# Presentation: 307276

## Variability of the Atlantic North Equatorial Countercurrent (NECC)

_**Gustavo Jorge Goni**_**, Claudia Schmid and Molly Baringer**
**PIRATA-XII MEETING**
**Miami, Florida**
**November 2006**
**Gustavo.Goni@noaa.gov**

**NOAA/AOML**

**Collaboration:** Carlos Fonseca, Bill Johns, and Pedro DiNezio

## The MOC and wind driven circulation

- PIRATA MEETING, MIAMI 2006

**The MOC and wind driven circulation**

**Notes:**
MOC

## The NBC and NECC

**The NBC and NECC**

- PIRATA MEETING, MIAMI 2006

## The ITCZ

**The ITCZ**

**( - )**

**( + )**

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**Notes:**
MOC

## XBT high density lines

**AX08:**
-   **Started:  2000**
**  ****Transects/year: 4**
**  ****No. transects:****	****20**
**  ****XBTs/deg of lat:  4**
**  ****XBTs/transect:  280**

**XBT high density lines**

- PIRATA MEETING, MIAMI 2006

**Notes:**
Same map of MOC but with HD lines, schedules, autolauncher

## Temperature Sections

**Temperature Sections**

- September 2002

- PIRATA MEETING, MIAMI 2006

**Notes:**
Typical temp transect, dynh from XBT

## Velocity Sections

**Velocity Sections**

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## XBT-dynamic heights

**XBT-dynamic heights**

- PIRATA MEETING, MIAMI 2006

**Notes:**
Correlat dynh and temp, slope g’, dispersion =B’

## Altimetry-sea heights

**Altimetry-sea heights**

- September 2002

- PIRATA MEETING, MIAMI 2006

**Notes:**
Dynh from xbt and altimetry, differences

## XBT-dynamic heights and altimetry-sea heights

**XBT-dynamic heights and altimetry-sea heights**

- September 2002

- PIRATA MEETING, MIAMI 2006

**Notes:**
Dynh from xbt and altimetry, differences

## Sea heights and the depth of 20°C

**Sea heights and the depth of 20****°****C**

- PIRATA MEETING, MIAMI 2006

**Notes:**
One section and one map of dynh from altimetry

## Mean dif=-3m  mean rms dif=8m

**D20 from altimetry in the tropical Atlantic**

**Mean dif=-3m  mean rms dif=8m**

- PIRATA MEETING, MIAMI 2006

**Notes:**
Pirata and correlation between SHA and d20

## Core of the NECC

**Sea height (****η****) **- ηmean **= **ε (h-hmean)
**Geostrophic velocity (V****g****): **g/f** * **Δη/Δy  =  g’/f * Δh / Δy
**Geostrophic transport (S****g****): **g/f** * **Δη * Δz  =   g’/(2f) Δh2   [Goni et al, 1996]

**Core of the NECC**

- Sept 2002

- PIRATA MEETING, MIAMI 2006

**Notes:**
Identification of the core.  Sample meridional profile, location of max, min and max gradient.

## Variability of the Core of the NECC

**Variability of the Core of the NECC**

**Mean location: ~ 6****°****N**

- PIRATA MEETING, MIAMI 2006

**Notes:**
Time series of location of core, monthly means, anomalies and wavelets

## Variability of the Core of the NECC

**Variability of the Core of the NECC**

- PIRATA MEETING, MIAMI 2006

**Notes:**
Separation between western and eastern region.

## Variability of the Core of the NECC

**Variability of the Core of the NECC**

- PIRATA MEETING, MIAMI 2006

**Notes:**
Separation between western and eastern region.

## The Second Core of the NECC 

**The Second Core of the NECC **

- September 2003

- September 2004

- November 2004

- PIRATA MEETING, MIAMI 2006

**Notes:**
Second core of the NECC ?

## Geostrophic Transport of the NECC

**Geostrophic Transport of the NECC**

**Geostrophic transport: **
**Mean: 15 Sv**

**Sg: **g/f** * **Δη * **Δ****z** =   g’/(2f) Δh2

- PIRATA MEETING, MIAMI 2006

**Notes:**
Transport, computation, means, anomalies, wavelets, w-e regions

## Conclusions

- HD XBT transects and altimetry (using a 2-layer reduced gravity scheme) can be used with confidence to monitor the dynamic height and depth of selected isotherms in the tropical Atlantic (TA).
- The location of the core of the NECC exhibits main annual and semiannual components in the western TA.
- The location of the core of the NECC exhibits a main annual
- component in the eastern TA.
- The mean location of the core of the NECC shifted 1 degree to the south in 1997, but returned to its historical mean value in 1998.
- The geostrophic transport is mainly annual.
- There is no conclusive evidence (from 20 HD XBT transects and altimetry) of the existence of a second, northernmost, core of the NECC.

**Conclusions**

- PIRATA MEETING, MIAMI 2006

## Future Work

**Future Work**

- Continue the monitoring of the NECC location and transport.
- Investigate possible links between the variability of the NECC other components of the MOC.
- Use a combination of satellite altimetry and surface drifter fields to estimate the ageostrophic component of the surface currents.

- PIRATA MEETING, MIAMI 2006

## Thank you 

**Variability of the Atlantic North Equatorial Countercurrent (NECC)**
**Gustavo Jorge Goni, Claudia Schmid, Molly Baringer**
**November 2006**

- PIRATA MEETING, MIAMI 2006