Corrections of Radiosonde‐Based Precipitable Water Using Ground‐Based GPS and Applications on Historical Radiosonde Data Over China

Abstract

The usage of radiosonde humidity data in climate studies and atmospheric reanalysis has been greatly hampered by the inhomogeneity issue mainly caused by radiosonde sensor changes. In this work, high‐quality precipitable water (PW) products derived from a national Global Positioning System (GPS) network in China covering the period from 1999 to 2015 were used to quantify errors in radiosonde‐derived PW products for different radiosonde types. Correlations between PW biases and factors including the station location, mean PW, weighted mean temperature (Tm), and solar elevation angle were carefully analyzed. Biases in PW products derived from the mechanical radiosondes (GZZ2, used at most stations before 2001) show strong correlations with the station elevation and Tm, and a PW correction model was then developed. For GTS1 and GTS1‐1 (widely used in current operational system), due to the unobvious correlations between PW biases and these factors, corrections were estimated as mean values of PW biases at all collocated stations. For GTS1‐2, GTS2(U)‐1, and TD2‐A (used at a few stations), subject to insufficient GPS‐radiosonde collocated stations, they are left uncorrected. The corrected radiosonde‐derived PW products (referred as Corr) were compared with the uncorrected products (referred as Raw) as well as PW products derived from the radiosonde data homogenized using the method proposed by Dai et al. (2011; referred as Dai, https://doi.org/10.1175/2010JCLI3816.1). Corr products show better agreements with GPS‐derived PW than Raw and Dai, and artificial significant decreasing PW trends in the recent two decades in Raw products were greatly reduced after applying the proposed corrections.

Impact Analysis of processing strategies on Long-term GPS ZTD

“…Dai et al (2011) detected changepoints first in daily tropospheric dewpoint depression (DPD) time series, then used the most recent segment as a reference to adjust the time series for eliminating discontinuities. Such homogenized time series show generally more realistic long-term trends reported in several previous studies (e.g., Zhao et al, 2012Zhao et al, , 2015Zhang et al, 2019). Therefore, the homogenized radiosonde products processed by Dai et al (2011) were taken as a reference to evaluate the GPS ZTD trends, while the original radiosonde products (referred to as Raw hereafter) were also compared.…”

Implementation of Ready-Made Hydrostatic Delay Products for Timely GPS Precipitable Water Vapor Retrieval Over Complex Topography: A Case Study in the Tibetan Plateau

“…Additionally, a total of 13 radiosonde (RS) stations from Integrated Global Radiosonde Archive (IGRA) that are nearest to the test GPS stations are also used to derive the RS-PWV because it is commonly used to make comparison with GPS-PWV for cross-validation. The RS-PWV is calculated by numerical integration of the humidity profiles as described in [17]. Moreover, a quality control strategy suggested by [11] is applied to circumvent the adverse impacts of outliers on comparison.…”

A New Method for Estimating Tropospheric Zenith Wet-Component Delay of GNSS Signals from Surface Meteorology Data

“…The ZWD obtained using Equation (25) from the radiosonde data is usually used as a reference to evaluate the accuracy of the ZWD obtained by other means.…”

“…China has approximately 120 operable radiosonde stations. From 1950 to 2010, three generations of radiosonde sensors (type 49, type 59-7-1, and GTS1) were used at these stations [24,25]. The replacement of sensors introduced inhomogeneity into the historical records, leading to a systematic bias in the homogenized time series.…”

“…The performance of the new ZWD model was evaluated by using as a reference the ZWD values retrieved using Equation ( 25) from the measurements collected at the 85 radiosonde stations during 2018. In addition, the accuracies of two empirical models (Askne-Nordius and Callahan) were assessed using benchmark values derived from radiosonde data based on Equation (25). In addition, the University of New Brunswick (UNB) series of models (UNB1-UNB4) has been extensively used in several regions around the world.…”