Volcanic contribution to the 1990s North Pacific climate shift in winter.

It is debatable whether external forcing can change the state of the climate. By investigating decadal changes with and without including the 1990s stratospheric volcanic aerosols, we explored the volcanic eruptions contribution to decadal climate regime shifts occurring in boreal winter over the North Pacific. The volcanic eruptions contribution can be characterized as a series of rapid changes, including the strengthening and poleward shift of the midlatitude westerly jet stream. In addition to the short-lived radiative effects primarily induced by the 1991 Mount Pinatubo eruption, the volcanically driven decadal change can be observed in the mid-to-late 1990s, suggesting a time-lagged characteristic of the volcanic climate impact. Compared with the decadal change irrelevant to volcanic eruption, the decadal state more dramatically enters into the next phase when volcanic forcing is included. The climate oscillation-related pattern shifts that occurred across the 1990s can provide insights into volcanically induced changes in decadal atmospheric circulation. [ABSTRACT FROM AUTHOR]