12.07.10: Analysis of 5145, 6401, 6891 and 5143 ARGO floats - an update

We update and complete the basic analysis of ARGO floats started in this note. Notice that

1. The nutrient sensor of 5145 has stopped on 09/10/2010 so no data after that date are being used
2. I am showing the analysis for the float 5143 which has been deployed in 2008 near Station Papa to constrast the relationship between the potential density σ and nitrate between the subtropic and subarctic gyres.

Some comments:

1. The events of upwelled nitrate and density contours in the subtropical observations do not match in amplitude nor in frequency the regular vertical oscillations observed in the subarctic observations, suggesting that the former are not associated with internal waves, the cause of the latter. This is also confirmed by analysis of the high-frequency (time step less than 10 minutes) WHOTS data (see this note) that shows that a) the internal wave field is not dominant at frequencies larger than 1 one day and b) the internal wave field does not aliased much in the 5-day snapshots of ARGO observations.
2. Unlike in the subtropics, the nitrate does not follow density contours; this justifies that upwelling of nitrate due to frontogenesis (for which the crossing of nitrate and density contours are essential) may be important in the subarctic but not in the subtropical gyre.

The trajectories of 5145, 6401 and 6891 are shown in Fig. 1, that of 5143 in Fig. 2.

Figure 1: Trajectories of the ARGO floats: up to Sept. 2010 for 5145 and Dec. 2010 for 6401 and 6891.

Figure 2: Trajectory of the ARGO float 5143 up to Dec. 2010.

5145Hawaii

Figure 3: Nitrate measured by ARGO float 5145Hawaii up to Dec . 2010.

Figure 4: σ measured by ARGO float 5145Hawaii up to Dec . 2010.

Figure 5: Vertical average between 150 and 200 m: (a) σ anomalies (defined from the deviation from the monthly averaged ARGO data from APDRC climatology (computed with APDRC_ARGO_monthly_mean_script.m in RESEARCH/PROJECTS/MARINE_BIOLOGY/SUBMESOSCALE_PROCESSES/FSLE/analysis/Johnson_etal_09 and (b) nitrate. The correlation is 0.70.

6401Hawaii

Figure 6: As in Fig. 3 but for 6401.

Figure 7: As in Fig. 4 but for 6401.

Figure 8: As in Fig. 5 but for 6401. Because the climatology is not available up to Dec. 2010 yet, the anomalies in σ are missing toward the end of the record. The correlation is 0.71.

6891Hawaii

Figure 9: As in Fig. 3 but for 6891.

Figure 10: As in Fig. 4 but for 6891.

Figure 11: As in Fig. 5 but for 6891. Because the climatology is not available up to Dec. 2010 yet, the anomalies in σ are missing toward the end of the record. The correlation is 0.60.

5143StnP

Figure 12: As in Fig. 3 but for 5143.

Figure 13: As in Fig. 4 but for 5143.

Figure 14: As in Fig. 5 but for 5143. Because the climatology is not available up to Dec. 2010 yet, the anomalies in σ are missing toward the end of the record. The correlation is 0.23.