Warm air intrusions reaching the MOSAiC expedition in April 2020—The YOPP targeted observing period (TOP)

In the spring period of Multidisciplinary drifting Observatory for Study Arctic Climate (MOSAiC) expedition, an initiative was in place to increase radiosounding frequency during warm air intrusions Atlantic sector. Two episodes with increased surface temperatures were captured April 12–22, 2020, a targeted observing (TOP). The large-scale circulation efficiently guided pulses into and observed temperature from −30°C near melting conditions marking transition spring, as did not return values below −20°C. Back-trajectory analysis identifies 3 pathways transport. For first maximum, airmass over northern Norwegian coast then MOSAiC site. second pathway south, it passed Greenland ice sheet arrived at observational site but dry due precipitation on windward side. third along arriving both moist. back trajectories originating pressure levels between 700 900 hPa line up vertically, which is somewhat surprising this dynamically active environment. processes acting trajectory 800 MOSAIC are analyzed. Vertical profiles energy exchange presented depict transformation based ERA5 reanalysis fields. TOP could be used model evaluation Lagrangian studies improve representation small-scale physical that important transformation. A comparison observations demonstrates challenges processes, such turbulence contributions various terms budget, often misrepresented numerical weather prediction climate models.