A global ocean temperature and altimeter data assimilation system for studies of climate variability |
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Authors: | S Masina N Pinardi A Navarra |
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Institution: | (1) Istituto Nazionale di Geofisica, Rome, Italy E-mail: s.masina@isao.bo.cnr.it, IT;(2) Corso di Laurea in Scienze Ambientali, University of Bologna, Ravenna, Italy, IT |
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Abstract: | An ocean data assimilation (ODA) system which can assimilate both temperature and altimeter observations has been applied
to the global ocean and tested between January 1993–October 1996. A statistical method has been used to convert sea surface
height (SSH) anomalies observations from TOPEX/POSEIDON into synthetic temperature profiles. The innovative aspect of this
method is the introduction of time dependency in the correlations used to transform the altimeter observations into temperature
corrections. The assimilation system is based on a univariate variational optimal interpolation scheme applied to assimilate
both in situ and synthetic temperature profiles. In addition, a longer global analysis for the upper-ocean temperature starting
from January 1979 and ending November 1997, has been produced to examine the skill of sea temperature assimilation with a
rather simple and practical method. The temperature analysis shows encouraging improvement over a corresponding ocean simulation
when compared to independent (not assimilated) temperature data both at seasonal and interannual time scales. However, the
univariate data assimilation of hydrographic data does not result in an improvement of the velocity field. In fact the assimilation
of sparse in situ data can introduce unrealistic spatial variability in the temperature field which affects the velocity field
in a negative way. This deficiency is partially overcome when we also assimilate altimeter observations since the coverage
is complete and uniform for this data. In particular, our study shows that temperature corrections due to the altimeter signal
have a positive impact on the current system in the tropical Pacific.
Received: 28 May 2000 / Accepted: 6 November 2000 |
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