The objective of this study is to investigate the effect of Atlantic meridional
overturning circulation (AMOC) changes on tropical coupled ocean-atmosphere system
via oceanic and atmospheric processes. A suite of numerical simulations have been
conducted and the results show that both oceanic and atmospheric circulation changes
induced by AMOC changes can have a profound impact on tropical sea surface
temperature (SST) and sea surface salinity (SSS) conditions, but their dominance varies
in different parts of the tropical oceans. The oceanic process has a dominant control on
SST and SSS response to AMOC changes in the South Tropical Atlantic, while the
atmospheric teleconnection is mainly responsible for SST and SSS changes over the
North Tropical Atlantic and Pacific Oceans during the period of reduced AMOC.
The finding has significant implication for the interpretation of the paleotemperature
reconstructions over the southern Caribbean and the western Tropical
Atlantic regions during the Younger Dryas. It suggests that the strong spatial
inhomogeneity of the SST change revealed by the proxy records in these regions may be
attributed to the competing oceanic and atmospheric processes that dominate the SST
response. Similar mechanisms may also explain the reconstructed paleo-salinity change
in the tropical Atlantic, which shows a basin-wide increase in SSS during the Younger
Dryas, according to recent paleo climate studies.
Finally, we show that atmospheric teleconnection induced by the surface cooling of
the North Atlantic and the North Pacific in response to a weakened AMOC, is a leading
physical mechanism that dictates the behavior of El Nino/Southern Oscillation (ENSO) response to AMOC changes. However, depending on its origin, the atmospheric
teleconnection can affect ENSO variability in different ways. The atmospheric process
associated with the North Atlantic cooling tends to enhance El Nino occurrence with a
deepened mean thermocline depth in the eastern Pacific, whereas the atmospheric
process associated with the North Pacific cooling tends to produce more La Nina events
with a reduced mean thermocline depth in the eastern Pacific. Preliminary analysis
suggests that the change in ENSO characteristics is associated with the change in
internal atmospheric variability caused by the surface cooling in the North Atlantic and
North Pacific. Complex nature of the underlying dynamics concerning the effect of the
AMOC on ENSO calls for further investigation into this problem.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2009-08-6975 |
| Date | 14 January 2010 |
| Creators | Wan, Xiuquan |
| Contributors | Chang, Ping |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation |
| Format | application/pdf |
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