The use of products from ground-based GNSS observations in meteorological nowcasting

Abstract

Abstract. Convective rainfall is often focalized in areas of moisture convergence. A close relationship between precipitation and fast variations of vertically-integrated water vapour (IWV) has been found in numerous cases. Therefore, continuous monitoring of atmospheric humidity and its spatial distribution is crucial to the operational forecaster for a proper nowcasting of heavy rainfall events. The microwave signals continuously broadcasted by the Global Navigation Satellite Systems (GNSS) satellites are influenced by the water vapour as they travel through the atmosphere. Estimates of IWV retrieved from ground-based GNSS observations may, then, constitute a source of information on the horizontal distribution and the time evolution of atmospheric humidity. At the Spanish Meteorological Agency (AEMET), a near-real-time map of IWV estimates retrieved from ground GNSS measurements in the Iberian Peninsula and West Mediterranean region is operationally built and presented to the forecaster. The maps are generated every 15 minutes following a one-dimensional variational assimilation scheme with the previous map as the background state. A case study is presented in order to illustrate some strengths and weaknesses of the product, to assess the potential benefit of using GNSS products in nowcasting and to define the steps to be done in order to make use of the full potential of the method.

Preface: 11th Plinius Conference on Mediterranean Storms

“…In addition, the authors test their procedure by considering several thunderstorms, which were observed during the summer of 2006, and analyze the results for three different thunderstorm stages (development, maturity and dissipation) and three types of thunderstorm intensities according to their maturity stage and cloudto-ground flash rate (weak, moderate and heavy). Terradellas and Téllez (2010) analyze a case study over the Valencia region to illustrate strengths and weaknesses of using, for nowcasting purposes, near-real-time maps of vertically integrated water vapor (IWV) estimates based on ground-based observations of the microwave signals continuously broadcasted by the Global Navigation Satellite System (GNSS) satellites. These authors conclude that this product constitutes a promising tool for the operational forecasters, since it displays areas with strong moisture convergence and, therefore, potential convection triggering, causing alarm bells to ring long before any sign appears in other remote sensing systems.…”