Equatorial Deep Jets: an Equatorial Deep Jets: an analysis of data sets at 10 analysis of data sets at 10

WWLucia BungeLucia Bunge

Christine ProvostChristine ProvostAnnie Annie KartavtseffKartavtseff

Organization of the Organization of the presentationpresentation

IntroductionIntroductionData year 2000Data year 2000Data year 2003 Data year 2003 ConclusionConclusion

Where is 10° W?Where is 10° W?

Definition of Equatorial Deep Jets Definition of Equatorial Deep Jets (EDJ)(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 (400-600 m).Small vertical scales (400-600 m).Found between the thermocline and Found between the thermocline and

2500 m, and between 1°S and 1°N.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 23LADCP profile at 23ºº W WVertical scale=distance between two positive or negative maxima

Snapshot summer 1999

Problems associated with Problems associated with measuring EDJsmeasuring EDJs

Very long time scales? Quasi-Very long time scales? Quasi-stationary?stationary?

Small vertical scales.Small vertical scales.Mixed up with other signals of similar Mixed up with other signals of similar

or larger amplitude, e.g. annual cycle or larger amplitude, e.g. annual cycle of baroclinic mode 3 or 4.of baroclinic mode 3 or 4.

Different ways of measuring Different ways of measuring velocityvelocity

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 10Mooring array for 2000 at 10ºº W W

840

1360

1525

S1

S2

S3

0.45˚S

745

1000

1120

1385

N1

N2

N3

N4

0.45˚N

E2

E3

E4

E5

E6

EADCP

930

1060

1190

1415

1460

825E113

currentmeters between 745 and 1525 m

To study the EDJs, we will focus To study the EDJs, we will focus on on

Zonal velocity componentZonal velocity componentVertical scalesVertical scalesOscillations of 50-80 days and lower Oscillations of 50-80 days and lower

frequencies (it is only a these time frequencies (it is only a these time scales that we observe vertical scales scales that we observe vertical scales comparable to those of EDJs) comparable to those of EDJs)

50-80 day oscillations50-80 day oscillations

Present in Present in almost all almost all records.records.

Phase Phase relations relations between between depths that depths that change…change…

Is it possible to speak about EDJs of 70-day duration?

The The annual annual cyclecycle

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

Two vertical scalesTwo vertical scales

Evolution of “u” with and without Evolution of “u” with and without the vertical meanthe vertical mean

Comparison with a LADCP profile Comparison with a LADCP profile made between July and August made between July and August

2000, at 102000, at 10ºº W. W.

Summarizing the 2000 dataSummarizing the 2000 dataWe find in the moorings a vertical We find in the moorings a vertical

scale of 500 m associated with a scale of 500 m associated with a temporal scale of 8 months. These temporal scale of 8 months. These scales seem to be related to the EDJs scales seem to be related to the EDJs observed at 700 and 1000 m in the observed at 700 and 1000 m in the LADCP data. LADCP data.

We also find a vertical scale of 800 m We also find a vertical scale of 800 m associated with a interannual associated with a interannual variation + 50-80 day oscillations.variation + 50-80 day oscillations.

Question-suppositionQuestion-suppositionDo EDJs “feel” each other?Do EDJs “feel” each other? If they do, do they do it only in If they do, do they do it only in

couples or is it the whole water couples or is it the whole water column (where jets are present) that column (where jets are present) that oscillates in a coherent manner?oscillates in a coherent manner?

Nine months of new data Nine months of new data (2003)(2003)

Single Single mooringmooring

77 currentmeters currentmeters in ~1000 m in ~1000 m

1600

1710

1265

1500

1120

775

930

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

745-1525 m775-1710 m

Evolution of “u” with and without Evolution of “u” with and without the vertical meanthe vertical mean

Vertical mean and residues

Only the 930 and 1265

currentmeters have a noticeable

negative correlation

MEAN

Summarizing the 2003 dataSummarizing the 2003 data The vertical means are in good agreement.The vertical means are in good agreement. The vertical scales observed match those The vertical scales observed match those

of EDJs, but they are not necessarily of EDJs, but they are not necessarily related to the measurable time scales (no related to the measurable time scales (no correlation between them). correlation between them).

In this case, EDJs timescales cannot be In this case, EDJs timescales cannot be determined.determined.

Comparing to data in 2000, in 2003 EDJs Comparing to data in 2000, in 2003 EDJs seem to be present during all the seem to be present during all the measuring time and at all depths.measuring time and at all depths.

General conclusions (and General conclusions (and questions)questions)

EDJ may have variable time scales. Data of EDJ may have variable time scales. Data of the array in 2000 show vertical scales the array in 2000 show vertical scales comparable to those of jets associated with comparable to those of jets associated with an ~8 month time scale, much shorter than an ~8 month time scale, much shorter than estimated before (at least 5 years).estimated before (at least 5 years).

Results suggest an intermittent behavior.Results suggest an intermittent behavior. Are EDJs events that occur by “couples”? In Are EDJs events that occur by “couples”? In

data of 2003, only EDJs at 930 and 1260 m data of 2003, only EDJs at 930 and 1260 m are synchronized. Is the jet at 1500-1600 m a are synchronized. Is the jet at 1500-1600 m a permanent eastward jet?permanent eastward jet?

For both time intervals, the position of EDJs For both time intervals, the position of EDJs did not change… but the direction did. Is the did not change… but the direction did. Is the presence of this permanent jet affecting the presence of this permanent jet affecting the formation of a jet just above? formation of a jet just above?

Fluctuations of 60-day period may have an Fluctuations of 60-day period may have an important role in triggering EDJs events.important role in triggering EDJs events.