Incidence of rough and irregular atmospheric ice particles from Small Ice Detector 3 measurements

Abstract

Abstract. The knowledge of properties of ice crystals such as size, shape, concavity and roughness is critical in the context of radiative properties of ice and mixed-phase clouds. Limitations of current cloud probes to measure these properties can be circumvented by acquiring two-dimensional lightscattering patterns instead of particle images. Such patterns were obtained in situ for the first time using the Small Ice Detector 3 (SID-3) probe during several flights in a variety of mid-latitude mixed-phase and cirrus clouds. The patterns are analysed using several measures of pattern texture, selected to reveal the magnitude of particle roughness or complexity. The retrieved roughness is compared to values obtained from a range of well-characterized test particles in the laboratory. It is found that typical in situ roughness corresponds to that found in the rougher subset of the test particles, and sometimes even extends beyond the most extreme values found in the laboratory. In this study we do not differentiate between small-scale, fine surface roughness and large-scale crystal complexity. Instead, we argue that both can have similar manifestations in terms of light-scattering properties and also similar causes. Overall, the in situ data are consistent, with ice particles with highly irregular or rough surfaces being dominant. Similar magnitudes of roughness were found in growth and sublimation zones of cirrus. The roughness was found to be negatively correlated with the halo ratio, but not with other thermodynamic or microphysical properties found in situ. Slightly higher roughness was observed in cirrus forming in clean oceanic air masses than in a continental, polluted one. Overall, the roughness and complexity are expected to lead to increased shortwave cloud reflectivity, in comparison with cirrus composed of more regular, smooth ice crystal shapes. These findings put into question suggestions that climate could be modified through aerosol seeding to reduce cirrus cover and optical depth, as the seeding may result in decreased shortwave reflectivity.

Vertical distribution of microphysical properties of Arctic springtime low-level mixed-phase clouds over the Greenland and Norwegian seas

“…This will allow to complete and validate the present results. For example, instruments like the small ice detector (SID-3; Ulanowski et al, 2014;Vochezer et al, 2016) or the cloud particle spectrometer with polarization detection (CPSPD; Baumgardner et al, 2014) should provide valuable measurements to differentiate droplets from ice crystals even at sizes lower than 50 µm. Both probes are an open path to avoid shattering artifacts.…”

A statistical comparison of cirrus particle size distributions measured using the 2-D stereo probe during the TC<sup>4</sup>, SPARTICUS, and MACPEX flight campaigns with historical cirrus datasets

“…(7), F (x) is, ideally, the universal, normalized PSD (Meakin, 1992;Westbrook et al, 2004a, b;D05;Tinel et al, 2005;D14). The quantities N * 0 and D m are the functions of 2D-S-measured PSD moments that are required for application to the D05/D14 parameterizations in order to produce parameterized, corrected 2DC PSDs and parameterized, uncorrected 2DC PSDs (see Fig.…”

“…Shattered-particle removal is based on modeling particle inter-arrival times by a Poisson process, assuming that each inter-arrival time is independent of all other inter-arrival times. posit that particle clustering (Hobbs and Rangno, 1985;Kostinski and Shaw, 2001;Pinsky and Khain, 2003;Khain et al, 2007), which would violate this basic assumption, is not likely a matter of significant concern as cirrus particles are naturally spread further apart than are liquid droplets and sediment over a continuum of size-dependent speeds.…”

“…However, while data from VIPS, fast FSSP, and Small Ice Detector-3 (SID-3; Ulanowski et al, 2014) probes are available to complement the OAP data used in this study, none of them are used on account of sizing uncertainties stemming from their small sample volumes and from spherical particle assumptions. The two publications wherewith comparison is made in this paper also restricted their datasets to OAPs.…”

Halo ratio from ground based all-sky imaging

“…Unlike in previous studies which tended to use slightly smaller angles (Auriol et al, 2001;Gayet et al, 2011;Ulanowski et al, 2014;Forster et al, 2017) we have used a ratio at scattering angles of 23…”