Surface roughness during depositional growth and sublimation of ice crystals

Jens Voigtländer,Cedric Chou,Henner Bieligk,Paul Herenz,Frank Stratmann,Tina Clauss,Dennis Niedermeier,Susan Hartmann,Georg Ritter,Zbigniew Ulanowski

doi:10.5194/acp-18-13687-2018

Abstract

Abstract. Ice surface properties can modify the scattering properties of atmospheric ice crystals and therefore affect the radiative properties of mixed-phase and cirrus clouds. The Ice Roughness Investigation System (IRIS) is a new laboratory setup designed to investigate the conditions under which roughness develops on single ice crystals, based on their size, morphology and growth conditions (relative humidity and temperature). Ice roughness is quantified through the analysis of speckle in 2-D light-scattering patterns. Characterization of the setup shows that a supersaturation of 20 % with respect to ice and a temperature at the sample position as low as −40 ∘C could be achieved within IRIS. Investigations of the influence of humidity show that higher supersaturations with respect to ice lead to enhanced roughness and irregularities of ice crystal surfaces. Moreover, relative humidity oscillations lead to gradual “ratcheting-up” of roughness and irregularities, as the crystals undergo repeated growth–sublimation cycles. This memory effect also appears to result in reduced growth rates in later cycles. Thus, growth history, as well as supersaturation and temperature, influences ice crystal growth and properties, and future atmospheric models may benefit from its inclusion in the cloud evolution process and allow more accurate representation of not just roughness but crystal size too, and possibly also electrification properties.

Highlights

Cloud properties and their effects remain the largest uncertainty in global climate models (Boucher et al, 2013)
The Ice Roughness Investigation System (IRIS) is a new laboratory setup designed to investigate the conditions under which roughness develops on single ice crystals, based on their size, morphology and growth conditions
An experimental system was developed to investigate lightscattering properties of single ice crystals grown on a glass fibre as a function of the prevailing thermodynamic conditions

Summary

Introduction

Cloud properties and their effects remain the largest uncertainty in global climate models (Boucher et al, 2013). Several cloud imaging probes like the Cloud Imaging Probe (CIP), Cloud Particle Imager (CPI) or various optical array probes (e.g. 2DC, 2DS), among others, have been developed over the last decades in order to characterize those parameters These probes have difficulties characterising the size and shape of smaller ice crystals, due to optical-resolution limitations. These probes do have a further limitation due to varying degrees of shattering of ice particles on their inlets, only partly reduced by various mitigation measures (Ulanowski et al, 2004; Field et al, 2006; Connolly et al, 2007; Jensen et al, 2009; Korolev et al, 2011; Baumgardner et al, 2017).

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Conclusion