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| Titel |
Beyond the tropical Pacific: Medieval climate dynamics and the role of Indian Ocean SSTs |
| VerfasserIn |
N. Graham, C. Ammann, D. Fleitmann |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250024671
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| Zusammenfassung |
| Proxy evidence suggests that climate during the Medieval Climate Anomaly (MCA) was
marked by a distinctive pattern of winter aridity through much of the Northern Hemisphere
subtropics, an intensified North Atlantic Oscillation (NAO), and there are clear indications for
a cooler, drier eastern tropical Pacific. Similarly timed shifts in marine and terrestrial climate
are seen in many other regions of the planet including the Southern Hemisphere.
The global distribution, persistence and general coherence of these changes imply
that tropical SSTs were a main forcing mechanism. To date, model experiments
exploring this “tropically-forced MCA” hypothesis logically have focused on the
idea of a “cool tropical Pacific”. The results show that while the “cool tropical
Pacific” simulations reproduce some important attributes of Medieval climate (e.g.,
aridity in the western US), other major attributes inferred from proxy records are not
well reproduced – these include a strengthened NAO, well-defined SST changes in
the North Atlantic, and increased aridity from northwest Africa into southwest
Asia.
We have looked beyond the tropical Pacific for regions important to forcing large-scale
MCA climate anomalies and present results from coupled model simulations in which
tropical Indian and far western Pacific SSTs were warmed slightly (0.5-1.0C). The model
response closely resembles many of the characteristics of MCA climate described earlier, and
agrees with a number of climate proxy records for boreal summer as well. Among the
features of the model response are a slightly cooler and much drier eastern tropical
Pacific, reduced precipitation in western North America and a persistently enhanced
NAO with related subtropical aridity extending through the Mediterranean, parts of
North Africa and into southwest Asia. The model results also show changes in
North Atlantic SSTs and sea ice in good agreement with marine proxy records. The
simulated circulation changes are quite similar to those from other model experiments
focused on the impacts of Indian Ocean during the second half of the 20th century. |
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