Variability of mixed-phase clouds in the Arctic with a focus on the Svalbard region: a study based on spaceborne active remote sensing

Abstract

Abstract. The Arctic region is known to be very sensitive to climate change. Clouds and in particular mixed-phase clouds (MPCs) remain one of the greatest sources of uncertainties in the modelling of the Arctic response to climate change due to an inaccurate representation of their variability and their quantification. In this study, we present a characterisation of the vertical, spatial and seasonal variability of Arctic clouds and MPCs over the entire Arctic region based on satellite active remote sensing observations. MPC properties in the region of the Svalbard archipelago (78 • N, 15 • E) are also investigated. The occurrence frequency of clouds and MPCs are determined from CALIPSO/CLOUDSAT measurements processed with the DARDAR retrieval algorithm, which allow for a reliable cloud thermodynamic phase classification (warm liquid, supercooled liquid, ice, mixing of ice and supercooled liquid). Significant differences are observed between MPC properties over the entire Arctic region and over the Svalbard region. Results show that MPCs are encountered all year long, with a minimum occurrence of 30 % in winter and 50 % during the rest of the year on average over the entire Arctic. Over the Svalbard region, MPC occurrence is more constant with time with larger values (55 %) compared to the average observed in the Arctic. MPCs are especially located at low altitudes, below 3000 m, where their frequency of occurrence reaches 90 %, particularly during winter, spring and autumn. Moreover, results highlight that MPCs are statistically more frequent above open sea than land or sea ice. The temporal and spatial distribution of MPCs over the Svalbard region seems to be linked to the supply of moister air and warmer water from the North Atlantic Ocean, which contribute to the initiation of the liquid water phase. Over the whole Arctic, and particularly in western regions, the increase of MPC occurrence from spring to autumn could be connected to the sea ice melting. During this period, the open water transports some of the warm water from the North Atlantic Ocean to the rest of the Arctic region. This facilitates the vertical transfer of moisture and thus the persistence of the liquid phase. Particular attention is also paid to the measurement uncertainties and how they could affect our conclusions.

Cloud vertical distribution from combined surface and space radar–lidar observations at two Arctic atmospheric observatories

“…Compared to surface-based observations, space-based observations show much fewer ice clouds and mixed-phase clouds, and slightly more liquid clouds from the surface to 1 km. These results are generally consistent with conclusions from previous studies (Protat et al, 2014;Blanchard et al, 2014;Mioche et al, 2015).…”

“…Among many valuable findings, they found that space-based radar-lidar measurements can depict a complete picture of the cloud vertical profile down to 2 km. Mioche et al (2015) compared vertical profiles of cloud occurrences from surface lidar and spacebased lidar, radar, and combined lidar and radar over the NyÅlesund station during March and April 2007, and showed similar results above 2 km as those in Blanchard et al (2014). The strengths and limitations of these observations are also discussed in other papers, e.g., Kay et al (2008), Gettleman (2009), andHuang et al (2012).…”

Characterisation of the artificial neural network CiPS for cirrus cloud remote sensing with MSG/SEVIRI

“…Over ice and snow the radiative contrast between the cirrus and the cold surface is reduced, making the cirrus cloud detection more difficult. Furthermore, mixed-phase clouds or supercooled liquid water layers above ice layers in the polar regions (Mioche et al, 2015;Verlinde et al, 2007;Shupe et al, 2006) may also reduce the POD as CiPS requires the water to be frozen to be classified as a cirrus. Moreover, temperature inversions, frequent in these areas (Wetzel and Brümmer, 2011), can make the cloud top of low ice clouds (Devasthale et al, 2011) appear warmer than the snow/ice-covered surface and thus reduce their detection (Wilson et al, 1993;Gao et al, 1998).…”

Summertime Arctic Aircraft Measurements during ACCACIA

“…When comparing these results to other campaigns, it must be noted that the Svalbard region, presents a larger occurrence of low-level MPCs compared to the average Arctic (e.g. Mioche et al 2015) and that the sea-ice cover in this region during July 2013 was the lowest on record, with coverage much lower than the years either side. As in previous 10 projects (e.g.…”

“…Shupe et al 2011). Mioche et al (2015), using satellite remote sensing, showed a large occurrence of MPCs all year, particularly in the Svalbard region, persisting for several days under a variety of conditions. These clouds have a substantial effect on the surface energy budget (e.g.…”