Midway Island (USA Trust) Site History
|Latitude||28° 13.0' N|
|Longitude||177° 22.0' W|
|Time Reference||GMT (hours 00-23)|
|Contributor||US Coastal Geodetic Survey (1947-1972)
National Ocean Service (NOS) (1973+)
National Ocean. and Atmos. Administration (NOAA)
|Instrument Type||Standard mechanical (1947-1974);
Analog-to-digital (ADR) recorder (1975-1991);
Aquatrak acoustic gauge, NOAA Next Generation
Water Level Measuring System (NGWLMS) (1992-2000)
|Site of Gauge|
|Observational Periods||1947 - 2000|
All heights have been referred to the station tide staff zero which is linked to fixed benchmarks.
Tide Gauge Benchmark (TGBM) Description
Benchmark 21(1959), the primary benchmark (PBM) is stamped '21 1959' and is set in a concrete manhole structure at the north east corner of Inner Harbor Boat Basin.
9 additonal benchmarks are levelled to the TGBM and the Tide Station on a yearly basis.
TGBM is 10.64ft above Tide Gauge Zero (Station Datum).
NOAA Chart Datum (MLLW) is 2.62ft above Station Datum.
Mean Sea Level (1960-1978) is 3.27ft above Station Datum.
Large fluctuations during November - April for most years are associated with meteorological events. Step-function signatures in the hourly residuals suggest level shifts on 27 September 1968 and on 01 August 1974. However, the mean level and differences with the PSMSL holdings have not warranted an adjustment.
The data for 1996-2000 were supplied with heights relative to MLLW. Consequently 799mm was added to refer the data to tide gauge zero.
The data for 1998-2000 were supplied in non-GMT format and had to be shifted into GMT.
Notable episodic events:
- 04-06 November 1952: Tsunami from Kamchatka
- 09-10 March 1957: Tsunami from C. Aleutians
- 23-25 May 1960: Tsunami from S.C. Chile
- 28 March 1964: Tsunami from Alaska
Gaps in the Data Record
The following gaps occur in the data set.
|Year||CI (%)||Missing Data||Replaced Gaps or Bad Data||Questionable