Tracking arctic boundary layer evolution during on-ice flow using CMET balloons

The atmospheric temperature profile in Arctic winter plays a key role in the observed Arctic amplification of global temperature changes. In the cold season, the Arctic atmospheric temperature and moisture profiles are a product of advection and transformation of air-masses from lower latitudes (Wexler, 1936, Curry, 1983). These poleward flowing air masses cool and dry over several days, losing the majority of their initial heat and moisture content along their trajectory. The occurrence of the resulting transition from an initially cloudy to a radiatively clear state (Stramler et al. 2011, Pithan et al. 2014) proves to be difficult to understand using Eularian, fixed in-space observations (e.g. Becker 2020, Lonardi 2024).

Here we show results from recent controlled meteorological (CMET) balloon (Voss 2012, Roberts et al. 2016) launches from Ny-Alesund, Svalbard. The balloons followed advected air parcels downwind over the ocean beyond the sea-ice edge. CMET balloons can drift at a variable altitude for multiple days along a quasi-Lagrangian trajectory, continuously resolving the vertical structure of the arctic boundary layer (ABL) column.

The observed low level ABL profiles show cooling (2.1 – 2.8K) within few hous after crossing onto the sea ice, leading to decoupling of the surface and an increase in near-surface relative humidity. The inversion layer depens by 100m over the course of 1-2 hours.

The ABL soundings are combined with ice surface temperature satellite imagery to determine the radiative processes driving changes in cloud state and properties. We hypothesise that the boundary layer typically decouples during cold-season on-ice flow within hours of the ice edge, allowing for strong low-level wind-turning. The resulting near-surface flow limits low-level heat and moisture advection towards the central Arctic. According to our hypothesis, intrusions in which the boundary layer remains coupled after crossing the ice edge lead to a much stronger heat and moisture transport towards the central Arctic ocean.

These observations provide a valuable step towards a better understanding of small-scale boundary layer processes, surface energy budgets and their representation in climate models.