Calculation of the MOC Time Series, Data Products and Availability

Paul WrightNational Oceanography Centre, Southampton

(based on work by Stuart Cunningham, Torsten Kanzow, Harry Bryden, Darren Rayner, Julie Collins, David Smeed, Lucas Merkelbach and

Joel Hirschi)

Outline

• How the observed MOC is calculated

• Data Availibilty

• Glider deployment on the Eastern Boundary

The Components of the MOC

The RAPID-MOC Mooring Array

Gridding and Merging the MicroCAT data

The moored MicroCAT data for each section of the Atlantic are merged together to produce profiles of and S.

This is carried out by interpolation and based on pressure as the moorings bend to a degree due to the currents.

The upper section of the eastern boundary 2007/2008, merging the moorings EBH4, EBH3, EBM1 and EBM6. Two other moorings were not recovered.

EBM1

EBH4

EBM6

EBH3

The Internal Mid-Ocean Transports

• The merged and gridded and S profiles are interpolated to form a continuous series.

• Geostrophic transport profiles are then calculated using the dynamic height relationship:

multiplied by the width of each ‘slice’ of the ocean.

• These baroclinic transports are referenced to zero at 4820 dbar.

Modelling the North-Atlantic

western basin

eastern deep basin

eastern/crossMAR basin

T(z) = T(z) west + T(z) east + T(z)crossMAR

Adding the AABW,Ekman, Florida Straits and Western Boundary Wedge Transports

• The mean observed AABW transport is added to the bottom section of the profiles, extending the depth to 6000m.

• The Ekman transports are calculated from the QuikSCAT gridded wind stress dataset produced by IFREMER/CERSAT, they are averaged over the top 100m of the ocean.

• The Florida Straits transports are obtained from underwater cable measurements and can be found at www.aoml.noaa.gov.

• The Western Boundary Wedge transports, between the island of Abaco and WB2 and/or WB3 are measured by current meters and the dataset is produced by Bill Johns at the University of Miami.

The Components of the MOC

Mass Compensation

The north and southwards transports are observed to balance for periods greater than 10 days. This mass compensation due to barotropic external transports can be observed in the bottom pressure anomaly records.

An approximation based on this is applied to the transport profiles using a hypsometric compensation.

T(z) = T(z)INT + T(z)EXT + T(z)GS + T(z)EK + T(z)wbw + T(z)AABW

The Stream Function

The MOC Time Series and Major Components

The eastern boundary variability compared directly with the AMOC anomaly timeseries.

Seasonal Variability of the AMOC transport anomaly due to the eastern boundary variability

Data Available Online

The RAPID-MOC website has links to the following data:

• The MOC time series and its components including: TEK, TGS, TUMO, TAABW, TNADW, TMO in NetCDF and ASCII (.MAT format can be supplied on request)

• Gridded and/or merged and S data sets from the RAPID-MOC array in .MAT and NetCDF

• www.noc.soton.ac.uk/rapidmoc

Schedule for Updating the MOC Time Series

Based on the current cruise schedule, the next instalment is likely to be completed by the late autumn 2009.

Trial Deployment of Gliders

• Region of most mooring losses – possibly due to fishing activity on the shelf.

• Gliders can send data back in near real-time, so reducing data losses.

• Gliders can be controlled from shore.• Gliders can be programmed to make a virtual mooring,

with a greater vertical resolution.• Some disadvantages are that they are more labour

intensive, susceptible to strong currents and limited to 1000m.

• Bellamite deployed last autumn, Dynamite on current deployment at the site of EBH4.

Air bag, fin and rudder, GPS, Iridium aerial, plug and drop weight

Science bay

Flooded nose cone with bladder for buoyancy engine, altimeter

Buoyancy engine pump, pitch battery

Electronics and batteries

Principle of Communication

dockserver

Glider Website

Created by Lucas Merklebach, it is updated every hour, on the hour.

Very useful for quickly and easily assessing the behaviour of the glider and the quality of the data.

Calibrated and gridded data will be available from the RAPID-MOC website after completion of the mission.

www.noc.soton.ac.uk/omf/projects/gliders.php

Comparison of Bellamite to EBH4

• Lucas Merklebach has worked on comparing the glider data from Bellamite to the mooring EBH4. For this he sampled the glider and S data where the glider is in the region of the mooring and at the same depth as the MicroCATs, averaging across depth profiles where necessary to coincide as close as possible to the MicroCATs reading.

• Comparison of the corrected gridded glider (based on the above) and eastern boundary mooring profiles is ongoing.

Bellamite gridded data at EBH4