Ice-nucleating particle versus ice crystal number concentration in altocumulus and cirrus embedded in Saharan dust: A closure study

Abstract

<p><strong>Abstract.</strong> For the first time, a closure study of the relationship between ice-nucleating particle concentration (INPC) and ice crystal number concentration (ICNC) in altocumulus and cirrus layers, solely based on ground-based active remote sensing, is presented. Such aerosol-cloud closure experiments are required (a) to better understand aerosol-cloud interaction in the case of mixed-phase clouds, (b) to explore to what extend heterogeneous ice nucleation can contribute to cirrus formation which is usually controlled by homogeneous freezing, and (c) to check the usefulness of available INPC parameterization schemes, applied to lidar profiles of aerosol optical and microphysical properties up to tropopause level. The INPC-vs-ICNC closure studies were conducted in Cyprus (Limassol and Nicosia) during a six-week field campaign in March–April 2015 and during the 17-month CyCARE (Cyprus Clouds Aerosol and Rain Experiment) campaign. Focus is on altocumulus and cirrus layers which developed in pronounced Saharan dust layers at heights from 5–11 km. Cloud top temperatures ranged from −20 °C to −57 °C. INPC was estimated from polarization/Raman lidar observations in combination with published INPC parameterization schemes for immersion and deposition nucleation. ICNC was estimated from combined Doppler lidar, aerosol lidar, and cloud radar observations of the terminal velocity of falling ice crystals, radar reflectivity and lidar backscatter in combination with modeling of backscattering at 532 nm and 8.5 mm wavelength. Good to acceptable agreement between INPC (observed before and after the occurrence of the cloud layer under investigation) and ICNC values was found in three proof-of-concept closure experiments. In these case studies, INPC and ICNC values matched within an order of magnitude (i.e., within the uncertainty ranges of the INPC and ICNC estimates), and ranged from 0.1–10 per liter in the altocumulus layers and 1–50 per liter in the cirrus layers observed between 8–11 km height.</p>

Retrieval of ice-nucleating particle concentrations from lidar observations and comparison with UAV in situ measurements

“…It also performs near-range measurements of two elastic and two Raman channels. More details about the instrument and its measurements are provided in Engelmann et al (2016) and Baars et al (2016). In brief, the nighttime backscatter (β p ) and extinction (α p ) coefficient profiles at 532 nm are derived using the Raman method proposed by Ansmann et al (1992).…”

“…We calculated the n INP profiles from the lidar measurements by first separating the lidar backscatter profile into its dust and nondust components using the aerosol-type separation technique introduced by Shimizu et al (2004) and . For this method we consider a dust particle linear depolarization ratio of δ d = 0.31±0.04 Ansmann et al, 2011a) and a nondust particle linear depolarization ratio of δ nd = 0.05 ± 0.03 (Müller et al, 2007;Groß et al, 2013;Baars et al, 2016;Haarig et al, 2017). The observed particle linear depolarization ratio in between these marginal values is therefore attributed to a mixture of the two aerosol types.…”

Dust mass, cloud condensation nuclei, and ice-nucleating particle profiling with polarization lidar: updated POLIPHON conversion factors from global AERONET analysis

“…Guided by these questions we studied the AERONET database regarding the relationship between dust extinction values and dust number, surface, and volume concentrations in large detail. The study presented here was also motivated by the growing PollyNET (Portable Lidar System Network) activities (Baars et al, 2016;Engelmann et al, 2016). Meanwhile, long-term observations are available, e.g., for Greece and Cyprus, Is-rael, the United Arab Emirates, Tajikistan, and South Korea, and recently also for southern Chile.…”

Ice crystal number concentration from lidar, cloud radar and radar wind profiler measurements

“…The complex aerosol-clouddynamics interaction currently poses major challenges for the numerical modeling of climate and weather phenomena because the majority of rain formation on Earth happens through the ice phase (Mülmenstädt et al, 2015). The process of heterogeneous ice nucleation in clouds is of particular importance because it constitutes the link between aerosol conditions -including ice-nucleating particle concentration (INPC) -and precipitation formation (Ansmann et al, 2019). An understanding of ice nucleation and growth is necessary for understanding precipitation formation, cloud stability (Korolev et al, 2017), secondary ice formation (Sullivan et al, 2017) and cloud radiative transfer (Sun and Shine, 1994).…”