Abstract
The vertical profiles of temperature and water vapour from the Atmospheric InfraRed Sounder (AIRS) have been validated across various regions of the globe as an effort to provide a substitute for radiosonde observations. However, there is a paucity of inter-comparisons over West Africa where local convective processes dominate and radiosonde observations (RAOBs) are limited. This study validates AIRS temperature and relative humidity profiles for selected radiosonde stations in West Africa. Radiosonde data were obtained from the AMMA and DACCIWA campaigns which spanned 2006–2008 and June–July 2016 respectively and offered a period of prolonged radiosonde observations in West Africa. AIRS performance was evaluated with the bias and root mean square difference (RMSD) at seven RAOB stations which were grouped into coastal and inland. Evaluation was performed on diurnal and seasonal timescales, cloud screening conditions and derived thunderstorm instability indices. At all timescales, the temperature RMSD was higher than the AIRS accuracy mission goal of ±1 K. Relative humidity RMSD was satisfactory with deviations <20% and <50% for both lower and upper troposphere respectively. AIRS retrieval of water vapour under cloudy and cloud-free conditions had no significant difference whereas cloud-free temperature was found to be more accurate. The seasonal evolution of some thunderstorm convective indices were also found to be comparable for AIRS and RAOB. The ability of AIRS to capture the evolution of these indices imply it will be a useful dataset for the African Science for Weather Information and Forecasting Techniques (SWIFT) high impact weather studies.
Highlights
Quantification of atmospheric temperature and water vapour are critical for assessing and improvement of numerical weather and climate prediction models ([1,2] and references therein)
radiosonde observations (RAOBs) of temperature and relative humidity profiles were obtained from African Monsoon Multidisciplinary Analysis (AMMA) and Dynamics-aerosol-chemistry-cloud interactions in West Africa (DACCIWA) databases for the period of 1 January 2006 to 31 December 2008 and 1 June to 31 July 2016, with locations of RAOB locations are distributed between longitudes 4◦W to 2◦E and latitudes 5◦N to 13◦N
The bias between Atmospheric InfraRed Sounder (AIRS) and RAOB temperature profiles was found to be reduced during daytime passes than the night with an overall pressure level difference about 0.33 K
Summary
Quantification of atmospheric temperature and water vapour are critical for assessing and improvement of numerical weather and climate prediction models ([1,2] and references therein). The initialization process for these models demand the use of denser and homogeneous satellite radiance which must be corrected for cloud contamination. This radiance correction allows for the effective and efficient retrieval of atmospheric profiles such as water vapour, temperature, ozone and other trace gases. Retrieval skill is dependent on sensor accuracy, the atmospheric transmittance functions, cloud clearing and inversion algorithms [2]. The availability and accuracy of observational calibration/validation data, especially observations from radiosondes is critical to the development of robust atmospheric profile retrieval algorithms and products. Understanding and modeling the spatiotemporal variability of atmospheric moisture is essential to weather and climate prediction
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