This study presents an overview of the Late Cenozoic evolution of the West African Monsoon (WAM), and the associated changes in atmospheric dynamics and oxygen isotopic composition of precipitation (δ18Op). This evolution is established by using the high-resolution isotope-enabled GCM ECHAM5-wiso to simulate the climatic responses to paleoenvironmental changes during the Mid-Holocene (MH), Last Glacial Maximum (LGM), and Mid-Pliocene (MP). The simulated responses are compared to a set of GCM outputs from Paleoclimate Model Intercomparison Project phase 4 (PMIP4) to assess the added value of a high resolution and model consistency across different time periods. Results show WAM magnitudes and pattern changes that are consistent with PMIP4 models and proxy reconstructions. ECHAM5-wiso estimates the highest WAM intensification in the MH, with a precipitation increase of up to 150 mm/month reaching 25°N during the monsoon season. The WAM intensification in the MP estimated by ECHAM5-wiso (up to 80 mm/month) aligns with the mid-range of the PMIP4 estimates, while the LGM dryness magnitude matches most of the models. Despite an enhanced hydrological cycle in MP, MH simulations indicate a ~50% precipitation increase and a greater northward extent of WAM than the MP simulations. Strengthened conditions of the WAM in the MH and MP result from a pronounced meridional temperature gradient driving low-level westerly, Sahel-Sahara vegetation expansion, and a northward shift of the Africa Easterly Jet. The simulated δ18Op values patterns and their relationship with temperature and precipitation are non-stationarity over time, emphasising the implications of assuming stationarity in proxy reconstruction transfer functions.

The presence, spatial extent and persistence of low-level clouds (LLCs) largely impact on the diurnal surface radiation and energy balance, as well as, the regional climate. Notwithstanding, there is limited understanding on their evolution and processes, particularly in southern West Africa. This paper assesses the development of LLCs and their dominant formative factors, as well as, their relationship with radiation and energy balance. Firstly, ceilometer and radiosondes deployed during the DACCIWA (Dynamics-Aerosol-Chemistry-Cloud Interactions in West Africa) field campaign were used in identifying the LLC. Afterwards, the cloud fraction was employed to characterize different LLC phases. Averagely, break-up, dissipation and build-up of LLC were marked at 0900 GMT, 1200 GMT and 2200 GMT respectively. Moreover, composites of LLC diurnal evolution and their relationship with net radiation, energy storage and surface stability showed that LLCs significantly impact on net radiation flux, by reducing downwelling shortwave radiation. Additionally, LLC onsets were characterized by a near-steady state in net radiation flux, whereas the rate of energy storage within the lower layers marginally oscillated about equilibrium. Finally, with observations from selected intensive observation periods (IOPs), the dominant factors influencing LLC development were evaluated. Horizontal cold air advection, with enhancement by nocturnal low-level jets, was observed to primarily influence the development of LLCs for the study period. Findings of this paper are necessary for improving the understanding of LLC characteristics, formation and interactions with surface properties, particularly over southern West Africa.

Agro-climatic zones are geographical areas delineated based on climate homogeneity and impact on agriculture. Ghana's agro-climatic zones have been in use since the 1960s, with no consideration given to current climate change and variability. The continued use of this age-old classified zones suggest Ghana's climate remains stable despite previous research findings to the contrary. In this study, we reconstructed a more appropriate and dis-aggregated agro-climatic zone map of Ghana that is in tandem with the current climate change and variability. Our findings revealed significant changes in the number of climate zones, their boundary sizes and geographical orientation. The newly proposed agro-climatic zones map consist of five distinctive climate regimes namely Sudan Savannah, Guinea Savannah, Transition, Forest and Coastal zones. The Sudan and Guinea Savannah zones showed a southerly expansion. The transition zone shriveled in size as the Guinea Savannah zone took over most of it, notably in the southeast. The forest zone also shrank in size with a northwest shift while the coastal belt grew to encompass the whole coast of Ghana. These changes are strong evidence of climate change and possible food production changes. The findings of this study are useful to agriculture sector in planning their activities, the health sector in predicting specific diseases caused by changes in weather and climate, Ghana Meteorological Agency for weather forecasting purposes, and the National Disaster Management in identifying disaster prone zones.

J. N. A. Aryee1*, M. A. Ahiataku2, K. T. Quagraine3, P. Davies1, N. Agbenor-Efunam4, G. Agyapong5, L. P. Poku5, D. Acheampong2, J. Agyekum1, J. Ameho2, S. O. Ansah2, J. Asamoah2, R. Bediako2, M. K. E. Donkor4, N. A. Frimpong2, M. O. Gyanewa2, M. A. Osei1,6, N. K. Opoku2, M. E. Pardie2, D. Quaye2,  F. Q. Cudjoe2, B. Yahaya2, L. K. Amekudzi1, S. K. Danuor4, Benjamin Lamptey7 Department of Meteorology and Climate Science, KNUST, Kumasi, GhanaGhana Meteorological Agency (GMet), Accra, Ghana.Indiana University - Bloomington, Department of Earth and Atmospheric Science, Bloomington, USA.Department of Physics, KNUST, Kumasi, GhanaUniversity of Lille - Department of Physics, Lille, France Centre for Ecology and Hydrology, Wallingford, Oxfordshire, UK West African  Science Service Centre on Climate Change and Adapted Land Use, Accra, Ghana