Abstract
We form a new ‘blended’ data set of sea level anomaly (SLA) fields by combining gridded daily fields derived from altimeter data with coastal tide gauge data. Within approximately 55–70 km of the coast, the altimeter data are discarded and replaced by a linear interpolation between the tide gauge and remaining offshore altimeter data. To create a common reference height for altimeter and tide gauge data, a 20-year mean is subtracted from each time series (from each tide gauge and altimeter grid point) before combining the data sets to form a blended mean sea level anomaly (SLA) data set. Daily mean fields are produced for the 22-year period 1 January 1993–31 December 2014. The primary validation compares geostrophic velocities calculated from the height fields and velocities measured at four moorings covering the north-south range of the new data set. The blended data set improves the alongshore (meridional) component of the currents, indicating an improvement in the cross-shelf gradient of the mean SLA data set.
Highlights
More than 20 years of altimeter data have greatly improved our understanding of upper ocean processes, including large scale ocean circulation[1,2], mesoscale variability[3,4], sea floor topography[5,6], climate variability[7,8,9], and the distribution within eddies of chlorophyll concentration[10] and macrofuna feeding[11]
The tide gauge derived sea level data were interpolated from the coast to the offshore AVISO fields using the Delaunay triangulation method[28,29]
In an effort to validate our decision to use the National Centers for Environmental Prediction (NCEP) Reanalysis fields here rather than, for example, the ERA-Interim fields we calculated the root mean square (RMS) error between daily mean sea level pressure data collected by National Oceanic and Atmospheric Administration (NOAA) Buoy 46050 and the ERA-Interim and NCEP Reanalysis grid cells closest to the 46050 location (44.656 °N, 124.526 °W) for the period 1993–2014
Summary
More than 20 years of altimeter data have greatly improved our understanding of upper ocean processes, including large scale ocean circulation[1,2], mesoscale variability[3,4], sea floor topography[5,6], climate variability[7,8,9], and the distribution within eddies of chlorophyll concentration[10] and macrofuna feeding[11]. We use an inverse-distance weighted interpolation method to blend low-pass filtered, daily mean tide gauge observations with daily, 0.25° latitude x 0.25° longitude AVISO SLA fields This data set covers the 22-year period 1 January 1993–31 December 2014 from 32–48.5 °N and 135–115 °W. Much of our validation (see the ‘Technical Validation’ section below) of the improvement of the new data set, in comparison to the original AVISO daily data, follows Saraceno et al.[27] by comparing geostrophic velocities derived from the SLA fields to observed velocities from moorings, stretching from northern Washington to southern California This comparison amounts to an indirect validation of the gradients in the surface height fields and requires some discussion. The results of our validation and verification efforts are described in the Technical Validation section
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