The Southern Ocean Sea Level Centre continues to progress and develop its contacts with the scientific community. A few current projects are coming to a close and the first phase of the Centre has been completed.
The proceedings from the Southern Ocean Workshop held in April 1996 will be distributed within the next few weeks (i.e. around April 1997). The workshop was very successfull in gathering the Australian scientists working on this area together.
The aquisition of a new Aquatrak Tide Gauge Station at Jackson Bay, New Zealand, adds to the number of sea-level measurement stations in the Southern Ocean that we currently hold data for. NIWA is funding this gauge, and hopes to establish an array of sea level recorders around the New Zealand coast. This will significantly increase the dataset available for the Southern Ocean.
An Aquatrak gauge is being planned for Mawson, and extensive preparations for this have been undertaken by Roger Handsworth and other members of the Antarctic Division. They hope to have it operational by the end of the summer.
As the Centre is responsible for the collection, quality-control, archiving and distribution of this data to the wider scientific community on a national and international scale, more access we have to current data is invaluable. We are actively participating in data-archaeology to extend the long-term time series of sea levels in the Southern Ocean and facilitate the availability of historical data.
Since 1990 difficulties have been encountered in the supply of tide gauge data to PSMSL and GLOSS. There was an unsuccessful attempt to switch over to locally made AWLR acoustic gauges which proved to be unsatisfactory. The expectation that acoustic data would be available post-1990 lead to the partial neglect of mechanical gauge output. Nevertheless my information is that the data supplied by the Hydrographic Office for the period up to and including 1995 were from the existing network of mechanical gauges. The data for 1996 will also be from the mechanical gauges. Any shortcoming in continuity of the record and quality of output was a result of these unforeseen circumstances.
Following a meeting with the SA Navy Hydrographic Office, the news for 1997 and beyond is more encouraging. Capt. Thompson has undertaken to send 1995 and 1996 GLOSS mechanical tide gauge data to Bidston within a month (by the time of the GLOSS meeting you will know whether this has occurred or not). All SA GLOSS sites (with the exception of Marion Island) have new Sonar Research and Development (SRD) acoustic gauges which are operational. These will provide data to GLOSS from 1997 onwards. The gauge at Marion Island (AWLR acoustic) was never successfully deployed. Although the Hydrographic Office are keen to mount a gauge at Marion Island, Capt. Thompson was not optimistic that this would happen in the short-term. On the Namibian coast, Walvis Bay has an operational AWLR gauge. It is possible that the Namport authorities will purchase a new SRD gauge for this GLOSS site. The SA Hydrographic Office have undertaken to provide logistical back-up to the Namibians should the purchase go ahead.
A Table summarizing the status of the SA (and Namibian) tide gauge network has been included in this document and is shown below.
SUMMARY OF SOUTH AFRICAN TIDE GAUGE DEPLOYMENTS
(Includes GLOSS sites)
SRD EMATECH MECH.
ACOUSTIC AWLR
Walvis Bay * Operational TBR GLOSS 314
Lüderitz * - Operational
Alex. Bay - Operational -
Port Nolloth Operational - Removed
Saldanha B. Operational - TBR
Cape Town Operational - TBR
S. Town Operational Operational TBR GLOSS 268
Mossel B. Operational - Removed
Knysna Operational - Removed
P. Elizabeth Operational Removed TBR GLOSS 76
E. London Operational Removed TBR
Durban Operational Removed TBR GLOSS 13
Richards B. Operational Operational Removed
Marion I. - # - GLOSS 20
* - Namport authorities may decide to buy 2x new SRD Tide Gauges.
# - Never successfully installed.
TBR - To be removed
Note. The AWLR gauge at Alexander Bay will be left to run until it ceases
to function and Port Nolloth will be the tide gauge site of choice for
this region.
S.R. Shetye Physical Oceanography Division, Ph. : (0091)(832) 22 6253-56 National Institute of Oceanography, ext 310/224 Dona Paula, Goa 403 004, India. FAX : (0091)(832) 22 3340/1360 e-mail : shetye@csnio.ren.nic.in , shetye@bcgoa.ernet.inThe IOC-UNEP-WMO Pilot Activity on Sea-Level Changes and Associated Coastal Impacts (see IOC/INF-908) is being implemented in the Indian Ocean since 1993. The two primary objectives of this Pilot Activity are: (a) To improve understanding of the processes that control sea-level variability at sites where sea-level is monitored in the Indian Ocean. (b) To enhance capabilities of countries of the Indian Ocean to monitor and analyse sea-level data. The Pilot Activity envisages setting up of a network of Cell for Monitoring and Analysis of Sea-level (CMAS). The tasks of the scientists associated with each CMAS are to secure high quality sea-level data, to analyse these data to identify important features of variability, and to undertake research to understand the causes behind these features.
The following countries have established CMAS: Bangladesh, India, Kenya, Madagascar, Malaysia, Maldives, Mauritius and Mozambique. In addition, Tanzania participates in the activities of the Pilot Activity, Seychelles has offered to support it by making sea-level data from its stations available to interested researchers, Australia, throughout its National Tidal Facility, lends active support to the Pilot Activity and Sri Lanka has expressed interest in setting up a CMAS.
As decided during GE-GLOSS, Bordeaux, the IOC/GLOSS-GOOS Training Workshop on Sea-Level Data Analysis was held at the Geodetic & Research Branch, Survey of India, Dehra Dun, India during 21 November - 1 December 1995. One nominee each from Bangladesh, India, Kenya, Madagascar, Malaysia, Maldives, Mauritius and Tanzania attended the workshop which had faculty drawn from the TOGA Sea-Level Centre (USA), National Tidal Facility (Australia), Proudman Oceanographic Laboratory (UK), National Institute of Oceanography (India) and the Geodetic and Research Branch, Survey of India. The main body of the Workshop consisted of the following four components: lectures, hands-on training, discussion on activities of CMAS in different countries, and video presentations. Each trainee was given hands-on training in use of the sea-level data analysis package developed at the TOGA Sea-Level Centre. Subsequently a similar package developed at the PSMSL/Proudman Oceangraphic Laboratory, was sent to the participants. The workshop also provided a venue to review the status of the project and to examine possible future directions.
The next GE-GLOSS will need to (i) examine the progress made towards the project's principal objective, which is to encourage countries of the Indian Ocean to use sea level as a tool to understand physical oceanography of the region; and, (ii) decide on actions for the near future. Presentation during the meeting will summarize research being carried out by CMAS-India, and will propose a modest plan to get at least two other CMAS to expand the scope of their work.
GLOSS in Russia is based upon the observational network of the ROSHYDROMET, the Federal Service for Hydrometeorology and Environental Monitoring. Observations collected by regional bodies of the Roshydromet are sent to All-Russian Research Institute for Hydrometeorological Information - World Data Centre (ARRIHI-WDC) in Obninsk for cataloguing and archiving. Via that insitute monthly mean and annual mean sea levels from Russian GLOSS stations are forwarded to PSMSL in Bidstone and to the Specialized IGOSS Sea Level Centre in Pacific (Honolulu).
The initial set of sites, which was originaly offered by the USSR for GLOSS network, was included in the GLOSS plan and published in 1990. It is shown in Table 1.
Table 1 Initial set of GLOSS sites
GLOSS Site Period of observation PSMSL data
number name
97 Kaliningrad 1881-1986 1926-1986
274 Murmansk 1917-1997 1952-1995 1
231 Barentsburg 1933-1997 1948-1995 2
92 Nagaevo Bay 1932-1997 1957-1995
93 Petropavlovsk-Kamchatsky 1910-1997 1957-1995 3
99 Russkaya Gavan 1932-1991 1953-1991 *
90 Yuzhno-Kurilsk 1946-1994 1948-1994 **
98 Tuapse 1917-1997 1917-1993
Notes:
1. Murmansk 1994 data include only period January to April (gauge out of order), January and September 1995 data are missing;
2. Barentsburg data for 1994 contain only period for January till June;
3. July 1995 data for Petropavlovsk-Kamchatsky are missing;
* Because of problems with tide gauge there have been no observations in Russkaya Gavan since July 1991. In 1992 this station was closed. Regional Roshydromet body in Dicson made a proposal that instead this station another one called "Izvesty" should be included in the list of GLOSS stations. This proposal has not been endorsed yet because Izvesty station operation is not supported by the federal budget, and the staion itself belongs to the "additional" category.
** Observations stopped in November 1994 because of problems with tide gauge. Specialized IGOSS Sea Level Centre for Pacific (Honolulu) offered a tide gauge, but it has not yet been put into operation because of lack of funding.
All stations except Kaliningrad belong to PSMSL category 1. At present no observations are made in Kalinigrad. The station is a property of the fishing harbour (there is a pole, and measurements are made 4 times a day). A tide gauge and some funds are needed to restore the observations there.
In 1991 at GLOSS meeting in Leningrad it was suggested that the Russian GLOSS network be complemented with some Arctic and Antarctic stations. According to the proposal of some GLOSS experts the Antarctic network of Russian GLOSS stations comprises 5 sites.
Table 2 Russian GLOSS sites in Antarctic
Gloss Site Period of observation PSMSL data
number name
91 Leningradskaya - -
25 Mirny 1957-1958,1962, 1965-1967, 1969-1970 -
294 Molodezhnaya 1964-1971 -
270 Novolazarevskaya - -
135 Russkaya - -
However, that decision seemed to be taken without adequate account of the situation at Russian Antarctic stations. Actually, it is unlikely that sea level observations can be organized even at one or two Antarctic sites.
Some discussions took place between the Russian Antarctic Expedition and PSMSL 1995-1996 regarding a possibility to continue sea level observations at one of the Russian Antarctic Stations (most likely, Mirny). A tide gauge (with a cable connection or fully autonomous one) was offered by the PSMSL along with some training to be given to a Russian specialist to enable him to use the equipment. The Russian Antarctic Expedition had plans to conduct some surveys at station Mirny to prepare the site for the installation.
The Third Experts Meeting on GLOSS suggested that Russia icludes 5 more stations into its GLOSS network. They are given in Table 3.
Table 3 List of new Russian GLOSS stations
Gloss Site Period of observation PSMSL data
number name
309 Providenya Bay 1934-1997 1977-1990
310 Kronstadt 1804-1997 -
311 Nakhodka 1933-1997 -
312 Dikson 1915-1979, 1981-1997 -
313 Tiksi 1932--1979, 1981-1997 -
Since my last report on the GLOSS stations in the IOCEA region, the status of the GLOSS stations have not improved. Between January 1995 and June 1996 I have had the opportunity to visit the following countries on issues not related to GLOSS. On many of these visits, I visited the tide gauge stations in Dakar, Guinea, Cote d' Ivoire, and Cotonou. These visits have revealed that none of the tide gauges in these countries are operational. Since November 1995, the float tide gauge in Lagos has seized working for lack of chart paper and faulty stilus. Request was made to the GLOSS office in IOC Paris for these spare parts since then. But the parts have not been received. According to the GLOSS office four now tide gauges have been sent to the Gambia, Guinea, Cote D'Ivoire and Lagos for installation. This was in fulfillment of earlier plan to send the tide gauges donated by the government of Sweden. However, only Guinea have confirmed the receipt of their tide gauge. The Gambia, Cote, d'Ivoire and Lagos are yet to acknowledge the receipt of their tide gauges.
It is good to note however that the acoustic tide gauge (Next Generation water Level Instrument) in Lagos is still operational. Data is regularly sent to Bidston and the TOGA sea level center in Honolulu. The present status of GLOSS in the IOCEA region calls for new directions by implementing the following recommendations.
RECOMMENDATION
1. An IOC mission to the following countries should be initiated - Cote d' Ivoire (Abidjan), Togo (Lome), Ghana (Accra and Tema), Benin (Cotonou), Cameroon (Douala), Guinea (Conakry), Sao Tome, and Gongo (Point Noire) to collect first hand information on the status of the GLOSS Stations and the possibilities of either establishing the new stations or rehabilitating the old ones.
2. Training of regional scientists in the installation maintenance, collation and analysis of tidal data should be resumed. The Sea level training in Bidston In the United Kingdom was a good programme and should be reinstated.
3. Provision of chart papers, extra stilus, clocks and other spare parts for existing tide gauge stations. This will help maintain a continuous recording of sea level data. The present situation whereby spare parts are not available or takes months to receive is not conducive to a healthy GLOSS programme in the IOCEA region.
Tentative and incomplete list of proposed collaborators (US, China, Taiwan, and Hong Kong):
C. Shum, B. Tapley, Univ. of Texas, USA;
B. Chao, NASA/GSFC, USA;
R. Neilan, NASA/JPL, USA;
C. Huang, D. Zheng, S. Ye, Shanghai Observatory, Shanghai;
G. Lu, Nanjing Normal University, Nanjing;
J. Ma and J. Wang, National Marine Data and Information Service,
State Bureau of Oceans, Tianjin;
Y. Zhu, D. Han, H. Hsu, Institute of Geodesy and Geophysics,
Wuhan, China;
C. Hwang, National Chiao Tung University, Taiwan;
H. Lin, Chinese Univ. of Hong Kong;
W. Yim, Hong Kong University, Hong Kong.
Summary
During the last Ice Age, the sea level in the East China Sea is 150 m lower than today, and the eastern shoreline of China has moved considerably westward since then. Analyses using over 30 years of tide gauge data in the region indicates that the coastal sea level has been rising at at a rate of 2-3 mm/yr [e.g., Zheng et al., 1995; Chen, 1996; Ma et al., 1996]. Using satellite altimeter measurements over the last decade (1986-1996), the sea level in East China Sea region is observed to be rising at a rate of 3-4 mm/yr [Shum et al., 1996]. Recent studies indicates the average rate of land subsidence, for example, of the Shanghai metroplex is more than 5 mm/yr during the last decade [Shanghai Institute of Rock and Soil Report, 1994]. The primary objectives of the proposed project include establishing a long-term observational measurement system to monitor sea level change in East China Sea, and to measure land subsidences of the regions of interest.
The proposed approach is to use a combination of in situ data (tide gauges, gravimeters and leveling instruments), and space geodetic techniques (GPS, SLR, VLBI, altimetry), within an accurately determined vertical datum reference system, for the long-term monitoring of sea level change and land subsidences in regions of interest. GPS instruments will be collocated with existing or new tide gauges [Hwang, 1996]. Historic, contemporary, and future satellite altimeter measurements (Seasat, Geosat, ERS-1, TOPEX/POSEIDON, ERS-2, GFO-1, Envisat, and Jason-1) will be used to construct a geocentric sea level time series in East China Sea over decades, to combine with tide gauge sea level measurements which will be collocated, to the extent possible, with GPS receivers, for long-term observations of absolute sea level and land subsidence. Gravimeter and leveling instruments will be integrated in some of the proposed measurement systems. It is the intention of the investigators to adopt an open data policy to routinely contribute data to PSMSL/GLOSS, and effort will be conducted to achieve this objective.
The proposed project will be conducted by multi-national research and academic institutions within the East China Sea region and in the US. The proposed project will also participate in the Asian-Pacific Space Geodynamics (APSG) Project (S. Ye, Project Scientist) funded by the Chinese Academy of Sciences and by the City of Shanghai. A partial list of regional funded and proposed investigations to support various elements of the proposed project include: "GIS based 3-D Modelling Support System for Coastal Change Studies" (PIs: G. Lu and H. Lin, funded by Research Grant Council of Hong Kong and State Education Commission of China); "Application of Satellite Altimetry on Marine Geophysics and Dynamic Topography in the China Sea" (PIs: Y. Zhu et al., funded by National Natural Science Foundation of China); "International GPS Service" (PI: Ruth Neilan, funded by NASA); "Monitoring of Eustatic Sea Level Rise in East China Sea (PI: C. Shum, pending, NASA Natural Hazards Program); and other funded or proposed projects in Taiwan and Hong Kong.
References:
Chen, J., On the relative vertical movement between crust and sea level along the Chinese coastal zone: a national basic research project in China, Marine Geodesy, 19, 99-104, 1996.
Hwang, C., Determination and analysis of a height system using satellite and terrestrial data: a case study in Taiwan, submitted, Jl. of Surveying Engineering, 1996.
Ma, J., Q. Zhang, and X. Chai, Rising trend of relative sea level along the coast of East Asia, Marine Geodesy, 19, 257-268, 1996. Shanghai Institute of Rock and Soil, Research on prediction and counter measure for Shanghai Earth subsidence, 1994.
Shum, C., B. Tapley, J. Ries, and M. Guman, Western Pacific mean sea level variations observed by satellite altimetry, Western Pacific Geophysics Meeting, Brisbane, Australia, 1996.
Zheng, D., C. Huang and N. Yu, Sea level change in the Pacific and along the coast of China, Global Sea Level Change Workshop, Univ. of Miami, 1995.
The new tide models recently made available to the scientific community, most of them issued from the analysis of satellite altimeter data (TOPEX / POSEIDON and ERS1/2), have shown major improvements by reference to the previous global ocean tide models published in the literature. Over the deep oceans, these new models have reached a high level of accuracy. A lot of them are indeed very similar (within one centimeter RMS difference, see Shum et al, 1997). But large differences between these models have been observed over continental shelves, of the order of tens of centimeters.
The evaluation of the quality of any global ocean tide model over shallow water areas is a difficult task, because of the complexity of the tidal characteristics over shelves and coastal basins. There, the typical wavelengths are shorter. Regional amplifications, often due to local resonance, result in sharp gradient which are difficult to catch in the models. And non-linearities are taking place, which lead to more complex tidal spectra than over the deep oceans.
It has been agreed at the last GLOSS meeting in Bordeaux that a dedicated effort will be undertaken in order to built a reference data base of harmonic constituents along the whole coastlines of the world ocean, with the aim to serve as a reference for testing the accuracy of the available or future tidal models over continental shelves and shallow water areas, in the same way as presently done for evaluating the quality of these models over the open ocean (cf Cartwright and Ray, 1991, Le Provost, 1994, Shum et al, 1997).
A rationale has been agreed for selecting this reference data base. The method rely on the use of the enormous amount of coastal data available in the International Hydrographic Bureau data bank, and the collection of any new available data set. A selection of stations uniformly distributed along the coastlines of the world oceans will be proposed, based on a careful evaluation of the intrinsic quality of the data issued from these stations, their spatial coherence, and their level of agreement with the ocean tide models themselves.
C. Le Provost, M. Smithson and P. Woodworth have started this study. However, because of too many commitments, things are progressing slowly. Benchmarks have already been produced on the quality of some of the ocean tide models which are now used for satellite altimetric data corrections, and for other geophysical applications, on the basis of the BHI data set. This has allowed to start a systematic critical analysis of the correspondance between models and data. this analysis is undeway.
Besides we have received tidal constants for M2, S2, K1, O1 for 49 sites from the Sea of Okkhotsk and 9 sites along the west coast of Sakhalin Island (northern Sea of Japan) from Gennady Kivman, Shirshov Institute, St. Petersburg. We have also received tidal records for the Malaysian peninsula and Borneo, 6 years of hourly values for 17 sites, from Teh Seng Hoe, Department of Survey and Mapping, Malaysia. There are some gaps in some of these data. Southern Ocean data is available from the Australian National Tidal Facility, Flinders.
This study will be completed as soon as possible.