Interpretation of the Tropospheric Gradients Estimated With GPS During Hurricane Harvey

Abstract

During the last decade Global Positioning System (GPS) Continuous Operating Reference Stations networks have become a new important data source for meteorology. This has dramatically improved the ability to remotely sense the atmosphere under the influence of severe mesoscale and synoptic systems. The zenith tropospheric delay (ZTD) is one of the atmospheric variables continuously observed, and its horizontal variations, the horizontal tropospheric gradients, are routinely computed nowadays within the dual‐frequency GPS processing, but their interpretation and relationship with the weather is still an open question. The purpose of this paper is to contribute in this direction by studying the effect that Hurricane Harvey had on the spatial and temporal behavior of the ZTDs and gradients, when it reached Texas coast, during 18–31 August 2017. The results show that ZTD time series present a clear and rapid increase larger than 10 cm in a few hours when the hurricane reached the area. Gradients behaviors show that the hurricane also produced significant changes on them, since the magnitude and predominant directions before and after the hurricane arrived are completely different. Noticeably, the gradient vectors before the landing are consistently related to the horizontal winds and pressure fields. In this manuscript we demonstrate that the ZTD gradients can show a consistent signature under severe weather events, strongly suggesting their potential application for short‐term weather forecasting.

Monitoring and prediction of hurricane tracks using GPS tropospheric products

“…Milliner et al (2018) were the first to monitor the amount of water drained by the ground from hurricanes across the Gulf and East Coasts of the USA. More recently, Graffigna et al (2019) showed a significant shift in ZTD gradients prior to the arrival of a hurricane. Ejigu et al (2020) assessed the connection between GPS-derived IWV and its influence on TC structure during Hurricane Florence in 2018.…”

Beyond Mapping Functions and Gradients

“…The modeling of the extra-delays caused by the atmosphere by the combination of mapping functions and gradients of Eq. (1) has proved very effective since Davis introduced his formula 30 years ago [49][50][51]. But what is the real meaning of effective?…”

“…Some authors [51,55,56] tried to assess the physical meaning of tropospheric gradients, but their effort were limited to qualitative assessments and correlations studies. Up to our knowledge [57], nobody is using gradients as data to constraint operational NWMs, albeit efforts having made to extract gradients from NWM numerical simulations [14] or make comparisons with NWMs outputs [58], or even to propose the use of slant delays for such a use [59].…”

An Improved Model for Detecting Heavy Precipitation Using GNSS-Derived Zenith Total Delay Measurements

“…GNSS signals propagating from satellites to the ground-based GNSS tracking stations are delayed by the neutral atmosphere (troposphere) [15], [16]. The tropospheric delay over a GNSS station, which is denoted by the zenith total delay (ZTD), together with other geodetic parameters such as site coordinates [17] and tropospheric gradients [18]− [20], can be accurately estimated from GNSS observations [21]− [23]. Previous studies have demonstrated that the accuracy of ZTDs obtained from GNSS data processing is about 3−10 mm [19], [24], [25] with a temporal resolution of 5−30 min, i.e., the so-called near real-time (NRT) products.…”