Estimation of Local-scale Precipitable Water Vapor Distribution Around Each GNSS Station Using Slant Path Delay

Abstract

A procedure for estimating the precipitable water vapor (PWV) distribution around ground-based stations of the global navigation satellite system (GNSS) on a scale of several kilometers is presented. This procedure utilizes the difference between the zenith total delay above a GNSS station and the zenith mapped slant path delay (SPD). This difference can be used to estimate the PWV gradient in each SPD direction by assuming an exponential distribution for the horizontal water vapor gradient.The procedure was tested using an estimation of the PWV variation associated with the parent storm of an F3 Fujita scale tornado that occurred in Ibaraki prefecture on 6 May, 2012. Differential reflectivity observed by a dual-polarimetric radar indicated the existence of a developed parent cloud approximately 1h before the tornado occurred. A high-resolution numerical weather model simulation suggested the existence of a strong PWV gradient around the parent cloud, made evident by the co-existence of a strong updraft and downdraft within an approximately 5-km radius. The PWV gradient, calculated using the GNSS observation network with an average spacing of approximately 17 km, could not detect such a small-scale, strong PWV gradient. The PWV gradient estimated using the proposed procedure revealed a strong PWV gradient and its enhancement. In this case, a higher-order inhomogeneity component of each SPD played a critical role.

Estimation of Local-Scale Precipitable Water Vapor Distribution Around Each GNSS Station Using Slant Path Delay: Evaluation of a Severe Tornado Case Using High-Resolution NHM

“…However, enhancement of vortices near the model surface was expressed, and an isolated area with a strong PWV gradient formed near the southerncentral part of Saitama Prefecture 1h before the tornado struck (Shoji et al 2014). The track of the strong PWV gradient area exhibited key features of the track of a high-Zdr area, as observed by MRI-C radar (Fig.…”

“…It is inherently difficult to capture local-scale water vapor distribution using GNSS-derived PWV. Shoji et al (2014) proposed a new method that utilizes GNSS slant path delays (SPDs) to estimate the PWV distribution around each GNSS station.…”

“…Sato et al (2013) compared the results of such studies with those of radiosonde observations and determined that zenith-scaled GNSS SPD, in which the path is closest to a radiosonde path, exhibited better agreement than zenith total delay (ZTD) retrieved using standard GNSS analysis. Utilizing the decomposed components of each SPD (i.e., gradient and higher-order inhomogeneity), Shoji (2013) proposed two new indices to express the degree of water vapor variation near each GNSS station, and Shoji et al (2014) proposed a new method for estimating PWV distribution near ground-based GNSS stations on a scale of several kilometers. The new method demonstrated the capability to capture a strong PWV gradient associated with the parent storm of the F3 tornado that struck Tsukuba City in Ibaraki Prefecture, Japan, on 6 May, 2012 (hereafter, Tsukuba tornado).…”

“…The purpose of this study is to quantitatively evaluate the method of Shoji et al (2014) using the simulation results of a high-resolution NWP model. Section 2 describes our methodology for evaluating the new method.…”

Localized Delay Signals Detected by Synthetic Aperture Radar Interferometry and Their Simulation by WRF 4DVAR

“…In the end of the twentieth century, the Global Navigation Satellite System (GNSS) has been demonstrated to be capable of estimating the precipitable water vapor (PWV) in the zenith direction (Bevis et al 1992) with a precision comparable to that derived from radiosonde observations (Ohtani and Naito 2000). Although the recent development of the GNSS system contributed to improve the spatial resolution of the water vapor observation, the spatial resolution of the GNSS observation is a few tens of kilometers at best (Shoji et al 2014), which is insufficient to resolve kilometer-scale phenomena such as individual convective cells. On the other hand, PWV mapping with 1 km resolution has been achieved by multi-spectrum infrared observations in the Moderate-Resolution Imaging Spectroradiometer and the Medium Resolution Imaging Spectrometer satellites (Li et al 2012).…”