A new approach for using altimeter measurements
Healy, Sean ; Anesiadou, Katerina ; Semane, Noureddine ; Browne, Philip ; Zuo, Hao ; Massart, Sebastien ; Abdalla, Saleh
Data assimilation (DA) is used in numerical weather prediction (NWP) to establish the initial conditions of forecasts based on the latest observations and an earlier short-range forecast. A new approach for exploiting satellite radar altimetry sea-surface height (SSH) information in a coupled DA system has been investigated as part of the German National Meteorological Service's (DWD's) STEP UP! Fellowship programme for ECMWF. One of the Fellowships from 2023 to 2025 built upon preliminary ideas developed at ECMWF: the project was based on recognising that the 'atmospheric delay corrections' currently applied in the retrieval of ocean SSH information from altimeter measurements are essentially the same information as the ground-based Global Navigation Satellite System (GNSS) observations now assimilated in many operational NWP systems, which provide useful humidity information over land. Therefore, it was investigated whether, instead of correcting the altimeter measurements, it is possible to retrieve potentially useful humidity information over the ocean in a similar way to ground-based GNSS. This has required running a complex, state-of-the-art coupled data assimilation system. Some of the initial, proof-of-concept results are reviewed here, and areas for further work are suggested.</p>
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