Since 1990, signals from global positioning system (GPS) satellites have been recorded by networks worldwide. From these GPS observations the zenith total delay (ZTD) can be computed. Using surface measurements of pressure and temperature, these ZTD values can be turned into water vapour amount and used for atmospheric research. The main aim of the COST action ES1206 “Advanced Global Navigation Satellite Systems tropospheric products for monitoring severe weather events and climate” (GNSS4SWEC) is to coordinate the research and the development of new, advanced tropospheric products derived from GNSS signal delays, exploiting the full potential of multi-GNSS (GPS, GLONASS and Galileo) water vapour estimates on a wide range of temporal and spatial scales, from real-time monitoring and forecasting of severe weather to climate research. The potential impacts of this work are great: improved severe weather forecasting, leading to a decreased risk to life and national infrastructure; improvement of climate projections also has major global significance. In addition the action will promote the use of meteorological data in GNSS positioning, navigation, and timing services.

The main topics envisioned in the special issue include the following:

• The development of advanced and new GNSS tropospheric products related to
  • multi-GNSS constellation signals for water vapour remote sensing,
  • water vapour anisotropy (horizontal gradients, satellite slant delays, tomography, etc.),
  • real-time/ultra-fast water vapour remote sensing in support of nowcasting ,
  • improvement of the temporal and spatial resolution capability of GNSS water vapour remote sensing.
• The exploitation of these products in numerical weather prediction (NWP) and nowcasting, such as
  • the development of new initialization/assimilation methods in NWP,
  • the development of forecasting tools (water vapour maps, convective indexes, alarm systems, etc.) for nowcasting and severe weather events.
• The assessment of these GNSS tropospheric products (see first point) derived from a common benchmark reference data set.
• The assessment of the standardized methods/tools for NWP/nowcasting (see second point) based on the GNSS products built on the benchmark data set.
• Exploiting re-analysed/reprocessed GNSS tropospheric products for climate studies:
  • comparison/assimilation in the regional/ global climate models,
  • comparisons with other in-situ, ground-based and satellite water vapour retrievals,
  • development and assessment of homogenization methods for GNSS-based product time series,
  • analysing the variability and trends in GNSS-based water vapour retrievals.
• Establishment of new GNSS analysis centres for monitoring the atmosphere.

Submissions of papers dealing with broader GNSS4SWEC objectives are also encouraged:

• synergy between GNSS and GNSS radio occultation (RO),
• monitoring the other components of the hydrological cycle (soil moisture, snow cover, terrestrial water storage) with GNSS.