Metadata Report for BODC Series Reference Number 541698

• 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

Public domain data

These data have no specific confidentiality restrictions for users. However, users must acknowledge data sources as it is not ethical to publish data without proper attribution. Any publication or other output resulting from usage of the data should include an acknowledgment.

The recommended acknowledgment is

"This study uses data from the data source/organisation/programme, provided by the British Oceanographic Data Centre and funded by the funding body."

Narrative Documents

No Narrative Document information held in the BODC database

Project Information

World Ocean Circulation Experiment (WOCE)

The World Ocean Circulation Experiment (WOCE) was a major international experiment which made measurements and undertook modelling studies of the deep oceans in order to provide a much improved understanding of the role of ocean circulation in changing and ameliorating the Earth's climate.

WOCE had two major goals:

• Goal 1. To develop models to predict climate and to collect the data necessary to test them.

• Goal 2. To determine the representativeness of the Goal 1 observations and to deduce cost effective means of determining long-term changes in ocean circulation.

The ACCLAIM Programme in the South Atlantic and Southern Oceans

Introduction

The ACCLAIM (Antarctic Circumpolar Current Levels by Altimetry and Island Measurements) programme in the South Atlantic and Southern Oceans consists of measurements from coastal tide gauges and bottom pressure stations, together with an ongoing research programme in satellite altimetry. ACCLAIM is the Proudman Oceanographic Laboratory's main contribution to WOCE (and, in particular, to WOCE Core 2) and one of its objectives is the study of variations of the Antarctic Circumpolar Current. ACCLAIM is managed within the Global Sea Level Change (GSLC) group at POL led by Dr.J.M.Vassie.

The history of the development of ACCLAIM is described in the report by Spencer et al. (1993)

Phase 1

From Spencer et al. (1993) it can be seen that in Phase 1 of ACCLAIM from 1983, measurements at coastal tide gauge sites took the form of sub-surface pressure (SSP) measurements (units of pressure e.g. mbar) rather than sea level (units of length e.g. centimetres). SSP is here defined as the total, measured pressure recorded by a sub-surface pressure transducer, a measurement which includes the pressure load from the atmosphere as well as from the water column. It is absolutely essential that any user of ACCLAIM data realises which data type (either SSP or sea level) is being analysed.

The Phase 1 coastal SSP data were acquired in different ways (e.g. with a diver-replaced Aanderaa pressure gauge at Ascension, or with a Digiquartz in the sea sensor at St.Helena, see Spencer et al. 1993 for details) and with different pressure integration periods (e.g. quarter hour, half hour, one hour). For WOCE Centre purposes the original data have generally been filtered to give one hour sampling.

However, common to all records is an uncertainty connected with potential offset biases and drifts in the pressure sensors. At some sites (e.g. St.Helena) extensive tide pole data are also available and biases and long term drifts in the sensor data may eventually be rectified (this is under study at present). However, the drifts in general mean that in most cases the records should not be used, without further careful attention in particular studies, for the study of timescales seasonal or longer.

Phase 2

From around early 1993, the gauges at many of the sites were replaced by Phase 2 ACCLAIM 'B gauges' which record SSP, air pressure and sea level as described in Woodworth et al. (1996)

The Phase 2 coastal sea level data have precise datum control (see Woodworth et al. 1996 for details) and can certainly be used for long term studies. These data have also been contributed to the Permanent Service for Mean Sea Level (PSMSL) and Global Sea Level Observing System (GLOSS).

Ancilliary Data

Some of the Phase 1 data and all the Phase 2 coastal data will also contain ancillary information on air pressures and sea temperatures from ACCLAIM sensors. Several of these records contain large gaps. However, the GSLC group at POL has collected extensive sets of such ancillary data from meteorological agencies for its own analysis purposes, and should be able to provide further advice.

Deep Ocean Measurements

SSP measurements at deep ocean bottom pressure stations (together with inverted echo sounder and temperature measurements) have also been a feature of ACCLAIM. Measurements at Amsterdam and Kerguelen in the Indian Ocean are described in Vassie et al. (1994).

While most recording is now concentrated in the Scotia Sea - Drake Passage area of the Southern Ocean as part of WOCE Core 2. Tidal constituents from these recorders have contributed to the IAPSO Pelagic Constants data base maintained by the PSMSL at Bidston on behalf of IAPSO.

References

Spencer, R., Foden, P.R., McGarry, C., Harrison, A.J., Vassie, J.M., Baker, T.F., Smithson, M.J., Harangozo, S.A. and Woodworth, P.L. 1993.
The ACCLAIM programme in the South Atlantic and Southern Oceans. International Hydrographic Review, 70, 7-21.

Vassie, J.M., Harrison, A.J., Woodworth, P.L., Harangozo, S.A., Smithson, M.J. and Thompson, S.R. 1994.
On the temporal variability of the transport between Amsterdam and Kerguelen Islands. Journal of Geophysical Research, 99(C1), 937-949.

Woodworth, P.L., Vassie, J.M., Spencer, R. and Smith, D.E. 1996.
Precise datum control for pressure tide gauges. Marine Geodesy 19(1), 1-20.

Data Activity or Cruise Information

No Data Activity or Cruise Information held for the Series

Fixed Station Information

Fixed Station Information

Rothera Phase 1 Site History

History Summary

Parameters recorded

where

• ST = TEMPPR01 = Sea Temperature
• PR = PRSTRS01 = Residual
• LT = CTLGPR01 = Logger Temperature
• WT = TEMPPH01 = Well Temperature
• AP = CAPHSL01 = Atmospheric Pressure
• SSP = PRSTPS01 = Sub Surface (total) Pressure
• HTP = PRSTPH01 = Half Tide (total) Pressure

Completeness Index

Note: In 1998 91% of the data were corrupted (Quality Index 7.4%)

Datum Information

Not yet available.

Quality Assessment

All data have been tidally analysed and constants and residuals checked. Records have been visually inspected for spikes and datum shifts.

December 1992 to December 1994

Spikes and Gaps December 1993 to December 1994

Harmonic analysis of the file gives excellent agreement with later files, suggesting that overall, the timings are good.

Datum of HTP gauge drifts 30 mb over first 5000 scans, before settling. Appear to have some sort of 'overshoot' in HTP record between scans 17000 and 23000. Over the whole record, there's a steady drift in HTP datum of 4 mbar. Comparing the SSP and HTP sensors suggests that 3 mbar of this drift is due to the HTP sensor.

January to December 1995

Agreement between HTP and SSP, over the high water period, is quite poor, prior to the gap in the data. There is a variability of approximately 1.5 mbar, and an offset of of 3 mbar between the two signals.

Comparing HTP and AP, the HTP cut off is very well defined prior to the gap in the data. There are some spikes, however only on one occasion, is this greater than 1 mbar. Following the data gap, the HTP record is very 'noisy' until day 280, where there is an apparent datum shift. The recorded pressure difference at LW, varies between 224-226 mbar.

The residuals appear very good. There is a spike at day 299, and a drop out between day 335(14.875) - day 336(19.625) which has not be infilled. Day 339 (16.125 - 16.375) has been corrected, with data based on the harmonic analysis predictions.

Harmonic constants agree well with the other files.

January to November 1996

HTP definition is very poor, until day 135. As comparisons between AP and LW HTP are generally good, it appears that there may be a problem with the SSP.

Residuals appear excellent, harmonic constants are in good agreement with the other data.

January 1997 to December 1997

Comparing HTP and AP gives a 12.7 mbar offset at LW. HTP cut-offs are generally well defined, although there are some overshoots.

SSP and HTP show differences between the observed full tide at times.

Residuals look excellent until day 335, when it looks like there is a timing error. Harmonic constants are in excellent agreement with other files.

December 1997 to November 1998

It is recommended these data not be used. However, it maybe possible to reconstruct the signal from the HTP sensors using predictions to infill the low tide.

December 1998 to October 1999

Comparison between HTP and AP, also SSP and HTP indicate a 2 mbar drift on the HTP sensor over the period of the data.

Residuals show intermittent timing errors. Harmonic contstants are in excellent agreement with previous data files.

Related Fixed Station activities are detailed in Appendix 1

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:

Appendix 1: Rothera - Phase 1

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