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Assessment of reanalysis datasets against radiosonde observation over the Eastern Mediterranean region

Hassan Rokaya Mohamed, Salah Zeinab, Karacostas Theodore, Abdel-Wahab Mohamed Magdy

Acta Geophysica

2023

Vol. 71, no. 6

2989--3005

Four meteorological components (geopotential height Z, air temperature T, dew point temperature Td, and relative humidity RH) collected from ERA-5 and ERA-Interim were compared with the observations of nine radiosonde stations with different climatic changes, at different isobaric levels (850, 700, 500, and 200 hPa) during the period 2000-2017, in order to assess the accuracy of the aforementioned reanalysis datasets. The results showed that both reanalysis datasets have a strong correlation with the observed variables, except with dew point temperature and relative humidity in the upper troposphere. The mean values of geopotential height and temperature from both grid dataset are generally consistent with the radiosonde values, whereas considerable bias in the mean Td and RH exists and increases upwards. The study clearly proved that the reanalysis datasets can be used to compensate for the lack of radiosonde observation. Furthermore, air temperature (during 1959-2021) showed an increasing trend from the surface to the lower troposphere, while the temperature decreased in the upper troposphere and lower stratosphere. Finally in this study, the impact of the North Atlantic Oscillation Index (NAOI) on the air temperature was also examined, and a negative relationship was found between NAOI and temperature at the levels: surface, 850, 700, and 500 hPa, while a positive relationship was found, only in winter, at 200 hPa. At the level of 100 hPa, the correlation is positive for both seasons.

Spatial and temporal evaluation of global rainfall products in a data-scarce region: The Dez Basin, Iran

Khoshchehreh Mostafa, Ghomeshi Mehdi, Shahbazi Ali, Bolboli Hossein, Saberi Hamed, Gorjizade Ali

Journal of Water and Land Development

2021

no. 48

148--161

The limitation in approachability to rainfall data sources with an appropriate spatial-temporal distribution is a significant challenge in different parts of the world. The development of general circulation models and mathematical algorithms has led to the generation of various rainfall products as new sources with the potential to overcome the shortage in datascarce basins. In this study, the performance of the PERSIANN-CCS and CMORPH satellite-based rainfall product, as well as the ERA5 and ERA-Interim reanalysis, was evaluated based on detection skill and quantitative metrics in a daily, monthly and seasonal time scales in the Dez basin located in the southwest of Iran. The basin has a wide topographic variation and scattered rain gauge stations. Overall results denote that the ERA5 dataset has the best performance in all statistic verification than other rainfall products. Based on the daily evaluation of all rainfall products, the false alarm rate (FAR) is higher than 0.5, so none of the datasets could capture the temporal variability of rainfall occurrence. This study has covered the western parts of the Zagros steep slopes in which the topographic conditions have a significant effect on the activity of rainfall systems. On a monthly scale, the mean value of the correlation coefficient (CC) for ERA5, ERA-Interim, PER-SIANN-CCS, and CMORPH was equal to 0.86, 0.85, 0.51, 0.39, respectively. The results of seasonal evaluation suggested that all datasets have better rainfall estimation in autumn and winter, and the capability of all datasets dramatically decreased in the spring. The current paper argues that the ERA5 reanalysis typically outperforms ERA-Interim and can be considered as a reliable rainfall source in the future hydrological investigation in the southwest of Iran.