Atmosphere

Advance process and system understanding of the changing Arctic atmospheric composition and dynamics and the resulting changes to surface energy budgets

Over the industrial period, Arctic surface air temperature has increased more rapidly than in other parts of the globe due to a complex interplay of processes—a phenomenon called “Arctic Amplification” (Serreze and Barry 2011). Mechanisms and feedbacks governing atmosphere-surface heat exchange (i.e., meridional [north-south] heat transport and radiative forcing23), coupled with changing surface properties, drive this enhanced warming. Conversely, changes in Arctic conditions may impact circulation that changes weather and climate patterns over the Northern Hemisphere (Cohen et al. 2014) and beyond.

To address all IARPC policy drivers, IARPC collaboration teams must advance an integrated understanding of atmospheric processes as well as the resulting radiative forcing in the Arctic. The Arctic atmosphere is linked through large-scale circulation with global weather and climate systems (Arctic-Global System).

Regionally, atmospheric processes drive changing weather patterns and influence sea ice amounts and distribution, knowledge of which is critical for managing emergency response and law enforcement efforts (Security). These changing weather patterns and sea ice distributions, along with changes in precipitation, snow cover, and permafrost melting, affect terrestrial ecosystems and other environmental conditions that alter subsistence systems and how Arctic residents interact with their environment.

Further, changes in the environment have led to increased wildfire activity in the Arctic and at lower latitudes, causing air quality problems (Well-being) for Arctic residents (Kasischke et al. 2010).

The atmosphere links with many of the interdependent components of the Arctic climate system—the ocean and marine ecosystems, sea ice, land surface and permafrost, and terrestrial ecosystems.

Accordingly, the Atmosphere Goal is linked to several other Goals that focus on these systems and with Environmental Intelligence. The interface between each of these climate sub-systems and the atmosphere can be measured by the surface energy budget (heat and radiation) and fluxes of moisture, aerosol, and gases (Bourassa et al. 2013). Characterizing these energy and mass fluxes across the Arctic is essential for understanding the future state of Arctic weather and climate. But a paucity of detailed observations of each of these atmospheric constituents over the different Arctic surface types precludes definitive, empirically-based understanding of the trends and variability in heat and mass fluxes over different domains and seasons and of the various radiative forcing mechanisms that control this variability.

Atmospheric constituents that drive radiative forcing—aerosols, clouds, and gases—affect the radiation and energy budget in the Arctic differently than at lower latitudes due to unique surface, atmospheric stability, and solar intensity states. Aerosols can change the Arctic radiation balance through direct radiative forcing of the atmosphere (Quinn et al. 2008), through aerosol-cloud indirect effects (e.g., de Boer et al. 2013), or by lowering the albedo of (typically) bright Arctic surfaces after deposition of black carbon or other absorbing species, potentially hastening snow and ice melt (Flanner et al. 2007). The abundance of aerosols and some gases (e.g., ozone) in the Arctic are affected by transport and removal processes between source regions at lower latitudes and the Arctic. Improving quantitative understanding of these processes at lower latitudes and within the Arctic is key to improving predictability of Arctic climate forcing (AMAP 2015; Arnold et al. 2016).

Due to seasonally low sun angles and high surface albedos and the absence of solar radiation during the polar night, Arctic clouds have a limited ability to cool the surface by reflecting solar energy, but cloud infrared radiation significantly warms the surface (Intrieri et al. 2002). As a result, the net annual cloud radiative forcing at the Arctic surface is positive (a warming), opposite to the global cloud radiative effect. The Arctic cloud radiative forcing and its seasonal variability plays a critical role in modulating the surface energy budget and thereby affects the state of sea ice, ice sheets, permafrost, and snow cover (Kwok and Untersteiner 2011). Cloud forcing is dictated by lifetime, physical properties, and precipitation, which are governed by complex interactions between local- and large-scale processes involving dynamics, moisture supply, and aerosol influences on cloud nucleation (Garrett and Zhao 2006). The greatest challenge for those studying Arctic clouds currently is in understanding and representing the controls on cloud phase (Shupe 2011; Morrison et al. 2012).

In addition to cloud and aerosol influences on radiative forcing, Arctic carbon stores have the potential to greatly impact future climate states. The Arctic contains vast amounts of sequestered carbon in permafrost and marine hydrates, with an uncertain potential for CO2, methane, and other releases into the atmosphere (AMAP 2015). Methane has a global warming potential (GWP) 28 times that of carbon dioxide(CO2)per molecule, averaged over a 20-year period: though the atmospheric lifetime of methane is about a decade, that of CO2 is several hundred years. When considering methane’s 12-year atmospheric lifetime, its GWP increases to 84 times that of carbon dioxide over 20 years (IPCC, 2014).

Understanding current methane emissions and potential scenarios under a warmer Arctic is imperative. Many global circulation models overlook carbon feedback loops from Arctic tundra; carbon release from thawing and decomposing tundra could, in turn, further accelerate carbon release—a scenario known as the Permafrost Carbon Feedback. Observations and recent analyses indicate that warming has not led to significant methane release from the permafrost (Sweeney et al. 2016); but the distribution of measurements precludes a definitive determination of methane sources and their strengths.

The Atmosphere Goal focuses on advancing observational systems of atmospheric constituents and surface energy fluxes, synthesizing existing and planned observations and models for better process understanding, and working within IARPC Collaborations to enhance knowledge of how the Arctic atmosphere and other parts of the climate system interface to produce the observed Arctic amplification and the corresponding observed changes in surface air temperature and sea ice loss. The team will draw from a range of surface-based observational systems maintained by multiple agencies including the long- term National Oceanic and Atmospheric Administration (NOAA) Barrow, Alaska Observatory, National Aeronautics and Space Administration’s (NASA) Aerosol Robotic Network (AERONET) and Micro-Pulse Lidar (MPL) networks, and the Department of Energy’s (DOE) facilities on the North Slope of Alaska, among others. Sub-orbital measurements from manned and unmanned aircraft will be exploited whenever possible, and support for enhancing and providing uniformity in both surface-based and sub- orbital observations will be pursued. The satellite contributions to this effort include top-of-atmosphere energy balance measurements from instruments such as Clouds and the Earth's Radiant Energy System (CERES), vertical distributions of aerosols and clouds from space-based lidar such as Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), and aerosol amount and type mapping, mainly over smoke and pollution source regions in the sub-Arctic from Moderate-resolution Imaging SpectroRadiometer (MODIS), Multi-angle Imaging SpectroRadiometer (MISR), Ozone Monitoring Instrument (OMI), and Visible Infrared Imaging Radiometer Suite (VIIRS), which, when combined with aerosol transport modeling, provide constraints on the flux of aerosols to the polar region.

The work focuses on the following objectives

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