INTERNATIONAL JOURNAL OF CLIMATOLOGY Int. J. Climatol. 25: 1421–1436 (2005) Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/joc.1204 JANUARY NORTHERN HEMISPHERE CIRCUMPOLAR VORTEX VARIABILITY AND ITS RELATIONSHIP WITH HEMISPHERIC TEMPERATURE AND REGIONAL TELECONNECTIONS ROBERT V. ROHLI,* KALYN M. WRONA and MAURICE J. MCHUGH Department of Geography and Anthropology, Louisiana State University, Baton Rouge, LA 70803-4105, USA Received 13 August 2004 Revised 10 February 2005 Accepted 29 March 2005 ABSTRACT Variability in the hemispheric-scale atmospheric circulation can be directly linked to variations in surface environmental features, such as temperature, precipitation, salinity of water bodies, and pollutant transport. One indicator of the behavior of the hemispheric-scale circulation is the circumpolar vortex (CPV). This research utilizes a geographic information system approach to characterize variability in the Northern Hemispheric (NH) CPV. Specifically, the area, shape, and centroid of the January NHCPV are analyzed for 1959–2001 because it may provide insight about relationships between hemispheric-scale circulation and global temperature change. We also use a new means of characterizing the hemispheric- scale circulation using a ‘circularity ratio’ (R c ). Results suggest that the January NHCPV has exhibited no long-term trends in area or shape, and that the mean centroid is positioned at approximately 85.3 ° N, 178.0 ° W. Regional patterns emerge, which suggest that the area and circularity are associated with variability in surface temperature and moist static energy. Furthermore, the area of the January NHCPV is associated with variability in the Arctic Oscillation, while the shape is tied to variability in the Pacific-North American teleconnection pattern. These results will facilitate understanding of the relationship between hemispheric-scale circulation, regional circulation, and local temperatures. Copyright  2005 Royal Meteorological Society. KEY WORDS: circumpolar vortex; atmospheric circulation variability; atmospheric teleconnections; climate variability and change 1. INTRODUCTION 1.1. The circumpolar vortex The hemispheric-scale atmospheric circulation has traditionally been an important topic of research in the atmospheric sciences. Geographers and climatologists are concerned with the spatial and temporal variability in circulation, including the causes of extratropical atmospheric circulation systems (Rogers et al., 2003). Because broad-scale atmospheric circulation impacts environmental surface features such as temperature and precipitation and a wide range of dependent environmental conditions, it is important to understand its characteristics (Davis and Benkovic, 1994). The circumpolar vortex (CPV) can be used to study the holistic hemispheric-scale extratropical circulation because it represents the characteristic long-wave upper-level ridge-trough configuration around the entire (Northern or Southern) hemisphere at a given point in time. The CPV is defined as the hemispheric-scale, upper-level cyclonic circulation in the middle and upper troposphere centered approximately on the polar region (Ahrens, 1999). In short, the CPV can be described as the region where the strongest meridional geopotential height (or pressure) gradient exists in the Northern or Southern Hemisphere (Frauenfeld and Davis, 2003). * Correspondence to: Robert V. Rohli, Department of Geography and Anthropology, Louisiana State University, Baton Rouge, LA 70803-4105, USA; e-mail: garohl@lsu.edu Copyright  2005 Royal Meteorological Society