 |
| Titel |
Impact of hydrographic data assimilation on the modelled Atlantic meridional overturning circulation |
| VerfasserIn |
G. C. Smith, K. Haines, T. Kanzow, S. Cunningham |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1812-0784
|
| Digitales Dokument |
URL |
| Erschienen |
In: Ocean Science ; 6, no. 3 ; Nr. 6, no. 3 (2010-08-05), S.761-774 |
| Datensatznummer |
250003584
|
| Publikation (Nr.) |
 copernicus.org/os-6-761-2010.pdf |
|
|
|
|
|
| Zusammenfassung |
Here we make an initial step toward the development of an ocean assimilation
system that can constrain the modelled Atlantic Meridional Overturning
Circulation (AMOC) to support climate predictions. A detailed comparison is
presented of 1° and 1/4° resolution global model simulations with
and without sequential data assimilation, to the observations and transport
estimates from the RAPID mooring array across 26.5° N in the Atlantic.
Comparisons of modelled water properties with the observations from the
merged RAPID boundary arrays demonstrate the ability of in situ data assimilation
to accurately constrain the east-west density gradient between these mooring
arrays. However, the presence of an unconstrained "western boundary wedge"
between Abaco Island and the RAPID mooring site WB2 (16 km offshore) leads to
the intensification of an erroneous southwards flow in this region when in situ
data are assimilated. The result is an overly intense southward upper
mid-ocean transport (0–1100 m) as compared to the estimates derived from the
RAPID array.
Correction of upper layer zonal density gradients is found to compensate
mostly for a weak subtropical gyre circulation in the free model run (i.e. with no assimilation). Despite the important changes to the density
structure and transports in the upper layer imposed by the assimilation,
very little change is found in the amplitude and sub-seasonal variability of
the AMOC. This shows that assimilation of upper layer density information
projects mainly on the gyre circulation with little effect on the AMOC at
26° N due to the absence of corrections to density gradients below
2000 m (the maximum depth of Argo).
The sensitivity to initial conditions was explored through two additional
experiments using a climatological initial condition. These experiments
showed that the weak bias in gyre intensity in the control simulation
(without data assimilation) develops over a period of about 6 months, but
does so independently from the overturning, with no change to the AMOC.
However, differences in the properties and volume transport of North
Atlantic Deep Water (NADW) persisted throughout the 3 year simulations
resulting in a difference of 3 Sv in AMOC intensity. The persistence of
these dense water anomalies and their influence on the AMOC is promising for
the development of decadal forecasting capabilities. The results suggest
that the deeper waters must be accurately reproduced in order to constrain
the AMOC. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|