 |
| Titel |
Impact of the SH sea-ice cover and ocean surface on the Southern Ocean atmospheric variability |
| VerfasserIn |
N. Merz, J. Sedlacek, C. C. Raible |
| Konferenz |
EGU General Assembly 2012
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250062993
|
|
|
|
|
|
| Zusammenfassung |
| Satellite observations of the last 30 years have shown a slight increase in the Antarctic sea-ice
area (SIA). This increase seems to be counterintuitive regarding global warming and the
strong decrease observed in Arctic SIA. Thus, dynamical processes rather than
thermodynamical processes would be a more plausible cause for the Southern Hemisphere
(SH) sea-ice increase. This raises interest in understanding the dynamics of the Southern
Ocean climate system and its recent changes.
Based on ERA-40 reanalysis data and satellite-borne HadISST1 observations for
1979-2008 we detect synchronous variability in the Southern Ocean mean sea-level pressure
(SLP), sea surface temperatures (SST) and sea-ice concentration (SIC) fields. The strength of
the Amundsen-Sea low (ASL) is strongly connected with the phase of a dipole-pattern in
SICs and SSTs identified across the Western longitudes.
With the aid of a comprehensive climate model, we further investigate the one-way
impact of the lower boundaries on the Southern Ocean atmosphere. Therefore, a set of
sensitivity atmosphere-land-only simulations is performed forced either with inter-annually
variable (the HadISST1 observations) or climatological input data of SICs and
SSTs.
The sensitivity experiments exhibit a clear impact of both, the SSTs and the sea-ice cover
on the Southern Ocean atmospheric inter-annual variability. For example, the variability of
the ASL is drastically reduced in the experiment with climatological lower boundaries. The
strongest decrease is due to the missing SST variability in the mid-latitudinal Pacific
suppressing the generation of the so-called Pacific South America teleconnection, an
ENSO-related wave pattern significantly influencing the state of the ASL. The wave
generation is inhibited due to reduced variability of the latent heat flux. Further, variable sea
ice impacts the SLP variability but to a lower degree. In summary, there is clear evidence that
the Southern Ocean atmospheric variability is very sensitive to the variability of the lower
boundary conditions and that any changes in SH sea-ice and its variability also feedbacks into
the atmosphere. This result has also implications for the representation of the Southern Ocean
climate in coupled Atmosphere-Ocean General Circulation Models (AOGCMs). |
|
|
|
|
|
|