Characteristics of land and sea breezes along the Guinea Coast of West Africa
This study utilized 34-years hourly data of wind speed and direction, precipitation, and air temperature over land to investigate the climatology of land and sea breezes (LSB) at seven coastline stations along the Guinean Coast of West Africa. Daily sea surface temperature from the adjacent Atlantic Ocean and Tropical Rainfall Measurement Mission daily precipitation data was used. Ten years reanalysis data of ERA-Interim, Climate Forecast System Reanalysis version 2 (CFSRv2), and National Centers for Environmental Prediction (NCEP2) were also used for comparison with the observations. Adopted criteria were based on both surface and upper air information to identify LSB days. The results show that LSB is a seasonal phenomenon but most frequent in winter. All reanalyses underestimated the monthly occurrence and seasonal cycle of LSB, although CFSRv2 is better in reproducing the observations than ERA-Interim and NCEP2. The wind roses revealed the existence of night/early morning offshore winds. Except in summer when the southwesterly monsoon winds prevail all day, onshore winds are observed from about 1100 local solar time (LST), with a mean cessation time at 0100 LST, giving a mean duration of about 14 h. However, in Abidjan, they occurred at all hours. The vertical plots confirmed the wind direction reversals for LSB days and give an indication of its depth and speed in different months. It has been found that LSB height is influenced by the West African monsoon as intertropical discontinuity advances northwards from January. This was also seen in LSB increased speed from December to August.
This research was supported by the German Federal Ministry of Research and Education through the West African Science Service Centre on Climate Change and Adapted Land-Use (WASCAL) at the Doctoral Research Programme on West African Climate Systems (DRP-WACS), Federal University of Technology, Akure, Nigeria. We thank the Institute of Geophysics and Meteorology, University of Cologne, Germany, and the WASCAL Competence Centre of Ouagadougou, Burkina Faso, for their collaboration. We are deeply grateful to Prof. Andreas Fink and his staff including Dr. Volker Ermert and Dr. Robert Schuster in the Institute of Geophysics and Meteorology, University of Cologne, Germany, for their sincere collaboration and assistance for providing data and analysis throughout this work. We thank Nigerian Meteorological Agency (NIMET) for providing one time daily (12 h) radiosonde data for Oshodi-Lagos in 2014 and 2015. The TRMM dataset was downloaded from National Aeronautics and Space Administration (NASA) from their web site (available online at http://trmm.gsfc.nasa.gov). The ERA-Interim dataset was downloaded from the European Centre for Medium-Range Weather Forecasts (ECMWF) (available online http://apps.ecmwf.int/datasets/data/interim-full-daily/levtype=sfc/). The CFSv2 dataset was downloaded from the Environmental Modeling Center at NCEP (available online ftp://nomads.ncdc.noaa.gov/modeldata/cfsv2_analysis_flxf). The NCEP_Reanalysis 2 data was provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA, from their website at https://www.esrl.noaa.gov/psd/. The mean daily SST data from adjacent Atlantic Ocean were obtained from National Centers for Environmental Information of NOOA (available online ftp://eclipse.ncdc.noaa.gov/pub/OI-daily-v2/NetCDF). We especially thank Prof Douw Steyn in Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia for his personal communications and contributive comments and suggestions, which considerably improve the quality of this work. We also thank Felix Keis and Christian Chwala in Institute of Meteorology and Climate Research—Atmospheric Environment Research (IMK-IFU), Karlsruhe Institute of Technology (KIT) for discussions on some plot aspects and computational tools such as Python.
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