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07.22.11: Behavior of density surfaces around WHOTS – comparison of WHOTS observations and HYCOM model – Part 2

I keep going the analysis started in this note.

  • There is an important difference between the model and the observations. The anomalies in depth of the isopycnal surface σ = 24.4 kg/m3 that is on average within the nutricline are smaller and biased toward negative values in the HYCOM model compared to the observations (compare Figs. 3 and 4). The histogram of the depth anomalies are shown in Fig. 1:

Figure 1: Histogram of the depth anomalies of σ = 24.4 kg/m3 in (a) WHOTS and (b) HYCOM at WHOTS location.

  • This is in part due to the mesoscale field in that part of the domain of the HYCOM model that is less energetic than in the observations (Fig. 2):

Figure 2: SSH STD: (a) from AVISO over the full WHOTS period, (b) from AVISO over the HYCOM period and (c) from HYCOM over the HYCOM period.

  • I have been thinking that the large depth anomaly event in Spring of 2010 in the HYCOM model may appear in the full SSH but not in an AVISO-like SSH (which would have given the possibility that we could detect these events by comparing AVISO SSH and SSH deduced from dynamic height). Unfortunately, this is not the case (Fig. 3):

Figure 3: SSH at WHOTS location in HYCOM: (a) full and (b) AVISO-like component. The AVISO-like SSH is the 7-day averaged SSH high-pass filtered to leave only scales larger than 2°.

This is consistent with Fig. 5 of this note that shows that the overall shallowing of the isopycnal is associated with a mesoscale SSH anomaly. That is mainly the peak in SSH seen in Spring 2010 in Fig. 3. It is only the submesoscale structure where the isopycnal surface outcrops that does not have an equivalent submesoscale structure in SSH. The questions is then why in Spring 2009 in WHOTS data, the AVISO SSH does not capture the shallowing of the isopycnal surface?

  • Consistent with the Spring 2010 event in HYCOM, there are events in the WHOTS data for which high-frequency anomalies in depth appear when there is an eddy (end of Spring 2005, early Spring 2006, Spring 2007). Is this wishful thinking?

Plotted thanks to the script full_WHOTS_sig_analysis_1.m in RESEARCH/PROJECTS/MARINE_BIOLOGY/SUBMESOSCALE_PROCESSES/WHOTS/analysis on the main disk.