Comparison of Different Techniques for Tropospheric Wet Delay Retrieval Over South America and Surrounding Oceans

Abstract

Water vapour (WV) plays a fundamental role in several weather processes that deeply influence human activities. Satellite based radiometers, Ground based Global Navigation Satellite Systems (GNSS) and Numerical Weather Models (NWM) permit to obtain either measurements or estimates or forecasts of WV. This work presents a 2 years systematic comparison to address the agreement on the tropospheric wet delay retrieved by the three mentioned independent techniques over permanent stations belonging to SIRGAS (Sistema de Referencia para las Américas) GNSS network. SIRGAS tropospheric total delay estimations are compared with the official International GNSS Service (IGS) ones, with the measurements from the Jason-1 satellite radiometer (JMR) in terms of Zenith Wet Delays (ZWD) and, finally, with the ZWD computed from ERA Interim, the last reanalysis dataset from the European Center for Medium-Range Weather Forecasts (ECMWF). All the differences between the techniques, which were considered in order to yield a reliable comparison, are discussed. . It has been clearly understood that the knowledge of high accurate WV content and its distribution in the atmosphere improves short term weather forecasts significantly. At the same time, WV reveals very rapid changes both in the temporal and in the spatial domains such that, at present, there are no theoretical models that can reliably predict its behaviour. Retrieving WV content in the atmosphere can be performed in different ways using independent techniques: starting from the more traditional and established ones, such as radiosondes and ground-based microwave radiometers, up

Multi-year GNSS monitoring of atmospheric IWV over Central and South America for climate studies

“…Moreover, previous regional analysis of GNSS-derived water vapour in South America had narrow spatial and temporal coverage, employed GPS-only observations, and were focused on the validation of the methodology by comparison against radiosondes measurements (Sapucci et al, 2007), or radiosondes and satellite-based observations (Fernández et al, 2010). Another regional inter-technique comparison was performed by Calori et al (2015), using GPS-only observations, comprising about 30 sites, and spanning 2 years. Recently, a 1-year-long experiment employing an episodic but highly dense meteorological GNSS network in Amazonia studied water vapour-convection interactions in the tropics (Adams et al, 2015).…”

Estimation of integrated water vapor derived from Global Navigation Satellite System observations over Central-Western Argentina (2015–2018). Validation and usefulness for the understanding of regional precipitation events

“…The applied methodology requires observations of atmospheric pressure and temperature at each site, a topic that, in view of the limited in-situ observations, has been addressed through the use of reanalysis products for all SIRGAS-CON stations over the Latin America region (Calori et al, 2015). The uncertainty associated with the input variables depends on the method selected for the correction of pressure, based on the height difference between GNSS sites and MetS.…”

“…Latin America has a permanent GNSS observation network, SIRGAS-CON (Geocentric Reference System for the Americas-Continuous GNSS network), which, by the end of 2017, already exceeded 420 operational stations (Cioce et al, 2018). It densifies the International Terrestrial Reference Frame (ITRF) in Latin America (Sanchez et al, 2015;Brunini et al, 2012), and it can be used for atmospheric monitoring, as shown in Brunini et al (2008) and Calori et al (2015). The Integrated Water Vapor (IWV) is the total amount of water vapor present in a vertical atmospheric column over a specific site, such as a GNSS site.…”