Overview: Quasi-Lagrangian observations of Arctic air mass transformations – Introduction and initial results of the HALO–(AC)3 aircraft campaign
Authors: Wendisch Manfred , Crewell Susanne , Ehrlich André , Herber Andreas , Kirbus Benjamin , Lüpkes Christof , Mech Mario , Abel Steven J. , Akansu Elisa F. , Ament Felix , Aubry Clémantyne , Becker Sebastian , Borrmann Stephan , Bozem Heiko , Brückner Marlen , Clemen Hans-Christian , Dahlke Sandro , Dekoutsidis Georgios , Delanoë Julien , De La Torre Castro Elena , Dorff Henning , Dupuy Regis , Eppers Oliver , Ewald Florian , George Geet , Gorodetskaya Irina V. , Grawe Sarah , Groß Silke , Hartmann Jörg , Henning Silvia , Hirsch Lutz , Jäkel Evelyn , Joppe Philipp , Jourdan Olivier , Jurányi Zsofia , Karalis Michail , Kellermann Mona , Klingebiel Marcus , Lonardi Michael , Lucke Johannes , Luebke Anna , Maahn Maximilian , Maherndl Nina , Maturilli Marion , Mayer Bernhard , Mayer Johanna , Mertes Stephan , Michaelis Janosch , Michalkov Michel , Mioche Guillaume , Moser Manuel , Müller Hanno , Neggers Roel , Ori Davide , Paul Daria , Paulus Fiona , Pilz Christian , Pithan Felix , Pöhlker Mira , Pörtge Veronika , Ringel Maximilian , Risse Nils , Roberts Gregory C. , Rosenburg Sophie , Röttenbacher Johannes , Rückert Janna , Schäfer Michael , Schäfer Jonas , Schemannn Vera , Schirmacher Imke , Schmidt Jörg , Schmidt Sebastian , Schneider Johannes , Schnitt Sabrina , Schwarz Anja , Siebert Holger , Sodemann Harald , Sperzel Tim , Spreen Gunnar , Stevens Bjorn , Stratmann Frank , Svensson Gunilla , Tatzelt Christian , Tuch Thomas , Vihma Timo , Voigt Christiane , Volkmer Lea , Walbröl Andreas , Weber Anna , Wehner Birgit , Wetzel Bruno , Wirth Martin , Zinner Tobias 
Published: March 2024

Abstract. The global warming is amplified in the Arctic. To collect data that help to constrain weather and climate models, which often do not realistically represent the enhanced Arctic warming, the HALO-(AC)³ aircraft campaign was conducted in March and April 2022 over the Norwegian and Greenland Seas, the Fram Strait, and the central Arctic Ocean. Observations were made over areas of open ocean, the marginal sea ice zone, and the central Arctic sea ice. Two low-flying and one long-range, high-altitude research aircraft have been employed. Whenever possible, the three aircraft were flown in collocated formation. The campaign focused on one specific challenge posed by the models: The reasonable representation of transformations of air masses during their meridional transport into (northward by moist and warm air intrusions, WAIs) and out of (southward via marine cold air outbreaks, CAOs) the Arctic. To observe the air mass transformations, a quasi-Lagrangian flight strategy using trajectory calculations was realized enabling to sample the moving air mass parcels twice along their trajectories. Eight distinct WAI and 12 CAO cases were probed extensively. From the quasi-Lagrangian measurements, we have derived the diabatic heating and moistening of the moving air masses during CAOs and WAIs, the development of cloud macrophysical and microphysical properties along the southward pathways of the air masses during CAOs, and the moisture budget of WAIs. As an example result, we have obtained typical values of the surface-driven diabatic heating between 1–3 K h-1 and of the near-surface moistening between 0.05–0.3 g kg-1 h-1 within the lowest about 0.5 km. From the observations of WAIs, a weak diabatic cooling of up to 0.4 K h-1 and a moisture loss of up to 0.1 g kg-1 h-1 from the ground to about 5 km altitude were derived. In addition, we discuss the frequency of occurrence of the different thermodynamic phases of Arctic low-level clouds, the interaction of Arctic cirrus with sea ice, water vapor, and aerosol particles, and the characteristic microphysical and chemical properties of Arctic aerosol particles. Finally, we provide proof of a concept to measure mesoscale divergence and subsidence in the Arctic using data from dropsondes released during circular flight patterns.