HR: 1340h
AN: A43B-1142    [Abstracts]
TI: Pacific Sea Surface Temperatures in the Twentieth Century: An Evolution-Centric Analysis of Variability and Trend
AU: * Guan, B
EM: bguan@atmos.umd.edu
AF: Department of Atmospheric and Oceanic Science, University of Maryland, College Park, Computer and Space Sciences Bldg, College Park, MD 20742,
AU: Nigam, S
EM: nigam@atmos.umd.edu
AF: Department of Atmospheric and Oceanic Science, University of Maryland, College Park, Computer and Space Sciences Bldg, College Park, MD 20742,
AB: A consistent analysis of natural variability and secular trend in Pacific SSTs in the 20th century is presented. By focusing on spatial and temporal recurrence, but without imposition of periodicity constraints, this single analysis discriminates between biennial, ENSO and decadal variabilities, leading to refined evolutionary descriptions; and between these natural variability modes and secular trend; all without advance filtering (and potential aliasing) of the SST record. SST anomalies of all four seasons are analyzed together using the extended-EOF technique. Canonical ENSO variability is encapsulated in two modes that depict the growth (east-to-west along the equator) and decay (near-simultaneous amplitude loss across the basin) phases. Another interannual mode, energetic in recent decades, is shown linked to the west-to-east SST development seen in post climate-shift ENSOs; the non- canonical ESNO mode. The mode is closely related to Chiang and Vimont's meridional mode, and leads to some reduction in canonical ENSO's oscillatory tendency. Pacific decadal variability is characterized by two modes: The Pan-Pacific mode has a horse-shoe structure with the closed end skirting the North American coast; and a quiescent eastern equatorial Pacific. The mode exhibits surprising connections to the tropical/subtropical Atlantic, with correlations there resembling the Atlantic Multidecadal Oscillation. The second decadal mode---the North Pacific mode---captures the 1976/77 climate shift and is closer to Mantua's Pacific Decadal Oscillation. Our analysis shows, perhaps, for the first time, the striking links of the North Pacific mode to the western tropical Pacific and Indian Ocean SSTs. The physicality of both modes is assessed from correlations with the Pacific biological time series. Finally, the secular trend is characterized: Implicit accommodation of natural variability leads to a non-stationary SST trend, including mid-century cooling. The SST trend is remarkably similar to the global surface air temperature trend. Geographically, a sliver of cooling in found in the central equatorial Pacific in the midst of wide- spread but non-uniform warming in all basins. An extensive suite of sensitivity tests, including counts of the number of observational analogs of the modes in test analyses, support the robustness of this analysis.
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting