Surface roughness during depositional growth and sublimation of ice crystals
2018
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.
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