An overview of the vertical structure of the atmospheric boundary layer in the central Arctic during MOSAiC

Abstract

Abstract. Observations collected during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) provide an annual cycle of the vertical thermodynamic and kinematic structure of the atmospheric boundary layer (ABL) in the central Arctic. A self-organizing map (SOM) analysis conducted using radiosonde observations shows a range in the Arctic ABL vertical structure from very shallow and stable, with a strong surface-based virtual potential temperature (θv) inversion, to deep and near neutral, capped by a weak elevated θv inversion. The patterns identified by the SOM allowed for the derivation of criteria to categorize stability within and just above the ABL, which revealed that the Arctic ABL during MOSAiC was stable and near neutral with similar frequencies, and there was always a θv inversion within the lowest 1 km, which usually had strong to moderate stability. In conjunction with observations from additional measurement platforms, including a 10 m meteorological tower, ceilometer, and microwave radiometer, the radiosonde observations and SOM analysis provide insight into the relationships between atmospheric vertical structure and stability, as well as a variety of atmospheric thermodynamic and kinematic features. A low-level jet was observed in 76 % of the radiosondes, with stronger winds and low-level jet (LLJ) core located more closely to the ABL corresponding with weaker stability. Wind shear within the ABL was found to decrease, and friction velocity was found to increase, with decreasing ABL stability. Clouds were observed within the 30 min preceding the radiosonde launch 64 % of the time. These were typically low clouds, corresponding to weaker stability, where high clouds or no clouds largely coincided with a stable ABL.

Forcing for varying boundary layer stability across Antarctica

“…These six near-surface stability regimes range from near neutral conditions (NN; dθ/dz < 0.5 K (100 m) −1 ) to extremely strongly stable conditions (ESS; dθ/dz > 30 K (100 m) −1 ). Thresholds to distinguish between these six regimes -near neutral (NN), weak stability (WS), moderate stability (MS), strong stability (SS), very strong stability (VSS), and extremely strong stability (ESS) -were defined by Dice et al (2023) and Jozef et al (2024) (Table 2) and were found to have robust applications in both the Antarctic and Arctic. Stability regimes aloft, just above the boundary layer, were also defined, as many of the radiosonde profiles have enhanced stability above layers of weaker, near-surface stability.…”