A Possible Volcanic Signal in NCEP/NCAR Reanalysis Data

In this study we used the multi-channel singular spectrum analysis (MSSA) to extract climate signals from National Centers for Environmental Prediction / National Center for Atmospheric Research (NCEP/NCAR) reanalysis monthly mean temperature data between 1950 and 1998. The signal associated with three major volcanic eruptions during this period was clearly shown in the sixth principal component (PC) of the MSSA. The CD was clearly shown in the sixth principal component (PC) of the MSSA. The time evolution of this PC revealed both interannual and interdecadal scale variations suggesting that major volcanic eruptions not only have an effect on short-term climate variability but may also be associated with interdecadal variability in the atmospheric temperature field. The associated anomaly patterns of this PC showed general cooling in the lower atmosphere and warming in the upper atmosphere. Furthermore its time lag maps show anomaly patterns in the equatorial Pacific similar to those of EI Nino-Southern Oscillation (ENSO) warm events. These results suggest that a major volcanic eruption might enhance the strength of an ENSO warm event. Nevertheless, since these eruptions occurred rarely and since each one of them roughly coincided with an ENSO warm event, we are unable to assert that there is a relationship from observed data alone. Despite the irregular occurrence of major volcanic eruptions in history, this study demonstrated that MSSA has the ability to extract temporally irregular but meaningful signal from observed data. Hence MSSA is a very valuable tool for climate study.

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