Abstract
Abstract. Ground-based Global Navigation Satellite System (GNSS) measurements from nearly 50 stations distributed over the Caribbean arc have been analysed for the period 1 January–29 February 2020 in the framework of the EUREC4A (Elucidate the Couplings Between Clouds, Convection and Circulation) field campaign. The aim of this effort is to deliver high-quality integrated water vapour (IWV) estimates to investigate the moisture environment of mesoscale cloud patterns in the trade winds and their feedback on the large-scale circulation and energy budget. This paper describes the GNSS data processing procedures and assesses the quality of the GNSS IWV retrievals from four operational streams and one reprocessed research stream which is the main data set used for offline scientific applications. The uncertainties associated with each of the data sets, including the zenith tropospheric delay (ZTD)-to-IWV conversion methods and auxiliary data, are quantified and discussed. The IWV estimates from the reprocessed data set are compared to the Vaisala RS41 radiosonde measurements operated from the Barbados Cloud Observatory (BCO) and to the measurements from the operational radiosonde station at Grantley Adams International Airport (GAIA), Bridgetown, Barbados. A significant dry bias is found in the GAIA humidity observations with respect to the BCO sondes (−2.9 kg m−2) and the GNSS results (−1.2 kg m−2). A systematic bias between the BCO sondes and GNSS is also observed (1.7 kg m−2), where the Vaisala RS41 measurements are moister than the GNSS retrievals. The IWV estimates from a collocated microwave radiometer agree with the BCO soundings after an instrumental update on 27 January, while they exhibit a dry bias compared to the soundings and to GNSS before that date. IWV estimates from the ECMWF fifth-generation reanalysis (ERA5) are overall close to the GAIA observations, probably due to the assimilation of these observations in the reanalysis. However, during several events where strong peaks in IWV occurred, ERA5 is shown to significantly underestimate the GNSS-derived IWV peaks. Two successive peaks are observed on 22 January and 23–24 January which were associated with heavy rain and deep moist layers extending from the surface up to altitudes of 3.5 and 5 km, respectively. ERA5 significantly underestimates the moisture content in the upper part of these layers. The origins of the various moisture biases are currently being investigated. We classified the cloud organization for five representative GNSS stations across the Caribbean arc using visible satellite images. A statistically significant link was found between the cloud patterns and the local IWV observations from the GNSS sites as well as the larger-scale IWV patterns from the ECMWF ERA5 reanalysis. The reprocessed ZTD and IWV data sets from 49 GNSS stations used in this study are available from the French data and service centre for atmosphere (AERIS) (https://doi.org/10.25326/79; Bock, 2020b).
Highlights
The overarching goal of EUREC4A (Elucidate the Couplings Between Clouds, Convection and Circulation) is to improve our understanding of how trade-wind cumuli interact with the large-scale environment (Bony et al, 2017)
A small “island effect” might show up here as the moisture profiles over the island of Barbados seemed to be slightly moister than those over the nearby sea during the EUREC4A field campaign (Fig. A4 in Stephan et al, 2021). Another contribution might arise from moisture transport associated with land and sea breezes as was previously evidenced in Colombo, Sri Lanka, where the land–sea breezes contributed to a daytime boundary layer moistening and nighttime drying observed in radiosoundings (Ciesielski et al, 2014a)
This paper describes the data processing streams and discussed the quality of Global Navigation Satellite System (GNSS) zenith tropospheric delay (ZTD) and integrated water vapour (IWV) retrievals from four operational streams run by IGN and ENSTA-B/IPGP and one research stream (GIPSY repro1); see Table 1
Summary
The overarching goal of EUREC4A (Elucidate the Couplings Between Clouds, Convection and Circulation) is to improve our understanding of how trade-wind cumuli interact with the large-scale environment (Bony et al, 2017). Water vapour is one key ingredient of the atmospheric environment controlling the life cycle of convection with strong feedback on the large-scale circulation and energy budget (Sherwood et al, 2010). Most of the distant open-seawater vapour measurements were made by research vessels (R/Vs) embarking radiosonde systems, lidars, and microwave radiometers for what concerns water vapour measurements. They were completed by aircraft platforms leaving from the Grantley Adams International Airport (GAIA), Brigdetown, Barbados, embarking dropsondes, in situ, and remote sensing measurement systems. In addition to the research instrumentation deployed on these platforms, ground-based and ship-borne Global Navigation Satellite System (GNSS) receivers were operated to provide high-temporal-resolution integrated water vapour (IWV) measurements. This paper focuses on the ground-based GNSS network measurements
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
