Three-dimensional analysis of oceanographic data with the software DIVA

In oceanography, the process of gridding data is frequently used for various purposes,
e.g. initialization of hydrodynamic models, or graphical representation of sparse data.
DIVA (Data-Interpolating Variational Analysis) is designed to perform such gridding
tasks. It has the advantage of taking into account the intrinsic nature of oceanographic
data, i.e. uncertainty in in situ measurements and anisotropy due to advection and
irregular coastlines and topography.
Three-dimensional reconstruction of temperature and salinity fields is achieved by
stacking horizontal layers where independent analysis with DIVA are performed. Nevertheless,
analysis in regions void of data may result in the presence of static instabilities
between two or more consecutive layers.
The method implemented in DIVA to remove such kinds of instabilities is the object
of the present work. It consists of adding pseudo-data from one layer to the upper
adjacent layer in order to create stable stratification in the vicinity of instabilities.
Two approaches for assigning values to the pseudo data are tested: the first is called
the mixing approach and aims at simulating a mixing process between two layers; the
second is called the minimal perturbation, as it strives to minimise the perturbations
inthe pseudo-data.
A realistic application using temperature and salinity profiles in the North Atlantic is
carried out and the results are compared with World Ocean Atlas climatologies.