23 
where R min is the e-folding scale at the coast line (D=0), and R max is the maximum e-folding 
length scale in the open ocean. The spatial correlation scale R max is set as 450 km in our 
calculation and is intended to represent typical signal scales, D min is set as 500 km. The 
spatial distribution of the decorrelation length scale is given in Fig.13. 
4.4. Computational details 
A set of 45 standard levels was selected for which the objectively analysed property fields 
were computed: 
0, 10, 20, 30, 40, 50, 75, 100, 125, 150, 175, 200, 250, 300, 350, 400, 450, 500, 600, 700, 
800, 1000, 1100, 1200, 1300, 1400, 1500, 1750, 2000, 2250, 2500, 2750, 3000, 3250, 3500, 
3750, 4000, 4250, 4500, 4750, 5000, 5250, 5500, 5750, 6000 meters. 
We note that the NOAA climatologies are available for 33 levels for the depth range 0-5500 
meters. 
For each grid point, data are initially selected in a large subdomain, whose radius is arbitrary 
set as 750 km (about 2 times larger than the space correlation scale). The first-guess field 
estimate is taken as the mean of the data in the subdomain. Next, data are selected for the 
objective mapping: inside a subdomain up to 150 nearest observations are retained 
80 
60 
40 
20 
0 
-20 
-40 
-60 
-80 
-160 -120 -80 -40 0 40 80 120 160 
100 200 300 400 950 
Fig. 13: Decorrelation length scale (km). 
To avoid averaging of the data from basins essentially separated from each other optimal 
interpolation was done for a number of oceanic basins or coastal areas. These interpolation 
areas are shown in Fig. 14.