Unravelling the microphysics of polar mesospheric cloud formation

Duft, Denis; Nachbar, Mario; Leisner, Thomas

doi:10.5194/acp-2018-1018

Cited by 6 publications

(22 citation statements)

References 42 publications

(62 reference statements)

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“…We found that the primary ice phase forming on the MSP analogues at the conditions of the summer mesopause is Amorphous Solid Water (ASW) (Nachbar et al, 2018b;Nachbar et al, 2018c). Additionally, we showed that MSPs adsorb up to several layers of water until ice growth activates as soon as the saturation exceeds the saturation vapor pressure of ASW including the Kelvin effect for the ice-covered or "wet" particle radius, and considering the collision radius of water molecules (Duft et al, 2018). Asmus et al (2014) pointed out that MSPs may heat up in the low density atmosphere of the mesopause by absorbing solar and terrestrial irradiation.…”

Section: Introductionmentioning

confidence: 94%

“…In this section we discuss the impact of solar radiation on the critical temperature of the environment T cr,env needed to activate ice growth. To this end we combine our previously presented ice growth activation model (Duft et al, 2018) with the equilibrium temperature model of this work. A description of the method can be found in Appendices A and B.…”

Section: The Impact Of Solar Radiation On Ice Particle Formation 10mentioning

confidence: 99%

“…In order to estimate the maximum impact of solar radiation, we assume that the particles are composed of FeO, the potential MSP material with the highest iron content and which is therefore expected to heat up the most. To calculate the water coverage 15 on FeO particles we use an energy of desorption 0 = 42.7 kJ/mol, which was previously determined for Fe 2 O 3 particles (Duft et al, 2018). For the incoming solar irradiation we use the maximum solar zenith angle of 46.5°(21 st June, noon) at 69°N, a typical latitude of MSP observations.…”

Section: The Impact Of Solar Radiation On Ice Particle Formation 10mentioning

confidence: 99%

“…We only analyse data with coverages above 1 mono-layer for which the desorption energy is expected to depend only weakly on H 2 O coverage (Mazeina and Navrotsky, 2007;Navrotsky et al, 2008;Sneh et al, 1996). For such coverages we did not observe any significant influence of the H 2 O coverage or the particle temperature on the values of 0 determined in our previous study (Duft et al, 2018). Therefore, we can determine the particle temperature under light illumination assuming a 25 constant 0 -value.…”

mentioning

confidence: 91%

“…In equilibrium, the adsorbing flux density j ads and desorbing flux density j des of water molecules are equal (Duft et al, 2018):…”

mentioning

confidence: 99%

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The impact of solar radiation on polar mesospheric ice particle formation

Nachbar¹,

Wilms²,

Duft³

et al. 2018

Preprint

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Abstract. Mean temperatures in the polar summer mesopause can drop to 130&#8201;K. The cold temperatures in combination with water vapor mixing ratios of a few parts per million give rise to the formation of ice particles. These ice particles may be observed as polar mesospheric clouds. Mesospheric ice cloud formation is believed to initiate heterogeneously on small aerosol particles (r&#8201;<&#8201;2&#8201;nm) composed of re-condensed meteoric material, so called Meteoric Smoke Particles (MSPs). Recently, we investigated the ice activation and growth behavior of MSP analogues under realistic mesopause conditions. Based on these measurements we presented a new activation model which largely reduced the uncertainties in describing ice particle formation. However, this activation model neglected the possibility that MSPs heat up in the low density mesopause due to absorption of solar and terrestrial irradiation. Radiative heating of the particles may severely reduce their ice formation ability. In this study we expose MSP analogues (Fe2O3 and FexSi1-xO3) to realistic mesopause temperatures and water vapor concentrations and investigate particle warming under the influence of variable intensities of visible light (405, 488, and 660&#8201;nm). We show that Mie theory calculations using refractive indices of bulk material from the literature combined with an equilibrium temperature model presented in this work predict the particle warming very well. Additionally, we confirm that the absorption efficiency increases with the iron content of the MSP material. We apply our findings to mesopause conditions and conclude that the impact of solar and terrestrial radiation on ice particle formation is significantly lower than previously assumed.

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Section: Introductionmentioning

confidence: 94%

Section: The Impact Of Solar Radiation On Ice Particle Formation 10mentioning

confidence: 99%

Section: The Impact Of Solar Radiation On Ice Particle Formation 10mentioning

confidence: 99%

mentioning

confidence: 91%

“…In equilibrium, the adsorbing flux density j ads and desorbing flux density j des of water molecules are equal (Duft et al, 2018):…”

mentioning

confidence: 99%

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The impact of solar radiation on polar mesospheric ice particle formation

Nachbar¹,

Wilms²,

Duft³

et al. 2018

Preprint

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The Phase of Water Ice Which Forms in Cold Clouds in the Mesospheres of Mars, Venus, and Earth

2021

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Water ice clouds can form in the coldest regions of rarefied planetary upper atmospheres, where particles grow through deposition from the vapor phase. Despite the very low partial pressures of water in the upper atmospheres of Venus, Earth, and Mars, the temperatures can be low enough (∼<150 K, depending on the planet) to lead to large supersaturations and the formation of ice particles. At these temperatures multiple metastable forms of ice can exist, but the phases that can form remain poorly defined. In this study, we focus on understanding the phase of ice that forms in this class of very cold clouds which exist in the upper atmospheres of three of the terrestrial planets in the solar system. In Earth's upper mesosphere (80-90 km), nanoparticles composed primarily of water ice form between 100 and 150 K, producing clouds known as Polar Mesospheric Clouds (PMCs) or noctilucent clouds (NLCs) (Hervig et al., 2001; Rapp & Thomas, 2006; Thomas, 1991). In the Martian atmosphere, water ice clouds have also been observed planet wide at altitudes up to 90 km where temperatures can drop to <120 K (Fedorova et al., 2020; Forget et al., 2009; Vincendon et al., 2011). In addition, water ice particles may serve as seeds for CO 2 ice particles in the Martian mesosphere (Plane et al., 2018). On Venus, the possibility of water Abstract Water ice clouds form in the mesospheres of terrestrial planets in the solar system (and most likely elsewhere) by vapor deposition at low pressures and temperatures. Under these conditions a range of crystalline and amorphous phases of ice might form. The phase is important because it influences nucleation kinetics, density, vapor pressure over the solid, growth rates and particle shape. In the past, the temperature range over which these different phases exist has been defined on the basis of depositing ice at low temperature and warming it while observing phase changes. However, the direct deposition of ice at a range of temperatures relevant for the terrestrial planets has not been systematically investigated. Here we present X-ray Diffraction (XRD) measurements of water ice deposited at temperature intervals between 88 and 145 K in a vacuum chamber. XRD patterns showed that low density amorphous ice was formed at ≤120 K, stacking disordered ice I formed from 121 to 135 K and hexagonal ice I formed at 140 and 145 K. Direct deposition results in the stable hexagonal phase at much lower temperatures than when warming stacking disordered ice. All three phases of water ice observed here are possible in clouds in the mesospheres of Earth and Mars, while on Venus only amorphous ice is likely to form. Plain Language Summary Ice clouds made up of water ice crystals can form in the thin upper atmospheres (mesospheres) of terrestrial planets where it can be extremely cold. Under these conditions a range of crystalline (hexagonal, cubic, or stacking disordered) and amorphous (lacking long range order) phases of ice might form. The phase is important because it influences a range of cloud properties. ...

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A Two‐Martian Years Survey of the Water Vapor Saturation State on Mars Based on ACS NIR/TGO Occultations

et al. 2022

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On Mars, condensation is the major factor constraining the vertical distribution of water vapor. Recent measurements of water and temperature profiles showed that water can be strongly supersaturated at and above the level where clouds form during the aphelion and perihelion seasons. Since 2018, the near‐infrared spectrometer (NIR) of the Atmospheric Chemistry Suite onboard the Trace Gas Orbiter has measured H2O and temperature profiles using solar occultation in the infrared from below 10 to 100 km of altitude. Here, we provide the first long‐term monitoring of the water saturation state. The survey spans 2 Martian years from Ls = 163° of MY34 to Ls = 170° of MY36. We found that water is often supersaturated above aerosol layers. In the aphelion season, the water mixing ratio above 40 km in the mid‐to‐high latitudes was below 3 ppmv and yet is found to be supersaturated. Around the perihelion, water is also supersaturated above 60 km with a mixing ratio of 30–50 ppmv. Stronger saturation is observed during the dusty season in MY35 compared to what was observed in MY34 during the Global Dust Storm and around the perihelion. Saturation varied between the evening and morning terminators in response to temperature modulation imparted by thermal tides. Although water vapor is more abundant in the evening, colder morning temperatures induce a daily peak of saturation. This data set establishes a new paradigm for water vapor on Mars, revealing that supersaturation is nearly ubiquitous, particularly during the dust season, thereby promoting water escape on an annual average.

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Unravelling the microphysics of polar mesospheric cloud formation

Cited by 6 publications

References 42 publications

The impact of solar radiation on polar mesospheric ice particle formation

The impact of solar radiation on polar mesospheric ice particle formation

The Phase of Water Ice Which Forms in Cold Clouds in the Mesospheres of Mars, Venus, and Earth

A Two‐Martian Years Survey of the Water Vapor Saturation State on Mars Based on ACS NIR/TGO Occultations

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