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- Title
- Expressions of 1976-1977 and 1988-1989 regime shifts in sea-surface temperature off Southern California and Hawai'i,
- Description
- Sea-surface temperatures off southern California from Scripps Pier and from Koko Head, Hawai'i, were examined to determine what impact regime shifts that occurred in 1976-1977 and 1988-1989 had on environmental conditions at each location. Cumulative sums were employed to enhance the detection process. The cumulative sum time histories revealed major turning points at both locations at the time of the 1976-1977 event. At both locations, increases in temperature were indicated, consistent with the phase change in the Pacific Decadal Oscillation that took place at that time. The cumulative sums also indicated major turning points at both locations during the 1988-1989 event. A new procedure called the method of expanding means was employed to determine the long-term impact of these events. By comparing means before and after a given event it is possible to observe the magnitude of the change and to what extent it is sustained. For the 1976-1977 regime shift, temperatures increased rapidly and remained consistently higher, by ∼1°C for 2-3 yr at Scripps Pier. This increase occurred over a period of approximately 7 months and accounts for more than half of the total warming that has occurred at that location since 1920. At Koko Head, a similar response was observed with a sustained increase of approximately +0.5°C. The oceanic response to the 1988-1989 event was quite different. At Scripps Pier, temperatures before and after this event did not show any tendency to converge to significantly different values out to periods of 2-3 yr. At Koko Head, mean temperatures did converge to slightly different values after 1 yr, with mean values being consistently lower after this event (∼-0.4°C). It was shown that in some cases changes associated with these events could be identified in the original data, but without the help of cumulative sums, it is usually not possible to make a clear distinction between changes of interest and other sources of variability. Finally, decorrelation time scales for the records at both locations were estimated and found to be on the order of a year, implying spatial scales that are at least synoptic (tens to hundreds of kilometers)., Cited By (since 1996):1, ,
- Author
- Breaker, Flora
- Date
- 2009-01-01T00:00:00Z
- Title
- The response of Monterey Bay to the 2010 Chilean earthquake,
- Description
- The primary frequencies contained in the arrival sequence produced by the tsunami from the Chilean earthquake of 2010 in Monterey Bay were extracted to determine the seiche modes that were produced. Singular Spectrum Analysis (SSA) and Ensemble Empirical Mode Decomposition (EEMD) were employed to extract the primary frequencies of interest. The wave train from the Chilean tsunami lasted for at least four days due to multipath arrivals that may not have included reflections from outside the bay but most likely did include secondary undulations, and energy trapping in the form of edge waves, inside the bay. The SSA decomposition resolved oscillations with periods of 52-57, 34-35, 26-27, and 21-22 minutes, all frequencies that have been predicted and/or observed in previous studies. The EEMD decomposition detected oscillations with periods of 50-55 and 21-22 minutes. Periods in the range of 50-57 minutes varied due to measurement uncertainties but almost certainly correspond to the first longitudinal mode of oscillation for Monterey Bay, periods of 34-35 minutes correspond to the first transverse mode of oscillation that assumes a nodal line across the entrance of the bay, a period of 26- 27 minutes, although previously observed, may not represent a fundamental oscillation, and a period of 21-22 minutes has been predicted and observed previously. A period of ~37 minutes, close to the period of 34-35 minutes, was generated by the Great Alaskan Earthquake of 1964 in Monterey Bay and most likely represents the same mode of oscillation. The tsunamis associated with the Great Alaskan Earthquake and the Chilean Earthquake both entered Monterey Bay but initially arrived outside the bay from opposite directions. Unlike the Great Alaskan Earthquake, however, which excited only one resonant mode inside the bay, the Chilean Earthquake excited several modes suggesting that the asymmetric shape of the entrance to Monterey Bay was an important factor and that the directions of the incoming tsunami-generated waves were most likely different. The results from SSA and EEMD produced results that differed. Although a period of 34-35 minutes was observed in the SSA, it was not detected in the EEMD. In previous comparisons, however, we have observed that oscillations detected in EEMD were not detected in SSA. SSA also revealed an oscillation with a period of 26-27 minutes, not observed in the EEMD. This oscillation, however, may not represent a fundamental mode but instead a harmonic related to the first longitudinal mode of oscillation whose period is ~55 minutes. We conclude that both methods were useful in helping to interpret the results of this study., Cited By (since 1996):2, Oceanography, ,
- Author
- Breaker, Murty, Flora, Hunter
- Date
- 2011-01-01T00:00:00Z