Scanning electron microscopy and molecular dynamics of surfaces of growing and ablating hexagonal ice crystals

Pfalzgraff, William; Hulscher, R. M.; Neshyba, Steven

doi:10.5194/acp-10-2927-2010

Cited by 67 publications

(98 citation statements)

References 36 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…10), in agreement with other work (Cross, 1969;Pfalzgraff et al, 2010;Neshyba et al, 2013). The emergence of grooves on sublimating prismatic faces may be due to the presence of stacking faults (Kobayashi and Ohtake, 1974;Kuhs et al, 2012).…”

Section: Discussionsupporting

confidence: 83%

“…We then examine possible causes of the observed roughness. In addition to growth processes we also consider sublimation, since ice surfaces can become rough during rapid sublimation (Cross, 1969;Kobayashi and Ohtake, 1974;Pfalzgraff et al, 2010). This is contrary to what currently appears to be the prevailing view, which postulates that atmospheric ice crystals merely become rounded (Nelson, 1998).…”

Section: Introductioncontrasting

confidence: 42%

See 1 more Smart Citation

Incidence of rough and irregular atmospheric ice particles from Small Ice Detector 3 measurements

et al. 2014

View full text Add to dashboard Cite

Abstract. The knowledge of properties of ice crystals such as size, shape, concavity and roughness is critical in the context of radiative properties of ice and mixed-phase clouds. Limitations of current cloud probes to measure these properties can be circumvented by acquiring two-dimensional lightscattering patterns instead of particle images. Such patterns were obtained in situ for the first time using the Small Ice Detector 3 (SID-3) probe during several flights in a variety of mid-latitude mixed-phase and cirrus clouds. The patterns are analysed using several measures of pattern texture, selected to reveal the magnitude of particle roughness or complexity. The retrieved roughness is compared to values obtained from a range of well-characterized test particles in the laboratory. It is found that typical in situ roughness corresponds to that found in the rougher subset of the test particles, and sometimes even extends beyond the most extreme values found in the laboratory. In this study we do not differentiate between small-scale, fine surface roughness and large-scale crystal complexity. Instead, we argue that both can have similar manifestations in terms of light-scattering properties and also similar causes. Overall, the in situ data are consistent, with ice particles with highly irregular or rough surfaces being dominant. Similar magnitudes of roughness were found in growth and sublimation zones of cirrus. The roughness was found to be negatively correlated with the halo ratio, but not with other thermodynamic or microphysical properties found in situ. Slightly higher roughness was observed in cirrus forming in clean oceanic air masses than in a continental, polluted one. Overall, the roughness and complexity are expected to lead to increased shortwave cloud reflectivity, in comparison with cirrus composed of more regular, smooth ice crystal shapes. These findings put into question suggestions that climate could be modified through aerosol seeding to reduce cirrus cover and optical depth, as the seeding may result in decreased shortwave reflectivity.

show abstract

Section: Discussionsupporting

confidence: 83%

Section: Introductioncontrasting

confidence: 42%

Incidence of rough and irregular atmospheric ice particles from Small Ice Detector 3 measurements

et al. 2014

View full text Add to dashboard Cite

show abstract

“…8). This has been observed regardless of the water model and the crystallographic plane exposed to the vapour phase (Bolton and Pettersson, 2000;Picaud, 2006;Vega et al, 2006;Bishop et al, 2009;Neshyba et al, 2009;Pereyra and Carignano, 2009;Pfalzgraff et al, 2011;Shepherd et al, 2012). The onset temperature of disorder is found to depend on the crystal facet exposed to the vapour phase; for example on the basal plane, the first sign of interfacial disorder occurs about 100 K below the melting point, whereas on the prism plane disorder was observed around T m − 80 K (Conde et al, 2008).…”

Section: Simulations Of Disorder On Pure Icementioning

confidence: 83%

“…The onset temperature of disorder is found to depend on the crystal facet exposed to the vapour phase; for example on the basal plane, the first sign of interfacial disorder occurs about 100 K below the melting point, whereas on the prism plane disorder was observed around T m − 80 K (Conde et al, 2008). The thickness of the disordered interface also shows small differences for different crystal facets (Conde et al, 2008;Pfalzgraff et al, 2011). It appears that the disorder on the basal plane is slightly thicker; a similar trend can also be observed in experiments (Sect.…”

Section: Simulations Of Disorder On Pure Icementioning

confidence: 91%

A review of air–ice chemical and physical interactions (AICI): liquids, quasi-liquids, and solids in snow

et al. 2014

View full text Add to dashboard Cite

Abstract. Snow in the environment acts as a host to rich chemistry and provides a matrix for physical exchange of contaminants within the ecosystem. The goal of this review is to summarise the current state of knowledge of physical processes and chemical reactivity in surface snow with relevance to polar regions. It focuses on a description of impurities in distinct compartments present in surface snow, such as snow crystals, grain boundaries, crystal surfaces, and liquid parts. It emphasises the microscopic description of the ice surface and its link with the environment. Distinct differences between the disordered air–ice interface, often termed quasi-liquid layer, and a liquid phase are highlighted. The reactivity in these different compartments of surface snow is discussed using many experimental studies, simulations, and selected snow models from the molecular to the macro-scale. Although new experimental techniques have extended our knowledge of the surface properties of ice and their impact on some single reactions and processes, others occurring on, at or within snow grains remain unquantified. The presence of liquid or liquid-like compartments either due to the formation of brine or disorder at surfaces of snow crystals below the freezing point may strongly modify reaction rates. Therefore, future experiments should include a detailed characterisation of the surface properties of the ice matrices. A further point that remains largely unresolved is the distribution of impurities between the different domains of the condensed phase inside the snowpack, i.e. in the bulk solid, in liquid at the surface or trapped in confined pockets within or between grains, or at the surface. While surface-sensitive laboratory techniques may in the future help to resolve this point for equilibrium conditions, additional uncertainty for the environmental snowpack may be caused by the highly dynamic nature of the snowpack due to the fast metamorphism occurring under certain environmental conditions. Due to these gaps in knowledge the first snow chemistry models have attempted to reproduce certain processes like the long-term incorporation of volatile compounds in snow and firn or the release of reactive species from the snowpack. Although so far none of the models offers a coupled approach of physical and chemical processes or a detailed representation of the different compartments, they have successfully been used to reproduce some field experiments. A fully coupled snow chemistry and physics model remains to be developed.

show abstract

“…Note, however, that aspect ratio could depend on size (Auer Jr and Veal, 1970;Um et al, 2014). Cloud chamber, in situ, and remote sensing observations indicate that distorted, roughened ice crystals are generally prevalent (Baran, 2009;van Diedenhoven et al, 2013;Pfalzgraff et al, . Simulated Q with respect to view zenith angle for liquid (blue) and ice clouds, including an ice cloud comprised of pristine crystals (green, roughened crystal clouds are shown in red).…”

Section: Observabilitymentioning

confidence: 99%

Cloud thermodynamic phase detection with polarimetrically sensitive passive sky radiometers

et al. 2015

View full text Add to dashboard Cite

Abstract. The primary goal of this project has been to investigate if ground-based visible and near-infrared passive radiometers that have polarization sensitivity can determine the thermodynamic phase of overlying clouds, i.e., if they are comprised of liquid droplets or ice particles. While this knowledge is important by itself for our understanding of the global climate, it can also help improve cloud property retrieval algorithms that use total (unpolarized) radiance to determine cloud optical depth (COD). This is a potentially unexploited capability of some instruments in the NASA Aerosol Robotic Network (AERONET), which, if practical, could expand the products of that global instrument network at minimal additional cost.We performed simulations that found, for zenith observations, that cloud thermodynamic phase is often expressed in the sign of the Q component of the Stokes polarization vector. We chose our reference frame as the plane containing solar and observation vectors, so the sign of Q indicates the polarization direction, parallel (positive) or perpendicular (parallel) to that plane. Since the fraction of linearly polarized to total light is inversely proportional to COD, optically thin clouds are most likely to create a signal greater than instrument noise. Besides COD and instrument accuracy, other important factors for the determination of cloud thermodynamic phase are the solar and observation geometry (scattering angles between 40 and 60 • are best), and the properties of ice particles (pristine particles may have halos or other features that make them difficult to distinguish from water droplets at specific scattering angles, while extreme ice crystal aspect ratios polarize more than compact particles).We tested the conclusions of our simulations using data from polarimetrically sensitive versions of the Cimel 318 sun photometer/radiometer that compose a portion of AERONET. Most algorithms that exploit Cimel polarized observations use the degree of linear polarization (DoLP

show abstract

Scanning electron microscopy and molecular dynamics of surfaces of growing and ablating hexagonal ice crystals

Cited by 67 publications

References 36 publications

Incidence of rough and irregular atmospheric ice particles from Small Ice Detector 3 measurements

Incidence of rough and irregular atmospheric ice particles from Small Ice Detector 3 measurements

A review of air–ice chemical and physical interactions (AICI): liquids, quasi-liquids, and solids in snow

Cloud thermodynamic phase detection with polarimetrically sensitive passive sky radiometers

Contact Info

Product

Resources

About