This project seeks to understand and quantify the role of large-scale, low-frequency atmospheric circulation anomalies and moisture transport on the ice climate system of the North Atlantic sector of the Arctic (North Atlantic Arctic, NAA). Recent changes in low-frequency atmospheric circulation in the NAA have increased sensible heat and moisture advection from the mid-latitudes into the Arctic. This, in turn, has altered the surface energy budget over the Greenland Ice Sheet (GrIS) and adjacent sea ice and contributed to unprecedented melt and freshwater runoff events. For example, the extreme 2012 melt across Greenland, which was followed by other intense melt events in subsequent years along with record or near-record warmth and lack of sea ice in the Arctic Ocean, provide an exceptional opportunity for timely investigation on the multiple ways in which large-scale atmospheric circulation drives land- and sea-ice changes across the NAA. These extreme events have significant and yet unexplored impacts on Department of Defense (DoD) infrastructure and operations in the NAA: freshwater runoff alters acoustic profiles of subsurface waters adjacent to DoD installations in Greenland; warmer air and ocean temperatures open surface transit lanes in newly ice-free areas; surface melt leads to uncertain aircraft operations on the GrIS; increased melt challenges waste management at legacy infrastructure on the GrIS; and unusual wind, visibility, precipitation, and ice all disrupt mission training at DoD installations across the region.

To anticipate and reduce the negative consequences of these extreme events, the objectives of this research are to: (1) quantify the contributions from large-scale atmospheric circulation and moisture transport to ice melt events across multiple time scales; (2) understand how atmospheric blocking and Rossby wave breaking impact, and are impacted by, the transport of moisture from mid-latitudes into the NAA; and (3) investigate the role of this moisture advection in altering radiative and turbulent fluxes, winds, precipitation, surface melting, and snow accumulation in the NAA.

To better understand and quantify impacts of low-frequency atmospheric circulations on GrIS melt, surface energy balance, mass balance, and sea ice variability, a long-term (1980-present), systematic investigation of moisture transport and blocking in the NAA region is needed. As atmospheric blocking can be described in a number of ways, the research team will adopt the classical Tibaldi and Molteni (1990) and Pelly and Hoskins (2003) methods to identify such events. They will examine metrics of moisture transport, including integrated water vapor (IWV) and vertically integrated horizontal water vapor transport (IVT), particularly during periods of atmospheric blocking. The impact of Rossby wave breaking (RWB) on moisture transport into the NAA region will be explored using an approach similar to that of Liu and Barnes (2015), using contours of potential temperature and moisture transport fields to identify specific patterns of extreme moisture transport. Researchers are particularly interested in how moisture transport is related to changes in large-scale, low-frequency (interannual to intra-seasonal) atmospheric circulation in the NAA. To assess the impact of low-frequency atmospheric circulation variability on melting, atmospheric circulation indices will be created, including the Arctic Oscillation (AO), Greenland Blocking Index (GBI), and North Atlantic Oscillation (NAO), using the latest ERA-based reanalysis.

The research team has found recently that the climate of the NAA and surface melt and mass balance of the Greenland ice sheet are closely related to the phase and intensity of the AO, NAO, and, most critically, Greenland blocking (e.g., McLeod and Mote 2016), but they do not know how the NAA responds to teleconnections from the mid-latitudes and the tropics. The previous research has demonstrated that slowly-evolving tropical circulations, principally the 30-60-day Madden-Julian Oscillation (MJO), has significant impacts on high-latitude snow (Barrett et al. 2015) and Arctic sea ice (Henderson et al. 2014). However, that influence on variables relevant to DoD operations (snow conditions, visibility, precipitation, wind) has not been examined in the level of detail necessary to be useful to planners. Researchers will fill that gap by applying the statistical composite techniques that they successfully used in the Arctic (Barrett et al. 2015; Henderson et al. 2014) to circulation and melt in the NAA.

An ensemble approach using multiple high-quality atmospheric reanalysis products, such as National Centers for Environmental Prediction, Climate Forecast System Reanalysis, ERA-Interim/ERA5, and the National Aeronautics and Space Administration Modern-Era Retrospective analysis for Research and Applications, Version 2 (NASA MERRA2), will be used in conjunction with self organizing map (SOM) analysis (with which they have had recent success studying the high latitudes; Henderson et al. 2017) following Mattingly et al. (2016) to understand how well patterns of large-scale atmospheric variability are represented in the CMIP-6 models. Researchers will focus particularly on periods of extreme circulation anomalies, and note their impacts on ice and snow melt across the GrIS. The resulting SOM nodal clusters will be used to composite atmospheric moisture and energy budget components to investigate the magnitude of the impact on the Greenland ice sheet and sea ice in the NAA. These composites will include the above-mentioned impact-driven surface meteorological (e.g., wind, precipitation) and cryospheric (e.g. surface melt, sea ice concentration) fields.

The primary benefit of this research to DoD is detailed, high-resolution maps that show not only composite atmospheric states but also composite melt for different phases of the MJO, AO/NAO, and GBI. Maps will include surface wind, precipitation rates, snow cover characteristics including surface melt, and change in sea ice concentration. These atmospheric, oceanic, and cryospheric variables are critical to high-latitude DoD operations on the GrIS and surrounding ocean, particularly the DoD installations and surface and submarine vessels that transit adjacent waters.

Specifically, this project will provide an assessment of the role of tropical and extra tropical teleconnections on extreme melt and runoff events and the resulting:

• runoff flux from GrIS, relevant to acoustic profiles of subsurface waters (NRC 2010);
• air temperature, sea surface temperature (SST), and sea ice concentration in newly ice-free areas, relevant to operations of surface vessels in the NAA;
• surface melt, firn density, and clouds at Camp Raven and Summit, relevant to training and support flight operations in Greenland by the ANG 109th Airlift Wing;
• surface melt rates at Camp Century, relevant as large increases in melt may lead to remobilization of abandoned waste (e.g., Colgan et al. 2016);
• and unusual wind, visibility, precipitation, and ice, relevant as all of these factors may disrupt operations and mission training at Thule Air Field and the three aforementioned DoD installations.