Geoscience Reference
In-Depth Information
TWC Sea Level Stations
The TWCs operate a small subset of coastal tide stations (Figure 4.4). The WC/ATWC oper-
ates seven stations along southern Alaska and the Aleutian Islands with data being archived
for public use at National Geophysical Data Center (NGDC) (http://wcatwc.arh.noaa.gov/
WCATWCtide.php). The PTWC stations are distributed throughout the Paciic and Hawaii. In
Hawaii, PTWC maintains 14 sea level gauges solely for local predictive and diagnostic value; the
data from these gauges are archived under separate NOAA support (http://ilikai.soest.hawaii.
edu/arshsl/techrept/arshsl.html). In general, the TWC stations are not maintained to the speci-
ications of the NWLON but have historical precedence and ill gaps in the observing array or
ill speciic local needs. For example, the PTWC gauges on the Big Island of Hawaii will provide
about 20 minutes of warning for Honolulu should a large amplitude tsunami be generated by
an earthquake or landslide on the Big Island. The TWCs have indicated they do not have the
resources to properly maintain these gauges or to process, distribute, and archive the data.
International Sea Level Stations
The Intergovernmental Oceanographic Commission (IOC) Global Sea Level Observing
System (GLOSS) has about 290 stations worldwide, and many are conigured for near-real-time
reporting of rapidly sampled data relevant to tsunami applications. After the Indian Ocean
tsunami of December 26, 2004, the IOC established a centralized Sea Level Station Monitoring
Facility (http://www.vliz.be/gauges/), where most of the needed, rapidly sampled coastal sea
level observations are now available and reported in near-real time over the World Meteoro-
logical Ofice's (WMO's) Global Telecommunications System (GTS). The website serves as a cen-
tral clearinghouse of data from a range of international providers, including the data sources
mentioned above. The objectives of this service are to provide information about the opera-
tional status of global and regional networks of near-real-time sea level stations and to provide
a display service for quick inspection of the raw data stream from individual stations.
Since 2007, the Sea Level Station Monitoring Facility (SLSMF) also has the information
necessary to determine data stream reliability. SLSMF is an appropriate place to obtain such
reliability information because it lists only data that were initially made available in near-real
time over the GTS, not what was eventually available after internal memory was inally ac-
cessed during a maintenance operation. The sea level data that the TWCs employ in their
tsunami detection activities and which are acquired via the GTS are essentially the same data
now disseminated and archived at SLSMF, excluding the TWCs' own stations discussed above.
As with the data received by the TWCs via the GTS after a tsunami-producing earthquake, the
data lowing through SLSMF are not quality controlled, but the website provides additional
metadata for most of the non-U.S. stations. To the committee's knowledge, the level of adher-
ence of international stations used by the TWCs to either NWLON or Tsunami Warning Center
Reference Guide (U.S. Indian Ocean Tsunami Warning System Program, 2007) performance and
maintenance standards has not been determined.
