Abstract
During the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition, meteorological conditions over the lowest 1 km of the atmosphere were sampled with the DataHawk2 (DH2) fixed wing uncrewed aircraft system (UAS). Of particular interest is the atmospheric boundary layer (ABL) height, as ABL structure can be closely coupled to cloud properties, surface fluxes, and the atmospheric radiation budget. The high temporal resolution of the UAS observations allows us to subjectively identify ABL height for 65 out of the total 89 flights conducted over the central Arctic Ocean between 23 March and 26 July 2020 by visually analyzing profiles of virtual potential temperature, humidity, and bulk Richardson number. Comparing this subjective ABL height with the ABL heights identified by various previously published objective methods allows us to determine which objective methods are most successful at accurately identifying ABL height in the central Arctic environment. The objective methods we use are the Liu-Liang, Heffter, virtual potential temperature gradient maximum, and bulk Richardson number methods. In the process of testing these objective methods on the DH2 data, numerical thresholds were adapted to work best for the UAS-based sampling. To determine if conclusions are robust across different measurement platforms, the subjective and objective ABL height determination processes were repeated using the radiosonde profile closest in time to each DH2 flight. For both the DH2 and radiosonde data, it is determined that the bulk Richardson number method is the most successful at identifying ABL height, while the Liu-Liang method is least successful.
Highlights
The transfer of energy between the Earth's surface and the overlying atmosphere, at high latitudes, remains an area of substantial uncertainty in our understanding of the global climate system
The p-value tells us whether the relationship between subjective and objective atmospheric boundary layer (ABL) height is significant at the 5% significance level
When calculating the percent of DH2 cases in which the objective ABL height is within certain percent difference ranges from the subjective ABL height, the Richardson number (Rib) method with a critical value of either 0.5 or 0.75 is most successful (Fig. 10)
Summary
The transfer of energy between the Earth's surface and the overlying atmosphere, at high latitudes, remains an area of substantial uncertainty in our understanding of the global climate system (de Boer et al, 2012; Tjernström et al, 2012; Karlsson and Svensson, 2013). Collected over the central Arctic Ocean ice pack, focused on the structure of the lower atmosphere, its spatial and temporal variability, the intensity of turbulent energy fluxes, and its connection to surface features. To provide such measurements, uncrewed aircraft were deployed in the lower atmosphere during legs 3 (March through May 2020) and 4 (June through August 2020) of MOSAiC (Multidisciplinary drifting Observatory for the Study of Arctic Climate; Shupe et al 2020), a year-long expedition that took place from October 2019 to September 2020 in which the icebreaker RV Polarstern (Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, 2017). Discussion is included on the features that do or do not lend themselves to accurate identification of the ABL height by the objective methods, and findings are summarized to support future studies seeking to identify ABL height quickly, objectively, and accurately across large atmospheric datasets collected in the central Arctic
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