Abstract
Abstract. Radiosonde measurements from the 1930s to present give unique information on the distribution and variability of water vapor in the troposphere. The sounding data from the Integrated Global Radiosonde Archive (IGRA) Version 2 are examined here until the end of 2016, aiming to describe the completeness of humidity observations (simultaneous measurements of pressure, temperature, and humidity) in different times and locations. Upon finding the stations with a non-negligible number of radiosonde observations in their period of record, thus removing pilot-balloon stations from IGRA, the selected set (designated IGRA-RS) comprises 1723 stations, including 1300 WMO stations, of which 178 belong to the current GCOS Upper-Air Network (GUAN) and 16 to the GCOS Reference Upper-Air Network (GRUAN). Completeness of humidity observations for a radiosonde station and a full year is herein defined by five basic parameters: number of humidity soundings, fraction of days with humidity data, average vertical resolution, average atmospheric pressure and altitude at the highest measuring level, and maximum number of consecutive days without data. The observations eligible for calculating precipitable water vapor – i.e., having adequate vertical sampling between the surface and 500 hPa – are particularly studied. The present study presents the global coverage of humidity data and an overall picture of the temporal and vertical completeness parameters over time. This overview indicates that the number of radiosonde stations potentially useful for climate studies involving humidity depends not only on their record length, but also on the continuity, regularity, and vertical sampling of the humidity time series. Additionally, a dataset based on IGRA is described with the purpose of helping climate and environmental scientists to select radiosonde data according to various completeness criteria – even if differences in instrumentation and observing practices require extra attention. This dataset consists of two main subsets: (1) statistical metadata for each IGRA-RS station and year within the period of record; and (2) metadata for individual observations from each station. These are complemented by (3) a list of the stations represented in the whole dataset, along with the observing periods for humidity (relative humidity or dew-point depression) and the corresponding counts of observations. The dataset is to be updated on a 2-year basis, starting in 2019, and is available at https://doi.org/10.5281/zenodo.1332686.
Highlights
For about three-quarters of a century, the global radiosonde network designed and developed for weather forecasting has provided in situ observations of humidity from the surface up the middle troposphere, and eventually reaching the stratosphere
Reanalysis outputs based on past radiosonde data, assimilating satellite data when available, offer multiple-level, globally gridded, synopticscale moisture fields up to four times daily from a beginning year (e.g., 1948 in NCEP/NCAR Reanalysis 1; 1979 in NCEP/NCAR Reanalysis 2 and ECMWF’s ERA-Interim) to present time – even though radiosonde observations are scarce over the ocean, unevenly spaced over land, and taken normally twice a day, with significant differences in vertical coverage
The purpose of this paper is to study the completeness of humidity observations collected in Integrated Global Radiosonde Archive (IGRA) according to various needs – number and latitudinal distribution of observing stations, fraction of observing days in a year, resolution and range of vertical levels, length and continuity of the time series, minimal sampling between the surface and the 500 hPa level – aiming to facilitate the use of radiosonde humidity data by atmospheric and environmental scientists
Summary
For about three-quarters of a century, the global radiosonde network designed and developed for weather forecasting has provided in situ observations of humidity from the surface up the middle troposphere, and eventually reaching the stratosphere. Geographical and temporal sampling differences (Wallis, 1998), uncertainties related to observation time and balloon drift (Kitchen, 1989b; McGrath et al, 2006; Seidel et al, 2011; Laroche and Sarrazin, 2013), differences in vertical coverage and data gaps related to reporting practices of humidity (Dai et al, 2011, and references therein), and differences in humidity data accuracy – which depend on humidity sensors and vary with measured conditions (WMO, 1995; Nash, 2002; Sapucci et al, 2005; Moradi et al, 2013; Dirksen et al, 2014). The purpose of this paper is to study the completeness of humidity observations collected in IGRA according to various needs – number and latitudinal distribution of observing stations, fraction of observing days in a year, resolution and range of vertical levels, length and continuity of the time series, minimal sampling between the surface and the 500 hPa level – aiming to facilitate the use of radiosonde humidity data by atmospheric and environmental scientists.
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