Research Themes of the NSERC CREATE Training Program in Arctic Atmospheric Science

The Arctic is well known as an early warning system for global climate change. Some of the pressing questions in Arctic atmospheric science include the following:

Is the radiative transfer which governs climate in the Arctic changing?

Is ozone recovering after the Montreal Protocol placed controls on chlorofluorocarbon (CFC) usage and what does that imply for solar ultraviolet radiation at the surface?

How is the transport and deposition of pollution from lower latitudes affecting the Arctic in light of increased regulatory controls?

How are pollution transport pathways and processes being affected by the changing environmental conditions?

How are changing concentrations of carbon dioxide, ozone, aerosol and water vapour content in the middle atmosphere affecting the dynamics of the polar vortex?

What impact is this having on ozone depletion and tropospheric climate?

Has the Arctic climate reached a “tipping point”, and are there “early warning” signs of broader global change?

The questions are many. The research that will be undertaken by the CREATE trainees will help to answer them. The research program includes four major themes, which are briefly described below.

Arctic Troposphere Transport and Air Quality [ATTAQ]

Research in the ATTAQ theme is designed to identify and quantify toxic pollutants entering the Arctic troposphere and to locate their probable sources. The contamination has many forms, including gases such as ozone, CO, volatile organic compounds (VOCs), and aerosols. Contaminants found in the Arctic snow-pack show that many extremely dangerous substances are transported to the Arctic by atmospheric processes. These include radionuclides, mercury and other heavy metals, persistent organic pollutants (POPs), and other materials such as hydrocarbons and pesticides. The Arctic Monitoring and Assessment Programme (AMAP) reports that a significant part of the transport is via the atmosphere. This is particularly true for semi-volatile organic toxins, which are known to accumulate in the Arctic.

The ATTAQ theme has a focus on particulate matter, which serves as both a tracer for meteorological systems and a vector for transport of semi-volatile materials such as heavy metals and toxins, which are retained in the Arctic and become concentrated to dangerous levels in the food chain. The goal is to determine the composition of material deposited to the surface and to improve our understanding of its effects on plants, animals and human populations in the fragile Arctic ecosystem. To achieve this goal, we combine two in situ measurement techniques with modelling methods. An Aerosol Mass Spectrometer (AMS) allows us to distinguish among particles containing sulfate, nitrate, phosphate, ammonium and organic materials. Sun and star photometers measure the aerosol optical density of particles in the PM10 and PM2.5 size ranges. Collaborations within CANDAC allow us to access lidar observations of particulate matter and Fourier transform infrared measurements of trace gas abundances. We also use the FLEXPART/FLEXTRA Lagrangian modelling system to understand the transport that brings these measurements together and is at the heart of this theme.

The research program in the ATTAQ theme is unique. In situ measurement of particulate size and composition has never been attempted in the High Arctic. The fact that the PEARL ridge laboratory is in the free troposphere most of the time also provides a rare opportunity to identify the sources of significant pollution episodes through Lagrangian atmospheric transport studies. This allows us to teach trainees about the identities, quantities, sources, and atmospheric dynamics responsible for transport in the Northern Hemisphere and especially at high latitudes. These results clearly relate to issues such as trans-boundary transport, which have implications for Arctic sovereignty.

The Arctic Radiative Environment: Impacts of Clouds, Aerosols, and "Diamond Dust" [ARE]

The ARE theme seeks to comprehensively measure the radiative state of the Arctic atmosphere in order to better understand the dramatic changes seen in high-latitude climate over the past 30 years. Temperatures at the surface are largely determined by the radiative exchange, and detailed knowledge of processes that govern clouds, particulate matter and water vapour is needed to understand it. The annual average temperature at Eureka has increased by nearly 3°C since the mid-1980s, which is at the upper range of the observed Arctic warming shown in the 2007 IPCC report. A result of this pan-Arctic warming is that sea ice has been in steady decline for over 30 years, with the past three summers having the lowest coverage on record. The surprising loss of “permanent” old ice from the respective collapse and breakage of the Ayles (in 2006) and Markham (in 2008) ice shelves punctuates trends induced by atmospheric change.

The radiative environment of the high Arctic is much different from that at mid-latitudes due to the strong seasonal variations in solar insolation, very cold temperatures, a very stable winter boundary layer, extremely dry air, and the presence of ice crystals and Arctic haze. Early studies indicated that diamond dust (i.e., ice crystals that form spontaneously in clear skies) contributes an important infrared radiative forcing, although more recent studies, including our own, indicate that the impact is likely weak. On the other hand, recent case studies have identified ice crystals lofted from mountaintops and thin ultra-stable water clouds as important contributors to the radiative exchange. That water clouds should exist at all in the cold Arctic wintertime is surprising, and campaign data and modelling efforts have indicated that this may be due to vertical motions and a dearth of ice formation nucleii. Our studies have revealed the important effect of topography on the local circulation and ice crystal formation, but the effect of topography on Arctic water clouds is unknown. Aerosols are hypothesized to have an indirect impact on radiation by the dehydration-greenhouse effect, but this requires experimental investigation.

A comprehensive set of measurements is needed to investigate the small-scale processes that underlie each of these gaps in our understanding. The instrument complement at PEARL is unique, providing information on the optical properties of ice crystals, aerosols, and clouds, in addition to the down-welling infrared spectrum, temperatures, water vapour, horizontal winds and vertical motions. The site at Eureka currently represents the only concentrated effort to study the radiative transfer problem year-round anywhere in the High Arctic. Some of the instruments measure variables that have never before been regularly obtained at such high latitudes (e.g., continuous tropospheric temperature and water vapour profiles). Results have already helped further our understanding of the diamond-dust forcing problem. As we go forward, new issues of current debate that affect radiative transfer, such as the role of thin water clouds, dehydration from aerosols, dynamics, topography, and the 20-µm absorption-spectrum window will be investigated.

Satellite data, such as from the Moderate Resolution Imaging Spectrometer (MODIS), will be used to provide a regional context for interpretation of our results. A VHF radar is now providing our first view of the local dynamics, and this complements dynamical measurements in-cloud by the Millimeter Cloud Radar. The Rayleigh-Mie-Raman (RMR) lidar provides profiles of tropospheric temperatures and water vapour, in addition to aerosol, cloud, and ice crystal measurements that are also provided by the High Spectral Resolution Lidar. The Extended-range Atmospheric Emitted Radiance Interferometer (E-AERI) makes observations deep into the 20-µm window region through which the majority of radiative cooling to space uniquely occurs in the Arctic atmosphere. These continuous in situ measurements at cloud heights from the PEARL ridge observatory are unprecedented.

Arctic Middle Atmospheric Chemistry [AMAC]

The AMAC theme addresses two of the four “grand challenges in atmospheric chemistry” identified in the 2004 IGOS Atmospheric Chemistry Theme Report, namely “stratospheric chemistry and ozone depletion” and “chemistry-climate interactions”. We note that this report specifically states that “… the frequency of measurements deep in the Arctic vortex remains low. The situation is unsatisfactory given the highly non-linear sensitivity of Arctic stratospheric ozone to cold winters. … Chemical and dynamical perturbations caused by strong volcanic eruptions make it impossible to derive a linear trend [in total ozone], which highlights the importance of continuous measurements throughout the expected recovery of the ozone layer during the coming decades.”  The AMAC theme, and the datasets resulting from it, directly address this unsatisfactory situation.

The stratosphere contains about 90% of the total ozone column, which is well known as a highly effective absorber of harmful solar ultraviolet radiation. Stratospheric ozone concentrations have declined significantly since about 1980 in response to enhanced levels of chlorine resulting from anthropogenic emissions of CFCs. This is particularly true in the Arctic, where total ozone column trends derived from satellite data for 1978-2000 show that the largest Arctic trend is 1.04±0.39 % per year in March. With the signing of the Montreal Protocol (in 1987) and its subsequent amendments to regulate the production of CFCs, a gradual recovery of global stratospheric ozone is anticipated, with a minimum expected in the next two decades. However, predictions of the future evolution of Arctic ozone vary, given the interannual variability in the area, strength, and timing of the polar vortex, uncertainties related to the coupling of ozone with stratospheric cooling, and vulnerability to new perturbations, such as climate change and aerosols from volcanoes.

The overall goal of AMAC is to improve our understanding of the processes controlling the Arctic stratospheric ozone budget and its future evolution, using measurements of the concentrations of stratospheric constituents, in conjunction with dynamical, radiative, aerosol, polar stratospheric cloud, and meteorological observations also made at PEARL. These measurements will be used to help answer the following scientific questions:

This theme is providing us with a significant new long-term dataset of Arctic chemical composition measurements, which will yield better understanding of diurnal, day-to-day, seasonal, and interannual variability. The primary instruments are a Bruker 125HR Fourier transform infrared spectrometer, two UV-visible grating spectrometers, a stratospheric ozone lidar, Brewer spectrophotometers, and the E-AERI. The first two instruments have been certified by the international Network for the Detection of Atmospheric Composition Change (NDACC). There is a particular focus on measurements of chemical ozone loss at Eureka during each Arctic winter-spring, along with the determination of trends in ozone and related stratospheric constituents. This theme will result in improved understanding of processes and feedbacks between stratospheric ozone depletion, rising greenhouse gas concentrations, and climate change, as well as better predictive capabilities regarding the future evolution of the Arctic ozone budget.

Waves and Coupling Processes [WACP]

The WACP theme provides an observational catalyst for Canadian research in middle atmosphere dynamics of the middle atmosphere. It addresses the two key questions formulated during the 2005 CSA-sponsored community workshop “A Vision of Atmospheric Sciences for the Next 10 years: 2005-2015” for the middle atmosphere, namely:

  1. What are the dynamical and chemical effects (e.g., ozone loss) of stratospheric sudden warmings upon the lower and middle atmospheres over Southern and Arctic regions of Canada, including changes in surface weather, and how do they differ from other polar locations e.g. Europe-Scandinavia and Antarctica?

  2. What are the relative roles of atmospheric waves, global terrestrial processes and solar activity in providing variability and change in the winds and weather (10-100 km) above the Canadian Arctic, Scandinavia and Antarctica? What is the related evidence for and processes involved in “Solar Influences upon the Climate”?

With the installation of the E-Region Wind interferometer (ERWIN), the All Sky Imager (ASI), and the Spectral Airglow Temperature Imager (SATI) in winter 2007-08, Canada now has a polar-observing capability for middle atmospheric dynamics equal to any in the world. Observations of dynamical signatures from the troposphere through the stratosphere and up to the mesopause region are now being achieved and can provide insights into conditions over the pole.

With all the relevant instruments now producing data, we are optimizing observing strategies to allow details of the physical processes operating in the polar upper mesosphere to be investigated for the first time. Approaches for designing new observation sequences that take advantage of the complementarities between the instruments will be explored. Details of wave parameters will be determined using the wind, temperature and airglow measurements available in the mesopause region. Augmenting these data with lidar and spectrometer observations will allow the coupling throughout the atmosphere to be explored. The physical processes associated with dynamical events such as sudden stratospheric warmings, solar proton events and strong geomagnetic activity are still uncertain and will be studied using PEARL observations over the coming years.

Linkages with other observation sites have been established, providing contextual information for interpretation of the PEARL data. In turn, the PEARL data are a contribution to the validation and science of these groups. Collaborations have been established with scientists working at Svalbard, Tromso, and Resolute Bay, and a network of scientists through the National Science Foundation-funded IPY project “Pan-Arctic Studies of the Coupled Tropospheric, Stratospheric and Mesospheric Circulation”. One study involving Arctic tides has been completed using the wind observations from the PEARL and Svalbard meteor radars. Multi-year studies using the radar and the other PEARL instruments are part of future activities.

Satellite and modelling/assimilation groups with whom collaborations have been established include the CMAM modelling effort, the CMAM Data Assimilation System, MetO-UKMO, and the satellite mission teams associated with TIMED, OSIRIS, MIPAS and Aura MLS. From these, the WACP team has developed a range of methodologies for characterizing the Arctic winter vortex of the middle atmosphere, to allow atmospheric and chemical observations to be placed in hemispheric context. Studies of the vortices for the four winters of 2004-05 to 2007-08, including vertical and hemispheric coupling, have combined radar and Aura-MLS data. During stratospheric warmings over PEARL, the local regional mesopause is cooled and the Southern polar mesopause is warmed; the signs of correlations with the Arctic atmosphere are shown to be strongly dependent on longitude, and thus the position and distortion of the Arctic vortex. These are the first campaigns in what will become rich research topics over the IPY years of 2007-09 and beyond.

In addition, the PEARL observations are contributing to the international efforts associated with two CAWSES projects (“Atmospheric Wave Interactions with the Winter Polar Vortices (0-100 km)” led by Alan Manson and the CAWSES Global Tidal Campaign headed by William Ward). Finally, instruments from PEARL are among those involved in the Network for the Detection of Mesopause Change (affiliated with WMO’s Global Atmosphere Watch) which is being set up to monitor conditions in the mesopause region.