Abstract
Abstract. A ground-based network of more than 1200 Global Navigation Satellite System (GNSS) Continuously Operating Reference Stations (CORS) was analysed using GIPSY-OASIS II software package for the documentation of time and space variations of water vapor in atmosphere during the North Atlantic Waveguide and Downstream impact EXperiment (NAWDEX) during fall 2016. The network extends throughout the North Atlantic, from the Caribbeans to Morocco through Greenland. This paper presents the methodology used for GNSS data processing, screening, and conversion of Zenith Tropospheric Delay (ZTD) estimates to Integrated Water Vapor content (IWV) using surface parameters from reanalysis. The retrieved IWV are used to evaluate the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalyses ERAI and ERA5. ERA5 shows an overall improvement over ERAI in representing the spatial and temporal variability of IWV over the study area. The mean bias is decreased from 0.31±0.63 to 0.19±0.56 kg m−2 (mean ±1σ over all stations) and the standard deviation reduced from 2.17±0.67 to 1.64±0.53 kg m−2 combined with a slight improvement in correlation coefficient from 0.95 to 0.97. At regional scale, both reanalyses show a general wet bias at mid and northern latitudes but a dry bias in the Caribbeans. We hypothesize this results from the different nature of data being assimilated over the tropical oceans. This GNSS IWV data set is intended to be used for a better description of the high impact weather events that occurred during the NAWDEX experiment.
Highlights
The North Atlantic Waveguide and Downstream impact EXperiment (NAWDEX) is an international field campaign that took place during fall 2016
The goal of this paper is to describe the retrieval of Zenith Tropospheric Delay (ZTD) and Integrated Water Vapor content (IWV) estimates from the Global Navigation Satellite System (GNSS) measurements and to assess the quality of IWV estimates from the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalyses ERAI (ECMWF Reanalysis – Interim, Dee et al, 2011) and ERA5 (ECMWF Reanalysis 5, Hersbach et al, 2020) in the NAWDEX study area
It is necessary for the dates of the compared data to match exactly, i.e. GNSS data are resampled at 6 h for comparisons with ERAI and at 1 h for comparisons with ERA5
Summary
The North Atlantic Waveguide and Downstream impact EXperiment (NAWDEX) is an international field campaign that took place during fall 2016. The experiment aims at a better understanding of the effects of the diabatic process on the evolution of atmospherics disturbances along the North Atlantic Jet Stream and a better representation of these processes in Numerical Weather Prediction (NWP) models. The observational field campaign took place from 16 September to 16 October 2016 with the deployment of four research aircrafts and extensive ground-based instrumentation (Schäfler et al, 2018) In addition to this special ground-based instrumentation, measurements from more than 1200 Global Navigation Satellite System (GNSS) Continuously Operating Reference Stations (CORS) located along the North Atlantic Arc were analysed using a single software package for an extended period, from 1 September to 5 November 2016. It is quite common to use GNSS ZTD estimates retrieved from global or regional networks for climatological and meteorological studies (Poli et al, 2007; Wang and Zhang, 2008; Bock et al, 2008; Guerova et al, 2016; Parracho et al, 2018)
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