Table Of Contents

This Page

Study of potential density in the 1/30th-of-a-deg-OFES-snapshot

We study here the relationship between vertical velocity w and potential density σ in the 1/30th-of-a-deg-OFES-snapshot, completing recent analysis. The absolute vertical velocity w at 50 –the middle of the surface mixed layer (SML)– is shown in Fig. 1, revealing its submesoscale structure.

The mean depth (mean as the spatial average over the domain of Fig. 1) of a set of isopycnal surfaces is shown in Fig. 2, and the depth for three of them is shown in Figs, 3 to 5 together with contours of large w at 50 m. In the SML, the isopycnal surfaces display a submesoscale structure that seems to be largely due to lateral stirring by eddies. Only in several instances, their submesoscale structure is due to the vertical velocity field. One example is within the eddy near 135°W and 19°N (Fig. 4) and is best seen in the zonal section along 19°N (Fig. 6). Below the SML, however, the isopycnal surfaces appear to be mostly mesoscale.

To confirm this observation, the power density spectrum of σ in the zonal direction is computed at each depth and latitude, and its latitude average is plotted in Fig. 9, while Fig. 8 provides the mean stratification. Energy at high wavenumbers is the highest near the surface and declines with depth.

We learn from this that the submesoscale structure of isopycnal surfaces does not relate well with the submesoscale structure of the vertical velocity field as the latter is being formed mostly out of lateral eddy stirring.

../../../../../../_images/abs_w_202E230E_15N25N_30_OFES_Jan12001_50m.png

Figure 1: Absolute vertical velocity at 50 m.

../../../../../../_images/mdepth0_202E230E_15N25N_30_OFES_Jan12001.png

Figure 2: Depth (averaged over the domain of Fig. 1) of isopycnal surfaces.

../../../../../../_images/depth0_202E230E_15N25N_30_OFES_Jan12001_sig23_1.png

Figure 3: Depth of the isopyncal surface σ = 23.1 kg/m3. Contours of absolute vertical velocities at 50 m larger than 10 m/day are plotted in black.

../../../../../../_images/depth0_202E230E_15N25N_30_OFES_Jan12001_sig23_5.png

Figure 4: Depth of the isopyncal surface σ = 23.5 kg/m3. Contours of absolute vertical velocities at 50 m larger than 10 m/day are plotted in black.

../../../../../../_images/depth0_202E230E_15N25N_30_OFES_Jan12001_sig24_7.png

Figure 5: Depth of the isopyncal surface σ = 24.7 kg/m3. Contours of absolute vertical velocities at 50 m larger than 10 m/day are plotted in black.

../../../../../../_images/sig_abs_w_202E230E_19N_30_OFES_Jan12001.png

Figure 6: σ and absolute w along 19°N (only w larger than 10 m/day is plotted).

../../../../../../_images/mN_202E230E_15N25N_30_OFES_Jan12001.png

Figure 7: Stratification averaged over the domain of Fig. 1.

../../../../../../_images/sig_PDf_x_latav_202E230E_15N25N_30_OFES_Jan12001.png

Figure 8: Power density spectra of σ in longitude (between 211°E-230°E), averaged in latitude over the domain of Fig. 1. Zonal profiles have been mirrored before computing the Fourier transform.