Sea level from Altimetry and tide gauges'

1
Sea level from Altimetry and tide gauges.

• Ole B. Andersen, Per Knudsen J. L Høyer, A. A.
  Nielsen
• 1) Local direct comparison in the North Sea
  between
• Tide gauges and satellite altimetry (short
  time scales lt 1y)
• 2) Variation in Annual sea level variations (from
  8y of T/P).
• 2) Global sea level variations in extended EOFs
  / TMAF.

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Introduction to the North Sea

• Marginal Sea to the North Atlantic.
• Counterclockwise mean circulation
• External surges generated by wind forcing.
• Tides removed optimally using
  response method for both water level recorders
  satellite altimetry.

Norway
Water level recorders
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T/P and water level -High correlation
Temporal Correlation, T/P and Aberdeen
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ERS 12 and water level - lower correlation
Aberdeen vs. ERS 12

• Lower correlations than T/P
• Higher noise along some tracks.

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Correlations, Water level recorders
Autocorrelation
Crosscorrelation

• Short timescales, 10-60 Hours
• Tidal residuals at 12, 24 hours shallow water
  tides
• Counterclockwise propagation of sea level
  anomalies

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Large spatial scales
Amplitude, T/P EOF mode 1,2 and 3

• 93 of variance explained
• Other tracks show similar structure
• Rossby radius 100-400 km

Longitude
100 km
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2) Variation in Annual sea level variations
Wavelet analysis of 8 years of T/P data
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Amplitude and phase variation ofannual sea level
variation.
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Global sea level slope (1993-2001) from
TOPEX/POSEIDON altimetry.
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T/P sea level slopes regional features
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Atlantic Ocean. 20 sea level variations during
1993-2001.
cm / year
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Global sea level variationEOF extensions -
Temporal MAF
Maximum Autocorrelation Factors (MAF)
maximizing corr in Time (TMAF)