Abstract's details

Impacts of using different atmospheric models on altimeter-derived Sea Level Trends

M. Joana Fernandes (DGAOT, Faculdade de Ciências, Universidade do Porto, Portugal)


Telmo Vieira (DGAOT, Faculdade de Ciências, Universidade do Porto, Portugal); Pedro Aguiar (DGAOT, Faculdade de Ciências, Universidade do Porto, Portugal); Clara Lázaro (DGAOT, Faculdade de Ciências, Universidade do Porto, Portugal)

Event: 2023 Ocean Surface Topography Science Team Meeting

Session: Coastal Altimetry

Presentation type: Type Oral

Contribution: PDF file


In regions such as coastal and inland water zones, where wet path delays (WPD) derived from observations are not available, numerical weather models (NWM) may be the best source of information to correct satellite altimeter data for the effect of water vapour and cloud liquid water in the atmosphere.
This study presents and analyses of various NWM from the European Centre for Medium-Range Weather Forecasts (ECMWF), evaluating their accuracy and stability for the purpose of estimating the WPD of satellite altimetry measurements, with focus on their impact on sea level trends.
The ECMWF operational model (ECMWF Op.) and the most recent reanalysis (ERA5) are first evaluated against the SSM/I (Special Sensor Microwave Imager) and SSM/IS (Special Sensor Microwave Imager/Sounder) set of imaging radiometers, assumed to be a stable radiometric reference for climate studies. Then the two models are intercompared, both at global and regional scales.
Previous results had indicated that prior to 2004, the ECMWF Op. model was unsuitable for use in satellite altimetry, due to its lack of homogeneity, with errors increasing almost linearly as we go back in time, reaching almost 3 cm in the beginning of the altimeter era. After 2004, due to frequent model updates, ECMWF Op. still possesses significant discontinuities that induce errors in altimeter-derived sea level trends which, in some regions can exceed 1 mm yr-1 in absolute value, over periods of 7-8 years. The largest impacts occur over the periods when Jason-2 and Jason-3 are in the reference orbit (phase A).
Moreover, in spite of the finer spatial resolution of ECMWF Op. (0.125°×0.125°) when compared with ERA5 (0.25°×0.25°), ERA5 is the most accurate model before 2017 and only slightly worse after that date. The STD of the global daily WPD differences between ERA5 and the SSM/I and SSM/IS data set is between 1.0 and 1.2 cm, respectively, for the whole altimeter era.
For completeness, ERA Interim is also evaluated. Of particular significance is the observed degradation in model performance during its final decade of availability, from 2012 to 2019, when it was discontinued. Since ECMWF Op. is the only model provided in most altimeter products, the inclusion of the most recent reanalysis model (currently ERA5) is strongly advisable. Overall, ERA5 is the best compromise between model accuracy and stability, for sea/water level studies and generally all climate applications, over regions where WPD based on observations are not available, such as some coastal and continental water regions.


Oral presentation show times:

Room Start Date End Date
Tortuga Beach Room (#209A) Thu, Nov 09 2023,10:00 Thu, Nov 09 2023,10:15
M. Joana Fernandes
DGAOT, Faculdade de Ciências, Universidade do Porto