Abstract's details
How has global warming impacted the altimeter wet path delay over the altimetry record?
CoAuthors
Event: 2023 Ocean Surface Topography Science Team Meeting
Session: Instrument Processing: Propagation, Wind Speed and Sea State Bias
Presentation type: Type Oral
Contribution: PDF file
Abstract:
Thirty years of satellite radar altimetry allow the monitoring of the changes in sea level at global and regional scales. The accurate determination of these changes depends directly on the wet path delay (WPD) in the altimeter observations, mostly due to the atmospheric water vapor. It is known that the water vapor in the atmosphere increases at an average rate of 7% per 1°C of warming. Building upon this relationship, this study focuses on the impact of global warming on the WPD over the altimetry era (1993-2022). Near surface air temperature (T2m) and total column water vapor (TCWV) data provided by the European Centre for Medium-Range Weather Forecasts (ECMWF) ReAnalysis 5 (ERA5) and the corresponding ERA5-derived WPD have been analyzed.
Results reveal that global land-ocean temperature has increased at an average rate of 0.23°C/decade and, in close association with higher temperatures, TCWV has increased at a rate of 0.37 mm/decade. For the global ocean, these trends are 0.18°C and 0.43 mm per decade, respectively. This shows that, per 1°C of warming, TCWV increases at an average rate of 7% globally and 9% over the global ocean. This global warming over these 30 years was responsible for an average increase in TCWV of 1.3 mm over oceans, which represents an increase in WPD of 8 mm (0.26 cm/decade), equivalent to 1.4 cm (9%) per 1°C of warming.
The good performance of satellite radar altimetry to measure sea level requires regular assessments of all involved components (measurements, orbit, environmental corrections, etc.) both in terms of accuracy and long-term stability. This study shows that the global warming has induced a physical long-term variation in the altimeter wet path delay (0.26 mm/year), which can be misinterpreted as a long-term instability, such as a drift in the correction.
This study also shows that, in spite of the fact that satellite radar altimetry is a remote sensing technique to monitor the planet, the climate change itself is changing the way how this technique is working. This can cause a misleading between physical signals and instrument drifts, requiring a regular monitoring and possibly updates in the altimetry methodologies used to retrieve the WPD of satellite altimeter observations.
Results reveal that global land-ocean temperature has increased at an average rate of 0.23°C/decade and, in close association with higher temperatures, TCWV has increased at a rate of 0.37 mm/decade. For the global ocean, these trends are 0.18°C and 0.43 mm per decade, respectively. This shows that, per 1°C of warming, TCWV increases at an average rate of 7% globally and 9% over the global ocean. This global warming over these 30 years was responsible for an average increase in TCWV of 1.3 mm over oceans, which represents an increase in WPD of 8 mm (0.26 cm/decade), equivalent to 1.4 cm (9%) per 1°C of warming.
The good performance of satellite radar altimetry to measure sea level requires regular assessments of all involved components (measurements, orbit, environmental corrections, etc.) both in terms of accuracy and long-term stability. This study shows that the global warming has induced a physical long-term variation in the altimeter wet path delay (0.26 mm/year), which can be misinterpreted as a long-term instability, such as a drift in the correction.
This study also shows that, in spite of the fact that satellite radar altimetry is a remote sensing technique to monitor the planet, the climate change itself is changing the way how this technique is working. This can cause a misleading between physical signals and instrument drifts, requiring a regular monitoring and possibly updates in the altimetry methodologies used to retrieve the WPD of satellite altimeter observations.