Relationships between wintertime modes of atmospheric variability on intermediate and long timescales

• Main Author: Rennert, Kevin J
• Format: Thesis
• Language: English
• Published: 2007
• Subjects: Theses > Atmospheric sciences; Baffin Bay; Greenland; Gulf of Alaska; Pacific; Baffin; North Atlantic; North Atlantic oscillation; Alaska
• Online Access: http://hdl.handle.net/1773/10089

Thesis (Ph. D.)--University of Washington, 2007. Variability in daily wintertime (DJF) 500 hPa geopotential heights on short (< 6 days), intermediate (6-30 days), and long (> 30 days) timescales is examined. Sectoral EOF analysis shows the leading patterns of variability on short timescales to correspond to the climatological storm tracks, and on long timescales to resemble the North Atlantic Oscillation (NAO) and the Pacific-North America (PNA) pattern. The intermediate timescale variability is best described by large-scale, zonally-oriented patterns: In the Atlantic sector the leading pattern is a dipole with centers of action over Greenland and Scandinavia; The leading Pacific pattern is dominated by a center of action over the Gulf of Alaska, flanked by a pair of lower amplitude centers of opposing sign.Non-linear relationships between fluctuations on long timescales and shorter timescale variance are determined using maximum covariance analysis (MCA). In the Atlantic sector, the negative polarity of a pattern resembling the NAO is associated with enhanced intermediate-timescale variability in a region extending from Baffin Bay to Scandinavia. In the Pacific sector, the negative polarity of a PNA-like pattern is associated with an enhancement of intermediate-timescale variance for a region centered over Alaska and extending over the North Pacific. Similar relationships are demonstrated by regression of the variance fields onto monthly indices of the NAO and PNA, and by the compositing of intermediate timescale variance by polarity of these modes. Hence, the leading patterns of intermediate timescale variability are shown to be enhanced during low-index months of the NAO and PNA.The skewness of the 500 hPa height field, an indicator of blocking activity polewards of the midlatitude jet, is attributable to contributions from intermediate and monthly timescale skewness, as well as a cross-frequency term involving monthly anomalies and intermediate timescale variance. This cross-frequency term is shown ...