 |
| Titel |
ENSO regimes and the late 1970's climate regime shift: The role of synoptic weather and South Pacific ocean spiciness. |
| VerfasserIn |
Terence O'Kane, Richard Matear, Matthew Chamberlain, Peter Oke |
| Konferenz |
EGU General Assembly 2014
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250087121
|
| Publikation (Nr.) |
 EGU/EGU2014-1138.pdf |
|
|
|
|
|
| Zusammenfassung |
| South Pacific subtropical density compensated temperature and salinity (spiciness) anomalies
are known to be associated with decadal equatorial variability, however, the mechanisms by
which such disturbances are generated, propagate and the degree to which they modulate the
equatorial thermocline remains controversial. During the late 1970’s a climate regime
transition preceded a period of strong and sustained El Nino events. Using an ocean general
circulation model forced by the constituent mechanical and thermodynamics components
of the reanalysed atmosphere we show that the late 1970’s transition coincided
with the arrival of a large-scale, sub-surface cold and fresh water anomaly in the
central tropical Pacific. An ocean reanalysis for the period 1990-2007 that assimilates
subsurface Argo, XBT and CTD data, reveals that disturbances occur due to the
subduction of negative surface salinity anomalies from near 35°S, 100°W which
are advected along the Ïă = 25 - 26kg m-3 isopycnal surfaces. These anomalies
take, on average, seven years to reach the central equatorial Pacific where they may
substantially perturb the thermocline before the remnants ultimately ventilate in the region
of the western Pacific warm pool. Positive (warm–salty) disturbances, known to
occur due to late winter diapycnal mixing and isopycnal outcropping, arise due to
both subduction of subtropical mode waters and subsurface injection. On reaching
the equatorial band (10°S–0°S) these disturbances tend to deepen the thermocline
reducing the model’s ENSO. In contrast the emergence of negative (cold-fresh)
disturbances at the equator are associated with a shoaling of the thermocline and El
Nino events. Process studies are used to show that the generation and advection of
anomalous density compensated thermocline disturbances critically depend on stochastic
forcing of the intrinsic ocean by weather. We further show that in the absence of the
inter-annual component of the atmosphere forcing Central Pacific El Nino events are
manifest. |
|
|
|
|
|
|