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, with a weak elevated θv inversion. Profile observations from the DataHawk2 uncrewed aircraft system between 23 March and 26 July 2020 largely sampled the same profile structures, which can be further analyzed to provide unique insight into the turbulent characteristics of the ABL. The patterns identified by the SOM allowed for the derivation of criteria to categorize stability within and just above the ABL, which reveals that the Arctic ABL is stable and near-neutral with similar frequencies. In conjunction with observations from additional measurement platforms, including a 10 m meteorological tower, ceilometer, and microwave radiometer, the radiosonde observations provide insight into the relationships between atmospheric stability and a variety of atmospheric thermodynamic and kinematic features. The average ABL height was found to be 150 m, and ABL height increases with decreasing stability. A low-level jet was observed in 76 % of the radiosondes, with an average height of 401 m and an average speed of 11.5 m s−1. At least one temperature inversion below 5 km was observed in 99.7 % of the radiosondes, with an average base height of 260 m and an average intensity of 4.8 °C. The only cases without a temperature inversion were those with weak stability aloft. Clouds were observed within the 30 minutes preceding radiosonde launch 64 % of the time. These were typically low clouds, and high clouds largely coincide with a stable ABL. The amount of atmospheric moisture present increases with decreasing stability.

Variations in Boundary Layer Stability Across Antarctica: A Comparison Between Coastal and Interior Sites

“…Potential temperature gradients more than 5 K (100 m) -1 in nearly all of the SOM-identified patterns in Figure 2, with many greater than 15 K (100 m) -1 , and some even greater than 30 K (100 m) -1 , shows that strong stability is in fact common at this site. Potential temperature gradients in excess of 15 K (100 m) -1 , corresponding to our VSS regime (Table 2), are rarely observed outside of the interior of Antarctica, even in the Arctic (Jozef et al, 2023). Potential temperature gradients less than 1.75 K (100 m) -1 , corresponding to NN or WS regimes, occur only in patterns 6, 12, and 18 in the upper right of the SOM, emphasizing the dominance of strong stability at South Pole.…”

“…Various thresholds to distinguish near neutral (NN), weak (WS), moderate (MS), strong (SS), very strong (VSS), and extremely strong (ESS) stability were evaluated, and the thresholds listed in Table 2 were found to best separate meaningful differences in near-surface stability across all five sites. These thresholds were also evaluated, and found to be appropriate, in a separate study based on profiles observed over Arctic sea ice as part of the MOSAiC expedition (Jozef et al 2023).…”