Geodesy contributes to Atmospheric Science by providing some of the Essential Climate Variables of the Global Climate Observing System (GCOS) such as: sea level from radar altimetry, mass changes ofice and terrestrial water from satellite gravimetric missions, atmospheric water vapor from ground-based and space-based GNSS, as well as from VLBI and DORIS, atmospheric temperature from GNSS RO. Sensing of the neutral atmosphere with space geodetic techniques is an established field of research and applications, thanks to the availability of regional and global ground-based networks as well as satellite-based missions. Water vapor, the most abundant greenhouse gas of the atmosphere, is under-sampled in the current meteorological and climate observing systems, therefore obtaining and exploiting more high-quality humidity observations is essential to weather forecasting and climate monitoring. The production, exploitation and evaluation of operational GNSS-Meteorology for weather forecasting is well established in Europe due to two decades of outstanding cooperation between the geodetic community and European national meteorological services. Advancements in Numerical Weather Prediction Models (NWP) to improve forecasting of extreme precipitation, require GNSS troposphere products with a higher resolution in space and shorter delivery times than are currently in use. Homogeneously reprocessed GNSS observations on a regional and global scale have high potential for monitoring water vapor climatic trends and variability. With shortening orbit repeat periods SAR measurements are a new potential source of information to improve NWP models. At the same time, high-resolution NWP data have recently been used for deriving a new generation of mapping functions. In real-time GNSS processing these data can be employed to initialize Precise Point Positioning (PPP) processing algorithms, shortening convergence times and improving positioning. Furthermore, GNSS-reflectometry is establishing itself as an alternative method for retrieving soil moisture and has the potential to be used to retrieve near-surface water vapor.

We welcome, but not limit, contributions on the subjects below:

· Estimates of the state of the neutral atmosphere using ground-based and space-based geodetic data, use of those estimates in weather forecasting and climate monitoring.
· Multi-GNSS and multi-instruments approaches to retrieve and inter-compare tropospheric parameters.
· Real-Time and reprocessed tropospheric products for now-casting, forecasting and climate monitoring.
· Assimilation of GNSS tropospheric products in NWP and in climate reanalysis models.
· Production of SAR-based tropospheric parameters and use of them in NWP.
· Methods for homogenization of long-term GNSS tropospheric products.
· Studies of the delay properties of the GNSS signals for Earth-space propagation experiments.
· Usage of NWP data in GNSS data processing.
· Techniques on retrieval of soil moisture from GNSS observations and of ground-atmosphere boundary interactions.
· Usage of satellite gravity observations, as obtained from GRACE and its successor GRACE-FO, for studying the atmospheric water cycle.