Abstract
<strong class="journal-contentHeaderColor">Abstract.</strong> During the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition, meteorological conditions over the lowest 1â<span class="inline-formula">km</span> of the atmosphere were sampled with the DataHawk2 (DH2) fixed-wing uncrewed aircraft system (UAS). These in situ observations of the central Arctic atmosphere are some of the most extensive to date and provide unique insight into the atmospheric boundary layer (ABL) structure. The ABL is an important component of the Arctic climate, as it 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 manually identify the ABL height (<span class="inline-formula"><i>Z</i><sub>ABL</sub></span>) for 65Â out of the total 89Â flights conducted over the central Arctic Ocean between 23Â March and 26Â July 2020 by visually analyzing profiles of virtual potential temperature, humidity, and bulk Richardson number. Comparing this subjective <span class="inline-formula"><i>Z</i><sub>ABL</sub></span> with <span class="inline-formula"><i>Z</i><sub>ABL</sub></span> identified by various previously published automated objective methods allows us to determine which objective methods are most successful at accurately identifying <span class="inline-formula"><i>Z</i><sub>ABL</sub></span> in the central Arctic environment and how the success of the methods differs based on stability regime. The objective methods we use are the LiuâLiang, 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 <span class="inline-formula"><i>Z</i><sub>ABL</sub></span> 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 <span class="inline-formula"><i>Z</i><sub>ABL</sub></span>, while the LiuâLiang method is least successful. The results of this study are expected to be beneficial for upcoming observational and modeling efforts regarding the central Arctic ABL.
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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