Profiling of Atmospheric Boundary Layer at a Tropical Site in Ile-Ife, Nigeria during the DACCIWA Field Campaign

In the framework of the multi-institutional EU-funded research project Dynamics-Aerosol-Chemistry-Cloud Interaction in West Africa (DACCIWA) extensive ground-based measurements have been undertaken at three supersites in West Africa: Ile-Ife; Nigeria, Kumasi; Ghana, and Savé; Benin, between 13^th June and 31^st July 2016. The overall aim of DACCIWA project is to investigate the relationship between weather, climate, and air pollution and to inform policy making, so as to bring about improvements in the quality of life for the over 340 million inhabitants of southern West Africa.

Ground-based measurements of surface and atmospheric boundary layer (ABL) properties at the three designated supersites were integrated with data acquired from transverse flights made by three research aircrafts thereby providing ground to upper-level observations both on continuous and intensive modes. In addition, satellite data and forecast products from operational weather prediction models were utilized to determine intensive observation periods (IOPs). Specifically, the supersite located in Ile-Ife (7.5^oN; 4.5^oE) was tasked with investigations of surface energy balance (SEB), occurrences of nocturnal low-level jets and characterization of ABL structure.

Within the two-month study, fifteen (15) intensive observation periods, each lasting 24 hours (beginning 18:00 UTC) were so identified and ABL structure was dedicatedly observed. During the IOPs, coordinated for the three supersites, frequent radiosondes were launched hourly, 3-hourly, or 6-hourly, depending on instrument capacity of each site. At Ile-Ife supersite, soundings of temperature and relative humidity were taken using a tethered radiosonde system (GRAW Instruments, Germany). Depending upon the time of day and surface wind conditions, the radiosonde ascents could rise up to approximately 1 km. Together, vertical wind profiles (up to 510 m) were obtained from a 24-speaker phased array sodar (METEK, Germany). In addition, an eddy covariance system (CAMPBELL CSAT3 ultrasonic anemometer and LiCOR LI7500 infrared gas analyser) together with a 4-component radiation balance sensor (HUKSEFLUX NR01) and soil heat flux plate (HUKSEFLUX HFP01) were maintained at the supersite.

The DACCIWA field campaign at Ile-Ife supersite represents the most intensive and comprehensive single station observations of the ABL characteristics in Nigeria to date. The resulting datasets showing evolution of ABL structure at the DACCIWA supersite will be presented.