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Verification of a global weather forecasting system for decision-making in farming over Africa

Kartsios Stergios, Pytharoulis Ioannis, Karacostas Theodore, Pavlidis Vasileios, Katragkou Eleni

Acta Geophysica

2024

Vol. 72, no. 1

467--488

In the framework of AfriCultuReS project, operational deterministic weather forecasts provide valuable information on the expected weather conditions over the African continent as a part of federation of services within the project. In this study, we investigate the performance of the National Centers for Environmental Prediction (NCEP) Global Forecast System (GFS) over pilot regions in Africa by utilizing available surface observations, satellite and reanalysis data. The verification period covers two consecutive years (June 2018-May 2020). In addition, we assess the ability of the model to provide skillful forecasts through three high-impact precipitation events that occurred during this period. The results show that the model presents both positive and negative biases with respect to its predicted near surface air temperature, underestimates the near surface relative humidity and the mean sea-level pressure, while overestimates the wind speed at 10 m. The neighborhood-based statistical verification of the 24-h accumulated precipitation reveals that the model forecasts the precipitation events more accurately as the verification area is increasing but at higher precipitation thresholds its performance deteriorates. Different variability, errors and correlation between simulated and observed precipitation exist in each forecast lead day and region. A range of model behavior and forecast skill is found with respect to the examined three precipitation events. Skillful forecasts up to four days ahead were provided in the cases of the Tropical Cyclone IDAI and the flash flooding events in northern Tunisia, while the lowest performance was found in the region of the West African Monsoon.

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.