Sea-Level Rise for the Coasts of California, Oregon, and Washington Past, Present, and Future (2012) / Chapter Skim
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Appendix D: Long-Term Tide Gage Stability From Leveling Data
Appendix D: Long-Term Tide Gage Stability From Leveling Data
Pages 179-190
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From page 179... ...
corresponding steps remain uncorrected in the sea-level time series data. Abstract INTRODUCTION Leveling observations from tide gage benchmark networks can be used to assess the long-term stability The observations recorded by tide gages are relative of the tide gage with respect to the benchmarks, to pro- sea-level values, and are a linear combination of real vide estimates on the degree to which short-term (e.g., changes in local sea level as well as any local vertical decadal timescale)
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From page 180... ...
The long-term relafrom the coast. Although tide gage locations are chosen tive vertical velocity of the tide gage with respect to carefully in an effort to ensure long-term stability and the primary benchmark is not applied as a correction a minimum of vertical motion, it is impossible to guar- to the sea-level time series.
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Benchmarks interpreted as being unstable are identified from their time series, RESULTS either objectively by virtue of very high variance about their mean trend (typically greater than 10 mm2, in San Diego contrast to most benchmarks which have variances typically less than 2 mm2) , or more subjectively due Three benchmarks -- 9, N 57, and RIVET-to having high apparent relative vertical v elocities, showed anomalous vertical motions and were excluded uncorrelated with their neighboring marks, by com from the spatial analysis.
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The exceptional rates in the 1980s are possibly due to a small, unmodeled residual step in the tide gage leveling time series, either at the tide gage itself, or possibly at the primary benchmark, as the other benchmark time series also show excursions at this time. With less consistent and rigorous field operational procedures, data prior to 1970 are noisier, 1 and this is reflected in the increased range and errors 0.5 for the velocity estimates for this period.
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Time series of apparent decadal-scale vertical velocities. All benchmarks shown in gray except tide gage mark AQUATRAK San Francisco (green)
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Time series of apparent decadal-scale vertical velocities. All benchmarks shown in gray except tide gage marks velocities.
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Time series of apparent decadal-scale vertical uplifted for several years before subsiding back to their velocities. All benchmarks shown in gray except tide gage marks long-term baselines.
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tide gage leveling network. All past this date, perhaps indicating a problem with the benchmarks shown in gray except tide gage marks AQUAREF tide gage monument, as the AQUATRAK mark, ob- (magenta)
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From page 187... ...
the correction constant. Unfortunately, although the In particular, the San Francisco tide gage network ap- values of these constants and when they were changed pears to have been significantly affected by the Loma have been recorded and archived, they are mostly in TABLE D.1 Long-Term Vertical Motion Estimates for Primary Benchmarks and Tide Gage Reference Marks, with Respect to a Network Defined Vertical Reference Tide Gage Location Benchmark Vertical Velocity (mm yr-1)
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From page 188... ...
and other long-term signals. Detailed analyses of the The analysis of the stability of decadal-scale ve- noise character of GPS coordinate time series (Mao et locity estimates suggests that, for most tide gages and al., 1999; Williams et al., 2004)
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Dixon, 1999, Noise in GPS coordinate time series, Journal of Geophysical Research, 104, AQUATRAK Physical point on tide gage used for 2797-2816. leveling Shinkle, K.D., and R.K.
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