Metadata Report for BODC Series Reference Number 2028023

• Metadata Summary

• Problem Reports

• Data Access Policy

• Narrative Documents

• Project Information

• Data Activity or Cruise Information

• Fixed Station Information

• BODC Quality Flags

• SeaDataNet Quality Flags

Metadata Summary

Problem Reports

No Problem Report Found in the Database

Data Access Policy

Open Data supplied by Natural Environment Research Council (NERC)

You must always use the following attribution statement to acknowledge the source of the information: "Contains data supplied by Natural Environment Research Council."

Narrative Documents

RD Instruments- Ocean Surveyor 75kHz Vessel mounted ADCP.

¹ Ranges at 1 to 5 knots ship speed are typical and vary with situation.
² Single-ping standard deviation.
³ User's choice of depth cell size is not limited to the typical values specified.

Profile Parameters

• Velocity long-term accuracy (typical): ±1.0%, ±0.5cm/s
• Velocity range: -5 to 9m/s
• # of depth cells: 1 - 128
• Max ping rate: 0.7

Bottom Track

Maximum altitude (precision <2cm/s): 950m

Echo Intensity Profile

Dynamic range: 80dB
Precision: ±1.5dB

Transducer and Hardware

Beam angle: 30°
Configuration: 4-beam phased array
Communications: RS-232 or RS-422 hex-ASCII or binary output at 1200 - 115,200 baud
Output power: 1000W

Standard Sensors

Temperature (mounted on transducer)

• Range: -5° to 45°C
• Precision: ±0.1°C
• Resolution: 0.03°

Environmental

Operating temperature: -5° to 40°C (-5° to 45°C)*
Storage temperature: -30° to 50°C (-30° to 60°C)*

*later instruments have greater range.

Web Page

Further details can be found on the manufacturer's website or in the specification sheet

Processing by BODC of MeRMEED cruise Vessel Mounted ADCP data

The data arrived at BODC in three mstar (NetCDF subset) format files containing data collected from the 75kHz ship mounted ADCP on three MeRMEED project cruises (WS16336, WS17305, and WS18006). The data were reformatted to BODC's internal NetCDF format. The following table shows the mapping of variables within the mstar files to appropriate BODC parameter codes:

The reformatted data were visualised using the in-house EDSERPLO software. Suspect data were marked by adding an appropriate quality control flag, and missing data were set to an appropriate value and flagged.

Processing by Originator of MeRMEED cruise Vessel Mounted ADCP data

The following were taken from the three MeRMEED cruises, WS16336 in 2016, WS17305 in 2017, and WS18066 in 2018. Data were collected using a Teledyne RDI Ocean Surveyor 75 kHz vessel mounted ADCP on board the research vessel Walton Smith. The instrument was set to sample throughout the cruises, off the East coast of North America.

Data were acquired using the UHDAS software package.

ADCP setup

For all three cruises the instrument was set in "narrowband" mode and no "bottom track". The ADCP data was available to download in 5 minute averages in netcdf format during the cruise from an onboard web server. Following the cruise the data were reprocessed in 1 minute averages.

Real time data acquisition and monitoring

Data acquisition and processing were handled by UHDAS (University of Hawaii Data Acquisition System). This software handles both acquisition and CODAS (common ocean data access sytem) first pass processing. UHDAS automates the removal of ship velocity and heading correction with GPS derived heading.

Tracks

During the second MeRMEED cruise, WS17305, several ADCP transects were made in an ADCP-VMP lawnmower/radiator pattern east of Abaco. During initial transects, the originators experimented with the vessel speed and found that a maximum of 5 kts resulted in reasonable data quality (no gaps) in the 5-minute averages. During more intensive transects, the vessel speed was reduced to 3.5 kts (6.5 kph) resulting in an along-track resolution of about 540 m for the 5-minute averages. During VMP sections the speed was 1-2 kts (1.85-3.7 kph) resulting in an along-track resolution of 150-310 m.

During the third MerMEED cruise, WS18066, it was again determined that a maximum of 5 kts resulted in reasonable data quality (no gaps) in the 5-minute averages. During more intensive transects, the vessel speed was reduced to 3.5 kts (6.5 kph) resulting in an along-track resolution of about 540 m for the 5-minute averages. During VMP sections the speed was 1-2 kts (1.85-3.7 kph) resulting in an along-track resolution of 150-310 m.

References

Frajka-Williams, E. et al, 2017. RV Walton Smith Cruise WS16336, 01-07 Dec 2016, Miami to Miami, USA. MeRMEED microstructure cruise report. Southampton, UK: National Oceanography Centre, Southampton, 60pp., National Oceanography Centre Cruise Report, No. 44.

Frajka-Williams, E. et al, 2018. RV Walton Smith Cruise WS17305, 31 Oct - 10 Nov 2017, Miami - Miami. MeRMEED microstructure cruise report. Southampton, UK: National Oceanography Centre, Southampton, 80pp., National Oceanography Centre Cruise Report, No. 50.

Evans, D.G. et al, 2018. RV Walton Smith Cruise WS18066, 4 - 16 March 2018. MeRMEED microstructure cruise report. Southampton, UK: National Oceanography Centre, Southampton, 70pp., National Oceanography Centre Cruise Report, No. 54.

These cruises took place on an American vessel and were not fully funded by NERC, therefore BODC only hold the data funded directly by the MeRMEED project.
The following DOIs contain the vessel underway data for each cruise:

Project Information

Mechanisms Responsible for Mesoscale Eddy Energy Dissipation (MeRMEED)

Background

MeRMEED investigates the processes responsible for the widespread dissipation of oceanic mesoscale eddies at western boundaries. The project combines focussed measurements of small-scale turbulence in four short research cruises, multi-year mooring and satellite observations, and multi-month glider surveys of mesoscale eddies impinging on the continental slope east of the Bahamas.

Over the last decades, oceanographers have been searching for the missing mixing in the ocean to complete the ocean energy budget. Answering questions of where energy is added to the oceans, and where it is removed, helps us to understand the drivers of ocean circulation. With the advent of high-resolution satellite measurements of surface currents in the 1990s, scientists could see that the oceans were filled with swirling vortices of water called mesoscale eddies. While eddies are present in all ocean basins, with currents inside the eddies sometimes exceeding 1 m/s, they disappear from satellite measurements preferentially at western boundaries. There are several possibilities for why eddies disappear at western boundaries: they may radiate energy away, contribute energy to large scale ocean circulation, or lose energy locally through turbulence and dissipation. Of these candidate terms, previous work has suggested that local dissipation is strong enough to explain a substantial part of the eddy disappearance.

The aim of MeRMEED is to determine how and why eddies are losing energy at the western boundaries. These results and the measurements will then be made available to scientists involved in numerical simulations of the ocean. As a longer-term goal, the results of this research may help guide how eddies are represented in ocean models, which is one of the critical areas needing improvement in climate simulations. However, due to the fledgling nature of the science in this field, that eventual goal is still several steps away. Fundamental physics dictate that most eddies move slowly westward, and these eddies are visible in satellite measurements of sea surface height a few months before they arrive at the boundary. In the project MerMEED, the eddies will be watched in near real-time satellite data, and when an appropriate eddy approaches the east coast of North America, a small team of researchers will deploy, with advanced instruments, to meet the eddy upon arrival. There, the eddy will be surveyed using high-resolution profilers deployed from small boats and autonomous underwater vehicles called Seagliders. After the ship-based survey is completed, the gliders will continue to observe the eddies for several months, as the eddies are slowly disappearing. These gliders transmit their measurements via satellite communications back to the base station in England. The plan includes the use of the existing observations from the joint UK/US-funded RAPID programme, measuring ocean circulation at 26N. Additional high-resolution velocity and temperature meters will be installed on one of these moorings, to make continuous observations of the eddies over 18 months. The survey, glider, and moored measurements will allow for the assessment of how important local dissipation is to the disappearance of eddies. The findings will be used to shed light on the processes responsible for eddy disappearance from the oceans, and how those processes change in time

Fieldwork

There are three main observational data streams for MerMEED.

1. Additional instruments (thermistors and two 75 kHz ADCPs) were added to one of the RAPID project moorings in 1400 m of water east of the Bahamas, to make high time resolution (10 s sampling on the thermistors) and high vertical resolution (every 50 m for thermistors, 16 m bins for the ADCPs) measurements at the edge of the continental slope where the eddies encounter topography. These were deployed in autumn 2015 and recovered in winter 2018.
2. Very small scale measurements of ocean velocities and temperature are made in the top 1000m of the water, near steep topography, by a tethered microstructure profiler and shipboard 75 kHz ADCP. These specialised instruments made direct estimates of dissipation in the eddies from on board the RV Walton Smith in December 2016, October - November 2017, and March 2018.
3. Autonomous underwater vehicles (Seagliders) were deployed to make multi-month observations of temperature and salinity in the top 1000 m. These observations will give a detailed look at the changes in the subsurface structure of the eddy as it encounters topography. They can additionally be used to estimate turbulent dissipation through methods that are still under development.

Together, these observations span the space- and timescales of mesoscale eddies down to 10-cm scale turbulent vortices in the water, to enable us to better understand the processes by which eddies lose their energy when they encounter topography.

Participants

• Dr Eleanor Frajka-Williams (Principal Investigator) University of Southampton, School of Ocean and Earth Science
• Professor Alberto Naveira Garabato (Co-Investigator) University of Southampton, School of Ocean and Earth Science

Funding

This project was funded by the Natural Environment Research Council, under grant NE/N001745/1 from the 1^st of September 2015 to the 14^th of August 2018.

Data Activity or Cruise Information

Cruise

Complete Cruise Metadata Report is available here

Fixed Station Information

No Fixed Station Information held for the Series

BODC Quality Control Flags

The following single character qualifying flags may be associated with one or more individual parameters with a data cycle:

SeaDataNet Quality Control Flags

The following single character qualifying flags may be associated with one or more individual parameters with a data cycle: