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- ItemThe Arctic Cloud Puzzle: Using ACLOUD/PASCAL Multiplatform Observations to Unravel the Role of Clouds and Aerosol Particles in Arctic Amplification(Boston, Mass. : ASM, 2019) Wendisch, Manfred; Macke, Andreas; Ehrlich, André; Lüpkes, Christof; Mech, Mario; Chechin, Dmitry; Dethloff, Klaus; Velasco, Carola Barrientos; Bozem, Heiko; Brückner, Marlen; Clemen, Hans-Christian; Crewell, Susanne; Donth, Tobias; Dupuy, Regis; Ebell, Kerstin; Egerer, Ulrike; Engelmann, Ronny; Engler, Christa; Eppers, Oliver; Gehrmann, Martin; Gong, Xianda; Gottschalk, Matthias; Gourbeyre, Christophe; Griesche, Hannes; Hartmann, Jörg; Hartmann, Markus; Heinold, Bernd; Herber, Andreas; Herrmann, Hartmut; Heygster, Georg; Hoor, Peter; Jafariserajehlou, Soheila; Jäkel, Evelyn; Järvinen, Emma; Jourdan, Olivier; Kästner, Udo; Kecorius, Simonas; Knudsen, Erlend M.; Köllner, Franziska; Kretzschmar, Jan; Lelli, Luca; Leroy, Delphine; Maturilli, Marion; Mei, Linlu; Mertes, Stephan; Mioche, Guillaume; Neuber, Roland; Nicolaus, Marcel; Nomokonova, Tatiana; Notholt, Justus; Palm, Mathias; van Pinxteren, Manuela; Quaas, Johannes; Richter, Philipp; Ruiz-Donoso, Elena; Schäfer, Michael; Schmieder, Katja; Schnaiter, Martin; Schneider, Johannes; Schwarzenböck, Alfons; Seifert, Patric; Shupe, Matthew D.; Siebert, Holger; Spreen, Gunnar; Stapf, Johannes; Stratmann, Frank; Vogl, Teresa; Welti, André; Wex, Heike; Wiedensohler, Alfred; Zanatta, Marco; Zeppenfeld, SebastianClouds play an important role in Arctic amplification. This term represents the recently observed enhanced warming of the Arctic relative to the global increase of near-surface air temperature. However, there are still important knowledge gaps regarding the interplay between Arctic clouds and aerosol particles, and surface properties, as well as turbulent and radiative fluxes that inhibit accurate model simulations of clouds in the Arctic climate system. In an attempt to resolve this so-called Arctic cloud puzzle, two comprehensive and closely coordinated field studies were conducted: the Arctic Cloud Observations Using Airborne Measurements during Polar Day (ACLOUD) aircraft campaign and the Physical Feedbacks of Arctic Boundary Layer, Sea Ice, Cloud and Aerosol (PASCAL) ice breaker expedition. Both observational studies were performed in the framework of the German Arctic Amplification: Climate Relevant Atmospheric and Surface Processes, and Feedback Mechanisms (AC) project. They took place in the vicinity of Svalbard, Norway, in May and June 2017. ACLOUD and PASCAL explored four pieces of the Arctic cloud puzzle: cloud properties, aerosol impact on clouds, atmospheric radiation, and turbulent dynamical processes. The two instrumented Polar 5 and Polar 6 aircraft; the icebreaker Research Vessel (R/V) Polarstern; an ice floe camp including an instrumented tethered balloon; and the permanent ground-based measurement station at Ny-Ålesund, Svalbard, were employed to observe Arctic low- and mid-level mixed-phase clouds and to investigate related atmospheric and surface processes. The Polar 5 aircraft served as a remote sensing observatory examining the clouds from above by downward-looking sensors; the Polar 6 aircraft operated as a flying in situ measurement laboratory sampling inside and below the clouds. Most of the collocated Polar 5/6 flights were conducted either above the R/V Polarstern or over the Ny-Ålesund station, both of which monitored the clouds from below using similar but upward-looking remote sensing techniques as the Polar 5 aircraft. Several of the flights were carried out underneath collocated satellite tracks. The paper motivates the scientific objectives of the ACLOUD/PASCAL observations and describes the measured quantities, retrieved parameters, and the applied complementary instrumentation. Furthermore, it discusses selected measurement results and poses critical research questions to be answered in future papers analyzing the data from the two field campaigns.
- ItemSpatiotemporal variability of solar radiation introduced by clouds over Arctic sea ice(Katlenburg-Lindau : Copernicus, 2020) Barrientos Velasco, Carola; Deneke, Hartwig; Griesche, Hannes; Seifert, Patric; Engelmann, Ronny; Macke, AndreasThe role of clouds in recent Arctic warming is not fully understood, including their effects on the solar radiation and the surface energy budget. To investigate relevant small-scale processes in detail, the intensive Physical feedbacks of Arctic planetary boundary layer, Sea ice, Cloud and AerosoL (PASCAL) drifting ice floe station field campaign was conducted during early summer in the central arctic. During this campaign, the small-scale spatiotemporal variability of global irradiance was observed for the first time on an ice floe with a dense network of autonomous pyranometers. A total of 15 stations were deployed covering an area of 0.83 km×1.59 km from 4–16 June 2017. This unique, open-access dataset is described here, and an analysis of the spatiotemporal variability deduced from this dataset is presented for different synoptic conditions. Based on additional observations, five typical sky conditions were identified and used to determine the values of the mean and variance of atmospheric global transmittance for these conditions. Overcast conditions were observed 39.6 % of the time predominantly during the first week, with an overall mean transmittance of 0.47. The second most frequent conditions corresponded to multilayer clouds (32.4 %), which prevailed in particular during the second week, with a mean transmittance of 0.43. Broken clouds had a mean transmittance of 0.61 and a frequency of occurrence of 22.1 %. Finally, the least frequent sky conditions were thin clouds and cloudless conditions, which both had a mean transmittance of 0.76 and occurrence frequencies of 3.5 % and 2.4 %, respectively. For overcast conditions, lower global irradiance was observed for stations closer to the ice edge, likely attributable to the low surface albedo of dark open water and a resulting reduction of multiple reflections between the surface and cloud base. Using a wavelet-based multi-resolution analysis, power spectra of the time series of atmospheric transmittance were compared for single-station and spatially averaged observations and for different sky conditions. It is shown that both the absolute magnitude and the scale dependence of variability contains characteristic features for the different sky conditions.