Retrieval of microphysical characteristics of particles in atmospheres of distant comets from ground-based polarimetry

Dlugach, Janna M.; Ivanova, Oleksandra; Mishchenko, Michael I.; Afanasiev, V. L.

doi:10.1016/j.jqsrt.2017.10.002

Cited by 20 publications

(8 citation statements)

References 40 publications

(67 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…However, Model 6, 9, and 11 aerosols containing large amounts of refractory materials could cause much larger LDRs and could even reproduce exceptionally high, spectrally dependent values such as those measured by Burton et al [14] for a plume of aged smoke. Our results demonstrate that spectral LDR measurements can be used to identify the presence of morphologically complex smoke particles, even though additional observations (e.g., with a passive polarimeter [87,88,[118][119][120][121] or a bistatic polarization lidar [122][123][124][125]) may be required to narrow down the plausible ranges of particle morphology (including size) and composition.…”

Section: Discussionmentioning

confidence: 88%

Scattering and Radiative Properties of Morphologically Complex Carbonaceous Aerosols: A Systematic Modeling Study

Liu

Mishchenko

2018

Remote Sensing

View full text Add to dashboard Cite

This paper provides a thorough modeling-based overview of the scattering and radiative properties of a wide variety of morphologically complex carbonaceous aerosols. Using the numerically-exact superposition T-matrix method, we examine the absorption enhancement, absorption Ångström exponent (AAE), backscattering linear depolarization ratio (LDR), and scattering matrix elements of black-carbon aerosols with 11 different model morphologies ranging from bare soot to completely embedded soot-sulfate and soot-brown carbon mixtures. Our size-averaged results show that fluffy soot particles absorb more light than compact bare-soot clusters. For the same amount of absorbing material, the absorption cross section of internally mixed soot can be more than twice that of bare soot. Absorption increases as soot accumulates more coating material and can become saturated. The absorption enhancement is affected by particle size, morphology, wavelength, and the amount of coating. We refute the conventional belief that all carbonaceous aerosols have AAEs close to 1.0. Although LDRs caused by bare soot and certain carbonaceous particles are rather weak, LDRs generated by other soot-containing aerosols can reproduce strong depolarization measured by Burton et al. for aged smoke. We demonstrate that multi-wavelength LDR measurements can be used to identify the presence of morphologically complex carbonaceous particles, although additional observations can be needed for full characterization. Our results show that optical constants of the host/coating material can significantly influence the scattering and absorption properties of soot-containing aerosols to the extent of changing the sign of linear polarization. We conclude that for an accurate estimate of black-carbon radiative forcing, one must take into account the complex morphologies of carbonaceous aerosols in remote sensing studies as well as in atmospheric radiation computations.These fresh soot aerosols are mostly hydrophobic and externally mixed with other aerosol constituents, but tend to become semi-externally and internally mixed (according to the mixing classification in Ref.[21]) as they age in the atmosphere. The aging processes include condensation of sulfates, nitrates, organics, and water on soot particles' surfaces; coagulation with preexisting aerosols; and heterogeneous reactions with gaseous oxidants [22][23][24][25]. Meanwhile, the soot aggregate morphology changes and exhibits compaction from fluffy to more densely packed formations [26][27][28].According to Ueda et al. [29,30], carbonaceous aerosols can be classified into seven types based on their dominant morphology: soot aggregates, spherical particles, coccoid particles, dome-like particles, clusters of spherical and coccoid bodies, crystalline coarse bodies, and re-crystallized droplet particles. China et al. [31,32] classify the soot component of carbonaceous aerosols into four major morphological types: embedded, with soot fully engulfed by, e.g., a sulfate host; partly coated, wherein the coating ma...

show abstract

Section: Discussionmentioning

confidence: 88%

Scattering and Radiative Properties of Morphologically Complex Carbonaceous Aerosols: A Systematic Modeling Study

Liu

Mishchenko

2018

Remote Sensing

View full text Add to dashboard Cite

show abstract

“…Also, it was considered that the nature of the dust particles presented in cometary coma does not depend on the heliocentric distance (Dollfus et al 1988). However, new investigations show differences between the activity of comets close to the Sun and distant comets (see, e.g., Mazzotta Epifani et al 2007Ivanova et al 2011Ivanova et al , 2015bDlugach et al 2018). Most likely the particles which form the comae are different.…”

Section: Discussionmentioning

confidence: 99%

Photometry, spectroscopy, and polarimetry of distant comet C/2014 A4 (SONEAR)

Ivanova

Lukyanyk

Kolokolova

et al. 2019

A&A

View full text Add to dashboard Cite

Context. The study of distant comets, which are active at large heliocentric distances, is important for better understanding of their physical properties and mechanisms of long-lasting activity. Aims. We analyze the dust environment of the distant comet C/2014 A4 (SONEAR), with a perihelion distance near 4.1 au, using comprehensive observations obtained by different methods. Methods. We present an analysis of spectroscopy, photometry, and polarimetry of comet C/2014 A4 (SONEAR), which were performed on November 5 -7, 2015, when its heliocentric distance was 4.2 au and phase angle was 4.7 • . Long-slit spectra and photometric and linear polarimetric images were obtained using the focal reducer SCORPIO-2 attached to the prime focus of the 6-m telescope BTA (SAO RAS, Russia). We simulated the behavior of color and polarization in the coma presenting the cometary dust as a set of polydisperse polyshapes rough spheroids. Results. No emissions were detected in the 3800 -7200 Å wavelength range. The continuum showed a reddening effect with the normalized gradient of reflectivity 21.6±0.2% per 1000 Å within the 4650 -6200 Å wavelength region. The fan-like structure in the sunward hemisphere was detected. The radial profiles of surface brightness differ for r-sdss and g-sdss filters, indicating predominance of submicron and micron-sized particles in cometary coma. The dust color (g-r) varies from 0.75±0.05 m to 0.45±0.06 m along the tail. For aperture radius near 20 000 km, the dust productions in various filters were estimated as A f ρ = 680±18 cm (r-sdss) and 887±16 cm (g-sdss). The polarization map showed spatial variations of polarization over the coma from about -3% near the nucleus to -8% at cometocentric distance about 150 000 km. Our simulations show that the dust particles were dominated (or covered) by ice and tholin-like organics. Spatial changes in the color and polarization can be explained by particle fragmentation.

show abstract

“…Particles with D falling between 2 and 3 are fluffy and contain voids that disappear when D approaches 3. Although the recent findings on comet 67P/Chutyumov-Gerasimenko point out that the pristine porous aggregates can be described with fractal dimension of 1.7, we adopted the value of D to be about 2.8, which characterized rather compact aggregates, in accordance with the results of light scattering numerical modeling of distant comets (Dlugach et al 2018). The bulk density and size of a subunit were put at 3200 kg m −3 and 0.1 µm, respectively.…”

Section: Discussionmentioning

confidence: 99%

Physical activity of the selected nearly isotropic comets with perihelia at large heliocentric distance

Kulyk

Rousselot

Корсун

et al. 2018

A&A

View full text Add to dashboard Cite

Context. The systematic investigation of comets in a wide range of heliocentric distances can contribute to a better understanding of the physical mechanisms that trigger activity at large distances from the Sun and reveals possible differences in the composition of outer solar system bodies belonging to various dynamical groups. Aims. We seek to analyze the dust environment of the selected nearly isotropic comets with a perihelion distance between 4.5 and 9.1 au, where sublimation of water ice is considered to be negligible. Methods. We present results of multicolor broadband photometric observations for 14 distant active objects conducted between 2008 and 2015 with various telescopes. Images obtained with broadband filters were used to investigate optical colors of the cometary comae and to quantify physical activity of the comet nuclei. Results. The activity level was estimated with Afρ parameters ranging between 95 ± 10 cm and 9600 ± 300 cm. Three returning comets were less active than the dynamically new comets. Dust production rates of the comet nuclei were estimated between 1 and 100 kg s−1 based on some assumptions about the physical properties of dust particles populating comae. The measured colors point out reddening of the continuum for all the comets. The mean values of a normalized reflectivity gradient within the group of the comets amount to 14 ± 2% per 1000 Å and 3 ± 2% per 1000 Å in the BV and VR spectral domains, respectively. The comae of the dynamically new comets, which were observed on their inbound legs, may be slightly redder in the blue spectral interval than comae of the comets observed after the perihelion passages. The dynamically new comets observed both pre- and post-perihelion, seem to have higher production rates post-perihelion than pre-perihelion for similar heliocentric distances.

show abstract

Retrieval of microphysical characteristics of particles in atmospheres of distant comets from ground-based polarimetry

Abstract: We summarize unique aperture data on the degree of linear polarization observed for distant

Cited by 20 publications

References 40 publications

Scattering and Radiative Properties of Morphologically Complex Carbonaceous Aerosols: A Systematic Modeling Study

Scattering and Radiative Properties of Morphologically Complex Carbonaceous Aerosols: A Systematic Modeling Study

Photometry, spectroscopy, and polarimetry of distant comet C/2014 A4 (SONEAR)

Physical activity of the selected nearly isotropic comets with perihelia at large heliocentric distance

Contact Info

Product

Resources

About