INTERNATIONAL JOURNAL OF CLIMATOLOGY Int. J. Climatol. (in press) Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/joc.1326 ON THE ASIAN EXPRESSION OF THE PDO

The causes and mechanisms of Pacific Decadal Variability (PDV) are still being investigated. One reason that such variability is not better understood is the scarcity of high-resolution paleoclimatic records from the Asian side of the North Pacific. Here we present a reconstruction of the boreal spring (March–May) Pacific Decadal Oscillation (PDO) index, spanning A.D. 1565–1988, that is the first to represent the large-scale Asian expression of this phenomenon using tree-ring data. Intervention analysis reveals significant (95 % level) regime shifts corresponding to those in the instrumental PDO during the mid-1920s, mid-1940s and mid-1970s, the latter period associated with the famed 1976 shift in Pacific climate. Shifts in the preinstrumental period show varying correspondence with those of a North American-based tree-ring reconstruction of the North Pacific index (NPI), another indicator of Pacific decadal climate variability. Differences between these two time series hint at modulation of local climate from Asian monsoon, El Niño-Southern Oscillation (ENSO) and volcanic forcing, which could be partly masked by combining data from these sensitive regions in future PDO reconstructions. Overall, however, comparison of the reconstructions from both Asia and North America (NA) is useful for evaluating the distinct expressions of the PDO on both sides of the North Pacific and their interactions with the tropics. Copyright 2006 Royal Meteorological Society