The Arctic Cloud Puzzle: Using ACLOUD/PASCAL Multiplatform Observations to Unravel the Role of Clouds and Aerosol Particles in Arctic Amplification

Abstract

Clouds 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.

Radiative Effect of Clouds at Ny-Ålesund, Svalbard, as Inferred from Ground-Based Remote Sensing Observations

“…In the last decade, the Arctic has experienced significant changes (Stroeve et al 2012;Jeffries et al 2013) and exhibited an increase in near-surface air temperature that is more than twice as large as the observed increase in global mean temperature (Serreze and Barry 2011;Wendisch et al 2017). This so-called Arctic amplification is due to many feedback processes, the mechanisms and relative contributions of which are still under debate and the focus of current research (e.g., Wendisch et al 2017;Screen et al 2018;Goosse et al 2018). On a local scale, clouds strongly influence Arctic climate feedbacks (Kay et al 2016).…”

“…Sedlar et al (2011) presented results from the Arctic Summer Cloud Ocean Study (ASCOS), which took place near 87.58N from August to early September 2008, and found a net warming effect of clouds for this time and location. Recently, comprehensive cloud and radiation observations were performed during the ship-and airborne-based Physical Feedbacks of Arctic Boundary Layer, Sea Ice, Cloud and Aerosol (PASCAL) and Arctic Cloud Observations Using Airborne Measurements during Polar Day (ACLOUD) campaigns (Wendisch et al 2019), which took place in May/June 2017 in the vicinity of Svalbard, Norway.…”

The importance of the representation of air pollution emissions for the modeled distribution and radiative effects of black carbon in the Arctic

“…The mixing and aging, as well as the related removal of aerosol particles along the various transport pathways, are important processes that need to be described accurately in the models (Vignati et al, 2010). The representation of emissions is, however, a prerequisite for correctly simulating the transport fluxes and is therefore a key source of uncertainties (Stohl et al, 2013;Arnold et al, 2016;Winiger et al, 2017). Both the coverage of all BC sources and their temporal variability contribute to the ability to reproduce vertical BC distributions (Stohl et al, 2013).…”

“…Both the coverage of all BC sources and their temporal variability contribute to the ability to reproduce vertical BC distributions (Stohl et al, 2013). The relative source contributions are, however, still discussed with different results (Winiger et al, 2017). Bond et al (2004) estimate the uncertainty in BC emission inventories to be a factor of about 2.…”

Local and Remote Controls on Arctic Mixed‐Layer Evolution

“…At the center of PASCAL is the Polarstern research vessel (PS, Knust, ), carrying instrumentation for measuring near‐surface meteorology, turbulence, radiation, clouds and aerosol. Collocated measurements were performed by two research aircraft from the ACLOUD campaign (Wendisch et al, ). The PS was attached to an ice floe from 4–16 June, on which a network of additional instrumentation was installed and operated.…”