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| Titel |
The Role of Warm North Atlantic SST in the Formation of Positive Height Anomalies over the Ural Mountains during January 2008 |
| VerfasserIn |
Zhe Han, Shuanglin Li, Mu Mu |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250047909
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| Zusammenfassung |
| The most severe snowstorm and freezing-rain event in the past 50 years hit central and
southern China in January 2008. One of the main reasons for the anomalous climate event
was the occurrence of atmospheric circulation anomalies over middle and high latitudes,
particularly the persistent blocking that occurred over the Ural Mountains. Along with
atmospheric anomalies, a strong La Niña event in the Pacific and warm sea surface
temperature anomalies (SSTAs) in the North Atlantic were the most significant in the
lower boundary. Since a brief analysis suggests that La Niña exerts no significant
impact on the Urals, the role of the warm SSTAs in the North Atlantic was focused
on.
Based on an observational composite, North Atlantic SSTAs pattern when the height
anomaly over the Urals was strongly positive was found similar to that in January
2008, but no significant SSTAs occurred elsewhere, such as the Pacific. Using two
atmospheric general circulation models, MPI-ECHAM5 and GFDL-AM2.1, the impact
of North Atlantic SSTAs on the extratropical atmosphere circulation in the event
was investigated. First, the model’s ability of simulating atmospheric response to
mid-latitude SSTAs was examined. Two models can reproduce the observed wave-like
low-frequency variability and strom track from North Atlantic to the Urals. This
meant, to a large extent, the modeled atmospheric responses to mid-latitude SSTAs
were believable. Then, model simulation and observation were compared. The
geopotential height anomalies over the Urals were positive and significant. Besides, the
local atmospheric response over North Atlantic was similar to the observation.
Model results indicated the warm SSTAs can strengthen blocking high over the
Urals, which favored a cold-air pile-up in the north that then broke out toward the
south. Last, the mechanism by which the SSTAs influenced atmospheric circulations
was analyzed, and we found that anomalous transient eddies played an important
role for the maintenance of blocking. The consistency between the models and
the observation indicated that the warm SSTAs in the North Atlantic were indeed
an important factor in the formation of the snowstorm disaster of January 2008. |
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