Department of Geography

Nicolas Cullen - Research

Research Interests

Nicolas' research interests are in all aspects of meteorology and climatology. The study of the atmosphere inevitably involves an understanding of other components of the global environment, which for Nicolas has been primarily the cryosphere.  Much of his research has focused on the interactions of the atmosphere with snow and ice surfaces in the high and mid-latitudes, as well as on a number of high mountains in the tropics (e.g. Kilimanjaro). Nicolas is also interested in the impacts of atmospheric processes on human behaviour, in particular air pollution meteorology, utilizing wind for energy through turbine development and issues related to climate change on local to global scales.  The research that Nicolas undertakes is dependent on a combination of field data, remote sensing observations and modelling.

The following outlines the main research projects Nicolas is presently linked to and how he undertakes this research:

  1.     Project: Brewster Glacier, New Zealand: Collaborators: 1. Associate Professor Sean Fitzsimons and Dr. Pascal Sirguey, University of Otago, 2. Dr. Andrew Mackintosh and Dr. Brian Anderson, University of Victoria, 3. Dr. Andrew Lorrey, National Institute of Water and Atmospheric Research. Motivation: Understanding the response of temperate glaciers to climate variability is important in improving our current knowledge of global climate change.  Temperate glaciers, including those in New Zealand, are sensitive indicators of climate change and though their contribution to global sea level rise may not be as significant as cold polar and subpolar glaciers and ice caps in the future their retreat will continue to be an important source of terrestrial water to our oceans.  Though complete loss of all glacial ice in New Zealand would only have a minor impact on global sea level rise, understanding the links between glacier behaviour in the Southern Alps and climate is critical in efforts to unravel past patterns of Southern Hemisphere climate and in developing tools to predict future trends. Research activities: Long term measurements of climate (using automatic weather stations) and mass balance allow energy and mass balance models to be utilized, providing insights into the linkages between glacier variability and atmospheric processes on Brewster Glacier, and the greater Southern Alps.

  2.     Project: Kilimanjaro, Tanzania: Collaborators: 1. Dr. Georg Kaser and Dr. Thomas Mölg, University of Innsbruck, Austria, 2. Dr. Pascal Sirguey, University of Otago. Motivation: Glaciers in tropical regions have retreated drastically since the mid and second half of the 19th century, with glaciers on Africa's highest mountain, Kilimanjaro, being no exception to this trend.  The precise age of existing glaciers on Kilimanjaro is uncertain, as is the exact time their present disintegration commenced, though reconstruction of the climatic history of East Africa indicates that decades immediately preceding 1880 coincided with a probable glacier maximum. When Hans Meyer made the first observations of glaciers on Kilimanjaro in the late 1880s and 1890s the break up of ice bodies appeared to have just commenced.  The areal extent of the glaciers just prior to this has been estimated to be about 20 km2. Drastic shrinkage of the remaining glaciers continued throughout the 20th century, with total ice cover reduced to about 2 km2 in 2007. Understanding the recent and long term variations in ice extent on Kilimanjaro in the context of climate change in East Africa remains essential in efforts to better understand the broader impacts of global climate change.  Research activities: Energy and mass balance modelling is used to better understand the climatic controls on retreat of glaciers on Kilimanjaro. Field programs to Kilimanjaro allowed Nicolas and his co-workers to install three automatic weather stations, which are still being maintained, on and next to two different glaciers near the top of the mountain.  Regional atmospheric modelling and use of output from global climate models has enabled a multi-scale analysis of the atmospheric processes controlling glacier retreat.  Remote sensing has also been utilized to characterize the areal extent of the remaining ice bodies.

  3.     Project: Summit, Greenland: Collaborators: 1. Dr. Konrad Steffen, University of Colorado, Boulder, USA. Motivation: Our perception of the stability of the Greenland ice sheet (GrIS) has changed considerably over the last decade, and it is now well established that the largest source of fresh water in the Northern Hemisphere is contributing to sea level rise.  Airborne altimetry measurements obtained in the 1990s were among the first observations to show that the GrIS was thinning along its periphery, but such measurements were not able to determine the causes of the observed changes.  However, data from ice cores and snow pits in the upper accumulation area, combined with high resolution GCM experiments, were able to show that melting on the margins of the south-western sector of the GrIS was most likely responsible for some of the observed mass loss.  Despite uncertainty the majority of evidence suggests that the interior of the GrIS is slightly thickening but near-coastal thinning and acceleration in the velocity of glaciers along the margins of the GrIS appear to be outweighing any positive effect of additional mass input at the higher elevations, resulting in an overall reduction in ice sheet volume.  Recently, mass loss on the margins of the GrIS has been linked more carefully to regional warming in recent decades from studies dependent on both modelling and observations. Research activities: Ongoing efforts are being made to better characterize that atmospheric boundary layer near the highest point on the GrIS through measurement and modelling to improve our estimates of mass balance of this accumulation region .  Other field activities that Nicolas has been involved with are related to projects designed to better understand the climate and mass balance of the coastal margins of the GrIS.

  4.     Project: Air pollution in Southland, New Zealand: Collaborators:  1. Dr. Rachel Spronken-Smith, University of Otago, 2. Dr. Peyman Zawar-Reza, University of Canterbury, 3. Otago Regional Council. Motivation: Air pollution climatology is concerned with the study of atmospheric phenomena and conditions that lead to the occurrence of large concentrations of air pollutants that impact human behaviour.  Air pollution can be categorized into three components: (1) the emission of polluting substances into the air, (2) the pollution potential of the atmosphere characterized by its ability to transport, diffuse, chemically transform and remove the pollutants and (3) the response of the receptors (e.g. people, animals, and vegetation).  All of these components are important regionally throughout New Zealand and efforts to better understand the atmospheric controls on air pollution dispersion, in particular in southern towns of New Zealand, require careful investigation to mitigate the harmful effects of poor air quality. Research activities: Field measurement campaigns and numerical modelling are ongoing to better understand the atmospheric controls on air pollution in Southland, New Zealand.  

  5.     Project: Landscape assessment for wind energy in the Blueskin Bay region, Otago, New Zealand: Collaborators: 1. Dr. Rachel Spronken-Smith, University of Otago, 2. Blueskin Energy Project (BEP). Motivation: If future climate change policy being negotiated internationally is to have any chance of success developed countries will need to consider undertaking measures to modify their existing energy dependence on fossil fuels.  To achieve this, rapid expansion of renewable energy generation, including wind electricity, will be required.  Wind energy in New Zealand is commercially viable in many regions, yet opportunities for its exploitation are far from fully utilised.  Though many communities are showing a resistance to wind farm development, primarily because large wind farms are seen as intrusive, the development of small scale projects lead by local communities is only recently emerging as a possibility.  Successful development of wind turbine technology for power generation for local communities requires a detailed understanding of the wind field of any region being proposed to achieve this energy option. Research activities: Ongoing efforts are being made to develop a detailed understanding of the wind regime of the Blueskin Bay region using both in situ measurements and atmospheric modeling. 

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