Assessing the vertical structure of Arctic aerosols using balloon-borne measurements

Abstract

Abstract. The rapidly warming Arctic is sensitive to perturbations in the surface energy budget, which can be caused by clouds and aerosols. However, the interactions between clouds and aerosols are poorly quantified in the Arctic, in part due to (1) limited observations of vertical structure of aerosols relative to clouds and (2) ground-based observations often being inadequate for assessing aerosol impacts on cloud formation in the characteristically stratified Arctic atmosphere. Here, we present a novel evaluation of Arctic aerosol vertical distributions using almost 3 years' worth of tethered balloon system (TBS) measurements spanning multiple seasons. The TBS was deployed at the U.S. Department of Energy Atmospheric Radiation Measurement Program's facility at Oliktok Point, Alaska. Aerosols were examined in tandem with atmospheric stability and ground-based remote sensing of cloud macrophysical properties to specifically address the representativeness of near-surface aerosols to those at cloud base. Based on a statistical analysis of the TBS profiles, ground-based aerosol number concentrations were unequal to those at cloud base 86 % of the time. Intermittent aerosol layers were observed 63 % of the time due to poorly mixed below-cloud environments, mostly found in the spring, causing a decoupling of the surface from the cloud layer. A uniform distribution of aerosol below cloud was observed only 14 % of the time due to a well-mixed below-cloud environment, mostly during the fall. The equivalent potential temperature profiles of the below-cloud environment reflected the aerosol profile 89 % of the time, whereby a mixed or stratified below-cloud environment was observed during a uniform or layered aerosol profile, respectively. In general, a combination of aerosol sources, thermodynamic structure, and wet removal processes from clouds and precipitation likely played a key role in establishing observed aerosol vertical structures. Results such as these could be used to improve future parameterizations of aerosols and their impacts on Arctic cloud formation and radiative properties.

Annual cycle observations of aerosols capable of ice formation in central Arctic clouds

“…Spring and autumn clouds were still relatively cold and somewhat elevated above the surface, but enhanced below-cloud mixing (i.e., less variance in equivalent potential temperature 56 ) offers the potential for more interaction between clouds and the near-surface environment where coarse, biological or organic sea spray INPs active at cold temperatures 16 could be produced from more localized leads, melt ponds, or the MIZ. Indeed, high ice fractions in low-level clouds are observed at these times of year.…”

Controls on surface aerosol number concentrations and aerosol-limited cloud regimes over the central Greenland Ice Sheet

“…11), the potential temperature profile indicates that the boundary layer is initially well mixed up to cloud height (Fig. 11e) suggesting that surface aerosol concentrations were likely representative of concentrations in the cloud (Creamean et al, 2021). By the time the cloud had cleared and surface N 20 concentrations fell to < 10 cm −3 this coupling had broken down and a region of high static stability had formed near the surface (Fig.…”

“…Surface aerosol concentration is not necessarily representative of concentrations at cloud level (Igel et al, 2017;Creamean et al, 2021). Assuming that there are no significant local surface sources at Summit, surface aerosol concentrations are unlikely to be higher than concentrations at cloud level, but boundary layer processes that result in a higher rate of deposition at the surface than replenishment from above could result in significantly lower aerosol concentrations at the surface.…”

Observational data from uncrewed systems over Southern Great Plains

“…Expanding development and deployment of various uncrewed aircraft systems (UAS) result in increasing opportunities for these platforms to provide high-quality atmospheric measurements (Stephens et al, 2000;Hobbs et al, 2002;Villa et al, 2016;de Boer et al, 2020b). Several recent atmospheric science campaigns have provided perspectives on the planetary boundary layer with both UAS (Reuder et al, 2009;Fladeland et al, 2011;Villa et al, 2016;Adkins and Sescu, 2018;Barbieri et al, 2019;Chen et al, 2020; de Boer et al, 2020a, b) and tethered balloon system (TBS) de Boer et al, 2018;Creamean et al, 2021). These studies have taken advantage of various scales of UAS platforms, ranging from very small de Boer et al, 2019b) to very large (Intrieri et al, 2014).…”

“…The ARM Unmanned Areal Vehicle (UAV) program was first introduced in 1991 and demonstrated how measurements from UAV platforms contribute to our understanding of cloud and radiative processes through eight flight campaigns and over 140 h of science flights with three different UAV platforms (Stephens et al, 2000). With the continuing maturation of ARM TBS/UAS capabilities, the DOE ARM facility restarted UxS observing around 2013, supporting various TBS and UAS deployments within restricted airspace over Oliktok Point, Alaska (de Boer et al, 2016(de Boer et al, , 2018(de Boer et al, , 2019bCreamean et al, 2021). After re-engaging with such activities, the DOE ARM facility procured and instrumented a mid-size UAS intended to provide new sampling capabilities globally (de Boer et al, 2018).…”