Skewness modes in the Northern Hemisphere winter.

• Main Authors: Frank M. Selten, Rubén A. Pasmanter
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Pacific; North Atlantic
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.155.3716; http://www.knmi.nl/publications/fulltexts/skewnessstructures.pdf

The probability distribution of daily Northern Hemisphere streamfunction fluctuations at 500 hPa in winter is skewed at most locations. Large positive anomalies are more likely north of 50◦N with maximum values of the skewness in the North Pacific and North Atlantic region. In this study we develop two novel methodologies in order to diagnose the underlying circulation structures associated with the observed spatial distribution of skewness. The first method is based on a teleconnection calculation using a subset of the data characterised by extreme values of the streamfunction in the location of maximum skewness. The second method is based on the maximization of the skewness of linear combinations of dominant EOFs. Both methods yield structures that resemble blocking anomalies: north-south oriented dipole structures at various longitudes around the hemisphere, but in addition a weaker east-west oriented wave structure is often present as well. The structure of these skewness modes is consistent with a recently proposed physical explanation for the skewness based on a crossfrequency coupling between low-frequency stationary anomalies and retro-gressing Rossby waves of intermediate frequencies. 1.