Local time dependence of polar mesospheric clouds: a model study

Schmidt, Francie; Baumgarten, Gerd; Berger, Uwe; Fiedler, Jens; Lübken, Franz‐Josef

doi:10.5194/acp-18-8893-2018

Cited by 10 publications

(16 citation statements)

References 51 publications

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“…These calculations represent the lowest critical saturations currently assumed in mesospheric models (e.g. Berger and Lübken, 2015;Schmidt et al, 2018). However, it is expected that the majority of MSPs in the mesopause is smaller than r = 1.2 nm (Bardeen et al, 2008;Megner et al, 2008a, b;Plane et al, 2014).…”

Section: Critical Saturation For Ice Activationmentioning

confidence: 97%

“…Additional studies have shown that during NLC season local temperatures are highly variable with mean temperatures of about 140 K and extremes as low as 100 K (Lübken et al, 2009;Rapp et al, 2002). Typical H 2 O concentrations of a few parts per million (Hervig et al, 2009;Seele and Hartogh, 1999) then lead to highly supersaturated conditions, i.e. saturation ratios exceeding S h = 100 are frequently observed (Lübken et al, 2009).…”

Section: Introductionmentioning

confidence: 99%

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Unravelling the microphysics of polar mesospheric cloud formation

2019

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Polar mesospheric clouds are the highest water ice clouds occurring in the terrestrial atmosphere. They form in the polar summer mesopause, the coldest region in the atmosphere. It has long been assumed that these clouds form by heterogeneous nucleation on meteoric smoke particles which are the remnants of material ablated from meteoroids in the upper atmosphere. However, until now little was known about the properties of these nanometre-sized particles and application of the classical theory for heterogeneous ice nucleation was impacted by large uncertainties. In this work, we performed laboratory measurements on the heterogeneous ice formation process at mesopause conditions on small (r = 1 to 3 nm) iron silicate nanoparticles serving as meteoric smoke analogues. We observe that ice growth on these particles sets in for saturation ratios with respect to hexagonal ice below S h = 50, a value that is commonly exceeded during the polar mesospheric cloud season, affirming meteoric smoke particles as likely nuclei for heterogeneous ice formation in mesospheric clouds. We present a simple ice-activation model based on the Kelvin-Thomson equation that takes into account the water coverage of iron silicates of various compositions. The activation model reproduces the experimental data very well using bulk properties of compact amorphous solid water. This is in line with the finding from our previous study that ice formation on iron silicate nanoparticles occurs by condensation of amorphous solid water rather than by nucleation of crystalline ice at mesopause conditions. Using the activation model, we also show that for iron silicate particles with dry radius larger than r = 0.6 nm the nanoparticle charge has no significant effect on the ice-activation threshold.

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Section: Critical Saturation For Ice Activationmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

Unravelling the microphysics of polar mesospheric cloud formation

2019

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“…Satellites mostly operate in sun-synchronous orbits and are thus not able to cover NLC local time variations, with some exceptions (e.g., Stevens et al, 2009;De-Land et al, 2011). NLC variability during the solar day was also investigated by models (e.g., Stevens et al, 2010Stevens et al, , 2017Schmidt et al, 2018). In general, maximum values for occurrence and brightness are found in the first half of the solar day, which is attributed to temperature tides and tidal variations in background water vapor.…”

Section: Simultaneous Solar and Lunar Tidal Variationsmentioning

confidence: 99%

Solar and lunar tides in noctilucent clouds as determined by ground-based lidar

Fiedler¹,

Baumgarten²

2018

Atmos. Chem. Phys.

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Abstract. Noctilucent clouds (NLCs) occur during summer from midlatitudes to high latitudes. They consist of nanometer-sized ice particles in an altitude range from 80 to 90 km and are sensitive to ambient temperature and water vapor content, which makes them a suitable tracer for variability on all timescales. The data set acquired by the ALOMAR Rayleigh–Mie–Raman (RMR) lidar covers 21 years and is investigated regarding tidal signatures in NLCs. For the first time solar and lunar tidal parameters in NLCs were determined simultaneously from the same data. Several NLC parameters are subject to persistent mean variations throughout the solar day as well as the lunar day. Variations with lunar time are generally smaller compared to variations with solar time. NLC occurrence frequency shows the most robust imprint of the lunar semidiurnal tide. Its amplitude is about 50 % of the solar semidiurnal tide, which is surprisingly large. Phase progressions of NLC occurrence frequency indicate upward propagating solar tides. Below 84 km altitude the corresponding vertical wavelengths are between 20 and 30 km. For the lunar semidiurnal tide phase progressions vary symmetrically with respect to the maximum of the NLC layer.

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“…activation temperatures currently assumed in mesospheric models (e.g. Berger and Lübken, 2015;Schmidt et al, 2018). For < 1.1 nm, the size of most MSPs in the polar summer mesopause (Bardeen et al, 2010;Megner et al, 2008a;Megner et al, 2008b;Plane et al, 2014), the new activation model excluding solar irradiation predicts ice particle formation at higher temperatures than currently assumed in models.…”

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

confidence: 93%

“…Either activation-barrier free growth is assumed to set in for saturations in excess of the equilibrium saturation over the curved particle surface (e.g. Berger and Lübken, 2015;Schmidt et al, 2018), or ice particle formation is described using classical nucleation theory (e.g. Asmus et al, 2014;Bardeen et al, 2010;Rapp and Thomas, 2006;Wilms et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

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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Local time dependence of polar mesospheric clouds: a model study

Cited by 10 publications

References 51 publications

Unravelling the microphysics of polar mesospheric cloud formation

Unravelling the microphysics of polar mesospheric cloud formation

Solar and lunar tides in noctilucent clouds as determined by ground-based lidar

The impact of solar radiation on polar mesospheric ice particle formation

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