Statistical Validation of GNSS Radio Occultation data over Egypt

Abstract

Radiosonde (RS) measurements of the upper atmosphere have long been the principal source ofdata, with measurements spanning more than 60 years . RS have limited number of stations onEgypt. Thus, it has poor spatial and temporal resolution, and This negatively affectsmeteorological research, atmospheric observation, and weather forecasting studies over Egypt. Itis needed to find an additional technique characterized by the length of the available time seriesas well as with the high vertical resolution.Global Positioning System Radio Occultation (GPS RO) is the satellite technique received by alow-Earth orbiting satellites to profile the Earth's atmosphere with high vertical resolution andglobal coverage. This technique has been found to enhance weather forecasting and climatemonitoring. In this study, the GPS RO temperature and vapor pressure profiles of COSMICsatellite mission over Egypt from 2007 to 2019 have been validated with those of the availablesix Radiosonde stations (RS). GPS RO and RS profiles collocated by matching the position andthe time, The horizontal distance between the chosen RS stations and the GPS RO event iswithin 150 km and the time window was 3 hours. The comparison was performed only on thestandard pressure level.The main objective of this paper is to check the accuracy of the GPS RO at differentelevations. For this aim the differences between RS and GPS RO were sorted according topressure level in to 4 groups. It is found from the results that GPS RO profiles agree well withRS data. The mean temperature bias for all stations equal (0.22) with standard deviation (1.83).On the other hand, mean vapor pressure bias equal (-0.02) with standard deviation (0.12).According to pressure level sorting, the change of temperature mean bias and standard deviationare increasing with the pressure level decreasing.