Articles | Volume 15, issue 7
Research article
02 Apr 2015
Research article |  | 02 Apr 2015

A new temperature- and humidity-dependent surface site density approach for deposition ice nucleation

I. Steinke, C. Hoose, O. Möhler, P. Connolly, and T. Leisner

Abstract. Deposition nucleation experiments with Arizona Test Dust (ATD) as a surrogate for mineral dusts were conducted at the AIDA cloud chamber at temperatures between 220 and 250 K. The influence of the aerosol size distribution and the cooling rate on the ice nucleation efficiencies was investigated. Ice nucleation active surface site (INAS) densities were calculated to quantify the ice nucleation efficiency as a function of temperature, humidity and the aerosol surface area concentration. Additionally, a contact angle parameterization according to classical nucleation theory was fitted to the experimental data in order to relate the ice nucleation efficiencies to contact angle distributions. From this study it can be concluded that the INAS density formulation is a very useful tool to describe the temperature- and humidity-dependent ice nucleation efficiency of ATD particles.

Deposition nucleation on ATD particles can be described by a temperature- and relative-humidity-dependent INAS density function ns(T, Sice) with

ns(xtherm) = 1.88 ×105 · exp(0.2659 · xtherm) [m−2] , (1)

where the temperature- and saturation-dependent function xtherm is defined as

xtherm = −(T−273.2)+(Sice−1) ×100, (2)

with the saturation ratio with respect to ice Sice >1 and within a temperature range between 226 and 250 K. For lower temperatures, xtherm deviates from a linear behavior with temperature and relative humidity over ice.

Also, two different approaches for describing the time dependence of deposition nucleation initiated by ATD particles are proposed. Box model estimates suggest that the time-dependent contribution is only relevant for small cooling rates and low number fractions of ice-active particles.

Short summary
Ice nucleation in clouds has a significant influence on the global radiative budget and the hydrological cycle. Several studies have investigated the ice formation in droplets and parameterizations have been developed in order to include immersion freezing in climate models. In contrast, there are fewer studies regarding the conversion of water vapor into ice (so-called deposition nucleation) which is the topic of this paper which investigates deposition nucleation by Arizona Test dust in detail
Final-revised paper