Modeling of Zenith Tropospheric Delay using ERA5 data over East African region

Abstract

The Zenith Tropospheric Delay (ZTD) is a crucial parameter in meteorology and climate research, often estimated from surface meteorological parameters and Global Navigation Satellite Systems (GNSS) observations. In East Africa, the lack of reliable surface meteorological data and gaps in GNSS observations compromise the accuracy and reliability of ZTD data. To address this issue, site-specific ZTD models were developed using ERA5 data from 2013 to 2017, employing Empirical Orthogonal Function (EOF) analysis. The accuracy of the proposed EOF models was validated using the tropospheric product from the Nevada Geodetic Laboratory (NGL) as a reference and compared to the Global Pressure and Temperature 3 (GPT3) ZTD model. The results of the study show that the EOF ZTD models significantly outperformed the GPT3 model, reducing Mean bias (MnB) by 72.3% and Root Mean Square Error (RMSE) by 3.0%. EOF models performed particularly well for stations near the equator (latitudes 4°S and 4°N) and between latitudes 12° S and 4° S in terms of MnB and RMSE, respectively. Seasonally, EOF models surpassed the GPT3 model in MnB and RMSE across most seasons near the equator, except during the September–October–November (SON) period, where GPT3 showed an 85.5% better performance in MnB. For stations between latitudes 12° S and 4° S, GPT3 generally performed better in terms of RMSE, except during the March–April–May (MAM) period, where the EOF model excelled. However, the EOF model consistently showed better (reduced) MnB in this region. This study demonstrates that the EOF method is a viable alternative for estimating ZTD in areas with limited surface meteorological data and GNSS observation gaps. The site-specific ZTD models developed using the EOF method can significantly improve the accuracy and reliability of ZTD data, with broad applications in geodesy, atmospheric science, and navigation among others.