Following the previous paper (Part I, Hanawa et al., 1989), long-term wind stress vector (WSV) fields over the North Pacific are analyzed by means of the composite method with respect to the ENSO events (ENSO composite). As made in Hanawa et al. (1988), every winter during the 24 years from 1961 to 1984 was classified into one of four categorized winters, i.e., ENSO-1 year, ENSO year, ENSO+1 year and the other year winters. Among four categorized winters, WSV anomaly fields for the ENSO year winter are relatively wellorganized and those in the mid-latitudes of the western North pacific and in low-latitudes are quite similar to those for the warm winter of Part I. That is, the East Asian Winter Monsoon (Kisetsuhu) weakens and in the equatorial region, WSV anomaly fields suggest that the central to eastern Pacific is the strengthened convergence region of wind, i.e., convection region. The weakening of the East Asian Monsoon is responsible for the appearance of remarkably positive SST anomalies in the mid-latitudes of western North Pacific in the ENSO year winter described by Hanawa et al. (1988). However, although the mid-latitudes westerly shifts northward, it strengthens compared with the other three categorized winters and the warm winter of Part I. Composited sea-level pressure fields show the marked strengthening and eastward shift of the Aleutian Low, and positive and negative anomalies over the North Pacific appear in mid- and high-latitudes respectively, which is responsible for the strengthening of the mid-latitudes westerly. For the other three categorized winters except for the ENSO year winter, the stabilities of WSV anomalies are low, and the time series of scores of Degree of similarity introduced in Part I do not show that the composited WSV anomalies are typical for each categorized winter. That is, characteristic basin-scale WSV anomaly patterns could not be extracted using the present viewpoint. Therefore, it can be concluded that although ENSO events have remarkable effect on the atmospheric general circulation in the ENSO year winter, they are not necessarily good sampling conditions for the extraction of the characteristic pattern of mid- and high-latitude wintertime WSV fields over the North Pacific, at least in the frame of the present study.
ASJC Scopus subject areas
- Atmospheric Science