Author ORCID Identifier

Bushra, Nazla: 0000-0002-7007-0456

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The Northern Hemispheric circumpolar vortex (NHCPV) is the hemispheric-scale, middle- and upper-tropospheric wind belt circumnavigating the North Pole. It is delineated by the well-known polar front jet stream, and it bends poleward at ridges and equatorward at troughs at various amplitudes and positions over time. Previous work assessed the accuracy of representing the NHCPV using a new technique through correlations to air-sea teleconnections known to be related to broad-scale, extratropical steering circulation at the monthly scale. Results of that work suggested that the method allows for notable improvements in the calculation of area and circularity of the 500-hPa manifestation of the NHCPV. Because using monthly averaged data to represent the NHCPV may oversimplify analyses, especially for identifying meteorological impacts, this research employs the same technique for identifying the daily NHCPV. Results suggest that CPV area and circularity are even more closely related to variability in the North Atlantic Oscillation (NAO), Pacific/North American pattern, and (especially) Arctic Oscillation (AO) teleconnections, and the El Nino/Southern Oscillation phenomenon at the daily scale than at the monthly scale. A principal components analysis reveals the extent of the interrelationships between the teleconnections and NHCPV area and circularity. Results generally affirm that both the individual teleconnections, especially the NAO and AO, and interdependencies among these teleconnections and others, are strongly related to the NHCPV area and circularity. These findings are important because low- and high-frequency variability in the amplitudes and positions of the undulations in the broad-scale flow influence weather systems that exert important impacts on society. Plain Language Summary The broad-scale, west-to-east, upper-level atmospheric flow separates the frigid polar air from the much more moderate temperate air over the middle latitudes. Popularly known as the polar vortex, this circumpolar vortex (CPV) expands equatorward and contracts poleward, and becomes quasi-circular at times and wavier (with south-to-north or north-to-south components of flow) at other times on its general west-to-east trek around the North Pole. Previous work has defined the CPV's position at a given time using a predetermined, one-size-fits-all elevation at which 500 hPa of atmospheric pressure occurs. Our approach introduced in a previous study is based on the steepest gradient of that elevation. In this study, we demonstrate the effectiveness of this new delineation by showing that the CPV's area and waviness are linked at the daily scale to several known atmospheric circulation features that have been shown previously to be associated with the CPV. Two atmospheric flow patterns-the so-called Arctic Oscillation and the related North Atlantic Oscillation-are particularly closely linked to the Northern Hemisphere's CPV (NHCPV), and the El Nino/Southern Oscillation phenomenon is associated less directly with NHCPV variability. Results will help atmospheric scientists as they use model output of the CPV's position to identify steering patterns that affect daily weather.

Publication Source (Journal or Book title)

Earth And Space Science