Scaling and anisotropic heterogeneities of ocean SST images from satellite data

Oceanic fields display a large variability over large temporal and spatial scales. One way to characterize such variability, borrowed from the field of turbulence, is to consider scaling regimes and multi-scaling properties.

He we use 2D power spectral analysis as well as 2D structure functions <X(M)-X(N)^q>=F(q,d(M,N)), between tow points M and N belonging to the region of interest. By performing statistics with respect to the distance d(M,N), one may extract the scaling property of the 2D field, for a range of distances L_min<d<L_max, of the form F(q,d)=d^ζ(q). This approach can be used even for irregular images (having missing values due to cloud coverage) or for part of images in order to estimate the statistical heterogeneity of different zones of a given image.

In the framework of the French CNRS/IMECO project, we consider MODIS Aqua SST images, in France (English Channel versus Gascogne Golf) and in Chili (Eastern Boundary Upwelling System). We illustrate the use of the 2D structure function analysis for different part of these images and also different times. Scaling ranges and also scaling exponents are compared. To take into account the anisotropy of some of these zones, an anisotropic version of the 2D structure functions is also used.