Equatorial Deep Jets: an analysis of data sets at 10 W Lucia Bunge Christine Provost Annie Kartavtseff

Organization of the presentation Introduction Introduction Data year 2000 Data year 2000 Data year 2003 Data year 2003 Conclusion Conclusion

Where is 10° W?

Definition of Equatorial Deep Jets (EDJ) Presents in all tropical oceans. Presents in all tropical oceans. Strong zonal speeds (>10 cm/s). Strong zonal speeds (>10 cm/s). Small vertical scales ( m). Small vertical scales ( m). Found between the thermocline and 2500 m, and between 1°S and 1°N. Found between the thermocline and 2500 m, and between 1°S and 1°N. Zonal length??? Maybe 10 or 15°? Zonal length??? Maybe 10 or 15°? Time scale??? Time scale???

LADCP profile at 23º W Vertical scale=distance between two positive or negative maxima Snapshot summer 1999

Problems associated with measuring EDJs Very long time scales? Quasi-stationary? Very long time scales? Quasi-stationary? Small vertical scales. Small vertical scales. Mixed up with other signals of similar or larger amplitude, e.g. annual cycle of baroclinic mode 3 or 4. Mixed up with other signals of similar or larger amplitude, e.g. annual cycle of baroclinic mode 3 or 4.

Different ways of measuring velocity What it is important to distinguish jets are the vertical scales!!!!! Currentmeter time series LADCP profile Low spatial resolution No time scale

Mooring array for 2000 at 10º W S1 S2 S3 0.45˚S N1 N2 N3 N4 0.45˚N E2 E3 E4 E5 E6 E ADCP E1 13 currentmeters between 745 and 1525 m

To study the EDJs, we will focus on Zonal velocity component Zonal velocity component Vertical scales Vertical scales Oscillations of days and lower frequencies (it is only a these time scales that we observe vertical scales comparable to those of EDJs) Oscillations of days and lower frequencies (it is only a these time scales that we observe vertical scales comparable to those of EDJs)

50-80 day oscillations Present in almost all records. Present in almost all records. Phase relations between depths that change… Phase relations between depths that change… Is it possible to speak about EDJs of 70-day duration?

The annual cycle With the aim of eliminating variability coming from larger vertical scales (e.g. annual cycle), we calculate a weighted average of all series and then subtract it from each series.

Two vertical scales

Evolution of “u” with and without the vertical mean

Comparison with a LADCP profile made between July and August 2000, at 10º W.

Summarizing the 2000 data We find in the moorings a vertical scale of 500 m associated with a temporal scale of 8 months. These scales seem to be related to the EDJs observed at 700 and 1000 m in the LADCP data. We find in the moorings a vertical scale of 500 m associated with a temporal scale of 8 months. These scales seem to be related to the EDJs observed at 700 and 1000 m in the LADCP data. We also find a vertical scale of 800 m associated with a interannual variation day oscillations. We also find a vertical scale of 800 m associated with a interannual variation day oscillations.

Question-supposition Do EDJs “feel” each other? Do EDJs “feel” each other? If they do, do they do it only in couples or is it the whole water column (where jets are present) that oscillates in a coherent manner? If they do, do they do it only in couples or is it the whole water column (where jets are present) that oscillates in a coherent manner?

Nine months of new data (2003) Single mooring 7currentmeters in ~1000 m

How do the vertical means of 2000 and 2003 compare? m m

Evolution of “u” with and without the vertical mean

Vertical mean and residues Only the 930 and 1265 currentmeters have a noticeable negative correlation MEAN

Summarizing the 2003 data The vertical means are in good agreement. The vertical means are in good agreement. The vertical scales observed match those of EDJs, but they are not necessarily related to the measurable time scales (no correlation between them). The vertical scales observed match those of EDJs, but they are not necessarily related to the measurable time scales (no correlation between them). In this case, EDJs timescales cannot be determined. In this case, EDJs timescales cannot be determined. Comparing to data in 2000, in 2003 EDJs seem to be present during all the measuring time and at all depths. Comparing to data in 2000, in 2003 EDJs seem to be present during all the measuring time and at all depths.

General conclusions (and questions) EDJ may have variable time scales. Data of the array in 2000 show vertical scales comparable to those of jets associated with an ~8 month time scale, much shorter than estimated before (at least 5 years). EDJ may have variable time scales. Data of the array in 2000 show vertical scales comparable to those of jets associated with an ~8 month time scale, much shorter than estimated before (at least 5 years). Results suggest an intermittent behavior. Results suggest an intermittent behavior. Are EDJs events that occur by “couples”? In data of 2003, only EDJs at 930 and 1260 m are synchronized. Is the jet at m a permanent eastward jet? Are EDJs events that occur by “couples”? In data of 2003, only EDJs at 930 and 1260 m are synchronized. Is the jet at m a permanent eastward jet? For both time intervals, the position of EDJs did not change… but the direction did. Is the presence of this permanent jet affecting the formation of a jet just above? For both time intervals, the position of EDJs did not change… but the direction did. Is the presence of this permanent jet affecting the formation of a jet just above? Fluctuations of 60-day period may have an important role in triggering EDJs events. Fluctuations of 60-day period may have an important role in triggering EDJs events.