is discussed in this contribution.

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Derivation of aerosol profiles for MC3E convection studies and use in simulations of the 20 May squall line case

Atmospheric Chemistry and Physics ◽

10.5194/acp-17-5947-2017 ◽

2017 ◽

Vol 17 (9) ◽

pp. 5947-5972 ◽

Cited By ~ 19

Author(s):

Ann M. Fridlind ◽

Xiaowen Li ◽

Di Wu ◽

Marcus van Lier-Walqui ◽

Andrew S. Ackerman ◽

...

Keyword(s):

Case Studies ◽

Deep Convection ◽

Convective Cloud ◽

Single Mode ◽

Aerosol Size Distribution ◽

Squall Line ◽

Ice Crystal ◽

Airborne Measurements ◽

Ice Multiplication

Abstract. Advancing understanding of deep convection microphysics via mesoscale modeling studies of well-observed case studies requires observation-based aerosol inputs. Here, we derive hygroscopic aerosol size distribution input profiles from ground-based and airborne measurements for six convection case studies observed during the Midlatitude Continental Convective Cloud Experiment (MC3E) over Oklahoma. We demonstrate use of an input profile in simulations of the only well-observed case study that produced extensive stratiform outflow on 20 May 2011. At well-sampled elevations between −11 and −23 °C over widespread stratiform rain, ice crystal number concentrations are consistently dominated by a single mode near ∼ 400 µm in randomly oriented maximum dimension (Dmax). The ice mass at −23 °C is primarily in a closely collocated mode, whereas a mass mode near Dmax ∼ 1000 µm becomes dominant with decreasing elevation to the −11 °C level, consistent with possible aggregation during sedimentation. However, simulations with and without observation-based aerosol inputs systematically overpredict mass peak Dmax by a factor of 3–5 and underpredict ice number concentration by a factor of 4–10. Previously reported simulations with both two-moment and size-resolved microphysics have shown biases of a similar nature. The observed ice properties are notably similar to those reported from recent tropical measurements. Based on several lines of evidence, we speculate that updraft microphysical pathways determining outflow properties in the 20 May case are similar to a tropical regime, likely associated with warm-temperature ice multiplication that is not well understood or well represented in models.

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