冬季北半球500hPa高度と地上温度場の特異値分解解析

Abstract

A singular value decomposition (SVD) analysis between the Northern Hemisphere winter-mean 500-hPa geopotential height (Z500) and near-global surface temperature (land-surface air temperature + sea surface temperature) fields was conducted for the recent three decades. The leading mode, referred to as Polar/Eurasia (PEA), is considered as a hemispheric-wide atmospheric internal variability rather than a local teleconnection pattern. Winter mean Z500 of the leading mode is closely related to Eurasian surface air temperature from autumn to spring throughout the period. Both interannual and interdecadal time scales are dominant during the three decades in the time scales. No linear relationship between the tropical SST anomalies is found in this mode. The second and third modes can be identified as the Pacific/North American (PNA) and Western Pacific (WP)-type teleconnection patterns, respectively. Although they are also considered as internal modes of atmospheric variabilities, their interannual variabilities are also influenced by the tropical Pacific SST anomalies. These results are compared with the more popular SVDanalysis between geopotential height and SST, for which the leading mode exhibits the so-called “ENSO (El Niño/Southern Oscillation) related” winter circulation pattern. It is shown that this ENSO-related mode can be reconstructed from the linear combination of the second (PNA) and third (WP) modes of the present SVD mentioned above. These results suggest that inter-El Niño differences of atmospheric circulation in midlatitudes can be interpreted as the different strengths of the PNA and WP patterns on one hand, and on the other hand by the different magnitude of the PEA, which is linearly independent of ENSO. The characteristics of the vertical structure of the atmospheric variability were further examined by conducting a SVD analysis of 100-hPa temperature and Z500. The PEA and PNA patterns in the Z500 field extracted as the first and second SVD modes, respectively, exhibit contrasting features in association with lower stratospheric temperature. The PNA pattern is confined to the troposphere, while PEA extends further into the stratosphere. This suggests they are produced by different mechanisms.