Long-Term Behaviour of Temperature in the Lower Atmosphere of Niamey a West African Tropical Station

Document pages: 12 pages

Abstract: This paper highlights the global warming of the lower atmosphere of West African tropical area using in-situ data. The study is based on the analysis of 500-m interval vertical profiles of radiosonde temperature above Niamey (13.47°N; 2.16°E) a sub-Saharan meteorological station. The annual cycle of surface temperatures shows seasonally two peaks located in April May and in October and two minimum in December January and August respectively. In the mid-troposphere (between 5 km and 10 km height), time series of monthly mean temperatures from January 2001 to December 2018, shows an annual variability with a slight downward trend of -0.036°C per decade. In the lower stratosphere (25 - 30 km altitude) a cooling of -0.64°C decade is observed. Temperatures time series also highlight the presence of two breaking points associated with the El Niño-Southern Oscillation (ENSO) events. When performing a separation regarding Southern Oscillation Index (SOI) time series, model parameters of the linear regression indicate a tropospheric warming during the neutral and La Niña phases and a stratospheric cooling. The analysis of the lower stratosphere zonal wind highlights different behaviours of the quasi-biennial oscillation (QBO) during the neutral and La Niña phases.