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ARGO float survey - Case studies

Case study #1

For this case, there are two samplings a day for Jan. 10, 20 and 30, 2005 of a weak positive SSHA (Fig. 1). Each time, the two samplings measure different parts of the region around the eddy (Fig. 2). Remarkably, however, the depth anomaly does not change much from one location to another and over the 20 days (Figs. 1 and 3). For σ = 24.5 kg/m^3 (Figs. 4 and 5), although SSHA (from -4 to +7 cm) and W (from -8 to 10e-12 1/s^2) vary both a lot, the isopycnal surface stays at about the same depth (25-50 m deeper than its regionally-averaged depth). For σ = 26.5 kg/m^3, the isopycnal surface has about the same depth (40-70 m shallower) in 4 measurements, while in the other 2, the surface has near zero DA.

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Figure 1: (left) SSHA and location of the ARGO float, (middle) DA versus σ and (right) DA versus depth of each σ. Contours of SSHA are every 2 cm between -20 and +20 cm. See ARGO_iso_survey_case_studies.m in RESEARCH/PROJECTS/MARINE_BIOLOGY/SUBMESOSCALE_PROCESSES/ARGO/analysis.

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Figure 2: Averaged pattern for these 5 samplings and the location of each sampling relative to the center of the eddy (defined as the location of local maximum positive SSHA).

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Figure 3: DA versus σ (left) and DA versus depth of each isopycnal (right) for these 5 samplings.

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Figure 4: SSHA versus DA for σ = 24.5 (a) and 26.5 (b) kg/m^3.

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Figure 5: W versus DA for σ = 24.5 (a) and 26.5 (b) kg/m^3.

Case study #2

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Figure 6: (left) SSHA and location of the ARGO float, (middle) DA versus σ and (right) DA versus depth of each σ. Contours of SSHA are every 2 cm between -20 and +20 cm.

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Figure 7: Averaged pattern for these 5 samplings and the location of each sampling relative to the center of the negative-SSHA eddy (defined as the location of local maximum negative SSHA) in the lower right. The red and blue dots correspond to unusual DA profile (see Fig. 8), the first sample (Apr. 10, 2005) and the fifth one (May 20, 2005).

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Figure 8: DA versus σ (left) and DA versus depth of each isopycnal (right) for these 5 samplings.

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Figure 9: SSHA versus DA for σ = 24.5 (a) and 26.5 (b) kg/m^3.

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Figure 10: W versus DA for σ = 24.5 (a) and 26.5 (b) kg/m^3.

Case study #3

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Figure 11: Averaged pattern for all samplings and the location of each sampling relative to the center of the positive-SSHA eddy (defined as the location of local maximum positive SSHA).

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Figure 12: DA versus σ (left) and DA versus depth of each isopycnal (right) for each sampling.

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Figure 13: (a) SSHA and (b) W versus DA for σ = 24.5 kg/m^3.

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Figure 14: (a) SSHA and (b) W versus DA for σ = 26.5 kg/m^3.

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Figure 15: σ versus depth.

Case study #4

This case corresponds to the deepest isopycnal surface σ = 24.5 kg/m^3. In this case, all 5 measurements have about the same SSHA and W (e.g. Fig. 19). One possible reason is that the ARGO float has rotated with the eddy (Fig. 16) so that what it is sampling is about the same location of the eddy. If this is correct then we observe large depth anomalies (for instance at σ = 24.5 kg/m^3) appearing within a few weeks (Fig. 18) at the same location relative to the eddy. Either the whole eddy or part of it structure is going up and down, submesoscale processes are occuring, or something else.
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Figure 16: Averaged pattern for all samplings and the location of each sampling relative to the center of the positive-SSHA eddy (defined as the location of local maximum positive SSHA).

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Figure 17: σ versus depth.

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Figure 18: DA versus σ for each sampling.

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Figure 19: (a) SSHA and (b) W versus DA for σ = 24.5 kg/m^3.

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Figure 20: (a) SSHA and (b) W versus DA for σ = 26.5 kg/m^3.