Factors influencing the microphysics and radiative properties of liquid-dominated Arctic clouds: Insight from observations of aerosol and clouds during ISDAC

Abstract

[1] Aircraft measurements during the Indirect and Semi-Direct Aerosol Campaign (ISDAC) in April 2008 are used to investigate factors influencing the microphysics and radiative properties of springtime Arctic clouds. The analysis is focused on low-level, liquid-dominated clouds in two separate regimes with respect to cloud and aerosol properties: single-layer stratocumulus with below-cloud aerosol concentrations (N a ) less than 250 cm −3 (clean cases); and layered stratocumulus with N a > 500 cm −3 below cloud base, associated with a biomass burning aerosol (polluted cases). For each regime, vertical profiles through cloud are used to determine cloud microphysical and radiative properties. The polluted cases were correlated with warmer, geometrically thicker clouds, with higher droplet number concentrations (N d ), liquid water paths (LWP), optical depths (t), and albedo (A) relative to clean cases. The mean cloud droplet effective radii (r eff ), however, were similar (5.7 mm) for both aerosol-cloud regimes. This discrepancy resulted mainly from the higher LWP of clouds in polluted cases, which can be explained by both meteorological (temperature, dynamics) and microphysical (precipitation inhibition) factors. Adiabatic parcel model simulations demonstrate that differences in droplet activation between the aerosol-cloud regimes may play a role, as the higher N a in polluted cases limits activation to larger and/or more hygroscopic particles. The observations and analysis presented here demonstrate the complex interactions among environmental conditions, aerosol, and the microphysics and radiative properties of Arctic clouds.

Airborne Single Particle Mass Spectrometers (SPLAT II & miniSPLAT) and New Software for Data Visualization and Analysis in a Geo-Spatial Context

“…These observations of significant spatial variability in particle composition are consistent with previous reports of a highly stratified Arctic atmosphere [12,61,65]. Figure 4b provides another illustration of the use of NDScope to visualize, in GE display, the data collected during a spiral.…”

“…This approach is particularly useful when applied to composition-resolved size distributions. These densities, together with the mass spectra, are used to obtain quantitative information on particle composition, determine relative amounts of different components in the internally mixed particles, and convert the vacuum aerodynamic diameters into particle geometric diameters [54,60,61].…”

Dimethyl sulfide control of the clean summertime Arctic aerosol and cloud

“…The values of kappa used here (0.2 and 0.5) represent a more organic dominated particle (κ50.2) and a more sulfate dominated particle (κ50.5) as observed in the summer Arctic (Chang et al, 2011b) as well as at Alert during May of 2011 with the ACSM (Supplemental Material S1). The parcel lifting to form the simulated cloud is based on an updraft speed of 0.4 m s -1 as observed in clouds over north Alaska in April (Earle et al, 2011).…”

Arctic low-level boundary layer clouds: in situ measurements and simulations of mono- and bimodal supercooled droplet size distributions at the top layer of liquid phase clouds

“…This process was invoked by Lawson et al (2001) to explain the bimodal SDs in their observations. Further aerosol effects on ice nucleation, entrained in Arctic clouds, were observed and analyzed by Jackson et al (2012) and Earle et al (2011).…”