The ACCLAIM Programme in the South Atlantic and Southern Oceans
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 was the Proudman Oceanographic Laboratory's main contribution to the World Ocean Circulation Experiment (WOCE) and now provides data to the Climate Variability and Predictability Programme (CLIVAR) , Global Sea Level Observing System (GLOSS) and the Permanent Service for Mean Sea Level (PSMSL)
For a history of the development of ACCLAIM see:
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.
The main POL Principal Investigators involved in ACCLAIM are: Dr Ian Vassie, Prof. Philip Woodworth, Prof. Chris Hughes, and Peter Foden.
ACCLAIM COASTAL TIDE GAUGE SITES
Phase 1 of ACCLAIM Coastal Gauges
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 some data sets, the original data have 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 of ACCLAIM Coastal Gauges
From around early 1993, the gauges at several sites were replaced by 'B gauges' which record SSP, air pressure and sea level as described in:
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.
These gauges have precise datum control and are used to provide long term sea level change data to the PSMSL.
Some Phase 1 and all Phase 2 coastal data will contain ancillary information on air pressures and sea temperatures from ACCLAIM sensors. Several of these records contain large gaps. However, 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.
ACCLAIM Coastal Gauges
At the present time the tide gauge sites at Ascension, St.Helena and Port Stanley can be considered to be complete 'Phase 2' sites, while Tristan, Signy and Rothera remain 'Phase 1' (i.e. simple pressure transducer sites). At Faraday (which contains the longest tide gauge record in Antarctica and which is now called Vernadsky and operated by groups from the Ukraine) there is a conventional float gauge together with a 'Phase 1' transducer.
ACCLAIM BOTTOM PRESSURE RECORDS
Deep ocean bottom pressure recorder (BPR) measurements (together with inverted echo sounder and temperature measurements) have also been a feature of ACCLAIM. First measurements were at Amsterdam and Kerguelen in the Indian Ocean (see Vassie et al., Journal of Geophysical Research, 99(C1), 937-949, 1994) while most recording is now concentrated in the Scotia Sea - Drake Passage area of the Southern Ocean (see, for example, Woodworth et al., Journal of Geophysical Research, 101(C5), 11935-11947, 1996).
BPR measurement is something of a POL speciality and the data acquired during ACCLAIM (which were primarily for ocean circulation studies) benefited considerably from expertise acquired in bottom pressure recording for research into ocean tides (see Spencer and Vassie, Progress in Oceanography, 40, 423-435, 1997).
Tidal constituents from the bottom pressure recorders have continued to be contributed to the IAPSO Pelagic Constants data base maintained by the PSMSL on behalf of IAPSO.
ACCLAIM DATA SETS
To obtain ACCLAIM data, jump to:
http://www.pol.ac.uk/ntslf/acclaimdata/
which will contain three sub-directories of data:
'phase1', which contains data collected by Phase 1 coastal stations
'phase2', which contains data collected by Phase 2 coastal stations, and
'bprs', which contains data from POL BPR deep ocean stations.
In addition, it contains a file 'readme.formats' which describes the formats of data files.
Each of the three sub-directories contains a file INVENTORY which summarises the data holdings and provides short documentation. All data sets have been quality controlled.
In addition, there is a further sub-directory 'gloup' which contains data from the international set of BPR measurements now known as GLOUP.
FURTHER INFORMATION
For further information on Phase 1 or 2 coastal tide gauge data, please contact Dr. Philip Woodworth, while for information on BPR's and GLOUP, please contact Dr. Chris Hughes.Contact address and numbers:
National Oceanography Centre
Joseph Proudman Building
6 Brownlow Street
Liverpool L3 5DA
United Kingdom
Telephone: +44 (0)151-795-4800
Fax: +44 (0)151-795-4801
