Cloud‐aerosol interactions during autumn over Beaufort Sea

Abstract

Abstract. Cloud and aerosol properties were observed by aircraft in autumn over the Beaufort Sea during the 1994 Beaufort and Arctic Storms Experiment (BASE). The microphysical properties (particle size, concentration, mass, and phase) and vertical structure of autumn clouds are examined as a function of height and minimum in-cloud temperature, rmi n. Below 2 km, liquid clouds were observed at rmi n between -5 ø and-9øC, mixed-phase clouds were observed between -5 ø and -20øC, and clear-sky ice crystal precipitation was observed at rmi n as warm as -14øC. Between 2 and 5 km all clouds were mixed-phase and typically consisted of a thin layer of liquid with ice extending well below the liquid layer. These mixed-phase clouds were found at rmi n as low as -32øC. All clouds observed above 5.5 km were composed entirely of ice at rmi n as warm as -33øC. The concentration of ice crystals is observed to increase exponentially with decreasing rmi n. The Hallet-Mossop ice multiplication process did not appear to be an important in the production of ice crystals in the mixed-phase cloud observed in this study. The atmosphere was relatively clean with condensation nuclei (CN) concentrations rarely exceeding 300 cm -3. The smallest CN concentrations (as low as 50 cm -3) were observed in the boundary layer and just above the surface where precipitation and nucleation scavenging have cleansed the air. Thin layers of very large CN concentrations were often observed within and just above low-level clouds possibly resulting from gas-to-particle conversion which requires clean and humid air typical of lower Arctic atmosphere.

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

“…For cloud top temperatures below −20 • C, IWP and LWP reach values close to 30 and 50 g m −2 , respectively. The IWP decreases dramatically when the cloud top temperature increases; very low values close to 0 are encountered at temperatures above −8 • C. LWP reaches a maximum of 100 g m −2 at −13 • C and the smallest values (around 15 g m −2 ) are encountered when the cloud top temperature is typically around −18 • C. These findings are consistent with the main previous studies devoted to Arctic MPCs Pinto, 1998;Pinto and Curry, 2001;Shupe et al, 2006). They reported mean LWP values in the range of 20-70 g m −2 , with some maxima up to around 130 g m −2 , and IWP mean values less than 40 g m −2 .…”

Intercomparison of model simulations of mixed‐phase clouds observed during the ARM Mixed‐Phase Arctic Cloud Experiment. I: single‐layer cloud

“…A major finding of these experiments was the observed frequency and persistence of supercooled liquid water and mixed-phase stratiform clouds throughout the year Pinto et al, 2001;Intrieri et al, 2002;Shupe and Intrieri, 2004). In contrast to midlatitude cloud systems, there is little temperature dependence for the amount of liquid versus ice in Arctic mixed-phase clouds McFarquhar and Cober, 2004;Turner, 2005).…”

Ground-based lidar measurements from Ny-Ålesund during ASTAR 2007

“…Currently, cloud parameterizations distinguish ice and liquid phase of mixed-phase clouds mainly as a function of temperature alone and are in need of improvement of Arctic cloud parametrization (Vavrus and Waliser, 2008). On the other hand measurements have shown that the liquid water content at low temperatures is sometimes higher than expected and that apart from temperature other parameters such as cooling rates must be considered as well (Pinto et al, 2001). The influence of Arctic aerosol on the climate and radiation budget has been discussed in Treffeisen et al (2005) and Rinke et al (2004).…”