Pottiaux, E.

Invited talk presented at Belgian National Committee for GEODESY and GEOPHYSICS (BNCGG) 2021, Brussels, Belgium on 2021-01-21

Abstract: Atmospheric water vapour is a key parameter in meteorology and climate as it strongly influences atmospheric dynamics and the hydrologic cycle through surface evaporation, latent heat transport and diabatic heating, and is, in particular, a source of clouds and precipitation. It is also the most important natural greenhouse gas and is responsible for the largest known feedback mechanism for amplifying climate change. However, atmospheric water vapour is highly variable, both in space and in time, and measuring it remains a demanding and challenging task. If Global Navigation Satellite Systems (GNSS), such as the American system GPS (Global Positioning System) and its European counterpart Galileo, have been primarily designed with the mission to provide users with Positioning, Navigation, and Timing (PNT) services, they are also capable of remotely sensing the atmospheric water vapour. By using GNSS data recorded in permanently observing stations, one can derive the atmospheric water vapour (albeit the use of meteorological variables) at high temporal resolution and under all weather conditions. In addition, the number of permanent GNSS stations has significantly increased over the last two decades, with today about 5000 GNSS stations in Europe. GNSS has thus gradually become an important source of information for European weather forecast centres. Today, GNSS meteorology is a mature technique with products being assimilated operationally in Numerical Weather Prediction (NWP) models. Still, concurrent progresses in the geodetic and meteorological communities over the past decade, opened space for the development of new and enhanced GNSS products to contribute improving weather forecasting. This includes products representing the asymmetry of the atmospheric water vapour distribution, water vapour maps, and real-time products for nowcasting of severe weather. Aside from these latest developments in GNSS meteorology, the use of GNSS for climate research also gained interest recently in Europe. Indeed, with 24+ years of continuous observations in some of the GNSS permanent stations, on-going GNSS reprocessing efforts using state-of-the-art models will provide consistent time series of atmospheric water vapour content which are reaching the “maturity age” of 30 years typically requested for climate research. However, even with a careful reprocessing, inconsistencies in the GNSS time series due e.g. to instrumental and environmental changes at GNSS stations may remain, and make climate trend analysis challenging. A homogenisation process of these time series is thus necessary and a benchmarking activity of existing statistical homogenisation methods has been carried out in Europe. While waiting for these new reprocessed time series, the current length of the GNSS-derived time series already allows the evaluation of re-analysis and of climate models such as it was done in the CORDEX.be project or with the ALARO-0 model. In this presentation, we review the progresses made in and the status of using GNSS for meteorology and climate, highlighting the challenges and pitfalls, and outlining the major steps remaining ahead.

Keyword(s): GNSS ; GPS ; Troposphere ; Water Vapour ; Meteorology ; Numerical Weather Model ; Climate
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