Thermodynamics of homogeneous nucleation of ice particles in the polar summer mesosphere

Abstract

Abstract. We present the hypothesis of homogeneous nucleation of ice nano-particles in the polar summer mesosphere. The nucleation of condensed phase is traced back to the first step on the formation pathway, which is assumed to be the transition of water vapor to amorphous cluster. Amorphous clusters then freeze into water ice, likely metastable cubic ice, when they reach the critical size. The estimates based on the equilibrium thermodynamics give the critical size (radius) of amorphous water clusters as about 1.0 nm. The same estimates for the final transition step, that is the transformation of cubic to hexagonal ice, give the critical size of about 15 nm at typical upper mesospheric conditions during the polar summer (temperature T =150 K, water vapor density ρ vapor =10 9 cm −3 ).

On the detection of mesospheric meteoric smoke particles embedded in noctilucent cloud particles with rocket-borne dust probes

“…Homogeneous mechanisms, where the mesospheric water vapor condenses to amorphous and even solid states, have furthermore been shown to compete with heterogenous nucleation when the temperature gradient is moderately negative, as can be the case in temporarily strong cooling forced by gravity waves propagating upwards. 44,48 Measurements of NLC particle radii have been found to be consistent with a mean of around 50 nm for a monodispersive distribution and shifted downwards for polydisperse distributions. [49][50][51] These "large" particles must therefore have grown substantially, even if the initial nucleus was a MSP with a radius in the upper tail of their theoretical size distribution (see Hunten, Turco, and Toon 38 and Megner, Rapp, and Gumbel 52 ).…”

“…6,43 However, impurities such as molecules of meteoric origin and larger MSPs may amplify the growth significantly by lowering the surface energy barrier for nucleation. 44,45 On the basis of rocket measurements and modeling, Havnes and Naesheim 3 shifted this view of the traditional NLC particle towards an ice dust particle with many embedded MSPs, uniformly distributed as the different nucleation and growth mechanisms compete until a depletion of the local water density. Recently, this embedded MSP prediction has obtained further support from satellite observations, 4 which estimates a volume filling factor of meteoric material between 0.01% and 3% in dust from polar mesospheric clouds (PMCs).…”

Charged meteoric smoke as ice nuclei in the mesosphere: Part 1—A review of basic concepts

“…It remains an open question to what extent this is applicable to the extremely cold ice surfaces representative for summer mesospheric conditions. A deeper discussion of these ideas has recently been given by Zasetsky et al (2009). Just as in the neutral case, the use of liquid drop theory for charged nucleation in the form of the Thomson equation has to rely on a number of approximations.…”

Equilibrium structure of dense gases

“…The clusters in real gases now attract a large attention of researches [4][5][6][7][8]. The Water vapor clusters are responsible for clouds formation in upper layers of atmosphere [9].…”

“…An alternative approach to the molecular interactions in fluids is based on the simulations of the many particle systems behavior with different model potentials [4][5][6][7][8][9]13]. The problem of this approach lies in rather arbitrary assumptions about the model potentials describing interactions between molecules in fluids.…”